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The FAQ section provides you with general information on topics concerning stepper motors, BLDC motors, Plug & Drive motors, linear actuators and motor controllers.
The BLDC itself has no preferred rotation direction, but the hall sensors can only be adjusted with a certain tolerance to the motor. This may result in a better behavior in one direction. To compensate for this effect, adjust the load angle values of the controllers of the SMCI series.
Possible solution: reverse encoder direction, select the correct motor type/hall mode.
Stepper motors should be stored at temperatures between -20°C and +70°C. Condensation and corrosion must be avoided.
Temperature rise in motors is defined based on the rated current and rated voltage while the motor is at a standstill. During bipolar operation of the motor, however, the voltage rises. As a result, the motor overheats above its maximum permissible temperature during continuous operation and is destroyed.
Therefore, it must be ensured during continuous operation that the phase current multiplied by the supply voltage (= power output) does not exceed the product of the rated current and the rated voltage (= rated power output).
The current specified in the data sheet is always an effective (RMS) value.
No, because when the stepper motor is opened, the rotor makes contact with the stator and the magnetization is reduced. As a result, the torque of the motor will decrease appreciably. This primarily affects magnets with a lower coercive field strength, such as Alnico magnets, that are easily shifted from their optimum working point in their nonlinear magnetization curve and thus pass through a weaker magnetization characteristic. Higher-quality N magnets, on the other hand, splinter very easily without appropriate tools and are easily cracked by only slightly incorrect handling and can therefore sustain permanent magnetic damage..
The torque is directly proportional to the current (P = I² * R) or generated magnetic flux, provided that the magnetization is within the linear section of the magnetization curve, i.e. not yet in saturation. This means that if the current is doubled, the power is quadrupled. (Example of ST4118L1206-1W = 0.6A² * 3.1 = 1.11W at nominal current = 1.2A² * 3.1 = 4.44W). Since the voltage has to "drive" the current through the winding (P = V²/R) in order to generate a current flow and the electrical power is also P = V * I or P = V * (V/R) = V²/R, the power or the torque (P = Md * n = P/n(constant) = Md) also increases in proportion to the voltage. This means that if the voltage is doubled, the power is quadrupled. (Example of ST4118L1206-1W = 1.855V²/3.1 = 1.11W at a nominal voltage = 3.71V²/3.1 = 4.44W).
With a constant voltage control, this applies as long as the current can increase with the voltage and is not reduced by the impedance (square root of R² + X²). However, a series resistor must always precede the current limiter when the voltages are higher than the motor voltage. With a constant current control, the current can be kept constant up to its torque inflection point. In this range, the power increases proportionally whereas the torque remains constant. The torque does not decrease significantly (nominal current drops asymptotically because of the increasing counter EMF, the increasing impedance proportional to the speed) until far above the torque inflection point, specifically at 24V. The power or torque begins increasing proportionally with the voltage at this point. (Example ST5918M3008–P: at approx. 500rpm, the torque is approx. 0.9Nm at both 24V and 48V. While the power = 0.65Nm * 1000rpm * 3.14/30 = 68W at 1000rpm and 24V, the power = 0.65Nm * 2000rpm * 3.14/30 = 136W at 2000rpm and 48V. This means that it is possible to increase the power accordingly by applying a proportionally higher voltage. The problem is only that the eddy current losses, and hence also the power losses, increase with the square of the speed and that limits are set on the voltage increase due to the rise in temperature.
At lower frequencies or speeds, the resonance behavior is still very pronounced. The EMF, on the other hand, increases proportionally with the speed. As a result, the current becomes smaller (I = (UV – UEMF)/R) and the torque decreases markedly.
The lack of torque reserve in both cases causes the motor to lose steps, fall out of step, or actually come to a standstill if there is a brief increase in load or a small torque peak. This can be remedied by a higher supply voltage or, on the other hand, by a motor with a lower winding resistance or lower inductance at the same torque.
There are three basic versions of stepper motors:
I. Reluctance motors
II. Permanent magnet motors
III. Hybrid motors
Apart from the permanent magnet motors in the low-cost range, Nanotec offers mainly hybrid motors. These combine the advantages of reluctance and permanent magnet motors in one. They have a high step resolution, a high repeatability and an excellent holding and nominal torque up to high speeds.
The number of steps per revolution of a stepper motor is made up of the number of pole pairs and phase and stator windings, i.e. z = p * m. The rotor of 2-phase hybrid stepper motors consists of 50 soft magnetic teeth that form a north and south pole due to the magnets lying between them while the 2 phases are wound on the 4 windings A + A/ and B + B/ of the respective pole shoes offset by 90°.
See also the animation.
A further feature is the step angle for a full step of the stepper motor: a = 360°/z or a = 360°/p * m. The number of steps per revolution for the stepper motor STxx18 series is z = p * m = 50*4 = 200 steps, whereas the step angle for the STxx09 series is a = 360°/p * m = 360°/100 * 4 = 0.9°/step.
This data refers only to constant voltage operation; which is hardly ever deployed today because more economical and considerably more efficient constant current drivers such as the IMT901 and SMC(I) are now available. On applying the type plate voltage, the nominal current (I= V/R) appears after a finite period (i = V/R (1 – e^(-τ(L/R)), as does the torque.
To reduce the effect of the slow increase in current, motors are operated with far higher voltages today via modern constant current controlled controllers in order to reach higher torques at higher speeds as well.
The nominal current, by contrast, is a very important parameter as the torque is directly proportional to the current and hence represents a fixed variable relative to the torque. In addition, the current specifies the maximum power loss of the motor (P = I² * R) and should not be exceeded at a duty cycle of 100%.
Because of the law of conservation of energy, the sum of the potential energy and kinetic energy in a closed mechanical system always remains the same. This cannot be deduced from the laws of physics.
Physical findings have confirmed this law time and again, and we will do so now using the ST5918M3008 motor as an example.
The external torque at 24V and 48V, respectively, remains constant at 0.65Nm at a speed of 1000rpm. The power drain is P2 = Md * n * 3.14/30 = 0.65Nm * 1000 * 3.14/30 = 68W, no matter whether a supply voltage of 24V or 48V is fed to the power driver and motor. While the current at 48V = P = V/I = I = P/V = 68W/48V = 1.4A, the current at 24V = 68W/24V rises to 2.8A.
The power loss (Vsupply * Isupply = Pmotion + Ploss) of the motor, driver and power supply was not taken into account here as it would be no more than roughly 10% anyway and would therefore be negligible.
Particularly at higher speeds (from approx. 300–500rpm depending on the motor winding), a motor voltage that is too low has an adverse effect on the field weakening. This causes the torque to decrease proportionally with the drop in voltage. From this perspective, synchronized power supplies such as the NTS are advantageous because they keep the voltage constant up to the nominal current and quickly compensate voltage drops.
Often inquiries are received in which merely a well-mounted rotary disk (e.g. 5kg, diameter 30cm) needs to be rotated and only the dimensions, the weight and the required dynamics are known.
First, the inertia torque of the mass must be calculated. For a solid cylinder (formula J = 0.5 * m * r²) that rotates around the axis of symmetry, the following applies: (J [kg*m^2], m [kg], r [m]) = 0.056kgm^2 = 562kgcm^2 = 562000gcm^2
The inertia torque can then be calculated theoretically from ([rad/s^2]). For example, the disk should be repositioned by precisely 360° in 1s. The average speed is then 1rev/s; it is first accelerated to f = 2rev/s in 0.5s and then braked to 0 again in 0.5s (triangular profile). The following then applies to the angular acceleration: 25rad/s^2 => M = 1.4Nm.
But be careful:
The problem here is the acceleration. Because the stepper motor does not begin at 0 but with a starting speed (which often has to be selected quite high to avoid resonances), the true acceleration is appreciably higher than that calculated here. As this is difficult to calculate or measure (the encoder signal would have to be evaluated), the motor selection is made based on the following rule of thumb using a known external inertia torque.
Thus, a motor must be selected whose rotor has at least 1/20th of the external inertia torque, here 28125gcm^2 (Jred = Jex/i2). In this case, a gear must be used that reduces the external inertia torque with the square of the reduction ratio: A gear with 10:1 thus yields a reduction factor of 100 for 281gcm^2 in this case (Jm of the ST59 is ..). This means the combination of ST5818M2008 + GPLE40-2S-12 is suitable.
Due to the gear, the maximum speed is naturally also limited, which needs to be taken into account but presents no problem in this case.
Stepper motors are digitally controlled and regulated drives. Their high level of acceptance and prevalence can be attributed to the technology transition from analog to digital technology, the current software solutions and the favorable prices with a very long service life and few control requirements.
a) PC+PLC-capable (directly controllable via PC, PLC and microprocessor).
Through the use of PCs even at the lowest, decentralized machine levels, Plug & Drive motors have achieved the highest levels of productivity growth. Nanotec was the first supplier worldwide to meet the demand for a compact, efficient and cost-effective drive system with an industrial-grade Plug & Drive motor. Not only did these motors drastically reduce the development, wiring and installation effort for a complete drive unit and increase EMC compatibility and machine availability, but they also greatly simplified setup, installation and servicing. Nanotec continuously develops additional features to meet customer-specific requirements. This results in the steady growth of new and close partnerships that ultimately bring forth better and more economical end products.
b) Speed stability
"No drop in speed when the load changes": Stepper motors fulfill this requirement like no other motor without any additional effort. Particularly for precise speed, synchronicity or ratio controls (e.g. in precision dosing pumps), the stepper motor can reach higher and finer resolutions thanks to digital processing. The improved control, process and surface quality is not just a theoretical advantage in this context.
c) Direct drive
Stepper motors have their maximum torque in the lower speed range and the Nanotec microstep drivers still achieve acceptable concentricity properties to approx. 2rpm. Other motors often need gears in order to fulfill the requested speed and force requirements. Direct drives reduce system costs while increasing operating safety and the life span. Naturally, if the space available is limited or the external inertia torques are high, gears will be essential to achieve the necessary power and force.
d) Avoiding injuries and damages to machines
The disadvantage of "falling out of step" when a motor is blocked, which is an issue that is sometimes brought up in connection with stepper motors, can actually be of an advantage in some cases in view of increasingly stringent safety requirements. Slip and overload couplings are not normally required in statutory safety requirements in conjunction with stepper motors.
e) Positioning accuracy
As a result of the small step angle, stepper motors also have, in addition to the lowest over run, the smallest transient response. Even without external linear encoders or angle sensors, stepper motors are excellent at fulfilling speed and positioning tasks. The microstep switching of the Nanotec final output stages can actually further increase precision and resolution at no extra cost. All Nanotec stepper motors are also available with competitively priced encoders for detecting step loss and blockages as well as for closed loop applications.
f) High stiffness without brake
Stepper motors have the highest holding torque when idle and thus offer a high degree of system rigidity. Because of this property, no external braking mechanism is necessary unless safety braking is required for the Z axis. Even for normal stopping, the stepper motor can be advantageous. For example, when a servo motor needs to be stationary, the closed loop control must still operate at full speed. The drive control oscillates around the selected null point with a slight back and forth movement. In most applications, this is of no consequence. However, when positioning a mirror for a metrological task that deflects a laser beam, for example, this oscillation can quickly become disruptive. A stepper motor, on the other hand, would simply move to the required position and remain still.
g) Highly dynamic
Primarily in conjunction with the new dynamic closed loop SMCI motor controller and the PD6 Plug & Drive motors up to a speed of approx. 2000rpm, stepper motors achieve higher dynamics and angular acceleration than servo motors due to the high number of poles, the low rotor mass and the small air gap. This primarily has a favorable effect wherever small distances and movements must be positioned or reserved very quickly while an extremely small settling time or transient response is exhibited, such as is required in semiconductor technology, optics and also in textile machinery and testing equipment.
h) Easy controllability
Drive solutions using stepper motors can be realized very easily and cost-effectively because they can be implemented in an open loop, i.e. without external encoders. In addition to the motor, the power electronics (driver) and an appropriate power supply are required. An external time base (PLC, PC or simple RC oscillator) can take on the speed or position. With a small additional board, the clock could even be specified via an analog input (0–10V, 0–5V or +/-10V) or potentiometer, and hence would be controllable similar to a BLDC motor.
The direction of rotation is changed by swapping over two motor connection lines, e.g. phase A to A' and A' to A. Generally, however, the direction of rotation is changed by a high or low signal on the direction inputs of the Nanotec motor controllers.
Suppression measures should be carried out as directly as possible at the source of interference in order to prevent uncontrolled propagation of the electromagnetic faults through galvanic, inductive and capacitive coupling (also coupling between cables that run in parallel). There is a series of measures that can be implemented to minimize the transient emissions.
One possibility is to employ one of the various shielding methods:
Cable shields with nonmagnetic plastic webs or braids:
A voltage induced in the shield leads to a current, which in turn forms an induced magnetic field that opposes the original source. The residual induced effect on the cables is reduced in the shielding.
Double-sided grounding of the shielding also harbors disadvantages. It inevitably allows partial currents to flow via the shield if there are potential differences between the start and end of the cable. The ground loops hence reduce the actual shielding effect. In addition, couplings from the energy distribution network or lightning strike can lead to overloading of the shield.
In the case of higher frequency magnetic couplings, one side can be grounded directly and the other via a capacitor. Supply frequency currents are blocked and higher frequencies are compensated. Low loss ceramic capacitors of 10–100nF are typically used.
The motor cable should not be extended and should not be longer than 25m. It must have a minimum cross section as specified in the current load table. Longer connection lines can negatively affect the holding torque or rotating torque, above all at higher velocities or rotational speeds. Due to the greater current rise time constant of τ = L/RM * RL, the current time area drops as does – proportionally – the torque.
The cable should be shielded and preferably twisted in pairs. The shield is connected to the PE terminal of the stepper motor controller. It is important to make sure the motor cable has a good connection.
Nanotec offers a comprehensive range of customer-specific cable assembly options.
If a stepper motor is correctly dimensioned, it constitutes an absolutely reliable drive element. When stepper motors are overloaded, however, the assignment to the setpoint position is permanently lost. This behavior is described as "step offset" and is a disadvantage of stepper motors because the out-of-position cannot be detected due to the open control chain.
An additional measuring system with an encoder compares the measured actual position and the required setpoint. Any deviations are detected and corrected by a subsequent control process.
Nanotec offers extremely economical and high-resolution encoders for speed monitoring. The incremental 2-channel and 3-channel encoders offer a low-priced solution with long-term functional reliability and high measuring accuracy. The encoders are available with a small design, low masses and a high resolution. They are suitable for a wide temperature range and are resistant to vibration accelerations. For later attachment, all motors with a second shaft end already have appropriate mounting holes on the rear panel cover.
Speed monitoring with automatic correction is already integrated in the Plug & Drive motors.
The stepper motor drives of the SMCI series have an encoder input and can evaluate a 5V TTL signal.
If a direct measuring system is installed on the machine, errors and non-linearities of the mechanism are also balanced within the context of the measuring accuracy.
The smaller the microstep, the smaller the resonance problems. Due to the smaller step angles, the overshoot angle is also reduced and the system has less pronounced resonance points. From experience, the 1/8 microstep already results in operation that is relatively low in resonance, whereas there is almost no improvement beyond the 1/32 microstep. If no current compensation is provided or integrated in the microstep driver, a torque reduction of the motor occurs. This can be disadvantageous in some applications.
The higher the torque reserve, the higher the resonance stimulation. Accordingly, resonance stimulation is strongest during no-load operation and therefore results in the greatest resonance problems during testing. For this reason, tests should preferably be carried out in the application because frictional torques are usually present here and the complete system is therefore damped. In addition to reducing the tendency to oscillate, the phase current reduction also minimizes the stiffness and must be taken into account in the positioning accuracy if no current compensation is integrated in the driver.
The basic resonance of stepper motors during no-load operation is approx. 70–100Hz in full step and appears again more or less strongly at multiples or harmonics of the basic resonance. If the process allows, it is easiest to avoid the identified resonance frequency by choosing a frequency that is somewhat higher or lower (if necessary, through the interconnection of a gear or by changing the reduction gear ratio). Even small deviations from the critical step frequencies will show good results.
The friction generally has a damping effect on the system and the overshoot angles become smaller. However, it reduces the reserve torque and the efficiency deteriorates.
The dampers offered by Nanotec reduce the overshoot angle and absorb the vibrational energy. This greatly reduces the resonance frequencies because the speed difference between the oscillating rotor and the external mass is also reduced. The high running noise is lowered considerably by affixing a damper as well.
At a relatively low motor acceleration, the points of resonance that make the system unstable may be reached during the run up time. By contrast, a steep acceleration ramp has fewer sampling points. The high acceleration reduces the torque reserve and the system has more of a damping effect.
In addition to a reduction in the tendency to oscillate in microstep mode, the risk of oscillation declines with decreasing supply voltage due to the slower rise in current.
With its rotor inertia and magnetic retaining forces, each stepper motor constitutes a damped oscillating system with low inherent damping. Thus, vibrations can be induced that are superimposed on the actual step movements, potentially resulting in a decrease in torque, step loss or even a change of the direction of rotation.
Hence, it is possible to conceive of stepper motors in which the rotor follows the excitation field within narrow bounds, similar to synchronous motors or like a spring oscillating system. The stronger the excitation field, the greater is the stiffness and the more pronounced is the oscillation tendency and the natural resonant frequency.
At the natural resonant frequencies, the rotor loses the rotating field of the stator and the synchronicity, and a more pronounced loss of torque occurs so that the motor disengages after a short time. Usually, it can no longer reengage and comes to a standstill. If a motor is now operated near the natural resonant frequency, the rotor may begin vibrating with an increased amplitude and the motor falls out of step. Resonances are associated with pronounced running noise.
Ideally, therefore, stepper motors should be operated with a flange-mounted load. This base load, which corresponds to damping, is often sufficient to allow both low-resonance operation as well as a safe frequency run-up. In extremely rare cases, the motor can regain its synchronicity in the next rotary field phase. Due to a brief overload or overshoot in the positive or negative direction of rotation, the rotor drops into the next stable rotary field position.
Because the resonance in stepper motors is inherent to their design, it can only be reduced or partially eliminated through the application of special procedures.
The standard Nanotec motors of the ST series have insulation class B = 130°C. This temperature must not be exceeded in the windings and in the ball bearings. (In the SP series, the temperature relates to the insulation class E = 120°C and plain bearings).
If you suspect that the temperature is too high, it is recommended that you measure the surface temperature of the stepper motors with a suitable temperature sensor, possibly at different points in order to localize the least favorable location depending on the cooling surface. The surface of the stepper motor should never exceed 100°C as irreversible damage may otherwise occur. The cause of the high temperature, e.g. high ambient temperature and medium current, or high current with a low duty cycle, is irrelevant.
The temperature increase in nominal current operation in stepper motors is 80°C, i.e. the maximum admissible motor temperature of 130°C is reached in the winding, in the bearing and in continuous operation at an ambient temperature of 50°C.
Better air convection (or even forced air circulation with a fan) and hence motor cooling is achieved with the aid of an additional larger flange area, preferably of aluminum (which has a cooling ability that is 4 times better than that of steel). This enables a higher performance yield from the available motor size.
The lower the motor temperature, the longer the expected life span of the bearings.
Apart from the ohmic losses, it is primarily the magnetic hysteresis losses that increase with the speed. These increase with the square of the frequency.
If the motors are operated at high supply voltages, the nominal current can be kept constant in the winding for a relatively long time. Thus, the torque curve also remains constant for a fairly long time and only drops off considerably later.
At medium supply voltages (48–70V), the nominal current decreases earlier so that the ohmic losses can be compensated through the earlier current reduction and the quadratic hysteresis losses beginning at a certain speed. As a result, the motors do not overheat excessively, do not require an additional heat sink and achieve a longer life span.
The stepper motor has the highest torque in full step mode. On the other hand, a stepper motor in full step mode also has the most pronounced resonance points, which in turn have a negative effect on the torque. However, if the operating speed should be situated in the vicinity of one of these resonance frequencies, it may be more beneficial to change to the microstep mode since the full motor torque is not used at this frequency anyway.
As can be seen in the animation showing how a stepper motor works in half step mode, two windings (phases) are alternately energized. The vectorial sum or geometric addition of the two phase currents I (motor = √ Ia2 + Ib2) yields a half step torque of 70.7% with respect to the full step mode. The new SMCIxx microstep drivers have an automatically built-in current compensation. During the half step phase, the currently active phase of the current is increased by a factor of 1.4 (which is thermally permitted since the other phase is switched off at that moment). Because of this current increase, a torque of almost 95% of the full step mode can be reached in half step mode.
Similar to half step mode, the vectorial phase current in quarter step mode is slightly smaller still, and the resulting torque approaches 55%, and 45% in 1/8 step mode, compared to the full step mode.
Automatic current increases are integrated in Nanotec stepper motor drives of the Nanotec SCMI series and in all new Plug & Drive stepper motors, in both half step mode and in smaller microstep modes. Thus, approximately the same torque (95%) is reached as in the full step mode.
All torque curves were recorded in 1/4 step mode with current compensation.
A further advantage: Less energy is generally required in microstep mode. Among other things, the reason for this is the lower residual ripple, which largely avoids resonances due to more smooth running.
Unipolar controllers are suitable for 5-lead, 6-lead and 8-lead motors and are used for simple and economical applications. In the simplest case, the positive supply voltage is applied to the center tab of the two phases. The respective half windings are alternately connected to ground with only four switches or transistors (or four outputs from the PLC, for example) as shown in the circuit diagram. If stepper motors with relatively high winding resistances are used, the phase current is simply limited by the formula I = V/R, or roughly by I = V/2 * π * f * L at high frequencies. Unipolar controllers only reach a torque of around 70% of that of bipolar controllers.
Bipolar controllers are suitable for 4-lead, 6-lead and 8-lead motors and are used for high-performance and highly dynamic applications. The two phases are each connected to ground via two H-bridges from the positive supply voltage via the diagonal transistors (via a measuring resistor at a constant current). In the H-bridges, four transistors are diagonally and alternately connected to ground according to the circuit diagram. The torque of bipolar controllers exceeds that of unipolar controllers by around 30% (in bipolar controllers, all of the copper is in use at all times). Because of the high integration of the circuits and the higher torque, preference has long been given to highly integrated, high-performance, constant current microstep output stages, such as IMT901, IMT902 and SMC from Nanotec.
Stepper motors have the following advantages:
Stepper motors are synchronous motors. A stepper motor consists of a magnetic rotor and multiple offset stator windings. To generate a magnetic field, a current flows through the coils. A change in the direction of flow changes the polarity of the induced magnetic field. If this occurs in a specific sequence, the result is a rotating stator field that the toothed permanent magnet of the rotor follows. Thus, the electrical pulses determine the speed of the rotating magnetic field and the rotor converts these pulses to a mechanical rotary movement with a defined step angle.
The rotor of the motor is mounted in ball bearings on both sides of the motor. Because it contains neither commutators nor slip rings, the life span of the motor depends only on the load on the ball bearings. Our motors have an L10h service life of approx. 20,000 operating hours when operated at the rated loads (see data sheet).
The number of leads of a motor determines the mode or the controller with which the motor can be operated – unipolar, bipolar parallel, bipolar series or with one half winding. The configurations of stepper motors with 8 leads are the most diverse because they are suitable for all controller types and are therefore very flexible for use in a wide range of applications. Because of their flexible circuitry, 8-lead motors are frequently available in stock.
Two-phase and four-phase stepper motors with 8 leads can be operated in unipolar or bipolar mode (parallel, series or one half winding). (difference between unipolar and bipolar – animation link)
The stepper motor with 6 leads can be operated in unipolar mode, in bipolar series mode or in bipolar mode with one half winding. In case of open center taps, both connections need to be insulated separately. (Animation link)
In two-phase stepper motors with 4 leads, only the bipolar mode is possible. Because of the low power output (only 1/2 of the copper of the windings is in use), Nanotec does not offer unipolar final output stages.
Stepper motors are firmly established in the field of positioning and precise speed control. The characteristic properties of stepper motors are directly associated with electric signals and the rotary movement of the stepper motor.
The stepper motor converts electrical energy into precise mechanical motions, where each electric pulse results in a specific rotational angle. Using digital pulses, precise angle values can be specified using a simple circuit without requiring external feedback (e.g. from an encoder).
Stepper motors have been in use since 1950. Due to new materials and procedure, especially in digital technology and software, they have become widely distributed in a broad range of applications. New actuation methods with digital and very rapid signal processors have made stepper motors even more efficient and low-noise and open up an increasing number of application fields.
Positioning example: With 100 pulses, the 1.8° stepper motor rotates exactly 180°
The stepper motor is not only ideal for positioning applications but also for highly precise rotational applications since the rotating speed is directly proportional to the pulse frequency and is virtually independent of external load changes.
Speed control example: 1000 pulses/second (1000Hz) in a 1.8° stepper motor result in exactly 300rpm (1000/(360°/1.8°)*60s= 300rpm).
The process is also known as sine wave commutation via an encoder with field-oriented regulation. Signals from the encoder are used to determine the position of the rotor and sinusoidal phased currents are generated in the motor coils. The vector-based regulation of the magnetic field ensures that the stator magnetic field is always perpendicular to the rotor magnetic field and the field strength corresponds precisely to the required torque. The current thus controlled in the coils ensures that the motor runs smoothly and quietly and can be regulated with great precision.
The SMCI series controllers and the Plug & Drive motors already have an integrated closed-loop function and automatically compensate for any step loss at the end of a positioning movement.
For closed-loop operations, a 3-channel encoder or shaft encoder with at least 500 rpm must be mounted on the SMCI controllers; Nanotec’s Plug & Drive motors are already equipped with an encoder, except for the motor PD2-C.
Our controllers also integrate a dynamic closed loop and can not only compensate for step angle errors while moving, but also correct and adjust load angle errors within a full step. The stepper motors thus achieve a similarly dynamic performance (up to about 2000 rpm) as highly dynamic servo motors.
They also achieve higher speeds while resonances are minimized. They are much quieter (noiseless) and more efficient because they achieve the same performance with less power and remain significantly cooler, thus reducing energy resources.
dspDrive is a software-based current regulator. In the latest generation of the Nanotec hardware, the current in the motor is no longer regulated by an integrated component, but rather directly by means of a digital signal processor. In contrast with standard commercial ICs that can resolve current measurement in the coil and the specification of the set current with 6 or 8 bits, the new dspDrive can be used to perform all regulatory controls with a resolution of 12 bits. The parameters of the PI current regulator can be adjusted by the user both to the motor and in accordance with the speed.
This has the following advantages:
By directly controlling the half bridges with the digital signal processor it is now possible to control 3-phase stepper motors and BLDC motors in addition to 2-phase motors.
Connect RX+ to TX+ and RX- to TX-. Your 2-wire interface must be fast enough to switch between send and receive modes. If this is not the case, the baud rate of the Nanotec interface (115200 bps) must be reduced to 9600 bps for example (e.g. with Nanopro).
The green LED lights up when power is applied to the controller. If the green LED does not light up, the controller must be faulty. This error is caused either by overvoltage in the communication (irreparable) or an incorrect power supply connection. In this case the fuse needs to be replaced. The controller needs to be sent back to us for this purpose. Please use the RMA form for this.
The RED flashes several times when the operating voltage is switched on and then goes out.
The red LED lights up continuously when undervoltage or overheating occurs (LED lights up briefly when the controller is switched off). The LED goes out again when the temperature has dropped and the controller has been switched off and on again.
The red LED flashes slowly and no communication is available. Firmware must be reloaded using the firmware utility.
Some advice when working with EtherCAT/TwinCat:
Yes, if you follow these steps:
The controllers of the SMCI series and the Plug & Drive motors of the PDx-N series are equipped with an internal fuse. Therefore an additional external fuse is not required but would be an advantage in case the fuse is blown because then controller won’t need to be opened to replace the fuse (important for IP protection products).
The controllers of the SMCI series and the Plug & Drive motors of the PDx-N series are equipped with an internal fuse. Therefore an additional external fuse is not required but would be an advantage in case the fuse is blown because then controller won’t need to be opened to replace the fuse (important for IP protection products).
The encoders of the WEDL and NOE series generate an inverted signal in addition to the encoder signal, this leads to better interference immunity and is especially recommended for long lines lengths (> 500 mm) and applications with neighboring interference sources.
Positioning is used to turn the stepper motor to a required target position. This happens either by starting the stepper motor with the start/stop frequency and stopping it when it arrives at the target position. Or, in the event of higher positioning speeds, the stepper motor is started with the start/stop frequency and then accelerated to the maximum frequency via a frequency ramp. When the stepper motor is located just before the target, it is braked down to the start/stop frequency via a frequency ramp and stopped at the desired position.
When braking or stopping, a stepper motor acts like a generator and gives energy to the power supply so that the power supply voltage increases. Due to the maximum admissible voltage of the transistors used and elements in the power driver, the braking energy or the voltage increase can damage the components in the power driver. A generously dimensioned capacitor with a corresponding electric strength can accommodate this braking energy for a certain time and thus limit the voltage.
In addition to the charging capacitor, an active ballast switching is also used in part that converts the surplus energy into heat and in this way also limits the increase in voltage.
The active ballast switching acts considerably more effectively against fast voltage spikes than charging capacitors as it reacts just as quickly and, above all, works independently of the momentarily available storage capacity of the capacitors. Charging capacitors are nevertheless necessary as they can take up and deliver the energy almost free of loss, whereas the active ballast switchings provide additional fast overvoltage protection.
Because of the low-loss switching operation (chopper control or PWM) for controlling the current in all stepper motor drivers of the SMCxx series, the specified phase current no longer needs to be multiplied by two. Instead, the power output of the power supply units must be calculated using the mechanical power of the motor P = Md* n * π/30 plus the efficiency of the motor, motor controller and power supply unit.
Determining the power supply size (in W)
The overall power that needs to be supplied by the power supply unit is thus made up of the kinetic energy (product of the torque momentarily required in Nm at the desired speed in rpm and the factor π/30) and the power loss of the motor, final output stage and power supply unit:
Ptot = Pmech + Pv (motor + output stage + power supply unit)
Examples of the respective torque curves
The power losses are proportional to the phase current of the motor (I² * R) and must be taken into account, normally with a max. of 5–7% with respect to the kinetic energy.
That is to say, in the example a) (motor size 42): kinetic energy * 1.07= 36 * 1.07 = 38W.
As only certain standard sizes are offered on the market, a power supply of 50W must be selected here. Thus, another power consuming load could be connected if required.
In example b), on the other hand, a 150W power supply unit may be sufficient because a power reserve of approx. 25% should already be planned in anyway for a stepper motor drive solution. This would mean a real power consumption of 0.67Nm * 0.75 * 2000 * 3.14/30 = 105W.
Thus, a power supply unit with 150W would be advisable here.
With a certain power reserve, the motor and the power supply unit remain just warm to the touch. If you do not know the final speed and torque values, but you want to obtain the power supply unit on the same date of delivery as the motor order, the following simple guiding value is sufficient as an initial approximation: phase current * (0.7–0.8) * supply voltage, i.e. for a motor with 1-A phase current *0.7 * 24V = 16.8W and, hence, a standard 20W power supply unit.
At least a factor of 1.5 times the motor phase current should be used as the fuse value (slow blow fuse).
Category and type of the power supply unit
Because of their greater efficiency as well as their size and weight compared to power supply units with transformers, rectifiers and filters via capacitors (these also often have the problem of an excessive open circuit voltage), switch-mode power supplies are the type primarily deployed today.
overload protection of 105–150% means that an overload peak is detected in this range and leads to a current limitation. However, the customer must ensure that a sustained overload does not occur (a sustained overload of approx. 120% may not be detected and would greatly reduce the service life of the power supply unit.
The charging capacitor should be designed in such a way that the voltage ripple remains less than 2.5Vss and the minimum capacity lies very roughly at 2000µF/A. The minimum capacity also depends on the difference between the admissible voltage of the driver and the supply voltage, and on the delta braking time and the size of the external fly weight. In any case, the capacity should be selected to be large enough so that the energy to be recovered during deceleration, braking or sudden stopping can be absorbed by the capacitor without any appreciable increase in voltage occurring compared to the admissible voltage of the power driver.
Appropriate Nanotec power supply units for our SMCI motor controllers and Plug & Drive motors in suitable sizes can be found under Accessories on our website.
If the rotor needs to retain its position when idling, the stepper motor must remain actuated/energized. Nanotec motor controllers have an enable input which is used to deactivate the driver and deenergize the motor. The motor then engages in the next stable stator/rotor position, which means it can jump forwards or backwards by a maximum of 2 full steps. When it is switched on again, the same step pattern is activated and the rotor is pulled back into the same phase position via the transistors. If the voltage is switched off altogether, however, the motor can lose its final position when it is switched on again because it can engage either 2 full steps forwards or backwards.
Because the torque and the total input power of the stepper motor reach their maximum when idling, a current reduction is recommended in the case of prolonged idling periods.
Hybrid stepper motors have a relatively high detent torque/self-holding torque. Thus, the motor has a braking effect when idling, when the load torque is not greater than the self-holding torque.
The maximum speed and torque values are needed to be able to select the stepper motor. Ideally, the speed/torque curve would be helpful as well, but it is only rarely available.
In stepper motors, the mechanical output in W is not normally given. In many cases, however, it is very useful in order to make an initial estimation of which series might be possible.
Torque 10Nm at 200rpm
P = Md (Nm) * n (rpm) * π/30
or, somewhat roughly and greatly simplified P = Md * n * 0.1 (P [W], M [Nm], f [U/s] = 209W (M [Nm], n [rpm])= 10 * 200 * 0.1 = 200W (in this case, it is only possible to use one of the motors of the ST8918 series)
The approximation formula can be used to read the power practically directly from the curve without being far off the mark.
The power of the stepper motor increases up to the inflection speed and then remains relatively constant at higher speeds because the torque falls roughly inversely proportionally with increasing speed.
This depends greatly on the respective speed and above all on the requested speed range. If only a low/high speed is necessary, the rule of the highest possible/lowest possible microstep can be applied since resonance and noise are largely reduced at low speeds. In case of low speeds, however, a current compensation should be integrated in the driver in order to reach nearly the same torque. At high speeds, in contrast, often a half step or even a full step is sufficient for current to flow through the winding once more and to not excessively overload the external time base.
In applications with a wide speed range, it is often advisable for the driver to enable adaptive frequency switching such as in the SMCI motor controllers to achieve optimum and low noise operating behavior at all speeds that occur. If only a simple driver is available, the half step is often a good compromise because the half step already reduces resonance many times over compared to the full step.
The temptation to purchase a stepper motor driver that enables as high a microstep setting as possible in order to achieve a high resolution and hence also a high precision is often irresistible. However, a driver with a resolution of 1/128 (in a 1.8 stepper motor, this mathematically corresponds to 0.0140625/step = 25600 steps/rev), for example, would soon result in disappointment in terms of precision when testing.
The decisive factor is the torque reserve in the microstep at the current load angle or at the current position (the smaller the torque reserve, the greater the variation in the microstep). Without microstep current compensation, the holding torque or the torque reserve is reduced compared to the full step by 1/1=100%, half step by ½=70.7%, quarter step by ¼=38%, 1/8=19.5%, 1/16=10%, 1/32=5%, 1/64=2.5%, 1/128=1.25%.
At a microstep of 1/64 and 1/128, the current only varies by 2.5% and 1.25%, respectively, of the nominal current. Without current compensation, this small current change causes almost no angular change to the motor shaft because the pole sensitivity (static holding torque) is already greater than the magnetic flux change brought about by the differential current or the force field in the stator field.
When changing or reversing the direction of rotation, the error is even greater because here many microsteps are required before the motor shaft begins to rotate backwards at all, only to then make a big jump when the microsteps move to approx. 1/8 or ¼ step values.
Without current compensation, microstep operation is therefore still reproducible with a certain level of precision down to a step mode of ½ and possibly ¼; beyond this, it is really only used for reducing resonance and running noise as well as improved operating behavior at low speeds. Even here, there are no significant detectable advantages over 1/16 and 1/32 step operation.
First of all, suppliers of low-cost, high resolution microstep drivers should be asked whether the motor controller contains an integrated current compensation. This will help save money and time.
In addition to the current compensation, the stepper motors themselves do not generate a true sine curve over 360°. The distorted sine curves of the motors (neither a true nor real sinusoid, nor are they exactly dephased by 90° from one another) also impair the precision of the step angle and this, above all, in the microsteps. Nanotec has adapted the current curves of its new drivers to the somewhat distorted sine curves of its motors. Thus, a reduced step angle error of <3% can be reached. In Plug & Drive motors, step angle errors can even be improved further. This also applies to those in the microsteps, as the current curve is adapted to the sine curve of the motor since they form a single unit.
Because the holding torque is higher than the rotational torque, a holding torque of the same magnitude as the rotational torque is reached at a lower current.
In addition, only a fraction of the torque is required when idling in some applications so that often a reduced holding torque is entirely sufficient. Because the power loss is proportional to the square of the current, a current reduction of 25% reduces the torque by approx. 50%.
Example of the ST4118M1404 motor: power loss Pv = I2 * R = 1.42 * 1.2 = 2.35W, with a current reduction of 25% Pv = I2 * R = 1.052 * 1.2= 1.32W = 56%
Not only does this reduction bring advantages in terms of energy consumption, but it also reduces the average temperature of the driver and the motor. Ultimately, this temperature reduction results in an even longer expected life span of the components.
All Nanotec drivers have an integrated automatic or adjustable current reduction and thus considerably reduce power loss when the motor is at a standstill.
This function is supported as a standard feature by most of our motor controllers and by the PD-I motors of the Plug & Drive series. It is only possible to use other motor controllers if a superordinate PLC takes over the analysis of the 5V TTL level of the encoder and readjusts the clock of the clock input accordingly.
The maximum acceleration behavior of the motor is determined primarily from the torque reserve at the desired working point, but also from the external inertial masses and from the moment of inertia of the motor rotor.
The shortest run-up ramp type consists of an exponential acceleration with an initially very steep ramp that then asymptotically levels out at its maximum value.
The most frequently used ramp, however, is the linear ramp because it is relatively easy to program and to adjust via an operational amplifier. The dynamics of the linear ramp are not significantly greater than in the exponential ramp and play a rather subordinate role in the case of longer strokes. If the strokes and positioning times need to be as short as possible and the machine cycle is essential for the productivity of the machine, acceleration changes should be carried out and programmed during the ramp. The largest frequency jumps should be during start-up and the smallest at the maximum possible frequency.
Approx. 5–10 steps should be traveled with constant frequency between the run-up and braking ramp. Otherwise, double the speed change would occur and this would cause a dynamic overload of the motor and step loss.
In addition to the linear ramp and exponential ramp, Nanotec also supports the S ramp, which primarily ensures a smoother transport due to jerk free acceleration and smooth deceleration and avoids typical load oscillations. The advantages of the S ramp are its flexible and optimum movement control. In particular, the S ramp is suitable for a wide range of process methods, such as the closed-loop control of the constant tensile stress during winding and unwinding; it causes less wear on machine parts such as gears and cam plates.
The maximum possible start/stop frequency depends on the frictional load or frictional torque but principally on the inert external masses and is specified as fs in the torque curve when the motor is operating under no load.
If a straight line is placed between fs and the maximum torque, the possible start/stop speed can be found very roughly at the intersection point of the torque and straight line; here, the acceleration torque Ma = J * a must be added to the frictional torque.
The actual start/stop curve can only be plotted using elaborate measurement results with different external inertial masses, which are then entered as a plurality of characteristics in the torque curve in the form of parameters. On the other hand, as the exact moments of inertia are often not yet available at the beginning of the project, we can determine the possible start frequencies experimentally in our laboratory with different inertial masses.
NanoPro runs on the following operating systems:
Win 2000, Win XP 32bit/64bit, Win Vista 32bit/64bit, Win7 32bit/64bit. Win8 and Mac are not supported.
Yes, because you can only run one program at a time. This applies to all controllers of the SMCI/Plug & Drive generation.
No, this is not possible. You can only start/stop the program or read possible error messages.
All hybrid linear actuators from Nanotec contain thread nuts made of high-performance plastic polyetheretherketone (PEEK), which is extremely wear resistant even at high thermal and mechanical loads. The thermoplastic nuts from Nanotec therefore offer far better sliding properties than conventional bronze thread nuts. They create less wear and are almost twice as efficient. This extends the service life of motors, and the self-lubricating properties of the nut reduce maintenance requirements.
The achievable resolutions, feed speeds and forces are calculated on the basis of the screw pitch (p in mm), torque curve (Md in Ncm) and efficiency as follows:
The force specified in the data sheets is based on a duty cycle of approx. 10% – 20% and must be reduced accordingly for higher values. A detailed service life assessment is based on the total distance of linear movement. At the rated force, hybrid linear actuators with a single lubrication reach a total distance of 5 – 20 km. Because the service life depends on a variety of factors, such as the concentricity of the external equipment, the movement speed and the temperature, a service life test is essential in applications with a service life requirement that falls in the range specified above.
If a high time-to-maintenance is required, the drive will have to be over-dimensioned. In addition, the service life is also greatly affected by the temperature of the thread nut. At temperatures above 70° C at the thread nut, the service life drops rapidly because wear increases disproportionately. If the motor becomes too warm, it is recommended to operate the motor in closed loop mode to reduce heat development.
1. Greater operating safety on vertical axes
To prevent uncontrolled downward movement due to gravity in the event of a power failure or emergency stop, Nanotec brakes are primarily used in Z-axes for personal and property protection.
2. Safety brake and holding brake
All Nanotec brakes are holding brakes or safety brakes with two frictional surfaces (spring-applied brakes), and the brakes are ventilated or opened by applying a voltage of 24VDC. They are almost always installed on the B-bearing side of electric motors. Braking of motion is effected by the controlled drive, whose rotational speed is first reduced to zero (to a standstill) before the safety brake closes. BKE brakes are electromagnetically ventilated brakes for dry operation whose braking force is generated by permanent magnets.
BW and BL brakes are spring-force ventilated brakes whose braking force is generated by a compression spring. When no current is applied, springs push against the anchor disc of the brake. The friction linings of the rotor, which is connected to the motor shaft via toothing, are clamped between this anchor plate and the mounting surface (rear side of motor) of the brake. When current is applied to the brake coil, a magnetic field builds up that pulls in the anchor plate and releases the rotor with the friction linings. The brake is ventilated. The specified torques apply for dry operation with absolutely grease-free frictional surfaces. The torque is lower for greased frictional surfaces.
3. Emergency stop brake
The steps required to stop a system safely need to be examined and checked in the form of a risk analysis as part of a disaster management plan or machine safety program. Nanotec brakes meet the static holding torques specified in the data sheet but cannot additionally handle the often considerable dynamic loads that arise when braking a moving load. If the dynamic load is in the range of the static load on the brake (work of friction, rotational speed, kJ, duty cycle, etc.), the brake can be used as an emergency stop brake 10 times before it needs to be inspected and usually replaced. Especially in regions with unstable power supplies, power failures and emergency stops may be quite frequent (causing uncontrolled movements) and machine safety should not be underestimated in these situations.
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