SmoothnessAccuracy Improving Smoothness and Accuracy in Stepper Systems

High Performance Stepper Drives Applied Motion Products High Performance Stepper Drives from Applied Motion Products

About Applied Motion  Founded in 1978  Privately Owned  Headquarters in Watsonville, CA  30 Employees

About Applied Motion  Visit us on the web at

About Applied Motion  Motors from Asia We partner with motor manufacturers in Japan, China, and Taiwan. Our oldest partner, Tamagawa Seiki in Japan, has been our partner for almost 30 years.

About Applied Motion  Drives from the U.S.A. We research, develop, and design all of our drive electronics. We recently formed a joint venture with Shanghai Moons’ Motor Co. to develop new motor & drive products.

Products  We offer a wide range of Step Motors, Servo Motors, and Drives

Today’s Discussion  Applied Motion steppers drives improve upon two aspects of step motor system performance Smoothness – by eliminating resonance Accuracy – by closing the position loop

Inherent Problem  Resonance Step motors are resonant because in short their rotors behave much like a classic “mass on a spring”.

Inherent Problem  Resonance When a step motor takes a step, the rotor reacts to the changing stator field in the same way a mass on a spring reacts to a change in position.

Inherent Problem  Resonance Just like the mass on a spring, the motion of the rotor settles into position after each step. This settling can last as long as a second or more in worst cases!

Inherent Problem  Resonance If the settling doesn’t occur rapidly, or the ringing of the rotor gets worse, the motor can become unstable and lose position (stall).

Inherent Problem  Resonance There are two major, negative side effects of resonance.  Rough motion  Loss of torque, which can lead to loss of position

Inherent Problem  Resonance Rough motion  When step motors resonate they generally vibrate excessively.  This can be bad for sensitive equipment.

Inherent Problem  Resonance Loss of torque  When step motors resonate much of the torque available in the motor is used up in keeping the rotor synchronized with the stator field, and in worst cases the motor will not have enough torque to move the load.  Loss of torque often leads to stalling.

Solution  Resonance There are three main remedies for resonance.  Microstepping  Torque Ripple Smoothing  Electronic Damping

Solution  Microstepping Microstepping does not eliminate the natural resonant frequency of a step motor, but it does diminish the level of excitation. In other words, smaller steps mean smaller responses. coarse steps microsteps

Solution  Microstepping Stepper drives from Applied Motion can microstep even when the control signal is low resolution. This is called Microstep Emulation. coarse steps from external indexer microstep emulation performed by drive

Solution  Torque Ripple Smoothing Torque ripple smoothing reduces the inherent torque ripple that all step motors display at low speeds (typically well under 5 rps). Torque ripple smoothing works by applying a “negative” current to the motor which offsets the torque ripple. torque ripple negative current result = smoother motion

Solution  Electronic Damping Electronic damping remedies two aspects of the motor’s resonance.  Inherent resonant frequencies of the motor.  A complex interaction between drive and motor that happens at higher speeds, often called “mid-band resonance”.

Solution  Electronic Damping The end result of electronic damping is to minimize and even eliminate the resonant response of the step motor over a wide range of speeds. without electronic damping with electronic damping

Solution  High performance stepper drives from Applied Motion offer… Microstep Emulation Torque Ripple Smoothing Electronic Damping  All of which contribute to… Smoother motion from your step motor

Inherent Problem  Accuracy – Open Loop Systems When properly sized an open loop step motor system can be adequately accurate for most applications. Keys to proper sizing are knowing the load and knowing the move parameters ahead of time. However, the nature of an open loop system is such that no built-in mechanism exists for indicating a motor mis-position or stall.

Solution  Accuracy – Open Loop In situations where an extra layer of accuracy is required, step motors from Applied Motion can be fitted with high resolution, incremental encoders. The encoder is mounted to the rear shaft of the step motor (order “D” option).

Solution  Accuracy – Open Loop The encoder is then connected to the drive via a feedback cable.

Solution  Accuracy – Open Loop Applied Motion stepper drives can perform two main functions when an encoder is added to the system.  fool-proof Stall Detection  Stall Prevention w/ Position Maintenance

Solution  Fool-proof Stall Detection Stall detection works when the stepper drive monitors encoder position relative to commanded motor position. As soon as a mis-position occurs the drive stops motion and sets a fault to notify the user. This method is fool-proof because it works under all conditions, regardless of motor speed or load conditions.

Solution  Stall Prevention Like stall detection, Stall Prevention works when the stepper drive monitors encoder position relative to commanded motor position. As soon as a lag between the encoder position and the commanded motor position occurs the stepper drive starts to slow the motor speed.

Solution  Stall Prevention Slowing down the motor allows the motor to operate in a speed range where its torque output is higher, and therefore have a better chance of finishing the move.

Solution  Position Maintenance With Stall Prevention turned on the drive automatically corrects errors in motor position from external forces when the motor is at rest. In other words, if the motor is “bumped” out of position it automatically corrects itself.

Solution  High performance stepper drives from Applied Motion offer… Encoder feedback options  Which contribute to… A more accurate motion control system

Hardware  High Performance Stepper Drives from Applied Motion ST Series STAC6 Series

Hardware  ST Series: Two power ranges ST5  5 A/phase (peak)  VDC input ST10  10 A/phase (peak)  VDC input

Hardware  ST Series: Three levels of control -S  Step & Direction  Oscillator  Host command execution (SCL)  SiNet Hub compatible -Q  Drive with built-in motion controller -Si  Drive with built-in indexer

Hardware  ST Series: -S models ST5-S ST10-S  Microstep Emulation  Torque Ripple Smoothing  Electronic Damping  Small size

Hardware  ST Series: -Q models ST5-Q ST10-Q  Microstep Emulation  Torque Ripple Smoothing  Electronic Damping  Encoder feedback option

Hardware  ST Series: -Si models ST5-Si ST10-Si  Microstep Emulation  Torque Ripple Smoothing  Electronic Damping  Encoder feedback option

Hardware  STAC6 Series: High power drive 6 A/phase (peak) 160 VDC bus 110 or 220 VAC input UL recognized (110 VAC)

Hardware  STAC6 Series: Three levels of control -S  Step & Direction  Oscillator  Host command execution (SCL)  SiNet Hub compatible -Q  Drive with built-in motion controller -Si  Drive with built-in indexer

Hardware  STAC6 Series: Model Numbers STAC6-S STAC6-Q STAC6-QE (expanded I/O) STAC6-Si STAC6-220-S STAC6-220-Q STAC6-220-QE (expanded I/O) STAC6-220-Si

Hardware  STAC6 Series: All Models Microstep Emulation Torque Ripple Smoothing Electronic Damping Encoder feedback option UL recognized (110 VAC units)

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