ImprovingSmoothnessSmoothness and AccuracyAccuracy

in Stepper Systems

High PerformanceHigh PerformanceStepper DrivesStepper Drives

fromApplied Motion ProductsApplied 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 http://www.applied-motion.com

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 stepsfrom externalindexer

microstep emulationperformed 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.

withoutelectronic dampingwithelectronic 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.

Target Move Profil e

Target Time

Target Move ProfileActual Move Profilewith Stall Prevention

Target Time

Actual Time

Point at which torquedemand increases

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) 24-48 VDC input

ST10 10 A/phase (peak) 24-80 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)

Visit

www.applied-motion.com

for more information