applied motion products improving smoothness and accuracy in stepper systems presentation oct. 2007

Improving SmoothnessSmoothness and AccuracyAccuracy

in Stepper Systems

Toll Free Phone: 877-378-0240Toll Free Fax: 877-378-0249

sales@servo2go.comwww.servo2go.com

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High PerformanceHigh Performance Stepper DrivesStepper Drives

from Applied Motion ProductsApplied Motion Products

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About Applied Motion

Founded in 1978Privately OwnedHeadquarters in Watsonville, CA30 Employees

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Visit us on the web at http://www.applied-motion.com

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Motors from AsiaWe partner with motor manufacturers in Japan, China, and Taiwan.Our oldest partner, Tamagawa Seiki in Japan, has been our partner for almost 30 years.

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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.

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Products

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

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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

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Inherent Problem

ResonanceStep motors are resonant because in short their rotors behave much like a classic “mass on a spring”.

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Inherent Problem

ResonanceWhen 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.

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Inherent Problem

ResonanceJust 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!

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Inherent Problem

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

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Inherent Problem

ResonanceThere are two major, negative side effects of resonance.

Rough motion

Loss of torque, which can lead to loss of position

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Inherent Problem

ResonanceRough motion

When step motors resonate they generally vibrate excessively.This can be bad for sensitive equipment.

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Inherent Problem

ResonanceLoss 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.

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Solution

ResonanceThere are three main remedies for resonance.

MicrosteppingTorque Ripple SmoothingElectronic Damping

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Solution

MicrosteppingMicrostepping 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

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Solution

MicrosteppingStepper 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

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Solution

Torque Ripple SmoothingTorque 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 motionToll Free Phone: 877-378-0240Toll Free Fax: 877-378-0249

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Solution

Electronic DampingElectronic 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”.

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Solution

Electronic DampingThe 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

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Solution

High performance stepper drives from Applied Motion offer…

Microstep EmulationTorque Ripple SmoothingElectronic Damping

All of which contribute to…Smoother motion from your step motor

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Inherent Problem

Accuracy – Open Loop SystemsWhen 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.

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Solution

Accuracy – Open LoopIn 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).

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Solution

Accuracy – Open LoopThe encoder is then connected to the drive via a feedback cable.

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Solution

Accuracy – Open LoopApplied Motion stepper drives can perform two main functions when an encoder is added to the system.

fool-proof Stall DetectionStall Prevention w/ Position Maintenance

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Solution

Fool-proof Stall DetectionStall 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.

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Solution

Stall PreventionLike 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.

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Solution

Stall PreventionSlowing 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 Profile

Target Time

Target Move ProfileActual Move Profilewith Stall Prevention

Target Time

Actual Time

Point at which torquedemand increases

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Solution

Position MaintenanceWith 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.

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Solution

High performance stepper drives from Applied Motion offer…

Encoder feedback options

Which contribute to…A more accurate motion control system

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Hardware

High Performance Stepper Drives from Applied Motion

ST Series

STAC6 Series

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Hardware

ST Series: Two power ranges

ST55 A/phase (peak)24-48 VDC input

ST1010 A/phase (peak)24-80 VDC input

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Hardware

ST Series: Three levels of control-S

Step & DirectionOscillatorHost command execution (SCL)SiNet Hub compatible

-QDrive with built-in motion controller

-SiDrive with built-in indexer

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Hardware

ST Series: -S modelsST5-SST10-S

Microstep EmulationTorque Ripple SmoothingElectronic DampingSmall size

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Hardware

ST Series: -Q modelsST5-QST10-Q

Microstep EmulationTorque Ripple SmoothingElectronic DampingEncoder feedback option

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Hardware

ST Series: -Si modelsST5-SiST10-Si

Microstep EmulationTorque Ripple SmoothingElectronic DampingEncoder feedback option

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Hardware

STAC6 Series: High power drive6 A/phase (peak)160 VDC bus110 or 220 VAC inputUL recognized (110 VAC)

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Hardware

STAC6 Series: Three levels of control-S

Step & DirectionOscillatorHost command execution (SCL)SiNet Hub compatible

-QDrive with built-in motion controller

-SiDrive with built-in indexer

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Hardware

STAC6 Series: Model NumbersSTAC6-SSTAC6-QSTAC6-QE (expanded I/O)STAC6-SiSTAC6-220-SSTAC6-220-QSTAC6-220-QE (expanded I/O)STAC6-220-Si

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Hardware

STAC6 Series: All ModelsMicrostep EmulationTorque Ripple SmoothingElectronic DampingEncoder feedback optionUL recognized (110 VAC units)

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www.appliedwww.applied--motion.commotion.com

for more information

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applied motion products improving smoothness and accuracy in stepper systems presentation oct. 2007

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