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Did You Know? Synchronized Motion Using Encoder Following September 2, 2013

Posted by Servo2Go.com in Technical Support Information.
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Encoder following, which is also known as A/B Quadrature control mode, can be utilized on stepper and servo drives sold by Applied Motion Products.  An encoder is a feedback device most commonly found in servo systems where positional feedback is essential for closed-loop control. Incremental encoders are standard on all servo motors sold by Applied Motion and they may also be ordered pre-installed on our stepper motors and integrated steppers for use with our stall prevention and stall detection features.

But did you know that an encoder can also act as an input signal to control and synchronize the motion of two or more motors?

Because the output from an encoder is a series of pulses, consisting of an A and B channel, these signals are very similar to the Step Pulse & Direction outputs that are commonly found on a PLC or indexer. With a few simple configuration steps, an Applied Motion stepper drive or servo drive can be configured to accept these encoder pulses as a command source.

In motion control applications such as high speed insertion, line speed matching, adhesives application and labeling (all of which require one axis to be synchronized to another), this configuration can not only be very useful, but quite easy to set up and manage.  In those applications that require the secondary following axis to go faster or slower than the primary axis, the “Electronic Gearing” ratio can be manipulated to achieve this.

When configuring a stepper drive, the ST Configurator™ software is used to select A/B Quadrature as the signal type. When configuring a servo drive, Quick Tuner™ is used to make this selection. In both cases, the Electronic Gearing parameter (defined in units of steps per revolution), can be defined such that the motor following the encoder will run faster, slower, or at the same speed as the encoder itself. To illustrate this concept, picture a large machine equipped with a hand wheel connected to an encoder, which has been wired to a drive configured for encoder following. As the machine operator turns the hand wheel, the corresponding machine axis can be positioned at the desired rate of speed.

In more sophisticated control systems that require encoder following to be switched on only at specific times during the process, our Serial Command Language (SCL) can be used to issue commands to the drive to accomplish this.  This feature allows the system designer to synchronize, on demand, two or more axes of motion.

The FE (Follow Encoder) serial command can be issued to switch on encoder following while a drive is running in any other control mode.

Other SCL commands related to FE are:

  • EG – Electronic Gearing (sets ratio for following motor)
  • AC – Acceleration (controlled upon initiation of FE)
  • DE – Deceleration (controlled when FE is turned off)
  • DI – Distance (defined deceleration distance)

To learn more about SCL and Q Programmer, please visit our website.

For more information, please contact:

EDITORIAL CONTACT:
Warren Osak
sales@servo2go.com
Toll Free Phone:  877-378-0240
Toll Free Fax:       877-378-0249
www.servo2go.com

Tags:  Encoder Following, Applied Motion Products, Servo2Go, Step Motor, Servo Motor, Stepper Motor,

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Trapezoidal vs Sinusoidal Brushless Servo Amplifiers May 23, 2013

Posted by Servo2Go.com in New Product Press Releases, Technical Support Information.
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Originally posted on June 30th, 2011 by John Hayes at Galil Motion Control

Galil AMP-43540 Sinusoidal Servo Amplifier

Galil AMP-43540 Sinusoidal Servo Amplifier

The new Galil Sine drive amplifiers are a welcome addition to the existing DMC-40×0 and DMC-41×3 line-up of servo and stepper amplifiers – yet the addition of the new amplifiers also brings up a question  – “When should I use a sinusoidal drive instead of a trapezoidal drive?”.  This article will go over the Galil brushless servo drive architecture and highlight what you should know when making an amplifier selection.

Two Loop Architecture

In order to gain a better understanding of servo amplifiers and specifically how the Galil servo amplifiers work, the first thing to do is to understand the Controller/Amplifier architecture.  Unlike most single axis drives on the market, Galil uses a split sample rate.  The first and highest speed sample rate occurs on the amplifier and is used on the current loop.  The D3540 Sinusoidal amplifier runs its current loop at 33 kHz and the D3040 Trapezoidal amplifier runs at 66 kHz (which can be increased to 120 kHz for low inductance applications).  The benefits of a high speed current loop are:

  • Fast response to desired current/velocity command signal
  • Less destabilizing phase shift on the position loop
  • Tighter more accurate control – 16bit resolution
  • High Closed Loop Frequency (3-4 kHz)

The second loop in the system is the position loop.  Because of the limitations of real world mechanics, a position loop generally has a closed loop frequency in the range of 20 to 200 Hz.  The sample rate required to achieve this is only from 1 kHz to 4 kHz.  Note that the DMC-4000 can have a sample rate of up to 16 kHz and can control up to 8 axes allowing all axes to be tightly coupled.  General motion control applications run optimally at a 1 kHz position loop update.  High performance and high resolution applications can be run at higher rates depending on the required performance.

Separate processors for the Amplifier and Controller allow for this two loop Architecture which allows Galil to be extremely responsive and highly accurate and also perform whatever functions are required in a user’s application.

Trapezoidal vs. Sinusoidal Commutation

Trapezoidal commutation is the most cost effective way of controlling a brushless servo motor.  It is perfect for higher speed applications and applications where the motor and mechanics will eliminate the torque ripple that occurs during switching current from one phase to the next.  Hall sensors are required for Trapezoidal commutation.

Sinusoidal commutation is great for lower speed, direct drive or linear motor applications where the torque ripple of the motor phases needs to be minimized.  Since the current to the motor phases are weighted as sine waves, the torque going through the motor is smooth and has minimal ripple.  It also allows the mechanics to be simplified because Hall sensors can be eliminated.

Sinusoidal amplifiers rely on an initialization sequence at power-up to provide the correct commutation.  This can be done in one of 3 ways on the Galil.    The first and most common method is the BX command that uses an algorithm that energizes the phases and determines the brushless angle.  Only a small amount of motion (if any) is shown with this method.  The second method is to use the BC command that requires Hall sensors to be hooked up.  It will move the motor and use the first hall transition as the basis for the commutation.  This method is necessary if there is an external force on the motor such as a gravity load.  The third method uses the BZ command to drive the motor to the zero degree commutation point which can result in a jump to the closest zero phase.

More info on Galil Sinusoidal Amplifiers

The new AMP-43540 drives four brushless motors operating at up to 8 Amps continuous, 15 Amps peak, 20-80 VDC.  The gain settings of the amplifier are user-programmable at 0.4, 0.8, and 1.6 Amp/Volt.  The amplifier offers protection for over-voltage, under-voltage, over-current, short-circuit and over temperature. A shunt regulator option is available.  For more information, please see: DMC-40×0 Product Page .

For additional information on the DMC-40×0 Accelera Series and new AMP-43540 option, see

http://www.servo2go.com/product.php?ID=101658&cat=

For more information, please contact:

Editorial Contact:

Warren Osak
sales@servo2go.com
Toll Free Phone:  877-378-0240
Toll Free Fax:   877-378-0249
www.servo2go.com