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 software page on our website.