A majority of motion control systems that include feedback will use an incremental encoder. The draw back to incremental encoders is that upon power up the controller does not know the position of the motor in absolute terms. To compensate for this, system engineers will home a system upon power up by driving the motor to a switch at a known location. This works well for many systems, but sometimes systems demand that the controller retain knowledge of the absolute position even during a power cycle. For these applications an absolute encoder is required.
Galil motion controllers have standard options for communicating to a number of different absolute encoder technologies. Resolver feedback is a common type of absolute feedback that has been used in motion control systems for a number of years. This can be advantageous in systems where the mechanics are subject to a harsh environment.
An older technology that is still used by some encoders is binary parallel encoders. These feedback devices work by toggling a specific number of bits that represent the absolute position to the motion controller. The draw back to a parallel encoder is that there is a wire for every bit, which can quickly become cumbersome when you look at encoders with 24 bits or more of resolution, especially with a multi-axes control system.
By far the most popular, SSI (Serial Synchronous Interface) feedback is offered by a number of different encoder manufacturers. The advantage to SSI technology is that it is quickly becoming an industry standard due to its ease of use and simple set up. Besides power and ground, there is only a clock and a data signal that need to be connected. Building on SSI, some encoder manufacturers support a BiSS (Bidirectional Serial Synchronous Interface) protocol now. These encoders offer the ability for the encoder to store information locally and transmit them to the motion controller. This builds on SSI which only allows encoder position information to be transmitted.
Another new-comer to the encoder protocol world is the Distance Coded Index. These types of encoders are quasi-absolute. The encoder track is lined with various index pulses that are specific distances apart. Upon power up, with two short moves in either direction, the encoder can read the index pulses and determine the absolute position.
There are many types of encoder protocols to choose from in the current marketplace and Galil motion controllers offer you the flexibility to choose the one that meets the needs of your system. If you do not see the type of interface you require listed here, call Galil’s applications engineers to review your selected interface.