When selecting resolution values for motors used with Gemini servo drives or drive/controllers, it is important to understand the relationship between the encoder input signal resolution, set through the ERES command, and the encoder output signal resolution, set by the ORES command. Most of the time, these commands will be left at their default settings, but if modifications are desired, the following facts can be helpful in setting vales for these commands. REMEMBER TO ALSO READ THE COMMAND DESCRIPTIONS FOR BOTH OF THESE COMMANDS BEFORE CHANGING ANY VALUES.
The ERES command defines what the Gemini drive sees as the actual post-quadrature resolution of the encoder. In other words, ERES defines how many encoder pulses recieved by the Gemini unit is considered one complete revolution of the motor. The ORES command, on the other hand, defines the resolution of the encoder output pulses sent from the Gemini unit to the controller. Adjusting the value of the ORES command enables the Gemini unit to convert each incoming encoder pulse to a higher, equivalent, or smaller increment than the actual encoder resolution coming into the Gemini unit. A common reason for modifying the the ORES value is typically for converting the counts from a high resolution encoder to a more useable resolution for commanding moves (like setting a 20000 count/rev encoder to 3600 counts/rev, so as to more easily command moves in 1/10 degree increments).
Both the ERES and ORES values are automatically set upon download of the Gemini Motor Configuration file when performing the Gemini hardware setup (see the Gemini Hardware Installation Guide), but can be configured to any value within the range specified in the Command Description for ERES and ORES.
When the ORES value equals the ERES value, the actual native encoder counts are passed, unaltered, directly through the Gemini to the controller. When ORES is set to value higher or lower than the ERES value, the Gemini converts the incoming encoder pulses to "pseudo" counts, which are then output to the controller - as defined by the ERES/ORES ratio.
Note that setting the ORES value to a larger value than the ERES value does NOT increase the resolution of the encoder. In this situation, ORES simply acts as a multiplier. For example, if the ERES value is entered as 2 counts per revolution, and ORES is set to 5 counts to the controller, then every time that the encoder sends one pulse to the Gemini drive (each time an encoder pulse is detected by the Gemini drive from the encoder), the drive will output a "burst" of 10 "pseudo" counts to the controller; four encoder counts will appear as 10 "pseudo" counts at the controller, etc. In this case, ORES is simply scaling the encoder counts coming into the Gemini before they are output to the controller - nothing more. Additionally, if the encoder is somehow stopped between even multiples of counts, the ORES will not give partial counts to the controller. In the example above (ERES=2, ORES=5), if the encoder were somehow stopped at one encoder count, querying the encoder count at the controller would not come back with a response of 2.5 counts. The encoder count response that the controller will display will continually fluctuate between 0 and 5 counts.