Question:
How can a cam drive be adapted to a master value generation via absolute encoder?
Answer:
- Absolute encoder, e. g. FRABA, IVO, ... at system bus
- Position information of the encoder as an answer to the controller's Sync-telegram
- Extrapolation between the item values if Sync-cycle is > 1 ms
- Relationship between y-axis to x-axis should be 1:1
A general rule should be that for the demanded accuracy a resolution of the master value of 10 pulses is available. Example: Accuracy = 1 mm, resolution = 65536 pulses for a distance of 6550 mm.
In case of cam drives the pulses for an encoder revolution or for a cycle consisting of several revolutions, create the clock pulse length of the master value, this means the length of the x-axis. Referred to one clock pulse length the drive executes the motion profile (y-axis) once.
In order to pass the demanded accuracy of the master axis to the drive cam, the relationship between the maximum y-value to the clock pulse length should be factor <= 1. Discrepancies of y/x >> 1/1 result in an uneven running and noise of the drive.
If for registration of the position set value the Sync-telegram cannot be sent in the 1 ms pulse (high load of the system bus), an extrapolation between two set values will be necessary. For this purpose the EXTPOL2 function block must be applied and a cycle must be defined (2 ms, 3 ms, etc.). An extrapolation cycle, which is missing or too great, results in noise generation, as well.
