Applications of Robotic Arms

The customer needed precision rotary axis control in the lowest profile form factor for multiple sequential robot arm joints. Other major requirements included minimal movement at start-up to report absolute position, and minimal signal cabling also keeps the overall arm size as small as possible.

robot arm joints

The Solution

Celera Motion developed a series of custom-sized PCB-based encoder modules with FPGA control and BiSS communication interfaces, each featuring a Micro Motion Absolute™ (MMA) rotary grating disk and two standard ChipEncoder™ readheads. MMA grating technology makes use of a standard 40 micron pitch incremental counting track, combined with a reference track where each index is uniquely spaced. Multiple index marks are detected with just a small movement at start-up, and the measured spacing is compared to a lookup table in firmware in order to find out the absolute position.

PCB-based encoder modules

The Benefit

For improved rotational accuracy, the outputs of the two encoders are averaged and absolute position is established at start-up with minimal axial rotation. BiSS serial communication protocol enables each successive robot joint to be connected in a daisy-chain arrangement, instead of having dedicated bus cables for each axis, which together with the compact size of the ChipEncoder, helps lower the overall size of the each joint. High-speed serial communication (32 MHz clock, 1 µsec update rate) guarantees high robot responsiveness to the operator’s commands.


. .
PCB Diameter 20 mm
Scale Diameter 15 mm
Total Module Height 13.8 mm
Serial Interface BiSS C
Clock Rate 32 MHz
Position Update Rate 1 µsec
Resolution 85,280 CPR (15.2 arc-sec; 73.7 µrad)
Cable Wire Count 5 twisted pairs, 32 AWG


Celera Motion

This information has been sourced, reviewed and adapted from materials provided by Celera Motion.

For more information on this source, please visit Celera Motion.


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