Robotic Arms – Industrial Applications

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

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 uses a standard 40-micron pitch incremental counting track, in combination with a reference track where each index is uniquely spaced. Multiple index marks are detected with just a slight movement at start-up, and the measured spacing is compared to a lookup table in firmware to establish the absolute position.

PCB-based encoder modules

The Benefit

The outputs of the two encoders are averaged for better rotational accuracy, and absolute position is determined at start-up with very little axial rotation. BiSS serial communication protocol enables each successive robot joint to be connected in a daisy-chain arrangement, rather than having dedicated bus cables for every axis, which together with the small size of the ChipEncoder helps in reducing the overall size of the each joint. High speed serial communication (32 MHz clock, 1 µsec update rate) guarantees that the robot is highly responsive to the operator’s commands.

PCB-based encoder modules


. .
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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