In his Bachelor Thesis, Markus Behrens did several measurements about repeatabilty and absolute precision of one igus Standard Joint arm (5 DOF, big Version): RL-D-RBT-5532S-BC-AE.
A CPR (Commonplace Robotics) control unit was used for the evaluation. The main results and further details are given in the pdf document attached. Conclusion:
Our customers can choose between motor encoders / Ini switches and igus output encoders (both incremental angle sensors).
Motor encoder / INI (RL-D-RBT-xxxxx-BC):
+) proven industrial standard, double ended signal transmission (A/A-, B/B-), high resolution (500 signals / motorturn * transmission of the joint)
-) 3 cables per axis (motor, encoder, INI), reverse play of the joint is not noticed, mechanical changes in the joint are not noticed (i.e. temperature, load,..)
Output encoder (RL-D-RBT-xxxxx-BC-AE):
+) cheaper, less cables, easy to replace, we measured better repeatability values for multi axis arms in different use cases (detailed results will be shown in ~6 weeks)
-) not industrially proven, single ended signal transmission (A, B) => danger of signal loss is higher, EMC not proven
Conclusion: We recommend to use our output encoders for non critical (non industrial) applications, for industrial applications we recommend motor encoders or testing of the output encoder in the given environment.
DOWNLOAD SECTION. New data sheets for output encoders:
igus supplies “electromechanical joint arms“. They consist of:
- robolink joints with worm gears (RL-D) and strain wave gears (RL-S),
- igus stepper motors NEMA11, -17, -23 and -23XL,
- Ini-switches for the Zero-Point definition (BC version) or Output encoders (BC-AE version),
- connection parts between these joints (folded metal sheets RL-DC)
- a set of igus cables (5m long) and e-chains for the connection to a control unit
- OPTIONAL: an adapter for the connection of an Actuator (gripper, suction cup, camera,…)
Please find attached data sheets and STEP data for the different configurations:
“small version” with 2x RL-D-30 and 2x RL-D-20 (payload max. 1 kg, reach ~600 mm)
“big version” with 2x RL-D-50 1x RL-D-30 and 1x RL-D-20 (payload max. 3 kg, reach ~750 mm)
We supply 2 options of encoders for our joints / joint arms.
Option 1 (our Standard before HMI 2017): Motorencoder plus Ini switch for 0-point reference on the joint output (PRT bearing)
Option 2): Output encoder on the PRT bearing of the joint. This is our own development, we use a magnetic ring plus Encoderchip on the output with an aditional magnet and Hall Sensor as reference point. Please find attached a description of the output encoder attached in GER and ENGL. Advantage: less cables, higher resolution, more accuracy for the arm.
At the HMI trade show we released our strain wave gear (RL-S) as a product in addition to our worm gears (RL-D). The smallest version of the strain wave gear (RL-S-17-N11-00-28-020K0) is used for the fifth axis in the standard joint arms RL-D-RBT-5532S-XX and RL-D-RBT-3322S-XX. The RL-S-17 gear comes in two variations, both have a transmission rate of 28:1:
1. suitable for small motors (like NEMA11 stepper motors, holding torque = 0.1 Nm), output torque max. 1 Nm
2. suitable for slightly bigger motors (like NEMA17 stepper motors, holding torque = 0.5 Nm), output torque max. 3 Nm
The biggest available joint is the RL-S-20-N23-00-38-12000 with a transmission rate of 38:1. The maximum output torque is about 5 Nm, depending on speed and usage duration. Also here you are able to choose between two versions:
1. high-end: RL-S-20-N23-00-38-12030 (with PRT-01-20)
2. standard: RL-S-20-N23-00-38-12000 (with a standard PRT-02-20-AL)
attached are CAD data and the current data sheets: RL-S-STEP+Data
All gears can be purchased with igus stepper motors, initiator kits, encoder kits or customized to be combined with your motor!