we do several lifetime and performance tests with our robolink D joints. Until July, main topics were material and geometry optimisations for the gear and bearing components. Nowadays, we do lifetime tests for different joint types at different loads and speeds. The attached film shows or test unit with currently 9 test places, it will be enlarged in the next weeks up to 12 oor 14 test places.
Some numbers and facts that we found out until now:
# general efficiency factor for our current material combination (iglidur J with aluminum HC) is betweeen 0,28 and 0,35 (over all sizes).
# output torque at tooth-break: 19 Nm (size -20) and 30 Nm (size -30), measured at room temperature for first movement. Today we measure this “breaking torque” at continuous operation. Main influences are the rotation speed, and together with this, the temperature in the gear. We see a huge loss of “breaking torque” in operation. For size -20 we find a safe number at high speed rotation of 2,5 Nm (>100.000 cycles) and 3,5 Nm at low speed rotation.
we see good potential for improvement in the material combination and geometry optimisation.
We have defined 3 different quality standards for our robolink D joints and I want to explain the background of this issue. The 3 qualities are:
- “low cost”,
- “high end”
The main performance differences are stiffness, friction, precision (reverse play) and on the other hand cost. For size -20 and -30, the price difference between low cost and high end is ~factor 2, for size -50 it is ~factor 1,5. standard version ~ in the middle.
The high end version contains of our lubrication free worm gear with worm wheel made of iglidur J and worm shaft made of aluminum (hard anodized), it has ball bearings for the axial shaft load and for the back side (only version 102). The outer bearings are our PRT-01-xx (= high end rotary table made of aluminum with sliding elements made of iglidur J). Housing and inner connection parts are made of moulded plastic parts (our RN33), screws and nuts are stainless steel.
Most parts of the standard version are the same, but the back side has a sliding bearing (iglidur J) instead of the ball bearing (only version 102) and the PRT itsself is version PRT-02-xx-AL, which is a low cost version of PRT-01-xx. It has more plastic parts and thus is much lighter. Compared with PRT-01 is is a bit less stiff and a bit less precise. In a performanmce comparison of the to joints, we see no big differences for most applicaations as long as we do not get to the limits.
The low cost version of our RL-D in comparison contains a moulded plastic worm shaft and sliding axial bearings instead of the ball bearings. Also the PRT is not build with an aluminum outer ring but a moulded plastic outer ring (PRT-02-xx-LC). Friction is higher and precision worse than our “standard” version. It should be used only for “easy applications” as for example hand adjustments.
For size -20 and -30, all versions are available. For size -50, only version “high end” is available, as PRT-02-50 is yet under construction. We will have it in ~OCT 2015.