PROTECTING THE STRUCTURE

 

The structure of any manipulator has a large inertia. In addition the manipulator is used to handle heavy payloads at large radii.

 

How are these stress peaks / reversals caused?

The manipulator is designed to be a high performance machine and uses servo valves to provide a very good response on the 3 main axes. This responsiveness from the valves can cause an almost instantaneous change in direction of the high inertia (i.e. heavy!) structure resulting in a high peak of stress for a few milliseconds.

 

When the computer design programme was being verified by tests with strain gauges on the prototype manipulator very high stress levels were observed each time the operator changed the direction of the machine, even when the grippers had no payload.

 

There is a peak of stress (and also a peak in hydraulic oil pressure) and a stress reversal at each change in direction. These stress reversals with a high peak stress put a large strain on the structure and bearings. The Clansman manipulator is designed to accommodate these stress reversals but can their effect be modified?