Armed against damage

Written by: Tom Shelley | Published:

Innovative components are emerging that enable manipulator arms to be used in difficult environments. Tom Shelley reports



A novel design of hydraulic cylinder has made it possible to package manipulator arms so there are no loose hoses or sensor cables that can get caught on obstacles or otherwise be damaged.
The design makes use of hydraulic cylinders that have both ports on one end, and with novel hose fittings and rotary actuators.
While this makes them ideal for use on demolition robots and sub-sea, there is no reason why the same techniques cannot be applied to other types of construction and destruction equipment.
Both the components and complete arms are manufactured by Hydro-Lek, based in Finchampstead, Berkshire, and were demonstrated by managing director Chris Lokuciewski at the recent Ocean Business show in Southampton. The central port feeds the centre of the cylinder in the usual way, but the other port is connected to a passage, which goes down a gap between inner and outer tubes.
“The cylinder is made as a one piece machining with a sleeve over it, welded on at both ends,” says Lokuciewski. “Alternatively, we could use an internal feed.”
The advantage of this arrangement is that it allows the cylinders and hoses to be packaged inside box sections, so the hoses are protected against damage. The company also makes its own right-angled banjo fittings, with a much lower profile than standard fittings plus elbows, also helping to get cylinders inside box sections. The cylinders are made out of 316 stainless steel, hand polished, with standard strokes of 65, 100 and 135mm, or up to 1.5m on special order.
Most manipulators require a rotation axis, or even two, and for this purpose the company has another special product that produces rotation by using pistons to push a spline down the inside of a helix. This is much less prone to leak-induced slippage than a conventional rotary hydraulic actuator with an internal vane. It can also be made hollow, allowing hoses and potentiometer position sensor cables to be fed down the centre, which keeps them protected. These actuators are again machined out of single blocks, with 1.5 degrees of drift maximum, according to Lokuciewski.
For camera mounting, the company makes a pan and tilt unit that uses a hydraulic slip ring assembly, so it does not require the attachment of any flexible hoses at all.
As well as sub-sea and general demolition work, the company supplies equipment for nuclear power plant decommissioning, which clearly has to be undertaken by remote-controlled equipment of extreme reliability. Cutters can be hydraulic ram powered or use rotating discs. The company also supplies water jet units, venturi suction units used in conjunction with the water jets and a sub sea drill. This is designed to drill holes so that sacrificial anodes can be fitted under water. It uses a heavy-duty magnet to hold the drilling system in place, while a hydraulic motor rotates the drill. A cylinder with a flow control valve pushes the drill carriage down the guide rods to drill the hole.

Pointers

* Hydraulic cylinders can be supplied with both ports in one end

* Rotary actuators are made with pistons pressing a spline down a helix to overcome the leakage drift problems encountered with conventional rotary hydraulic actuators with vanes

* Manipulator arms can be supplied with boxed-in sections, partly because of the single end feeding, so there is no opportunity for hoses and sensor cables to catch on obstacles and become damaged


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