“We did have some very good results with that,” Greaves says. The project demonstrated that robots can be used for machining if operators take their dynamic operation into account.
The design of most robots makes it difficult for them to achieve accuracy. A robot can’t really cut a straight line, for example. “The reason is twofold. One is that a serial arm robot is made of six rotary joints. If you are trying to draw a straight line with six things spinning round, you essentially will never get a straight line. You will get your best attempt at a straight line,” Greaves says.
The other problem is that a standard robot consists of two big beams. “If you put any weight or force back through from your machining process through the arm, [it] tends to deflect out of the way. The robots are not very stiff,” he continues.
To overcome the stiffness problem, AMRC worked with the Swedish system manufacturer Exechon on the development of a lightweight parallel kinematic robot, which resembles an upside-down tripod. “By using the Exechon-style robot you get a very stiff structure, meaning that if you want to machine with it and put force through that structure it can resist the force and keep its position accuracy,” says Greaves. “That’s a massive advantage over a serial arm robot.”