Does torque affect prismatic joints in a gantry robot? If so, how can we reduce this?

Question

I was posed a question based on my project on a gantry robot, "Cancelling torques that affect the prismatic joints can help us choose components with a lower cost which increases the cost-effectiveness of our system, how can we cancel these torques? (Think about external guides and guide rails)".

I've been thinking about this for a couple of days, googling different stuff, but I haven't been able to come up with answer. I can't fathom how torque would affect a linear joint, and thus coming up with a solution is difficult.

Any help would be appreciated.

Answer 1

It sounds like you're thinking about the forces and strength of the powered components of the joints. The prismatic joints maintain their shape by transferring any torques applied to one link through to the connected link.

As an example, if you think about a classic tower crane with a tower and an arm across the top. When you pick up a load a the tip of the crane arm all of the new forces from the load are supported by torque at the top of the crane tower. This requires that joint to be very strong and take high torques due to the large lever arm. However if you were to build a second tower and attach it to the other end of the lifting arm you could then lift the same load with much less torque on any joint because the lever arm is much shorter to the closer support point. And the prismatic joints won't need to be build to counter as much torque. And thus the design can be more cost effectively built with lower load ratings for the prismatic joints. Lower load ratings will mean that you can have fewer or cheaper bearings to make sure that the prismatic joint keeps working.