Background: I'm designing a machine that uses an actuator to push an object. The connecting component may not take certain bending forces, therefore I'm trying to evaluate the system with a free body diagram.

The moving system is support by preloaded linear rails. The red component is a load cell that may only take limited bending forces (it is however rated to handle the 50N in tension or compression)

Both sliders are preloaded and can be assumed perfectly parallel

My intuition tells me that there will be some bending forces, but I'm not able to be clear about this!

partial free body diagram


1 Answer 1


Let's call the length of the handles L and the distance between the two vertical rollers D. This is for now ignoring the details of rails being preloaded. Add details to your question if you feel it may be consequential on that.

let's start off by noting that the red load sensor is not going to receive any moment because it is a pin support. It will just receive the 50N normal force from the left handle and will transfer it up to the end of right side handle.

Now let's look at the forces and reactions of the two parts.

On the left side we have a clockwise moment of 50L.N at the connection point of the handle to the square slider and this moment is balanced by two horizontal forces of 50L/D on the top right and bottom left rollers. The one on top right roller pointing to the right and the one on the bottom left pointing to the left.

At the connection point of the two handles we have a 50 N force directed up acting on the right handle. This causes another 50L N clockwise moment at the right slider which again will be balanced by two horizontal forces on the vertical rollers by the amount of 50L/D.N. One is acting on the top right roller to the right and the other on the bottom left roller to the left.


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