Force Driven Gripper V1

Eventually I’ll be building an entire force-driven robot arm, but for now I’m going to experiment with a gripper. There’s a video about this project, or scroll down for pictures and words. You can get the CAD and code from Github.

The finger design is the same as my Robot X Spiderman hands, scaled up. However this has given me some issues with the force required to actuate the fingers as it gets greater the more the finger needs to bend.

The gripper is driven with three servos, so each finger is independent. A spring connects the tendon to the finger.

We can calculate the force by measuring the stretch in the spring, i.e. the difference between the servo position and the actual finger position.

I used bend/flex sensors running along each finger to work out the approximate finger positions, although this is not an ideal solution as the results are not linear.

At the end of the video I turned the calculation around so that we can specify the force placed on each finger – this will attempt to keep the spring in each finger tensioned to the same amount. The result of this is that, when the force is turned down, the joints are actively back-driveable so they will comply with any force applied to them.