# Controlling Actuated Robot Hand in Underactuated Manner

We have an allegro hand in our robot, and it is in actuated behavior. In other words, each joint is controlled one or more than one actuator, that is motor. There are 3 actuators for each finger, since each finger has 3 joints. Since there are 4 fingers in allegro hand, it has totally 12 actuators.

However, we want to control the hand in under-actuated manner. Namely, movement of each finger must be controlled by only one actuator, not three actuators. To accomplish this, we think that we can parametrize other 2 actuators of a finger based on first actuator of the finger:

f$$_1(\theta) = \theta \rightarrow joint \,\, 1$$

f$$_2(\theta) = 0.43\theta \rightarrow joint \,\, 2$$

f$$_3(\theta) = 0.25\theta \rightarrow joint \,\, 3$$

The angle $$\theta$$ is total rotation of first joint. Rotation of second and third joint will be parameterized based on rotation of first joint. I aim to generate such a under-actuated system.

How can I do that ?

How can I determine these 3 functions and their coefficients like 0.43 and 0.25 ?

• Maybe i don’t understand...you can already control all joints? I dont know how you nornally control your motors, but do you not have to give a position to them already? Can’t you simply choose the parameters and multiple them by the theta you already know? Please explain your current method of control, ie programming, some kind of interface, whatever and how you find the angles for each actuator already, then maybe i can help :) – morbo Aug 19 '19 at 16:58
• I'm having a hard time imagining what this setup looks like. It's simply 2 motors to 1 input? Why does the gripper have two motors? Power? space? cost? are the inputs not the same? – tuskiomi Aug 19 '19 at 16:58