Hi,
I could use some advice/direction for a project to make a pick up gripper tool for a quadriplegic friend of mine. I want to adapt a common reacher grabber tool that has a squeeze handle to pick up items so that a motor controlled by voice command will do the squeezing, since my quadriplegic friend is incapable of squeezing.
I've taken the handle off the tool and found the pull cable that controls the gripper fingers requires the following range of force and distance to operate:
GRIPPER STATUS CABLE TRAVEL DISTANCE LBS FOR REQUIRED
FULLY OPEN 0” 0.0 LBS
CUPS JUST CLOSED .375” (9.5mm) 7.0 LBS
MAXIMUM CLOSURE 1.125” (28.6mm) 15.8 LBS
(HARDEST GRIP)
I would appreciate advice on the best motor and controller to pull the cable to do the squeezing using voice control. Currently I am considering using a mini linear servo like the LR-12 series with 30mm stroke and 210:1 gear ratio to get up to 18 lbs pull.
For voice controller I am looking at Sparkfun's EasyVR 3 Shield. Not sure what to use for a motor controller. I don't want to use a voice controller that requires using a cell phone, because my friend often drops his cell phone and needs to pick it up with this gripper device.
My concern is how to use speech to control the pull force which will be low for some objects (like a quarter on the floor) and high (to pick up a can of beans for example). The gripper can pick up to 5 lb objects.
Any advice on motors and controllers would be appreciated. I want to avoid pitfalls perhaps others of you see and get started on the right track. I don't think a joystick will work because my friend's arm will be busy placing the gripper over the object on the floor and can't control a joy stick at the same time.
Thanks so much!
I think you are missing the part about how fast you want these parts to close and open. Also, are they spring loaded so they open themselves with no power applied to the cable?
Paul
Thanks for responding. The time to open and close is not critical. I read the rate of travel to travel 30mm on the servo motor I mentioned and it was fine. When your cell phone is lying on the pavement and you are trying to retrieve it, whether it take 5 seconds or 20 seconds to close the gripper is not very concerning. The ability to retrieve it at all is more important. Obviously my quadriplegic friend can't wait for several minutes to close but i don't think a few seconds give or take matters. In fact if the closing is a little on the slow side, that may be a benefit for my friend to make adjustments to the placement of the gripper as it closes.
Yes, the commercial gripper does have a return spring but since I will be pulling the cable with a servo motor, it won't return until the motor control tells it to. That may not be true with other kinds of motors.
I imagine the return spring force will be equal to the pull force required to close the "fingers". (Actually 2 opposing rubber cups - bought on Amazon)
Do you have any thoughts on how to vary the closing strength using voice commands? I can imagine something like a verbal command "close #" where # is a number between 1 and 10 that would correlate to the travel distance the servo motor would travel might work.
Thanks for your thoughts!
Bart AF7JL
A link to the linear servo would be nice.
If you put a coil spring between the servo and the cable, the applied force, once the fingers lose, will be related directly to the additional distance traveled. The cable and fingers should move only slightly, but the pull will be linear as long as the spring is not over stressed.
Paul