Modelling of Robot contact with object

I am a PhD student working on multi fingered robot hand for grasping. For grasping issue, I need to model a contact between fingertip and stiff simple object with known location and geometry for measuring contact force. This can be done in simulink easily. I am trying to implement in Simmechanics. I already had a look at bouncing ball model. For example, I have 2 dof planar robot hand and a vertical wall model. I defined end link of robot and also defined wall with weld joint. Assume for simplicity that I will get force only in horizontal direction and also defined condition to get contact force. Now, do I need to put an extra degree of freedom between last link of robot body and object body? I am stucked at this point. If you have any option, I can send the file, too.

Your help will be appreciated. Thank you.

Rakibul Hasan

[TEJAS PHUTANE]

Hi,I am using simscape contact force library to model a gripper to grab a ball,however while using sphere to plane force block,the ball bounces off the gripper. I think it has something to do with non linear contact force,I can't get any example for the same. please help.

Answer 1

[Guy Rouleau]

You have 2 options:

1. You can model only the arm (no wall in SimMechanics). Use a Body sensor to get the pose of the EE in Simulink, then compute the contact forces/torques and apply them to the arm using a Body Actuator.

2. Connect a joint between the 2 parts (arm and wall). In your 2D example this would probably a planar. Then use a Joint sensor to measure the relative position of the 2 bodies. In Simulink, compute the contact forces/torques and apply back to the joint using a joint actuator.

This central submissions can give you an example of computing and applying contact forces with the ground:

http://www.mathworks.com/matlabcentral/fileexchange/21439-simulation-of-a-one-legged-hopping-robot

[Md Rakibul]

Dear Guy,

Thanks a lot for your response. I placed a planar joint between end-effector & object and found the contact force which is similar to the bouncing ball model. But the force does not act when it goes back to arm. For example, my command is to move the arm from 0 to 45 degree. And I defined the wall when arm position is about 30 degree. I get a huge contact force when the arm hits the wall. But it still reaches 45 degree crossing the wall (In Graphics). My aim is to generate contact force during collision and the arm should not be crossing the wall. Any suggestions? Thanks again.

Rakibul Hasan

[Md Rakibul]

Dear Guy,

I solved the problem. Thank you very much for your assistance. Nice meeting you. Take care.

Rakibul

[K E]

I am curious: how did you stop the arm from crossing the wall?

[Bahri SEKERCI]

Hi I have a very similar problem.

I have a human limbs. first of all I contacted human foot with ground. This is succesful. But when I worn robot foot, I can not contact with ground. Due to this problem, I can not measure that want to valuses(reaction forces) between human foot and robot foot.

How can I solve this problem.

Bahri.

Answer 2

[jone]

Hi Guys I have very similar problem and I hope to get help If I have two bodies and first one moves to impact with second one is there any way to know when the impact happens and after that how to calculate contact force (Fx,Fy,Fz) additional details : I don't know real position of second bodies because its may translate and rotate between specified rang

thank you

Answer 3

[Erick Oberstar]

I'm working on a compliant contact problem similar to this and the models outlined here may provide some insight. http://www.araa.asn.au/acra/acra2009/papers/pap125s1.pdf My problem is how to dynamically wire in the compliance force once the contact is detected. I am attempting to do this with a conditional path gated by if block wired into an action subsystem. However the model doesn't seem to like this as I get a simulink error:

Input data dependency violation due to action subsystems. See Subsystem Examples in the Simulink library for valid and invalid examples of action subsystems Component: Simulink | Category: Model error

The Action subsystem is just a input port wired to an output port.

[Bahri SEKERCI]

Hi I have a very similar problem.

I have a human limbs. first of all I contacted human foot with ground. This is succesful. But when I worn robot foot, I can not contact with ground. Due to this problem, I can not measure that want to valuses(reaction forces) between human foot and robot foot.

How can I solve this problem.

Bahri.