Modeling a parallel Scara

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GoComputing
Posts: 1
Joined: 08 May 2022, 14:02

Modeling a parallel Scara

Post by GoComputing »

Hello everyone,

I'm trying to model a parallel Scara robot. This kind of robots are controlled by two servos. There is an arm attached to each of these servos. For each arm, on the other side, there is another arm. These two last arms are connected. This connection point is attached to a pencil, so controlling each servo you can control the pencil position and then you can draw. A figure is attached.

Image

The model I model until now is attached to this thread. Right now, I am able to model it using the inverse kinematics functions of CoppeliaSim, but when I set the forearms (arms holding the pencil) as dynamic, they fall from the robot. The hierarchy is defined as the following image.

Image

I cannot find why they are falling. Any help is welcomed! The scene is uploaded at https://drive.google.com/file/d/1uUPGx1 ... sp=sharing

Thank you.

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Modeling a parallel Scara

Post by coppelia »

Hello,

the approach to take for a kinematic or dynamic construction is very different. For a dynamic construction, I'd use something like:

Code: Select all

base --> leftRevJoint1 --> leftLink1 --> leftRevJoint2 --> leftlink2 --> dummyA
     --> rightRevJoint1 --> rightLink1 --> rightRevJoint2 --> rightlink2 --> tipRevJoint --> dummyB
and have the two dummies linked via a loop closure constraint. Make sure to carefully read this page about designing a dynamics simulation, i.e. your joints need to be in force/torque mode (or dynamics mode), the shapes need to be non-static, etc.

Cheers

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