How to calculate friction and normal force of spatial contact force

I am building a model while using Spatial Contact Force. It is a controller whose job is the adjust the gripping force between an object and the gripper. However, I am not sure by the Spatial Contact Force documentation on how the Friction and Normal force is computed.

Answer 1

[Riya]

Hello Yi Farn Lim,

I see that you want to compute Friction and Normal force using Spatial Contact Force.

Please note that the Spatial Contact Force block models the contact between a pair of geometries in 3-D space. You can use the built-in penalty method or provide custom normal and friction force laws to model a contact.

The Spatial Contact Force block properties are divided into three expandable nodes: Normal Force, Frictional Force, and Sensing. Set these properties when using the Spatial Contact Force block to model the contact forces between two solid bodies.

• Normal Force - Parameters in the Normal Force section are used to determine the normal force, fn, that the two solid bodies exert on each other. You can specify the Stiffness, Damping, and Transition Region Width.
• Frictional Force - Parameters in the Frictional Force section are used to determine the frictional force, ff, that the two solid bodies exert on each other. If you set Method to Smooth Stick-Slip, then you can specify the Coefficient of Static Friction, Coefficient of Dynamic Friction, and Critical Velocity. These options are not available when the Method is set to None.

Besides modeling contact between two solid blocks, you can also use the Spatial Contact Force block to sense:

1. Separation Distance—The distance between two solid bodies
2. Normal Force—The normal force exerted by each solid body on the other.
3. Frictional Force Magnitude—The frictional force exerted by each solid body on the other.

To enable these options, open the Spatial Contact Force block properties. Under Sensing, select the properties that you want the block to sense. For each property, a port is exposed on the block. Connect these ports to a viewer of your choice.

For more information you can refer following articles:

• Spatial Contact Force: https://www.mathworks.com/help/sm/ref/spatialcontactforce.html
• Modelling contact force between two solids: https://www.mathworks.com/help/sm/ug/modeling-contact-force-between-two-solids.html

I hope it helps!