Workspace design of robots

-Nishant Iyer

What is a robot?

• A robot is a mechanical intelligent agent which can perform tasks on its own, or with guidance.

• It is usually an electro-mechanical machine which is guided by computer and electronic programming.

Some examples to understand them more

What is degree of freedom?

• It is the total number of independent motions that can be performed by a rigid body.

• Lets understand this in a little more detail.

Lets understand DOF

• Any free body in 3D space can perform translation and rotation along x , y and z axes.

• Just imagine a brick floating without gravity.

• This accounts to a total of 6 DOF.

What does DOF depend on?

• A maximum of 6 DOF is possible for any rigid body.

• Now the degree of freedom depends on the kind of joint and constraints on a robot.

• Different joints give different DOFs.• Lets see some examples.

Types of joints and their DOFs

• A pin joint gives a single degree of freedom as it permits rotation only along the pin axis.

• A ball and socket joint gives 3 DOFs as it allows rotational motion along the three axes. Translation motion is restricted in this.

Understanding workspace

• To understand workspace , lets consider a cylindrical configuration robot.

• This has the capability to perform linear motion along z and y axes.

• It also rotates along the z-axis.

• This its DOF will be 3.

Understanding workspace

• This is how its workspace/work volume be like.

• Lets work out step by step how this came about. Workspace of a

cylindrical configuration robot

Step by step formation of a workspace/work volume

• Keeping y co-ordinate at its maximum value, and tracing the path of a point on end effector by rotating only along z-axis, we get the shown curve.

• Similarly keeping the y co-ordinate minimum, we trace the smaller inner curve.

• This is the workspace of the robot along just 2 DOF. i.e. rotation along z-axis and translation along y-axis.

Finally the workspace is obtained

• Now this robot can perform translation motion along z-axis.

• Hence we extrude the one dimensional figure along the z-axis till the maximum value is reached.

• This gives us the three dimensional workspace of the robot.

Why is knowledge about work volume important?

• The work volume defines the total volume swept by the end effector of a robot.

• In industrial assembly lines there will be many robots and components nearby to each other.

• Its upto us to programme the motions of the links of the robot such that there are no collisions.

How can it be controlled or designed?

• The work volume can be designed as per requirements.

• This is possible by controlling the movements of links by setting maximum values to the actuators at the joints.

• The maximum values have to be set according to the obstructions around the robot.