Robotics - Need for minor axes?

[phiby]

I am just reading an introductory text on Industrial Robotics.
It talks about 3 Major Axes and 3 Minor Axes and Yaw, Pitch and Roll.

I am still confused as to the need for the minor axes. You locate the gripper at any point in spaces, 3 axes should be enough right? So what's the need for the 3 minor axes?

 

[adpr02]

I am just reading an introductory text on Industrial Robotics.
It talks about 3 Major Axes and 3 Minor Axes and Yaw, Pitch and Roll.

I am still confused as to the need for the minor axes. You locate the gripper at any point in spaces, 3 axes should be enough right? So what's the need for the 3 minor axes?

Can you give more detail on these major/minor axes?

You need 6 pieces of information to describe an object's exact orientation and location in 3D space: 3 distances for location and 3 angles for orientation.

For robotics, a rotation is usually described by the order of rotation: x - y - z. So Roll about x_0 by thetaA, pitch about y_0 by thetaB, roll about z_0 by thetaC. This is for the first rotation. Successive rotations are also WRT to the fixed frame.

 

[phiby]

Can you give more detail on these major/minor axes?

Most textbooks on industrial robotics (schilling etc) call the 1st 3 joint axes which position the end-effector/gripper as major axis & the next 3rd joint axes which orient it as minor axes.

You need 6 pieces of information to describe an object's exact orientation and location in 3D space: 3 distances for location and 3 angles for orientation.

Yes, this is clear now. I was asked the question when I had just started reading the book. Once I reached the orientation part, it became clear.

Till then, I was thinking of the end effector as a point rather than an object and hence the orientation part wasn't obvious to me.