Which joints provide translational motion?

• A. Rotary joints only.
• B. Screw-driven joints.
• C. Linear joints (type L) and orthogonal joints (type O).
• D. Universal joints and ball-and-socket joints.

Answer: (C)

Translational motion means moving along a straight line. Joints that are designed to allow pure sliding along an axis provide this kind of motion. A linear joint (prismatic joint) lets movement occur along a single straight line, while an orthogonal joint allows translation along two perpendicular directions, giving two translational degrees of freedom. The other joints either rotate about an axis (rotary joints) or combine rotation with translation (screw-driven joints), or mainly provide rotational freedom (universal and ball-and-socket). So the joints that provide translational motion are the linear and orthogonal types.