What is Motion Control?

Motion control generally refers to an open loop or closed loop electromechanical system in which things are moving. A motion control typically consists of a motor, mechanical parts that move and often feedback sensor(s).

Typical examples of motion control applications are:

• Servomechanisms
• Numerical control machines
• Industrial robots
• Variable speed drills
• Digital torque wrenches
• Hard-drive head-positioning systems
• Automatic guided vehicles
• NASA mars rover

Servomechanism

Servomechanism refers to a closed loop electromechanical control system that directs the precise movement of a physical object such as a robot arm. It does this by regulating the speed (velocity) and position of a motor based on a feedback signal. Typically either the output position or the output velocity (or both) is controlled.

Let’s consider an example of servomechanism i.e. the position system for a radar antenna as illustrated in the Figure (a) below.

In this particular example, the controlled variable is the antenna position. The antenna is rotated with an electric motor connected to the controller located some distance away. The user selects a direction, and the controller directs the antenna to rotate to a specific position. The position sensor detects the antenna position and provides this information in form of a feedback to the controller.

Numerical Control (NC)

This is a type of digital control used on machine tools such as lathes and milling machines. These machines can automatically cut and shape the workpiece without a human operator. Each machine has its own set of parameters that must be controlled.

Related: What is Process Control?

Robotics

The industrial robots are classic example of position control systems. Often, the robot has a single arm with shoulder, elbow and wrist joints as well as some kind of hand known as an end effector. The end effector is either a gripper or other tool like a paint spray gun.

Robots are employed in manufacturing industries to move parts from place to place, assemble parts, load and offload numerical controlled (NC) machines and perform other tasks like welding and spray painting.

The simplest robots (pick and place robots) pick parts and place them somewhere nearby. They are often run using open loop control i.e. using mechanical stops or limit switches to determined how far in each direction to go.

Advanced robots use closed loop position systems for all joints.