Motion Control Systems

Motion control systems are any system that control one or more of the following of a machine: its position, velocity, force, and/or pressure. They generally consist of the follow components:

• Motion controller: the central part that operates the system (I.e. the brain)
  Drive: receives low voltage command signals and then sends the necessary voltage and current to the motor
• Motor: converts the electrical energy to mechanical energy to power the system
• Feedback device: sends feedback to the motion controller to make necessary adjustments

There are two different types of motion control systems: open loop and closed loop systems. The basic difference between the two is that open loop systems do not use feedback; closed systems do use feedback.

Motion Controllers

As the brains of motion control systems, motion controllers calculate and generate the commands that guide the trajectory and velocity of the machine. They output these commands to the rest of the system and, if they receive feedback, adjust their commands to meet the necessary requirements of the system. Motion controllers use multiple algorithms (interpolators, control loops, step generators) to calculate the precise movements of the machine based on each segment or set point.

Drives

Drives receive commands from motion controllers in the form of low voltage signals. They use these signals to convey to the rest of the motion control system the amount of high-power current and voltage needed. There are many different types of drives that can be used:

• Digital drives: contain processing capabilities
  Analog drives: do not contain processing capabilities
• Linear drives: quiet, low-efficiency drives used for low power applications
  Switching drives: noisy, high-efficiency drives that use Pulse Width Modulation to switch voltage on and off
• Stepper or Microstepping drives: high resolution, low to mid-level torque drives that produce smooth rotation over wide speed ranges
• Servo drives: convert low-level analog command signals to high power current and voltage. They produce torque and use internal feedback loops to precisely control current

Motors

Motors power the motion control system by converting electrical energy into mechanical energy. There are many different types of motors:

• DC Motors: also known as a brushed or brush type motors. They use carbon brushes and a mechanical communicator to achieve torque. DC motors will continuously operate if they receive a constant source of DC power. They require simpler drives, are high maintenance and are generally larger than a brushless motor.
• Brushless Servo Motors: as their name implies, brushless motors do not use brushes. Instead, they achieve rotation through electrical communication from the drive. They have high acceleration and torque and require little maintenance.
• Linear Servo Motors: linear motors use linear, rather than rotary, motion. Electromagnetic forces produce thrust and eliminate the need for rotary to linear conversion. They are fast, precise, responsive, have zero backlash and are maintenance free. They also require a higher bandwidth and a larger footprint.
• Stepper Motors: DC motors that have multiple coils that are organized in phases. Each phase is energized in sequence, rotating the motor one step at a time. They move in precise, repeatable steps that allow for precise positioning, speed control, and low speed torque.

Feedback Devices

Only used in closed loop systems, feedback sensors provide feedback that motion controllers use to make necessary adjustments to the system, ensuring that the proper commands are given at all times. The most popular feedback device is an encoder (linear or rotary), which is an electromagnetic device that provides information on position, velocity and direction. There are also absolute encoders, which directly track positions using many unique values (serial, voltage, binary count, etc.).

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