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arm experiences as the arm moves through the work envelop. With either AC or DC servo motors, an encoder sends signals or pulses as the motor moves. When the robot is being taught the movements and positions, the controller counts and stores the motor pulses. In the replay, or automatic mode, the controller tells the motors how many pulses to move, which translates to the speed and stopping position for each axis motor. By duplicating the taught program, the robot performs the tasks exactly as it was programmed, without operator attention.

2. Stepping Motors

Stepping motors are another type of motor that is used in robots. Stepping motors have a narrower range of torque output than servo motors and are more suitable for the cylindrical coordinate and gantry robots where the torque requirements are more uniform over the range of arm movement.

Stepping motors move in response to pulses sent by the controller, each pulsing causing a small amount of motor movement, called a ''step.'' Because the controller counts and sends the appropriate number of steps to each motor, there is no need for an encoder to provide motor position information back to the controller. Controllers for stepping motor robots are simpler than for servo motors, resulting in reduced cost and controller complexity. For both price and performance reasons, stepping motors are used for simple robots, liquid handlers, and many other simple laboratory devices.

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