 Welcome to Analog Position Control, Closed Loop Position Cervo. Controlling the position of a physical object is achieved by a closed loop feedback system. The Cervo mechanism shown below is an application of position control. It uses pulleys, belts, gears, and a motor to drive a rack horizontally in both directions. Let's read about the elements of the Analog Closed Loop Position Cervo system. Actuator The actuator is the muscle of the system. It provides the physical power that drives the load. In this example, a DC motor is the actuator. Controlled variable The controlled variable is the actual variable being monitored and maintained at a desired value. In this example, the position of the rack is the controlled variable. Measured variable To monitor the status of the controlled variable, it must be measured. The condition of the controlled variable is referred to as the measured variable. In this example, it is the position of the rack. Measurement device The measurement device is the eye of the system. It senses the measured variable and produces an output signal that represents the status of the controlled variable. In this example, a potentiometer connected through belts and pulleys and shafts is the measurement device. As the motor turns, the potentiometer wiper arm rotates and provides a feedback signal that represents the position. Feedback signal The feedback signal is a zero to negative 15 DC voltage produced by the potentiometer. Setpoint The setpoint is the input signal applied to the closed loop system. It indicates the desired condition of the controlled variable. In this example, it is a zero to positive 15 DC voltage from a potentiometer that provides the desired setpoint position of the gear rack. Controller The controller is the brain of the system. It produces an appropriate output by comparing the status of the feedback signal to the setpoint. In this example, a summing op amp is the controller. It produces a DC voltage that is amplified before it drives the actuator. Operation The gear rack is all the way to the right. It is in the home position, which can also be considered the starting or the reference position. In this situation, the setpoint potentiometer is at zero volts, and the feedback position is at zero volts. Moving the gear rack left By moving the setpoint potentiometer up to positive 10 volts, the following conditions occur. The feedback signal is zero volts. A positive 10 volts setpoint and zero volt feedback at the summing op amp inputs cause its output to become negative 10 volts. The power amp amplifies and inverts its input to a positive output. The DC motor begins to turn clockwise. The rack is forced to move left. The feedback potentiometer's wiper rotates in the clockwise direction, and as it does, it provides a negative feedback signal that increases from zero volts. When the wiper arm of the feedback potentiometer reaches the negative 10 volt position, it cancels out the positive 10 volts applied to the top input of the summing op amp. The result is that the op amp output goes to zero volts. The motor shuts off, and the gear rack stops moving. Moving the gear rack right By decreasing the setpoint potentiometer down to positive 5 volts, the following conditions occur. The feedback signal is negative 10 volts. A positive 5 volt setpoint and a negative 10 volt feedback at the summing op amp inputs cause its output to become positive 5 volts. The power op amp amplifies and inverts its input to a negative output. Then the DC motor begins to turn counterclockwise. The rack is forced to move right. The feedback potentiometer wiper rotates in the counterclockwise direction, and as it does, the voltage decreases from negative 10 volts. When the wiper arm of the feedback potentiometer reaches the negative 5 volt position, it cancels out the positive 5 volts applied to the top input of the summing op amp. The result is that the op amp output goes to zero volts, the motor shuts off, and the gear rack stops moving. You have completed this activity. Analog position control. Closed loop position servo. If you're interested in more videos like this, subscribe to our channel. We'll notify you when we have something new for you to learn.