Editorial Feature

Let’s Build Robots: Feedback System

A feedback system is a device used within a robotic system for measuring a specific variable. There are mainly two types of feedback: positive feedback and negative feedback. In positive feedback mechanisms, the response is transmitted across the same direction of the stimuli. In negative feedback mechanisms, the response is transmitted in a direction opposite to that of the stimuli.

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Robots employ feedback systems to produce outputs based on the input received from a controller. The feedback systems are operated in combination with pneumatic, hydraulic and electric drive systems.

Closed-Loop System

In this type of feedback system, the output response is measured based on the feedback signal. The closed-loop system is operated by comparing the output response with the desired output, and adjusting the input signal accordingly.

Hence, the system includes a sensor for monitoring the output signal. After comparison, the output response is sent back to the input to produce new output. This type of feedback system can provide output with high accuracy.

The robots that employ closed-loop feedback systems are called as servo robots as the feedback signals are transmitted to a servo amplifier that detects any errors in the output. One advantage of this type of feedback system is that the output of the system can be automatically changed based on error signals produced during variation in load.

Open-Loop System

This type of feedback system measures the output only based on the input signal. Since it does not produce any feedback signals, the adjustments to the system have to be done manually. It has simple operation, where the output is generated when a controller responds according to the input signal.

Robots that employ this type of feedback system is known as nonservo robots that are relatively easy to operate and inexpensive.

Proportional Integral Derivative Controller

Proportional integral derivative (PID) controller is the most common robot controlling mechanism.

The difference between a parameter measured by a sensor and a desired result is calculated as an error. The controller operates by controlling the process inputs to reduce the error.

The calculation algorithm of the PID controller mainly employs three factors: derivative, integral and proportional values.


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