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Бухина пособие автоматизация и управление (1) (1)
| Closed Loop
The closed loop system has a feedback system to monitor the output of the motors. Closed systems are also able to correct errors in position, velocity, and acceleration, and also fault the system if the error is too large. Refer to the image below. As you can see from the image to the left, there are two closed loop system shown. The first system returns the feedback to the CNC controller. The second system returns the feedback into the computer. Regardless what some say, both systems are true closed loop systems. The system where the feedback is fed into the signal generator or computer is usually found on high end machines. The image on the left represents the most common type of closed loop controller system. In this type of system, an encoder, glass scale, or some other type of analog device is responsible for the feedback signal. Most of these closed loop controllers are PID or proportional–integral–derivative controllers. The encoder output is fed into the motor driver. A PID controller attempts to correct the error between a measured variable and a desired set point by calculating and then outputting a corrective action that can adjust the process accordingly and rapidly, to keep the error minimal. See the image below for a basic concept flow chart. T his type of control loop is set to fault at a preset value. This should stop the machine in case of excess error. Some people believe that this type of system can be inaccurate. This is untrue if setup properly. The resolution of this type of servo system should be designed to be one order of magnitude more precise than the machine. With this setup, even if the machine were to fault, the error is still less than the machine tolerance. If a controller faults when it is 124 steps out of position, the resolution of the system should be designed so that 124 steps is less than the machine tolerance. The disadvantages of closed loop systems are cost and complexity. Closed loop controllers can be harder to tune and have more parts that could fail. Text The automation of many electromechanical processes, such as the movement of machinery on an assembly line, is done through the use of small computers called programmable logic controllers (PLCs). A PLC contains a programmable microprocessor that is programmed using a specialized computer language. Typically, the program for the automated process is written on a computer and then is downloaded onto the programmable logic controller directly through a cable connection. The program is stored in the programmable logic controller in non-volatile memory. жүктеу/скачать 464,87 Kb. Достарыңызбен бөлісу:
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