In CNC systems, open and closed loop systems describes the two primary types of control systems:
Refers to a system using a stepper motor, where the communication between the controller system and motor is one way. The process is fairly simple. The machinist will decide what he/she wants to accomplish and will generate the g-code and the software will create the necessary steps and direction signals to perform the desired task. The computer will relay this information to the controller which then energizes the motor. What distinguishes open looped from a close looped system is after the motor moves to the desired position, there is no feedback to the controller system to verify the action. This is considered a drawback to the open loop system. If the motor does not operate as instructed there is no way for the system to know that this is occurring. The controller system will continue performing the next task or step as if there is no problem until a limit switch is tripped or the operator resets the machine. Open loop systems run the risk overloading the machine and losing steps which can ruin the work piece or cause harm to the machine. But if used effectively and not overloaded, there is no reason an open loop system should not be suitable and function properly.
As it was alluded to above, the primary difference between an open and closed loop system is feedback. A closed loop system, or one using a servo motor, has a feedback protocol to monitor the output of the motors. Closed systems are also able to correct any errors in position, velocity, and acceleration and also have the ability to fault the system if the error is too large. There are two types of closed loop systems; one where the system returns the feedback to the CNC controller and another which returns the feedback to the computer. The closed loop system uses a feedback subsystem primarily to monitor the actual output and correct any discrepancies from the programmed input. The feedback system could be either analog or digital. The analog systems measure the variation of physical variables such as position and velocity in terms of voltage levels. Digital systems monitor output variations by means of electrical pulses. Closed loop systems are very powerful and accurate because they are capable of monitoring operating conditions through feedback subsystems and automatically compensating for any variations in real time with extremely accurate results. MultiCam Canada is determined to provide clients with the most efficient and quality CNC cutting solution possible which is why we offer closed loop systems on our machines. Although open loop systems may provide adequate results, using a closed loop system eliminates much of the risk associated with CNC cutting, leaving the user with quality cutting results.