VFD Application Note – Jam Detection
This article is part of an ongoing series highlighting the special functions available with the KEB variable frequency drives (VFDs). In this post, we will look at our Jam Detection, which is commonly used in Shredder, Auger, and Extrusion applications.
What is Jam Detection?
As industries move to more automated systems to improve efficiency and throughput, avoiding costly downtime, premature component failure or product damage becomes more important to a company’s bottom line. In addition to the industry-leading motor shaft control and performance provided by KEB VFDs, many protection functions to help reduce downtime and avoid premature component failure and product damage are incorporated into the standard VFD firmware.
One such function is KEB’s Jam Detection. The Jam Detection function utilizes the advanced motor model control in the VFD to detect an abnormal occurrence during operation. When an abnormal situation is detected (e.g., jam or locked rotor), the system can be set to react in a manner that best suits the application by utilizing the extensive programmability of the KEB VFD. The reaction to the abnormal situation may be to reverse the motor direction, shut down, slow down, speed up, or send a signal to a control system (or possibly a combination of these options).
How Does Advanced Motor Control Work?
When utilizing the advanced motor control software available in KEB drives, the drive is able to monitor and control the output torque of the motor. This can be done on either an induction motor or permanent magnet – and with or without a feedback device. The motor model in the KEB VFD is updated every 250usec. This high-speed update allows the fastest possible reaction in case there is an abnormal operation. The system protection becomes more robust when this is incorporated into the VFD. In case the PLC communication is lost, the VFD can still detect and react if needed.
Application Example – Industrial Shredder
An example of utilizing the jam detection function is reversing the motor direction based on a programmed torque limit in a metal recycling machine. The recycling machine is used to crush waste metal into smaller pieces during the recycling process. During the crushing process, if the recycling drum becomes jammed and will not turn, the VFD would reach a torque limit defined in the drive.
At the same time, the advanced motor control software would detect that the speed of the motor does not match the set output speed. The system can have a delay time programmed to allow the system to self-correct in some cases, but if the system reaches this jammed state longer than the delay time, the VFD can automatically signal a control system that a jam has been detected and reverse the motor in an attempt to clear the jam.
The signaling of the control system may also be used to stop an infeed conveyor while the jam detection function in the drive is activated. The KEB VFD can then be programmed to run in the reverse direction for a specific time to clear the jam. After the programmed reverse time, the system returns to normal operation – and the VFD signals the control system that the jam has been cleared. In this case, the jam detection is used to keep the system running. This is an example where there is a high chance of a jam occurring, and if the system can self-correct, this reduces the amount of downtime or operator intervention in the process.
Application Example – Stuck Conveyor
Another example of utilizing jam detection is in cases where mechanical components and/or products may be damaged if there is a jam during a manufacturing process. In this case, the jam detection would work similar to above, but if the jam is detected, the response of the VFD may be to immediately shut down to avoid damaging mechanical components and/or the product – and at the same time signal the control system that a jam has occurred.
Designing Better Machinery with Jam Detection
By using the jam detection function incorporated into the KEB VFD software, the response time of the system to an abnormal condition in the operation can be minimized by allowing the VFD to perform a programmed response when the defined conditions are met.
Utilizing the jam detection function on the KEB VFD can help protect against costly downtime, premature component failure, or product damage. Contact a KEB Engineer today to discuss your application – and how Jam Detection can benefit your machine.
If interested, there are past articles that highlight KEB drive functions include the following:
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