Many times, more than one technology is suitable for a given motion control application. Pneumatic cylinders are frequently used for simple stroke limited or cut-to-length applications because of low cost and simplicity. Air cylinders may sometimes be an acceptable solution, but they are not always the best.
Take the case of a packaging equipment manufacturer with a machine based on a modular design that could be adapted to different boxes depending on the end customer. Let us consider that the primary function of this machine is filling, folding and sealing boxes. Some customers need desiccant bags put in the box before sealing, so a separate modular section will be added to the machine for this purpose.
The desiccant bags come on a reel with a registration hole punched in between each bag. The bags must be separated by cutting at, or near, the registration hole, and then placed one in a box. Typically, air cylinders are used as the feed-to-length and cutter actuators, and a PLC controls the motion. The PLC takes its input from a photocell used to detect the registration hole. Relays and solenoid valves on the output of the PLC control the air which in turn drives the cylinders.
This arrangement would work fine, but to be able to handle different sized desiccant bags the machine needs to be completely reworked. The desiccant bag feeders’ limiting factor is throughput. In addition to this, the air cylinders are the only things that need compressed air on the entire machine. Compressed air processes are known to be noisy, dirty, and they require regular maintenance.
IMS’s AC line driven stepper system would offer a vastly superior stepper solution. A pinch roller driven by an MDrive34AC Plus2 Motion Control stepper motor/driver and control system would replace the feed mechanism. The pneumatic cutter would be replaced with an electric cutter and actuated by a relay controlled by one of eight configurable I/O resident on the MDrive34AC Plus2 . The MDrive34AC Plus2 would be programmed to move at a constant velocity until the registration hole is detected. Once detected, the driver would advance a fixed number of microsteps from that position, then stop and fire the cutter. The desiccant bag cutter module would now work with any size bag without any adjustments or reprogramming required.
This stepper approach would result in a superior system. Precision would be improved and scheduled maintenance reduced to sharpening the cutter blade. Adaptability to different desiccant bags would go from very difficult to completely automatic and transparent. The stepper solution is smaller and requires considerably less wiring and panel space. Throughput would increase due to the vast velocity capability of the AC line driven system. The machine no longer would require compressed air. The stepper system solution would work more efficiently with fewer parts and offers an integrated motion solution in one small package.
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