Motion System Design
Design By Objective: Shrink that shrink wrapper

Design By Objective: Shrink that shrink wrapper

Two drives on one footprint save more than just space

Belco Manufacturing, Monrovia, Calif. designs and builds high quality packaging machines. The company has used brushed dc drives for several years on their shrink-wrapping systems. The basic SCR technology of the drives has proved reliable and cost effective. The drives control motors for the machine conveyors that move product toward the shrinkwrap station and separate it prior to the wrapping process.

In the old control scheme, there were two SCR brushed dc drives that were set up in a master-slave configuration using an analog signal isolator board. This system works well on relatively high profile objects — the separation between products is longer and the varying length of the tail is not an issue. However, with lower profile objects like CD jewel cases, product separation is minimal and more critical since the tail of the wrapping needs to be so much shorter.

In the low profile application with the follower isolation board, the delay of the analog signal between the master and slave caused wide variations in product separation and resulted in a poorly wrapped product.

The solution, devised by the Minarik Drives division of Minarik Corp., was to redesign its newly developed M1 brushed dc drive and populate two M1 drives onto one standard MM chassis footprint. The end result was the extremely compact 2-axis M2 brushed dc drive.

Since the M1 and M2 are microprocessor-based, the processor was reprogrammed to interface with both drive circuits on the M2 at the same time while looking for a manually set ratio signal from a multiposition switch on the operator’s control panel. By allowing the microprocessor to follow one start signal and control the acceleration, deceleration and speed of both drives at the same time, there is no delay in system response between the master and slave.

The benefits of using the M2 in this application are the following:

• The precise master-slave control using the microprocessor based drive results in higher quality shrink wrap output.
• Panel space is saved by combining two dc controls onto one chassis and eliminating the analog follower isolation board.
• There is simpler wiring and installation.
• By eliminating the board and the two stand-alone dc drives, as well as making the installation easier, the M2 reduced Belco’s drive system cost by more than half.

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