From a single-lift model in 1977, the core Pflow product line has grown to include six standard model series, each of which can be customized as needed to fit perfectly with the specifications of a particular customer.  Sometimes the modifications are minor, and sometimes they are far more involved. Recently Pflow customized two Series DB VRCs in a manner well beyond the norm for JL French Automotive Castings, Inc. of Sheboygan, WI.  

A steady increase in business meant that JL French needed to redesign its manufacturing floor to achieve greater production volumes. To maximize efficient use of the existing space, two separate areas were required where in-process castings could be automatically elevated to get to the next manufacturing module. In one area the lift was 14.5 ft; in the other, 16.2 ft. The key requirement for the elevation mechanism was speed, with low maintenance, reliability and safety also important. The castings were a uniform weight of 12-16 lb but they varied in size and shape, and each had to be lifted individually.

Initially JL French worked with material handling experts on various system designs, each of which had prohibitive features:

• A continuous vertical conveyor (CVC) system -- basically a continuous loop, vertical escalator with platforms -- was considered.  Certain height restrictions existed in the building, and the ceiling provided a clearance of less than 2 ft – not enough room for the platforms to hinge at the top and continue on the downward loop. Plus a clearance pit would be needed in the floor, and JL French was leery of the frequent maintenance likely required to operate the complex CVC system.
• Industrial elevators were evaluated, but in order to achieve the necessary throughput multiple parts would need to be lifted together -- a significant inconsistency to the desired production sequence.
• An inclined belt system -- a type of CVC with a slope and design similar to a straight staircase -- didn’t get past the discussion stages because the horizontal floor space required simply wasn’t available.

By the time JL French connected with Pflow, it was clear that innovative thinking was needed.  Pflow engineers examined the specifications and determined that a DB series lift might work; but in order to achieve the necessary cycle time, it would require a maximum vertical speed of 350 ft/min, almost six times the standard DB series speed of 60 ft/min.  Rather than shaking hands and moving on, the Pflow team confidently assured JL French that it could be done!

The resulting design collaboration between Pflow, JL French, and the area material handling dealer led to a system with the following features:

• A servo-controlled asynchronous ac motor that continuously provides torque while the platform is stationary, eliminating mechanical floor-level switches and the need to engage the brake during loading and unloading. This results in zero wasted time, incredibly smooth operation, and virtually infinite brake life (the brake is set only during extended idle periods). The motor has an absolute position encoder that provides motor rotation information to the controller, telling it exactly where to stop based on motor revolutions. The motor automatically adjusts to the varying product weight.
• Chain-mounted counterweights that reduce the torque requirement on the motor and allow for the necessary speed to be achieved with less horsepower.
• A 3 ft x 3 ft lift platform with chain-driven live rollers (CDLR), served by CDLR in-feed and discharge conveyors.
• A one-unit-at-a-time liftcycle with a weight capacity of 20 lb.
• An achieved cycle time of 13 seconds -- exactly as specified.

“We’ve always been the industry leader in using programmable control of motors on VRC applications,” said Mark Webster, Pflow vice president of engineering.  “We constantly evaluate variable speed drive advancements in terms of capability, reliability, and cost effectiveness. The technology used at JL French is scalable to higher capacity and higher speed applications.”