The Rolflor conveyor consists of front and rear drive subassemblies, each of which is housed in a rugged, welded steel enclosure. The enclosures are mounted at the front and rear of the trailer with a conveyor belt in between — a design reminiscent of casette audio tapes. The conveyor belt is not continuous, but, rather, is two belts. One end of each belt is attached to a drum at the front or rear of the trailer, and the other end of the belts are attached to each other. The narrower load puller belt is attached to the front drum and follows the wider as the trailer is unloaded. Thus, the front drive pulls the load into the trailer from the dock, and the rear drive (with the wider cargo floor belt) pushes the load out the back of the trailer.

A hydraulic power unit consisting of a totally enclosed fan-cooled threephase electric motor close-coupled to a hydraulic pump is installed on the undercarriage of the trailer. The HPU has 20-gal reservoir with filterbreather, level-temperature gauge, and clean-out door.

The two drive subassemblies consist of the hydraulic motors, gearboxes, and drums the belts wind on and off of. The rear assembly features a fiber-reinforced belt that is less than 3/16-in. thick. The upper (load) surface is coated with a special wear-resistant resin that has a high coefficient of friction against a wood pallet. The belt’s lower surface is made of polyester fabric impregnated with a wear and chemical resistant resin and low coefficient of friction against the trailer floor. The belt slides directly on the trailer floor and uses low-friction floor plates to further minimize the coefficient of friction to the load. The belt is about 92 in. wide and 3/16 in. thick, so no cargo space is sacrificed by the installation. Maximum loads of 30,000 to 55,000 lb can be accommodated by sizing the hydraulic components and the gearbox.

A typical installation has two identical operator stations — one for load and one for unload — mounted inside the dock doorway. A cable from the operator’s control panel plugs into the HPU on the trailer, placing load control on the dock where loading or unloading of the trailer can be observed. Electric power for the HPU is usually supplied by the dock, but it can be supplied by an optional diesel engine mounted within the hydraulic power unit. Electrohydraulics was chosen over an electromechanical drive due to the higher power density of hydraulics.

In control

The electrohydraulic control system was designed and implemented by Steve Byers, Electronics Application Specialist, from Scott Industrial Systems, Dayton. A Divelbiss HEC- 2000-E-R controller was chosen to replace an earlier relay logic controller because of the ease of programming coupled with the broad operating temperature range of –40° to 80° C necessary for the application.

The HEC-2000-E-R accommodates eight digital inputs (8-32 Vdc) and eight digital outputs (8-32 Vdc up to 4 A). Two of the inputs may be used as inputs for high speed counting and all of the digital outputs are PWM capable. A CAN port supports SAE J1939 and OptiCAN. This solid state design allows for easy adjustment of variables, providing a far more responsive and precise system overall.

Mike Colgin is marketing manager at Divelbiss Corp., Fredericktown, Ohio. For more information, contact him at or visit