Anti-static roller conveyor

Description

BACKGROUND OF THE INVENTION

One type of roller conveyor is powered by DC motors located in roller cylinders which are mounted with other rollers between the conveyor side plates. Electronic motor control modules are mounted on one of the side plates. Packages traveling on the conveyor rub against the side plates and rollers generating static electricity which can arc between the side plate and control module damaging the control module components.

BRIEF DESCRIPTION OF THE INVENTION

Damage to the control module from a discharge of static electricity is prevented by dissipating the static charge. This is accomplished by a combination of features. The metal side plates of the conveyor are finished with a conductive coating rather than a non-conductive coating in which the static charge can accumulate. Where the rollers are electrically isolated from the side plates as by resilient plastic bushings, a conductive plastic is used to dissipate the static charge developed in the rollers. In a curved section of the conveyor with tapered rollers, if the tapered roller surface sleeve is plastic, a conductive plastic is used, again dissipating any charge developed in the roller.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view of a conveyor section;

FIG. 2 is a side view of a conveyor section showing an electronic motor control module;

FIG. 3 is an enlarged view along line 3—3 of FIG. 2, showing a roller axle received in a plastic bushing; and

FIG. 4 is a perspective view of a curved section of the conveyor with tapered plastic sleeves on the rollers.

DETAILED DESCRIPTION OF THE INVENTION

A roller conveyor section 8, FIGS. 1 and 2, has side plates 10 and 12 between which are mounted carrying rollers 14. The side plates are metal, typically steel. The rollers 14 are also steel and have steel axles 16 received in openings in the side plates. A conveyor which is powered by motor-driven rollers (MDR) has a roller with a 24-volt DC motor inside the roller cylinder, typically at 24 inch increments along the length of the conveyor. In FIGS. 1 and 2, motorized roller 18 drives the rollers 14 of a conveyor zone 20 through O-ring like drive connections 22. Conveyor belts 24 may be provided around terminal rollers 26 of the zone 20 and across carrying rollers 14, to provide better traction for moving articles and to prevent small articles from falling between the rollers.

The motor in roller 18 is controlled by an electronic module 28 mounted on side plate 12 and connected with the motor through cable 30. The electronic control module comprises electronic components, including a control card, which are subject to damage by a discharge of static electricity.

In accordance with the invention, the side plates 10, 12 are finished with a conductive coating as a powder coating or paint. Static electricity developed in the rollers and side plates is readily dissipated by conduction through the coating. A static charge does not accumulate and the static discharge which might damage the control module 28 does not occur. Conveyor belts 24, where used, are also conductive to inhibit charge accumulation

The roller axles 16 are preferably isolated from the side plates to reduce noise and vibration, as by a plastic bushing 32, FIG. 3, as taught in Houghton U.S. Pat. No. 5,645,155. Static electricity developed in the roller is dissipated to the side plate by a bushing 32 of conductive plastic.

In a curved conveyor section 36 shown in FIG. 4, rollers 38 have a tapered surface to move conveyed articles around the curve. As described more fully in Houghton provisional application 60/698,822 filed Jul. 13, 2005 and continuation application 11/484,392 filed Jul. 11, 2006, the tapered rollers have a cylindrical metal core 40 with a tapered surface provided by plastic sleeves 42. A conductive plastic is used to dissipate the static charge developed in the sleeves.

The combination of a conductive coating on the side plates, the conductive plastic axle bushings 32, conductive plastic tapered sleeves 42 and conductive conveyor belts 24, if belts are used, provide a conveyor in which static charge cannot accumulate to arc with the motor control module 28.