# US 4,392,771 A · Lift safety switch system

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- Number: US 4,392,771 A
- Document ID: US4392771A
- Status: Granted
- Kind: A
- Application number: 06/218,613
- Filed: 1980-12-22
- Granted: 1983-07-12
- Earliest claimed: 1980-12-22
- Assignees: REB Manufacturing, Inc.
- Inventors: Raymond L. Smalley
- Web page: https://patentgrep.com/patent/US4392771A

## CPC

- A61G 3/06: Transfer using ramps, lifts or the like
- A61G 3/062: {using lifts connected to the vehicle}
- A61G 2220/16: Buses
- Y10S 414/134: Handicapped person handling
- A61G: TRANSPORT, PERSONAL CONVEYANCES OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS (appliances for aiding patients or disabled persons to walk A61H3/00); OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES (embalming corpses A01N1/00)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

An electrically controlled hydraulic lift, such as wheelchair lifts for vehicles, wherein the hydraulic reciprocating motor for operating the platform of the lift is mounted in a vertical slot so that any obstruction in the downward movement of the platform of the lift will cause the reciprocating motor to rise in the slot and operate a microswitch to automatically shut off the continued supply of fluid to the reciprocating motor. This arrangement not only prevents the crushing of obstacles that get in the downward path of the platform, but also limits the downward movement of the platform when it contacts the solid ground or floor level from which an object is to be lifted, such as an invalid in a wheelchair. If desired, the upward movement of the reciprocating hydraulic motor may be restricted by resilient means for maintaining it in the lower part of its mounting slot. The electrical control system for the supply of hydraulic pressure fluid to the reciprocating motor may also include a limit switch along the vertical path of movement of the platform. The fluid pressure supply may comprise an integral hydraulic pump and electric motor assembly unit having high and low pressure fluid outlets for respectively operating the reciprocating motor for raising and lowering the lift platform.

## Claims

### Claim 1

In a fluid-operated lift comprising:
(A) a frame,
(B) a platform vertically foldable and vertically movable relative to said frame,
(C) a fluid-operated reciprocating motor comprising a cylinder and a piston in said cylinder, said motor being connected between said platform and said frame for moving said platform to and from a vertical folded to a horizontal position and to and from its highest horizontal position to its lowest horizontal position,
(D) a source of power comprising an electric motor for operating said reciprocating motor,
(E) an electric circuit and manually operated switch means for controlling said electric motor for controlling said reciprocating motor intermediate the limits of travel of said platform relative to said frame, and
(F) a limit switch means for stopping the operation of said reciprocating motor when said platform is in its highest horizontal position between its limits of travel in a horizontal position, and manual switch means for overriding said limit switch to fold said platform into its vertical position;
the improvement comprising:
(1) vertical slot means between said cylinder and said frame for supporting said reciprocating motor and said platform in said frame,
(2) microswitch means mounted on said frame adjacent said reciprocating motor,
(3) cam means on said cylinder for operating said microswitch means when said reciprocating motor is raised in said vertical slot means caused by an obstruction in the downward path of movement of said platform from its vertical folded position through is highest horizontal position to its lowest horizontal position, and
(4) means responsive to the operation of said microswitch means for controlling said reciprocating motor to discontinue further downward movement of said reciprocating motor.

### Claim 2 (depends on 1)

A fluid-operated lift according to claim 1 including means for urging said reciprocating motor and said platform toward the lower end of said vertical slot means.

### Claim 3 (depends on 1)

A fluid-operated lift according to claim 1 wherein the frame is mounted in a vehicle.