Scissor lift descent control systems and methods

Patent metadata

Field	Value
Publication number	US-11945704-B2
Application number	US-202016811851-A
Country	US
Kind code	B2
Filing date	Mar 6, 2020
Priority date	Apr 5, 2019
Publication date	Apr 2, 2024
Grant date	Apr 2, 2024

Abstract

A lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and a descent control mechanism. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The linear actuator has an electric motor. The descent control mechanism is configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

First claim

What is claimed is:

1. A lift device comprising:
a base having a plurality of wheels;
a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position;
a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism;
a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor;
an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position, wherein the electromagnetic brake includes a pressure plate, a friction disk, an armature, a magnetic body, and a wire coil, the friction disk is rotationally coupled to a rotor of the electric motor of the linear actuator and is disposed between the armature and the pressure plate, and the armature is disposed between the magnetic body and the friction disk;
wherein, in the event of a power failure, the electromagnetic brake is biased toward the engaged position, wherein, in the engaged position, the armature is biased away from the magnetic body and into contact with the friction disk by at least one engagement spring, thereby preventing rotation of the friction disk, and, in the disengaged position, a current is applied to the wire coil to produce an electromagnetic force on the armature that overcomes a spring force of the at least one engagement spring, thereby compressing the at least one engagement spring, pulling the armature out of contact with the friction disk, and allowing the rotation of the friction disk; and
a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position, wherein the manual release device includes a manual pull handle configured to pull a release tab fixed to the armature through a Bowden cable, thereby moving the electromagnetic brake from the engaged position into the disengaged position.

2. The lift device of claim 1 , further comprising a descent control mechanism configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

3. The lift device of claim 2 , wherein the descent control mechanism is a centrifugal brake rotationally coupled to the rotor of the electric motor.

4. The lift device of claim 1 , wherein the electric motor of the linear actuator of is a permanent magnet motor having terminals that are biased toward a shunted position, such that, in the event of the power failure, when the electromagnetic brake is moved into the disengaged position by the manual release device and the work platform is being lowered, the permanent magnet motor acts as a generator, electromagnetically reducing a rotational speed of the rotor of the electric motor and, thereby, reducing a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

5. A lift device comprising:
a base having a plurality of wheels;
a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position;
a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism;
a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor;
an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position, wherein, in the event of a power failure, the electromagnetic brake is biased toward the engaged position;
a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position, wherein the electric motor of the linear actuator of is a permanent magnet motor having terminals that are biased toward a shunted position, such that, in the event of the power failure, when the electromagnetic brake is moved into the disengaged position by the manual release device and the work platform is being lowered, the permanent magnet motor acts as a generator, electromagnetically reducing a rotational speed of a rotor of the electric motor and, thereby, reducing the speed at which the retractable lift mechanism is moved from the extended position to the retracted position; and
a descent control mechanism configured to reduce a speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

6. The lift device of claim 5 , wherein the descent control mechanism is a centrifugal brake rotationally coupled to a rotor of the electric motor of the linear actuator.

7. The lift device of claim 6 , wherein the centrifugal brake is configured to reduce a rotational speed of the rotor once the rotor exceeds a predetermined rotational speed.

8. The lift device of claim 7 , wherein the predetermined rotational speed is between 1850 rpm and 2250 rpm.

9. A lift device comprising:
a base having a plurality of wheels;
a retractable lift mechanism having a first end coupled to the base and being moveable between an extended position and a retracted position;
a work platform configured to support a load, the work platform being coupled to and supported by a second end of the retractable lift mechanism;
a linear actuator configured to selectively move the retractable lift mechanism between the extended position and the retracted position, the linear actuator having an electric motor; and
an electromagnetic brake coupled to the linear actuator and movable between an engaged position, in which the retractable lift mechanism is prevented from moving between the extended position and the retracted position, and a disengaged position, in which the retractable lift mechanism is allowed to move between the extended position and the retracted position, the electromagnetic brake being biased toward the engaged position in the event of a power failure;
a manual release device configured to manually move the electromagnetic brake from the engaged position to the disengaged position, wherein the electric motor of the linear actuator of is a permanent magnet motor having terminals that are biased toward a shunted position, such that, in the event of the power failure, when the electromagnetic brake is moved into the disengaged position by the manual release device and the work platform is being lowered, the permanent magnet motor acts as a generator, electromagnetically reducing a rotational speed of a rotor of the electric motor and, thereby, reducing the speed at which the retractable lift mechanism is moved from the extended position to the retracted position.

10. The lift device of claim 9 , wherein the electromagnetic brake includes a pressure plate, a friction disk, an armature, a magnetic body, and a wire coil, the friction disk is rotationally coupled to a rotor of the electric motor of the linear actuator and is disposed between the armature and the pressure plate, and the armature is disposed between the magn

Assignees

• Oshkosh Corp

Inventors

• Bafile Louis
• Prasetiawan Eko

Classifications

• B66F17/006 Primary

  for working platforms · CPC title

• B66F7/0625

  with wheels for moving around the floor · CPC title

• B66F7/0666

  Multiple scissor linkages vertically arranged · CPC title

• B66F11/04

  for movable platforms or cabins, e.g. on vehicles, permitting workmen to place themselves in any desired position for carrying out required operations ({Working platforms on fork-lift trucks B66F9/127; } vehicle aspects of service vehicles B60P3/14; platforms for cleaning windows A47L3/02; devices for rescuing persons from buildings A62B1/02; liftable or lowerable platforms for use on ladders E06C7/16; maintenance travellers for bridges E01D19/10; scaffolds on an extensible sub-structure E04G1/22) · CPC title

• F16D55/02

  with axially-movable discs or pads pressed against axially-located rotating members · CPC title