Compact portable lift assembly
A knockdown, portable lift is relatively compact and lightweight for transport and use where there is no existing means for lifting a load between a lower surface and an upper surface or where the existing means cannot be used. Components of the lift are stored in a base portion of the lift and are assembled on site for forming a lift frame extending between the upper and lower surfaces. A platform and drive assembly are supported on the lift frame and are driven together up and down tracks on each side of the lift frame using a rotary drive, such as a hand crank or electric motor, to power the drive assembly. The drive assembly is operable by a person on or off the platform from either the upper or lower surface or traversing stairs over which the platform is moving. The drive assembly incorporates a unique overspeed braking system and a unique clutch arrangement.
1. An overspeed braking apparatus for use in slowing and ultimately stopping a moving load exceeding a pre-set operating speed, comprising:
a band brake comprising:
a circular brake drum having an axis;
one or more windings of a band wound circumferentially about the brake drum, opposing ends thereof being connected to the moving load; and
an escapement operatively arranged intermediate the moving load and the band brake for latching at speeds exceeding the pre-set operating speed and engaging the band brake to limit impact loading and to slow the moving load to a controlled stop, wherein the escapement comprises:
a toothed gear rotatably supported concentrically and coaxially within the brake drum and operatively connected to the moving load for rotation with movement thereof;
a rocking pawl pivotally supported in the brake drum, the pawl engaging teeth on the toothed gear; and
biasing means for biasing the pawl into engagement with the toothed gear, wherein at or below the pre-set operating speed, the pawl rocks reactively as the teeth on the gear engage the pawl, the biasing means acting to move the pawl toward the brake drum for preventing the pawl from latching to the gear; and
wherein at the speeds exceeding the pre-set operating speed, the biasing means cannot bias the pawl quickly enough to move the pawl away from the teeth and the pawl latches thereto, causing the toothed gear to rotate with the brake drum and apply tension to the band for slowing and stopping movement of the moving load.
2. The overspeed braking apparatus of claim 1 , wherein the band brake further comprises friction material between the brake drum and the band.
3. The overspeed braking apparatus of claim 1 wherein the escapement further comprises:
bearings and a bearing shaft for pivotally connecting the rocking pawl to the brake drum.
4. The overspeed braking apparatus of claim 3 wherein the bearings are spring mounted for displacing the bearings and bearing shaft into engagement with the brake drum for transferring load to the brake drum when the pawl is latched.
5. The overspeed braking apparatus of claim 4 wherein the bearings and shaft are lighter in weight and smaller than conventional bearings and shaft.
6. The overspeed braking apparatus of claim 1 wherein the band is wound 2 to 3 times around the brake drum.
7. The overspeed braking apparatus of claim 1 wherein the band is wound greater than 3 times around the brake drum.