Title:
STAIR TRAVERSING MECHANISM FOR HAND TRUCK
United States Patent 3788413


Abstract:
The present invention relates to a powered mechanism adapted to be attached to a standard hand truck to facilitate the ascending or descending of a stairway with a load. An auxiliary shaft, to which are attached two lifter or climber arms whose extending ends carry associated stair contacting roller means, is mounted parallel to but displaced from the main wheel-carrying axle of the hand truck and is gear-driven to rotate the attached arms and roller means between two predetermined angular limits, with the output of a reversible electric motor. The energizing circuit for the motor is designed so that the motor can only be rotated in the opposite direction after one of the limits has been reached and so that positive and abrupt dynamic braking of the motor occurs when either limit is reached. An energy storage element in the form of a tension spring is connected to receive and store energy from the motor preparatory to ascending a stair and subsequently releases this stored energy to assist the motor during the actual lifting operation.



Inventors:
MILLER L
Application Number:
05/287436
Publication Date:
01/29/1974
Filing Date:
09/08/1972
Assignee:
MILLER L,US
Primary Class:
Other Classes:
280/5.32
International Classes:
B62B5/02; (IPC1-7): B62B5/02
Field of Search:
180/8A 280
View Patent Images:
US Patent References:
3554309POWER-OPERATED LOAD TRANSPORTING DEVICE1971-01-12Abercrombie
3499501STAIR CLIMBING APPARATUS1970-03-10Fitzgerald et al.
2653672Hand truck step climbing mechanism1953-09-29Wessic
2641325Stair lift hand truck1953-06-09Hoffman et al.



Primary Examiner:
Friaglia, Leo
Claims:
I claim

1. The combination with a hand truck or the like having wheel means disposed to rotate about an axis of a mechanism adapted to be affixed to said hand truck and comprising,

2. The combination specified in claim 1 wherein said reciprocating arm means includes,

3. The combination specified in claim 2 wherein said stair engaging elongated arm means is a pair of elongated arm members each having one end affixed adjacent opposite ends of said auxiliary axle and each having its other end extending away from said auxiliary axle, said extending ends each being curved downward to assume engagement with a stair during ascent and descent thereof.

4. The combination specified in claim 3 further including roller means connected between the extending curved ends of said pair off arm members.

5. The combination specified in claim 2 wherein said power pick off means includes a first gear member connected to said motor means and a second gear member disposed to mesh with said first gear member and being connected to said auxiliary axle.

6. The combination specified in claim 1 further including an energy storage means connected to said motor means and said reciprocating arm means for receiving and storing energy from said motor means preparatory to ascending a stair and subsequently supplying said stored energy to said reciprocating arm means during the ascending of said stair.

7. The combination specified in claim 6 wherein said energy storage means is a tension spring.

8. The combination specified in claim 7 wherein said reciprocating arm means includes,

9. The combination specified in claim 8 wherein the angular displacement between said stair engaging arm means and said spring control arm member is selected so that said tension spring delivers maximum torque to said auxiliary axle when said stair engaging arm means is substantially horizontal during ascent of a stair.

10. The combination specified in claim 1 wherein said reversible motor means is a constant speed motor.

11. The combination with a hand truck or the like having wheel means disposed to rotate about an axis of a mechanism adapted to be affixed to said hand truck comprising,

12. The combination specified in claim 11 wherein said first limit switch defines an upper limit position wherein the extending end of said stair engaging elongated arm means is higher than a stair to be traversed when said wheels are resting on the next lower stair of said stairway.

13. The combination specified in claim 11 wherein said first and second limit switch means are disposed to be selectively actuated when said stair engaging elongated arm means arrives at its said upper and lower limit positions respectively and further including energizing circuitry for said reversible motor means comprising,

14. The combination specified in claim 13 and further including dynamic braking circuit means for said motor means rendered effective when either of said first and second limit switch means has been actuated.

15. The combination specified in claim 13 wherein said energizing circuitry comprises by-pass circuit means effective when one of said first and second limit switch means has been actuated due to rotation of said elongated arm means in one direction by said motor means and including the non-actuated one of said first and second limit switch means and said toggle switch means to permit said reversible motor means to be energized for rotating said elongated arm means only in the opposite direction.

16. The combination specified in claim 15 and further including dynamic braking circuit means for said motor means rendered effective when either of said first and second limit switch means has been actuated.

17. The combination specified in claim 16 further including,

18. The combination with a hand truck or the like having wheel means disposed to rotate about an axis of a mechanism adapted to be affixed to said hand truck and comprising,

19. The combination specified in claim 18 wherein said energy storage means is a tension spring.

20. The combination specified in claim 19 wherein said rotary arm means includes,

21. The combination specified in claim 20 wherein the angular displacement between said stair engaging arm means and said spring control arm member is selected so that said tension spring delivers maximum torque to said auxiliary axle when said stair engaing arm means is substantially horizontal during ascent of a stair.

22. The combination specified in claim 19 wherein said reversible motor means is a constant speed motor.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the art of handling burdensome loads of the class normally moved by hand trucks, specifically where stairs or steps are involved. In particular, the proposed device is a simplified and efficient power mechanism attachment of the type intended to permit an operator to more easily traverse stairways or steps in either direction with a hand truck, and yet designed so that the hand truck can readily be moved about on a horizontal floor in the usual manner.

2. Description of the Prior Art

The prior art is known to include several mechanisms capable of performing, at least in part, some of the more general functions attributable to the present invention. On the other hand, a study of these previously proposed mechanisms shows that most of them are quite complex; none of them make use of an energy-storing spring means to assist the motor during the stair ascending operation; and, none of them accomplish the load lifting and lowering functions by means of simple, rotary motion of the lifting mechanism about a single shaft, as employed in the apparatus of the present invention.

SUMMARY OF THE INVENTION

The proposed device of the present invention is capable (under control of one operator) of traversing stairways in either direction with a loaded hand truck. No engaging or disengaging devices are required as the hand truck goes from its normal hand-powered, roll-around use on a horizontal floor to the powered ascent or descent of a stairway. The wheels of the hand truck are not powered, or modified, in any way and are left free to rotate on the main axle. Rather, the powered portion of the hand truck mechanism comprises an auxiliary shaft to which are attached two lifter or climber arms which contact the stairs via associated roller means, a main driven gear, and a spring retaining lever arm. The auxiliary shaft is mounted to the hand truck frame so that it extends parallel to, but is offset from, the main axle of the hand truck. The pair of lifter arms extend perpendicularly from the auxiliary shaft and are coplanar, in order to hold step engaging roller means in a position parallel to the auxiliary shaft. The extending ends of the lifter arms are curved slightly downward to insure good engagement between the roller and the stair during ascent or descent of a stairway. The main driven gear is locked to this auxiliary shaft and, under power provided by the reversible motor and a smaller driving gear, applies torque in either direction to the auxiliary shaft, and thus applies force up or down to the step-engaging roller. The spring retaining lever arm is also attached perpendicularly to the auxiliary shaft and holds one end of a tension spring which has its other end anchored elsewhere on the hand truck frame; e.g., at the upper (handle) end of the hand truck.

The reversible driving motor is controlled by a three position UP-OFF-DOWN toggle switch and causes the auxiliary shaft to rotate back and forth, thus lifting and lowering the step-engaging roller as the hand truck ascends or descends a stairway. More specifically, preparatory to ascending a stair, the toggle control switch is actuated to the DOWN position and the driving motor causes the step engaging roller to be raised to the position wherein the roller can engage the next higher stair and the spring is simultaneously stretched, thereby storing energy for use during the actual load lifting portion of the operating cycle. In other words, when the motor is subsequently reversed, by moving the toggle switch to the UP position, to lower the lifter arms and thereby lift the load to the next stair, the energy stored in the spring is released and assists in lifting the load to this next stair. Moreover, the angle of displacement between the spring retaining lever arm and the step engaging roller is purposely selected so that the torque returned by the spring during the lifting part of the cycle is maximum when maximum torque is required; namely, when the auxiliary shaft and the step-engaging roller are in substantially the same horizontal plane.

Electrical limit switches are provided on the proposed hand truck mechanism and control the angular extremes to which the powered mechanism will rotate. When either limit switch is actuated, the motor is deenergized and is subjected to rapid dynamic braking, and thereafter, the motor can only be energized for the opposite direction of rotation. As noted earlier, the highest position of the roller, with the spring at maximum tension, is the angle limit at which the mechanism is ready to lift to the next higher step; whereas, the lowest position of the roller, with the spring at minimum tension, is the angle limit at which the main wheels are ready to be rolled onto the step at the end of the lifting operation. When it is desired to move the hand truck about on a horizontal floor, the toggle control switch is actuated as necessary to move the step-engaging roller means to a non-interfering position, with the hand truck and load in the normal or balanced position. The toggle switch is then turned to OFF, the motor stops, and the load can be moved about in the fashion of a conventional hand truck.

From the foregoing discussion it will be seen that a principal objective of this invention is to provide a stair traversing mechanism for hand trucks capable of powering a loaded hand truck up and down stairways, under the control of one operator.

Another objective of this invention is to provide a power mechanism adapted to be utilized on a hand truck or the like to facilitate use of the hand truck in ascending and/or descending a stairway with a load.

Another objective of this invention is to provide a powered stair traversing mechanism for hand trucks including an energy storage device which stores energy preparatory to ascending a stair and which subsequently releases this energy to assist in lifting the hand truck and its load during the actual stair ascending operation.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which is simple and economical to manufacture.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which has no engaging or disengaging clutches or devices of any kind to complicate its use by an operator.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which has no adjustments to complicate its use by an operator.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which does not detract from the normal use of the conventional, unpowered hand truck.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which can be built in various power capacities without modification of the basic configuration.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which can be driven by various power sources, such as a D.C. motor and battery, an A.C. motor powered from a line source, or a hand powered crank.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which will assist the loaded hand truck over a doorjam, pipe, or other small obstacle.

A further objective of this invention is to provide a stair traversing mechanism for hand trucks which will permit simple operation and safety to both the operator and the cargo during stair traversing operations.

Other objects, purposes, and characteristic features of the present invention will in part be pointed out as the description of the present invention progresses and in part be obvious from the accompanying drawings wherein:

FIG. 1 is a perspective view of a standard hand truck fitted with a powered stair traversing mechanism in accordance with the present invention;

FIG. 2 is a partial side view of the hand truck of FIG. 1 illustrating one manner of providing a power pick off for the stair traversing mechanism of the present invention;

FIG. 3 is a simplified side view of the hand truck of FIG. 1 illustrating the proposed stair traversing mechanism in its operating condition just prior to climbing a step (or just after descending a step);

FIG. 4 is a partial side view of the hand truck of FIG. 3 illustrating the power mechanism in its operating condition during the ascending or descending of a step;

FIG. 5 is a partial side view of the hand truck of FIG. 3 illustrating the stair traversing mechanism in its operating condition just after climbing a step (or just before descending a step); and

FIG. 6 is a schematic diagram of a typical motor control circuit employed in the illustrated embodiment of the invention when the reversible motor is of the permanent magnetfield type.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawings, the proposed stair traversing mechanism of the present invention is particularly adapted for use on a standard hand truck such as that designated generally at 10 in the drawings and comprising a handle portion 11, side rails 12, cross members 13, foot member 14, and non-driven wheels 15 which are bearing-mounted in the normal fashion so that they rotate freely on the main axle 16 whose ends extend through the usual wheel support brackets 17.

In accordance with the present invention, this basic hand truck structure is modified to carry the stair traversing mechanism of the present invention. More specifically, a generally flat mounting plate member 18 is suitably secured between the side rail members 12 and is adapted to have mounted thereon a rechargeable battery power supply designated at 19, reversible D.C. motor 20, and a motor power take-off assembly including gear reduction box 21, flexible coupling 22 and a driven worm 23 (see FIG. 2) supported in the illustrated gear housing 24. The motor 20 is preferably a constant speed motor such as, for example, of the shunt wound or permanent magnet field type.

A segmental worm gear 25 cooperates with the worm 23 and is affixed, for rotation, to an axle member 26 whose ends are suitably mounted in bearing supports of conventional design at the support brackets 17. If necessary, the segmental worm gear 25 can be notched, as shown at 25a, or otherwise configured to prevent it from hitting the main axle 16, when the worm gear 25 is rotated to the position shown in FIG. 2 of the drawings. It will be obvious to one skilled in the art that, if desired, the worm gear assembly 23-25 can be replaced by other gearing arrangements (e.g., a spur gear assembly) with the motor 20 mounted parallel to the truck side rails 12, in order to achieve the benefit of simpler lubrication of the spur gears.

The driven or auxiliary axle 26 is mounted parallel to, but displaced from, the main axle 16, as will be described in more detail hereinafter, and also has secured thereto a pair of stair contacting lifter arms 27 which extend in a common plane and whose extending ends support a roller assembly comprising rod 28 and a plurality of roller members 29 which are held in place by snap washer, for example. The extending ends of the lifter arms 27 are bent slightly downward in order to assure good engagement between the rollers 29 and a stair during operation of the present invention, as will be described in more detail hereinafter. Also secured to the driven or auxiliary axle 26, and angularly displaced from the lifter arms 27, is a spring-control arm 30 whose extending end is attached to one end of a tension or coil spring designated at 31. The opposite end of the spring 31 is secured to the side rail member 12 by means of bracket member 32.

The wheel support bracket 17 shown on the left-hand side of the hand truck of FIG. 1 also carries two microswitches designated at 33a and 33b which are adapted to be actuated by the left-hand lifter arm 27, as will be described in detail hereinafter, and define the limits of movement of the stair traversing mechanism proposed in accordance with the present invention. A toggle switch 34 is mounted in the handle portion 11 of the illustrated hand truck and is operable to UP-OFF-DOWN switch positions whereby the operator can control the selective energization of the reversible motor 20, as will be described in detail. Preferably, the toggle switch 34 is spring-loaded to its center or OFF position.

In preparation to ascending a stairway (represented at 35 in FIGS. 3 through 5 of the drawings), the operator would initially move the lifter arms 27, together with the associated rollers 29, to their uppermost position as shown in solid line form in FIG. 2 and in FIG. 3, by actuating the toggle switch 34 to its DOWN position to thereby properly energize the motor 20 so that it rotates the lifter arms (about shaft 26) until the limit switch 33b is reached, at which time the energizing circuit to the motor would be opened. More specifically, the energizing circuit for the motor 20 when toggle switch 34 is in its DOWN position includes, in series, (see FIG. 6) the upper left-hand contact of switch 34 and the lower or back contact of limit switch 33b. Therefore, when the limit switch 33b is actuated (lower contact opened and upper contact closed) by the lifter arm 27, this motor energizing circuit is interrupted and dynamic braking brings the motor 20 to a positive and abrupt stop by reason of the short circuit now connected across the motor through switch 34 in its DOWN position and the upper or front contact of limit switch 33b. When the operator releases toggle switch 34 to its center or OFF position, the short circuit across the motor 20 is removed and the motor 20 is now ready to be energized, but only for rotation in the opposite direction since the lower or back contact of limit switch 33b is open.

In this position of the stair traversing mechanism, the tension spring 31 is in its fully extended position, as shown most clearly in FIG. 3 of the drawings. The operator would then back up with the hand truck 10 until the wheels 15 just contact the lowermost step, as is also shown in FIG. 3, and the toggle switch 34 is then operated to the UP position. As a result, the motor 20 is now energized with an opposite current polarity over a circuit including the upper right-hand contact of toggle switch 34 and the lower or back contact of limit switch 33a, in FIG. 6. This causes a reversal in the direction of rotation of the reversible motor 20 and the worm gear 23--25. Accordingly, the auxiliary shaft 26 and the connected lifter arm 27 will be driven in a counter-clockwise direction effective to lift the loaded hand truck 10 onto the next stair.

In FIG. 4 of the drawings, the hand truck is shown in a partially raised position wherein the lifter arms 27 are in their most horizontal position. It has been determined that in this position, maximum torque is required about the auxiliary shaft 26 to lift the loaded hand truck. Accordingly, the angular displacement between the lifter arms 27 and the spring-control arm 30 is selected such that in this position of the lifter arms 27, the control arm 30 is essentially perpendicular to the hand truck and thereby is capable of providing a maximum amount of torque in the counter-clockwise direction to the auxiliary shaft 26 in order to maximize the assistance which the tension spring force can provide during the lifting operation. As shown in FIG. 5, the counter-clockwise rotation of the lifter arms 27 about the auxiliary shaft 26 (with the assisting torque provided by the tension spring 31) continues until the left-hand lifter arm 27 (see FIG. 1) actuates the limit switch 33a (opens the lower contact and closes the upper contact in FIG. 6) at which the energizing circuit to the motor 20 is again interrupted and dynamic braking is applied, as before. In FIG. 5 it will be noted that in this lowermost position of the lifter arms 27, the lowermost portion of the step engaging rollers 29 are substantially horizontal with the bottom of the wheels 15 so that the loaded hand truck may readily be pulled onto the stair.

Preferably, during the lifting operation, the operator will hold the wheels 15 of the hard truck against the vertical or rise edge of each step so that he may more readily pull the hand truck wheels onto the next higher step when the limit switch 33a halts the lifting motion, as just described, without the risk of the rollers 29 dropping off the steps. Moreover, the operator should preferably maintain a balancing pressure on the handle 11 of the hand truck because the support point of the hand truck; i.e., the step engaging rollers 29, will move beneath the center of gravity of the loaded hand truck, during the lifting motion. Once a step has been ascended and the main wheels 15 pulled onto the step, the operator would again actuate the toggle switch 34 to its DOWN position wherein the reversible motor 20 is energized so as to rotate the lifter arms 27 and the connected step engaging rollers 29 to their uppermost position defined by the limit switch 33b, as previously described, in preparation for ascending the next step in the stairway. The above-described process would then be repeated, step-by-step, until the wheels of the hand truck are pulled onto the horizontal floor portion of the top of the stairs, at which time the toggle switch 34 can be actuated, as necessary, to position the lifter arms 27 so that the stair traversing mechanism does not interfere with the usual roll-around mode of the hand truck.

To descend the stairway, the operator would actuate the toggle switch 34 to its UP position until the rollers 29 are moved to their lowest position as defined by the lower limit switch 33a in FIG. 1. The hand truck would then be rolled towards the edge of the top step (see FIG. 5) and the main wheels 15 of the hand truck would be rolled just over the edge of the top step so that the load is borne by the rollers 29 as they engage the upper step. The operator would then actuate the toggle switch 34 to its DOWN position and thereby reverse motor 20 to drive the rollers 29 to their upper limit as the wheels 15 are lowered to the step below (see FIG. 3). Once on this lower step, the operator would roll the truck forward just enough to clear the engagement of rollers 29 with the step, and again operate the toggle switch 34 to lower the lifter arm 27 and the rollers 29 to their position shown in FIG. 5. This process would be repeated, step-by-step, until the wheels 15 are deposited on the floor at the bottom of the stairway. If necessary, the toggle switch 34 would then be actuated to properly position the lifter arms 27 and the rollers 29 so that they do not interfere with normal roll-around operation of the hand truck.

It will be obvious to a person of ordinary skill in the art that in addition to the stair traversing function described hereinabove, the proposed mechanism of the present invention is very useful in lifting a loaded hand truck over a doorjam, a pipe or electrical cable on a floor or any other offset in a horizontal floor which would normally cause difficulty with a conventional hand truck. More specifically, the operator would simply roll the hand truck against the obstruction (with the lifter arms 27 raised, as in FIGS. 5) and then actuate the toggle switch 34 to lower the rollers 29 onto the obstruction. As the rollers 29 engage the obstruction, or come to the lower limit, the hand truck can be rocked between the main wheels and the rollers 29 to cross the obstruction.

By way of examples and without intending to in any way limit the scope of the present invention, the following table provides a listing of some typical values of various part dimensions and rating employed in one practical hand truck application of the proposed step traversing mechanism of the present invention:

Approximate Typical Dimensions and Ratings (for Standard Hand

Truck with 8 inches Diameter Wheels)

Angle of Travel of Lift Arms 27 -- = 95°

Length of Lift Arms 27 -- = 5 inches

Diameter of Rollers 29 -- = 1 inch

Length of Spring Control Arm 30 -- = 5 inches

Length of Spring 31 (Unstretched) -- = 35 inches

Length of Spring 31 (Stretched) -- = 41 inches

Spring Constant of Spring 31 -- = 3 pounds per inch (plus 7 pounds opening tension)

Angle Between Lift Arms 27 and Spring Arm 30 -- = 130°

Displacement Between Axles 16 and 26 -- = 1.75 inches

Motor 20 - RAE Motor Corp., Model 1605-G14 (12VDC) Constant speed, permanent magnet field motor.

Gear Reducer 21 - G-14 at 9.75:1

Worm Gears 23-25 - GLOBE W1280 and WG 12 (Worm Gear Reduction - 80:1)

Battery 19 - (Two) Gould Pb 690 GELYTE

Referring once again to FIG. 6 of the drawings, it should be noted that the illustrated circuitry provides, without the use of relays or other special control components, the necessary limiting of travel in one direction while leaving operation in the opposite direction possible, and simultaneously provides the needed positive stopping action caused by shorting the rotor of the motor through the upper or front contact whichever limit switch is actuated. The motor control circuitry can also be provided with a charging plug (shown dotted in FIG. 6) by which the battery 19 can be recharged.

Obviously, many other modifications and variation of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.