FIELD OF THE INVENTION

A mechanism for hand truck /trolley to climb stair smoothly.

BACKGROUND OF THE INVENTION

Hand trucks are commonly used for carrying loads, especially heavy loads. Conventional hand trucks usually comprise an elongated frame having a forwardly protruding platform at the bottom, a pair of opposite wheels beneath the platform and one or more handles at the top. Such devices are efficient but are not necessarily convenient, especially for moving heavy loads and articles up stairways. For example, a lot of effort on the part of the operator is required to adjust the inclination of the hand truck in order to provide for a stable transportation of the loads. The use of a conventional hand truck in the stairs may also present a danger if the operator gets out of control and the load roll back. Another problem is that these conventional hand trucks have a pair of ground engaging wheels which wear quickly because of the heavy load bearing downwardly directly on the wheels.

Other types of hand trucks have thus been developed. Examples of such hand trucks are disclosed, by way of non-restrictive. Such hand trucks possess a pair of wheel assemblies on each side of the frame rotating freely about a transversal main axle. Each assembly comprises three wheels mounted on a star-shaped plate, each wheel being mounted on stub axles on the legs of the star- shaped plate. Such a triangular configuration of the wheels aims at providing easier moving up stairs and a braking action when moving down stairs. Similarly, US Patent No, 4,312,417 discloses a hand truck having also a pair of star-shaped wheel assemblies. However, in this patent, each star-shaped assembly comprises four wheels instead of three, thereby forming a square configuration. Moreover, the hand truck also comprises a motor for simultaneously rotating the wheel assemblies.

The "multiple" wheel assemblies described above are efficient. However, they involve costly complicated mechanical structure which is susceptible to breakage, jamming and other mechanical problems. Also, the hand trucks provided with these wheel assemblies are heavy due to their structure that requires numerous pieces. Moreover, they may be used only for small stairs because of the size of their wheels which is limited to a maximum diameter due to the star-shape plate.

Finally, these hand trucks have automatically four wheels in contact with the ground (two on each side), and are thus less easy to handle when moving loads on flat grounds, for example in a warehouse, or with no-load, and they need more space to be put away when not used. Thus, there is still a need for an improved, low cost mechanism for hand truck to safely carrying loads up and down staircases, which will be able to overcome the above mentioned existing problems.

SUMMARY OF THE INVENTION

The mechanism consists of three (3] sequential phases to yield the objective of smooth stair climbing. The first phase is prepare to climb phase. The distance between front rollers and back rollers is set during this phase. Front rollers are in contact with ground of stair near to the edge of stair. Back rollers are in contact with ground of stair set as close as possible to vertical wall. The second phase is climb phase. User push handle asserting force on the hand truck/trolley, this action caused hand truck/trolley move forward with base slides on edge of stair. Simultaneously a moment action happened with contact between base of hand truck/trolley and edge of stair act as pivot line, this action caused back rollers climb stair and land on ground of next stair. The third phase is move to next prepare to climb phase. User asserts thrust force on handle caused hand truck/trolley tilted and move to position of next prepare to climb phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the structure of invented mechanism;

FIG. 2 is an exploded view of the structure of invented mechanism;

FIG. 3 shows key dimensions of fixed castor roller and height of steel balls measured from ground; FIG. 4 is a top view of array of steel balls;

FIG. 5 is a side view of array of steel balls;

FIG. 6 shows required additional base for carry object with length greater than base;

FIG. 7 shows an extended bar that acts as a support at rest position while climbs stair;

FIG. 8 shows prepare to climb phase;

FIG. 9 shows climb phase; and

FIG. 10 shows move to next prepare to climb phase.

DETAIL DESCRIPTION OF MECHANISM

The mechanism is with structure as shown in FIG. 2. A base (14) with length adjustable is intent to carry object, it is mounted with steel balls (24) at bottom face. Fixed castor rollers (18) are mount at front & back edge of bottom face of base (14). Distance between front & back castor rollers (18A, 18B) is 453mm by referring to stair with 19.7cm in height and 25.4cm in width. This FIG. also shows the end of handle (22) shall be fixed to the base (14). As shown in FIG. 3, selected fixed castor rollers (18) are with diameter 40mm and mounting height 50mm. This FIG. also shows height of steel balls (24) mounted at bottom face of base (14) is 70mm measured from ground. These are to guarantee base (14) is in contact and slides on edge of stair while climbs stair. Steel balls (24) mounted at bottom face of base (14) shall be in array form. FIG. 4 shows top view of array of steel balls (24) whereas F1G.5 shows side view of array of steel ball (24). The array form is to ensure steel balls (24) are in straight line contact with edge of stair while climbs stair.

Additional requirements of structure are (a) As shown in FIG. 6, if intend to cany object with length greater than length of base (14), an additional base (28) with height 19.7 cm from base (14) is needed for carry object to avoid object crashing with stair while climbing, (b) As shown in FIG. 7, if intend to carry large and tall object, a bar (30) extend from handle (22) needed to act as support at rest position while climbs stair.

The objective of smooth stair climbing is accomplished by utilising combination of rolling, sliding and moment action during stair climbing. Rolling means fixed castor rollers (18) with heavy load bearing capability roll and direction of roll are forward & backward. Sliding means base (14) of hand truck/trolley slides on edge of stair while climbs stair. Rolling element: steel balls (24) are mounted at bottom face of base (14) to reduce friction while sliding. Utilising moment action means reduce operating force required from user by eliminating action of lifting up hand truck/trolley while climbs stair. The mechanism consists of three (3] sequential phases. The first phase is prepare to climb phase as shown in F1G.8. The distance between front rollers (18A) and back rollers (18B) is set during this phase by adjusting the length of base (14). Front rollers (18A) are in contact with ground of stair near to the edge of stair. Back rollers (18B) are in contact with ground of stair set as close as possible to vertical wall. The second phase is climb phase as shown in FIG. 9. User push handle (22) asserting force on the hand truck/trolley, this action caused hand truck/trolley move forward with base (14) slides on edge of stair. Simultaneously a moment action happened with contact between base (14) of hand truck/trolley and edge of stair act as pivot line, this action caused back rollers (18B) climb stair and then land on ground of next stair. As shown the center of gravity of object carried is approximate center to pivot, means very small push force, Fp needed to cause back rollers (18B) climb stair and then land on ground of next stair. The third phase is move to next prepare to climb phase as shown in FIG. 10. User asserts thrust force on handle (22) caused hand truck/trolley tilted and move to position of next prepare to climb phase.