Load balancer

Abstract: A load balancer adapted to set the load of an article to substantially zero by utilizing an air pressure, and provided with a balance cylinder unit consisting of air brakes (20), a balance cylinder (13) and a weight sensing cylinder (11). This balance cylinder unit is formed by arranging the balance cylinder (13) and weight sensing cylinder (11) on the same axis, and air brakes (20) on both sides of the balance cylinder (13).

Description: This invention relates to a load balancer capable of transferring articles easily, and more particularly to a load balancer adapted to set the load of articles to substantially zero by utilizing an air pressure. A known load balancer of this kind is disclosed in, for example, Japanese utility model application Kokai publication No. 61-197079. In this conventional example, a wheeled chassis supports a load balancer in which an air brake cylinder is operated to control a piston rod of the balance cylinder unitarily with the balance cylinder, and the load of articles, which is transmitted from an article support arm, is transmitted to a weight sensing cylinder provided in series just as the balance cylinder, to generate a reference pressure corresponding to the load. The compressed air pressure which corresponds to the reference pressure is supplied to a chamber in the balance cylinder. When the air brake is then released, this compressed air causes a reaction force corresponding to the load to be generated, which is applied to the support arm via the piston and piston rod of the balance cylinder to set the load of the articles held on the support arm to substantially zero. This enables the articles to be treated and transferred easily by human power. However, in order to make the air brake, which is provided in series with respect to the balance cylinder, fix the piston rod of the balance cylinder when the load of the articles is transmitted to the weight sensing cylinder to set a reference pressure, the necessity of setting the axial length of the air brake considerably large occurs. Therefore, the axial length of a balance unit consisting of the weight sensing cylinder, balance cylinder and air brake is necessarily set large. Accordingly, the height of the load balancer necessarily becomes large, so that it becomes unsuitable to use the load balancer, for example, inside a building or under a construction machine and an aircraft. An object of the present invention is to provide a load balancer having a small height and capable of being used even inside a building or under a construction machine and an aircraft. In the load balancer according to the present invention which is capable of attaining this object, a piston rod of a balance cylinder is connected pivotally to one portion of a horizontal pin joined pivotally to an arm, and brake rods of air brakes to the portions of the horizontal pin which are on both sides of the piston rod-connected portion thereof. These brake rods are passed through air brake cylinders fixed to the balance cylinder which is secured to a balance frame, and the piston rod of the balance cylinder is passed freely through the balance frame, the lower portion of the balance cylinder forming a piston of a weight sensing cylinder. When the air brakes control the brake rods in this structure, the load of articles is transmitted to the brake rods, balance frame and balance cylinder in the mentioned order via the pin connected pivotally to the arm, and finally to the weight sensing cylinder to generate a load balancing reference pressure. Since the air brakes are fixed to the portions of the balance frame which are on both sides of the balance cylinder, the load is transmitted in a branching manner from the brake rods to the balance frame. Therefore, the air brakes can be miniaturized, i.e., it becomes possible to increase the diameter of the brake rods and reduce the length of the air brake cylinders, it also becoming possible to control the piston rod satisfactorily even when a large load is imparted thereto. Accordingly, the axial length of the air brakes can be reduced, i.e., it can be set correspondingly to the length of the balance cylinder and the length of the weight sensing cylinder. Fig. 1 is a side elevation of an embodiment of the load balancer according to the present invention; Fig. 2 is a block diagram of a control circuit for the load balancer shown in Fig. 1; The embodiments of the load balancer according to the present invention will now be described with reference to the drawings. As shown in Fig. 1, the load balancer includes an undercarriage 1 which consists of a chassis frame 4 supported on three wheels 2, 3. Out of the wheels 2, 3, the paired wheels 2 are supported vertically on the chassis frame 4 via bearings, and the remaining single rear wheel 3 on a steering frame 6 via a bearing, which steering frame 6 is supported via a bearing so that it can be turned around a vertical shaft 5 with respect to the chassis frame 4. A steering arm 7 is connected pivotally to the steering frame 6 so that the steering arm 7 can be vertically moved. A turntable 9 is placed on the portion of the chassis frame 4 which is close to the steering frame 6 so that the turntable 9 can be turned around a vertical shaft via a swing bearing 8 provided on the chassis frame 4. A horizontally extending pin 10 is provided on this turntable 9. As shown in Fig. 2, a weight sensing cylinder 11 which will be described later is connected pivotally to the intermediate portion of the pin 10. Swing arms 12 are connected pivotally to the portions of the pin 10 which are on both sides of and equally away from the weight sensing cylinder 11. A balance cylinder 13 is fitted slidably in the weight sensing cylinder 11, and fixed at the upper end thereof to a balance frame 14. A piston rod 16 fixed to a balance piston 15 provided in the balance cylinder 13 projects upward through a bore provided in the balance frame 14, and is joined pivotally at its upper end to a lower arm 18 of a rhomboidal link or parallel link mechanism 17 via a pin 19 which is parallel to the pin 10 provided on the turntable 9. Brake rods 21 of air brakes 20 are connected pivotally to the portions of the pin 19 which are on both sides of and equally away form the piston rod-connecting point thereon and they are passed through air brake cylinders 22 which are fixed to the balance frame 14. Each of these air brakes 20 consists of a known air brake adapted to release the brake rod 21 when it receives compressed air, and control the brake rod by the force of a spring when the supplying of the compressed air thereto is stopped. Each of the swing arms 12 connected pivotally to the horizontal pin 10 provided on the turntable 9 is shaped so as to extend first diagonally rearward from the pin 10, and then perpendicularly upward, and upper and lower arms 18, 25 of the rhomboidal link 17 are connected pivotally to the portions of the swing arm 12 which are in the vicinity of the upper ends thereof via two pivot pins 23, 24 which constitute a shorter side of the same link 17. These pivot pins 23, 24 are parallel to the horizontal pin 10 on the turntable 9 and the pin 19 via which the piston rod 16 and lower arm 18 are pivotally connected, and they are positioned on substantially the same vertical plane. A rod 26 is connected pivotally at one end thereof to the lower pivot pin 24, and at the other end thereof to the turntable 9, whereby the rod 26 draws the swing arm 12 via the lower pin 24 so that the swing arm 12 is not turned due to a load around the horizontal pin 10 provided on the turntable 9. A support frame 27 is connected pivotally to the front ends of the upper and lower arms 25, 18 of the rhomboidal link via horizontal pins 28, 29. The points at which the support frame 27 and the upper and lower arms 25, 18 are pivotally connected are in the same vertical plane, and the distance between these points of pivotal connection of the arms 25, 18 is equal to that of the points of pivotal connection thereof to the swing arm 12. Accordingly, the upper and lower arms 25, 18, swing arm 12 and support frame 27 form the rhomboidal link 17. A vertical shaft 30 is fixed to the front portion of the support frame 27, and a slide arm 31 capable of turning in the horizontal direction to this vertical shaft 30. The slide arm 31 is provided with an air brake 32, which consists of a known air brake capable of working on the vertical shaft 30. The air brake is adapted to set the slide arm 31 freely swingable when it receives the supply of compressed air, and hold the vertical shaft by the force of a spring and display its control force when the supply of compressed air is stopped. The slide arm 31 consists of three cross-sectionally rectangular telescopically extensible arms, i.e. first, second and third arms 33, 34, 35. Arm braking rods 36, 37 are fixed to the front ends of the lower portions of the second and third arms 34, 35 so as to extend in parallel with the extending and contacting direction thereof. These arms 34, 35 are passed through the air brakes 38, 39 provided on the first arm 33. The air brakes 38, 39 are adapted to control the movements of the rods 36, 37 when they receive the supply of compressed air, and determined the length of extension of the slide arms 34, 35. The slide arm 31 is provided at the front end thereof with an article support member or an article holding member (not shown). The balance cylinder 13 will now be described in detail. As shown in Fig. 2, an incompressible fluid 40 is held in a cylinder body of the weight sensing cylinder 11 connected pivotably to the horizontal pin 10 provided on the turntable 9, and the lower portion of the balance cylinder 13 forms a piston 41, which is fitted in the weight sensing cylinder 11 so as to enclose the incompressible fluid. A balance piston 15 is fitted slidably in the balance cylinder 13 and receives a predetermined level of air pressure in a cylinder chamber 42 to support the lower arm 18 of the rhomboidal link at the point of pivotal connection thereof to the piston rod 16 via the same piston rod 16. The controlling of the pressure of the air supplied to the chamber 42 of the balance cylinder 13 will be described later. The piston 41 consisting of the lower portion of the balance cylinder 42 has the same diameter as the balance piston 15. A control board 45 is provided at the back of the swing arms 12 so as to control a load balancer 100 (refer to Fig. 1). The operation of the load balancer 100 according to the present invention will now be described in connection with a control circuit therefor. As shown in Fig. 1, the load of an article placed on the front end portion of the slide arm 31 is imparted to the piston rod 16 of the balance cylinder 13 via the lower arm 18 of the rhomboidal link 17. When the supply of compressed air to the air brake 20 is stopped, the brake cylinder 22 controls the brake rod 21. Consequently, the load is transmitted to the balance cylinder 13 via the balance frame 14, and the piston 41 at the lower portion of the balance cylinder 13 presses the incompressible fluid 40 in the weight sensing cylinder 11 to generate a reference pressure P corresponding to the load of the article. This reference pressure P is transmitted to a precision reducing valve 50, and the compressed air supplied to the precision reducing valve 50 is regulated to a pressure corresponding to the reference pressure P, the pressure-regulated air being supplied from a compressed air source 60 to the interior of the chamber 42 of the balance cylinder 13. Thus, the balance cylinder 13 constantly receives a reaction force corresponding to the load of the article, which is placed on the front end portion of the slide arm 33, via the rhomboidal link 17, support frame 27 and slide arm 31, so that the article can be maintained substantially weightless. The controlling of the load balancer 100 according to the present invention shown with a control circuit 90 will now be described. When a manual selector valve 51 is switched from a position 51A to a position 51B, the compressed air in the air brakes 20 fixed to the balance frame 14 controls the rods 21 with respect to the balance frame 14 due to the force of a spring. When an article is then placed on the front end portion of the slide arm 33, the load of the article presses the incompressible fluid 40 in the weight sensing cylinder 11 via the lower arm 18 of the rhomboidal link, pin 19, air brakes 20, balance frame 14 and balance cylinder 13 to generate therein a reference pressure P for the air to be supplied to the balance cylinder 13. This reference pressure P is transmitted to a precision reducing valve 50, which correspondingly controls the pressure of the air supplied from a compressed air source 60 to the balance cylinder 13. When the manual selector valve 51 is then operated to supply the compressed air from the compressed air source 60 to the air brakes 20, the air brakes 20 release the piston rods 21. Also, compressed air the pressure of which corresponds to the load of the article is supplied from the precision reducing valve 50 to the balance cylinder 13, and this compressed air supports the lower arm 18 of the rhomboidal link through the piston 15 and piston rod 16 of the balance cylinder 13. An automatic selector valve 57 receives the air pressure at this time to be switched from a position 57A to a position 57B, whereby the reference pressure P from the weight sensing cylinder 11 is shut off. Accordingly, this reference pressure P is constantly applied to the precision reducing valve 50. Thus, the article placed on the front end portion of the slide arm 33 together with the weight of the slide arm 33 becomes substantially weightless. The manual valves 52, 53 are then operated to release or actuate a brake for the turntable 9 to set the rotary position in the horizontal direction of the arm 17, and the brakes 38, 39 engaged with the rods 36, 37 fixed to the slide arm 33, to determine the lengths of the slide arms 34, 35. A safety control operation to be carried out when an overload occurs on a load support system, i.e., on the rhomboidal link 17, support frame 27 and slide arm 33 will now be described. When a load, heavier than allowable, is imparted to the slide arm 33 in the load balancer 100 according to the present invention, the pressure in the weight sensing cylinder 11 exceeds an allowable level. When a control valve 56 constantly monitoring the pressure in the weight sensing cylinder 11 detects an excessive pressure, compressed air is sent from the compressed air source 60 to a circuit for the air brakes 20 to release the air brakes 20 and return the article to the ground surface so that the safety of the apparatus can be ensured.

Claims: A load balancer comprising an undercarriage (1), a turntable (9) capable of turning around a vertical shaft owing to a swing bearing (8) provided on a chassis frame (4) of said undercarriage (1), a horizontal pin (10) provided on said turntable (9), a weight sensing cylinder (11) connected pivotally to an intermediate portion of said horizontal pin (10) and extending substantially upward, a balance cylinder (13) provided with a piston (41) fitted in said weight sensing cylinder (11), and characterised by further comprising a balance frame (14) fixed to the upper end of said balance cylinder (13) with a piston rod (16) of a balance piston (15) of said balance cylinder (13) passed there-through, air brake cylinders (22) fixed to said balance frame (14) and positioned at the same distance on opposite sides of said balance cylinder (13), a pin (19) connected at an intermediate portion thereof to said piston rod (16) said pin being connected at the portions thereof which are on both sides of and equally spaced from said piston rod-connected portion to a lower arm (18) of a parallel link mechanism (17) and connected at both end portions thereof via bearings to brake rods (21) passed through said air brake cylinder (22), swing arms (12) supported upright upon said turntable (9) and connected to one end portion of each of upper and lower arms (18, 25) of said parallel link mechanism (17) via pivot pins (23, 24), a support frame (27) connected to the other end portions of said upper and lower arms (18, 25), at positions on said support frame (27) which are spaced at a distance equal to that between pivot pins (23, 24), and an article support member (31) fitted around a vertical pin (30) fixed to said support frame (27).

Inventors: OHASHI HIROTAKA, YASUNOBE TORU, OHASHI, HIROTAKA, YASUNOBE, TORU, Ohashi, Hirotaka, c/o Mitsui Engineering, Yasunobe, Toru, c/o Mitsui Engineering
Applicants: MITSUI SHIPBUILDING ENG, MITSUI ENGINEERING & SHIPBUILDING CO., LTD
Application year: 1992
Main classification: B66C23
IPC codes: B25J19, B66C23, B66F9