US3666086A

US3666086A - Walking beam conveyor

Info

Publication number: US3666086A
Application number: US51813A
Authority: US
Inventors: Heinz Brockmann
Original assignee: Brockmann & Bundt Ind Ofenbau
Current assignee: Brockmann & Bundt Ind Ofenbau; Brockmann & Bundt Industrie-Ofenbau
Priority date: 1970-01-12
Filing date: 1970-07-02
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30
Also published as: BE751914A; FR2074848A5; JPS4941004B1; SE364992B; DE2001052A1; AT299285B; ES380307A1

Abstract

A walking beam conveyor of the kind which comprises a series of stationary beams and a series of walking beams which have a driving mechanism by which they are moved upwards relative to the stationary beams to lift workpieces therefrom, then longitudinally to convey the workpieces along the stationary beams and subsequently downwards again to replace the workpieces on the stationary beams is provided with a mechanism for raising and lowering the walking beams in such a way as to minimize the impact of the working beams on the workpieces as they raise the workpieces from the stationary beams. This mechanism includes a number of hydraulic fluid pressure operated cylinders which are connected to the walking beams and operate successively. A number of the cylinders move the walking beams upwards until they come into contact with the workpieces and are then stalled. One or more further cylinders are then brought into operation in sequence until there are sufficient cylinders to increase the force acting on the walking beams until the walking beams are able to lift the workpieces from the stationary beams after which the walking beams are moved longitudinally by a further hydraulic fluid pressure operated cylinder and the beams are then lowered again.

Description

United States Patent Brockmann [54] WALKING BEAM CONVEYOR [72] lnventor: Heinz Brockmann, Dusseldorf-Gallberg,

Germany [73] Assignee: Brockmann & Bundt Industrle-Ofenbau,

Dusseldorf, Germany [22] Filed: July 2, 1970 [21] Appl. No.: 51,813

[30] Foreign Application Priority Data Jan. 12, 1970 Germany ..P 20 01 052.0

[52] U.S.Cl ..198/219 [51] Int. Cl. r ..B65g 25/04 [58] Field ofSearch ..198/219; 60/5l,52 HF, 221

[56] References Cited UNITED STATES PATENTS 2,224,956 12/1940 Ernst et al... ...60/52 HF 3,322,259 6/1967 Millazzo. 198/219 3,355,008 11/1967 Milazzo ..198/219 3,369,650 2/1968 Caretto et al.. ..198/219 3,451,532 6/1969 Manterfield... ..198/219 1,965,868 7/1934 Vickers ..198/219 Primary Examiner-Evon C. Blunk Assistant Examiner-H. S. Lane Attorney-Arthur O. Klein [5 7] ABSTRACT A walking beam conveyor of the kind which comprises a series of stationary beams and a series of walking beams which have a driving mechanism by which they are moved upwards relative to the stationary beams to lift workpieces therefrom, then longitudinally to convey the workpieces along the stationary beams and subsequently downwards again to replace the workpieces on the stationary beams is provided with a mechanism for raising and lowering the walking beams in such a way as to minimize the impact of the working beams on the workpieces as they raise the workpieces from the stationary beams. This mechanism includes a number of hydraulic fluid pressure operated cylinders which are connected to the walking beams and operate successively. A number of the cylinders move the walking beams upwards until they come into contact with the workpieces and are then stalled. One or more further cylinders are then brought into operation in sequence until there are sufficient cylinders to increase the force acting on the walking beams until the walking beams are able to lift the workpieces from the stationary beams after which the walking beams are moved longitudinally by a further hydraulic fluid pressure operated cylinder and the beams are then lowered again.

5 Claims, 6 Drawing Figures Patented May 30, 1972 3,666,086

3 Sheets-Sheet l W 140 12u--\ M /NVENT0R y, He/nz BROCK/7/ l lv Maw Attorney Patented May 30, 1972 3 Sheets-Sheet 2 INVENTOR Heinz BROfiK/M/VI m a m Altarnev Patented May 30, 1972 3,666,086

3 Sheets-Sheet 3 FlG 5 INVENTOR BY: l/emz BROCKNAIVA/ mag/;

WALKING BEAM CONVEYOR This invention relates to walking beam or jigging conveyors, which may be used for example for conveying workpieces through a tunnel furnace. Such furnaces with conveyors are usually called walking grate or jigging grate furnaces.

Walking beam conveyors have two groups of beams, one of which moves. The workpieces initially rest on the other fixed group of beams. The moving beams rise upwards under the workpieces, lift them, convey them through a certain distance in the direction of conveyance and then deposit the workpieces back again on to the other group of beams. The moving beams finally return to their initial positions. Each group of beams rests in contact with the workpieces for a limited period only, for example during only half of the time taken by the workpieces to move through the furnace. This fact makes walking beam conveyors particularly suitable for conveying hot workpieces.

When a walking beam conveyor is in operation the moving group of beams, that is to say the walking beams, move upwards under the workpieces, during the first phase of their movement, until they come into contact with the under sides of the workpieces, before lifting the workpieces from the upper faces of the fixed beams. At the instant when the walking beams make contact with the under sides of the workpieces a considerable impact can occur. This impact not only shortens the life of the walking beam conveyor, but, when the conveyor is part of a furnace, also damages the refractory lining of the furnace. A number of methods have therefore been proposed to prevent this impact. However all these proposed methods use as their starting point an instant when the two groups of beams are at the same height. This height remains constant until, after a period of operation, the two groups of beams become worn down differently, and become encrusted with scale, particles and the like. After that the instant when the two groups of beams are at the same height becomes increasingly displaced and the basis of the proposed methods is no longer valid.

The object of the present invention is to provide a walking beam conveyor in which this impact is reduced and which is useful for the rough operating conditions prevailing in a walking grate furnace.

According to this invention the walking beams of such a conveyor are driven in their upward and downward movements by a plurality of hydraulic fluid pressure operated pistons at least one of which is supplied with fluid from a hydraulic accumulator. The function of the hydraulic accumulator driven piston is to compensate the weight of the walking beams, at least to a large extent, so that the walking beams can be lifted from their initial positions up towards the workpieces on the fixed beams by correspondingly less lifting thrust from the other pistons, which may be called the lifting pistons. The effect obtained is that the impact produced when the walking beams make contact with the workpieces is considerably reduced.

The impact can be still further reduced, by using several hydraulic accumulator-operated compensating cylinders with a control valve interposed between each compensating cylinder and the accumulator. The control valves are actuated independently of each other. There are therefore a number of compensating pistons and a number of listing pistons. The lifting pistons move the walking beams upwards and overcome friction and the like, but support only a very small part of the walking beam weight. The accumulator operated compensating pistons, on the other hand, take the weight, or most of the weight, of the walking beams and subsequently of the workpieces. The control valves are opened successively in response to the amount of lifting thrust required to raise the workpieces from the fixed beams, that is to say with increasing lifting thrust required more of the control valves are opened, bringing into action more of the accumulator operated compensation pistons. After a first phase of the upward movement, in which the walking beams rise upwards from their initial positions, there is a second in which the workpieces are lifted from the fixed beams. For this second phase of the movement further accumulator operated compensating pistons are brought into operation, in addition to those which have hitherto supported the weight of the walking beam. The extra compensating pistons take the weight of the workpieces and consequently the lifting thrust supplied by the lifting piston is now sufficient to lift the workpieces, as well as the walking beams. Finally the workpieces are moved along horizontally, without touching the fixed beams.

At the end of the horizontal movement the workpieces are lowered again and deposited on the fixed beams. This is brought about by releasing the pressure in the lifting cylinders, with the result that the weight of the workpieces together with the weight of the walking beams becomes greater than the lifting thrust applied by the accumulator operated compensating pistons. The walking beams, with their load of workpieces. consequently move downwards, expelling fluid from the compensating pistons back into the accumulator.

When the workpieces come to rest on the fixed beams the control valves which were last actuated are returned to their initial positions, disconnecting the compensating pistons used for compensating the workpiece load. This leaves only those compensating pistons still operating which are used for compensating the weight of the walking beams. However as already mentioned these compensating pistons do not entirely support the weight of the walking beams, and consequently the walking beams continue to move downwards, hydraulic fluid being expelled from these compensating cylinders, back into the accumulators. When the walking beams and all the pistons have returned to their initial positions the accumulator pressure has also regained its initial value, less whatever pressure loss may have occurred due to friction and leakages. If the next cycle of operations is not due to begin immediately, the walking beam conveyor can now be stopped. The three phases of the vertical movements of the walking beams have now been completed, that is to say the first upward movement of the walking beams from their initial positions; the lifting of the workpieces and the depositing of the workpieces back onto the fixed beams, and it should be observed that each of these three phases is initiated by actuation of the control valves for the accumulator operated compensating cylinders.

Preferably at least percent of the upward thrust in all phases of the vertical movements is provided by the accumulator operated compensating cylinders, and consequently the impact produced when the walking beams make contact with the workpieces is negligibly small. A further advantage compared with previous walking beam conveyors is that the consumption of energy is less. This represents a considerable saving in operating costs even if the workpiece load is only a few tons. During the downward movements of the workpieces and walking beams the potential energy is not merely converted into heat but is converted back again into pressure energy. Two advantages are obtained, in the first place operating costs are saved because the energy is not wasted, and secondly it is unnecessary to provide arrangements for removing heat.

Losses of hydraulic fluid, by leakage and the like, are made up by supplying fresh hydraulic fluid to the accumulators.

In the preferred example of the invention, separate drives are provided for the upward and downward, and horizontal movements of the walking beams. The cylinders for bringing about the upward and downward movements of the walking beams act horizontally on a common transverse beam which drives lifting carriages, each of which runs on a sloping rail and is equipped with rollers which lift the walking beams. The lifting movement depends on the slope of the rail, giving a mechanical advantage which is preferably exploited to allow the walking beams to be lifted by cylinders of comparatively short stroke.

The transverse beam is preferably provided with a parallel guide system which ensures that all the walking beams are moved synchronously. The parallel guide system is of very simple construction, consisting of a rocking shaft extending parallel to the transverse beam and rotating in end bearings.

The rocking shaft is connected to the transverse beam by linkages spaced apart along the length of the transverse beam.

According to a further feature of the invention, the separate drive for bringing about the horizontal movements of the walking beams includes at least one hydraulic cylinder, the movements of which are determined by a sliding crank system with a crank arm which rotates at constant speed and an oscillating arm which performs a sine-wave oscillation. The horizontal movements of the walking beams follow this sinewave oscillation and therefore take place smoothly and without any jerking, that is to say without abrupt changes in velocity. When the conveyor is in operation this smooth horizontal oscillation is combined with the impact free vertical movements of the walking beams so that in the entire operation of the conveyor all movements are smooth and free from destructive impacts and abrupt accelerations. Both the conveyor and also the furnace, if the conveyor is mounted in one, therefore have long working lives.

The sine-wave oscillations of the oscillating arm are transmitted to the horizontally acting cylinder for bringing about the horizontal walking beam movements by means of a potentiometer bridge circuit which has two variable resistors with sliding electric contacts, one actuated by the oscillating arm and the other by the piston of the cylinder. The oscillating arm is pivoted on a bearing block which is adjustable in position relative to the crank arm. Adjustment of the position of the bearing block alters the amplitude of oscillation of the oscillating arm and therefore the amplitude of the horizontal oscillation of the walking beams.

An example of a conveyor constructed in accordance with the invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a walking grate furnace, with a number of fixed beams and a number of walking beams, each walking beam moving both vertically and horizontally;

FIG. 2 shows a driving mechanism for lifting and lowering the walking beams;

FIG. 3 shows a detail of the mechanism of FIG. 1;

FIG. 4 shows a control system for controlling the horizontal movements of the walking beams;

FIG. 5 shows a hydraulic control system for controlling the mechanism shown in FIGS. 2 and 3; and,

FIG. 6 shows an electrical circuit which cooperates with the control system shown in FIG. 4.

FIG. 1 shows a walking grate furnace with a furnace hood 1 a feed roller conveyor 2, a delivery roller conveyor 3, fixed beams 4 and walking beams 5. Each walking beam 5 has a lower rail 5a which has an extension connected through a joint 5b to a piston rod 60 of a driving piston in a cylinder 6, which is pivotally mounted in a pivot block 7. The axis of the piston is in line with the axis of the lower rail 50 so that when the conveyor is in operation the piston gives the lower rail 5a and with it the walking beam 5 a horizontal reciprocating movement.

Each walking beam 5 is moved vertically, to lift and lower it, by a lifting carriage 8 which comprises a housing

8a containing rollers

8b, 8c, 8d which rotate on axes extending across the longitudinal axis of the lower rail 50. The roller 8b runs on a horizontal rail 9. The roller 8d runs on an inclined rail 10 in the form of a wedge-shaped structure. The roller 80 supports the lower rail 5a.

Each lifting carriage 8 is moved by one end of a tension rod 11 the other end of which is attached to a traction carriage 12 (FIG. 2) comprising a transverse beam 120 equipped with brackets 12b. The transverse beam 120 is equipped at each end with four wheels 12c arranged in two pairs. One pair of wheels is supported directly by the transverse beam 12a, the other pair being supported by the brackets 12b. The brackets 12b form together with the transverse beam 12a a U-shaped structure arranged to prevent the traction carriage 12 from tipping over. The wheels 12c are guided between guides 13 arranged so that the traction carriage 12 can travel only horizontally. In order to ensure that the traction carriage 12 always remains positioned transversely, and cannot adopt a skew position, which would give different movements to the various walking beams, and might even stall the drive, the traction carriage 12 is guided in its movement by a parallel guide system comprising a rocking shaft 14a which rocks in bearings at its two ends. The rocking shaft 14a has crank arms 14b and links connected to the transverse beam 12a. The traction carriage 12 is reciprocated by a system of pistons in

cylinders

15 and 16, the pistons being connected to the transverse beam 12a by connecting

rods

15a and 16a.

With regard to the horizontal movements of the walking beams 5, FIG. 4 shows a simulator the movements of which govern the movements of the driving pistons in the cylinders 6. For this purpose the simulator acts, with a suitable gearing effect, through an electro-hydraulic control circuit. The simulator is essentially a sliding crank system including a crank arm 17 driven by a motor which is not shown in the drawing. A sliding sleeve 18 is pivoted on the crank arm 17 and slides on an oscillating arm 19 pivoted to a bearing block 20 which is adjustable in height. The oscillating arm 19 is in the form of a rod along which the sleeve 18 slides.

The bearing block 20, which is adjustable in height, moves on rollers 20a and is driven by an adjustment drive 20b, which can if desired be remote controlled and can be actuated hydraulically or if desired manually. For example the adjustment drive 20!) can be operated through a threaded spindle which provides an irreversible drive giving a self-locking ef' feet.

The electro-hydraulic control circuit shown in FIG. 6 includes a potentiometer bridge circuit with a measured value potentiometer 21b and a desired value potentiometer 21a. The potentiometer bridge circuit has two upper legs, such upper legs having resistances which are schematically shown in R and R respectively. The measured value potentiometer 21b has a sliding contact connected to the piston in the cylinder 6. The desired value potentiometer 21a has a sliding contact connected to the sliding crank system. The two

potentiometers

21a and 21b actuate a telescoping coil system 24 containing a permanent magnet armature 22 which forms part of a four-way slide valve 23 with edge control, which controls the movements of the piston in the cylinder 6. Consequently any voltage difference between the desired value potentiometer 21a and the measured value potentiometer 21b moves the armature 22, actuating the slide valve 23 and so causing the piston in the cylinder 6 to follow up movements of the upper end of the arm 19.

When the conveyor is in operation the workpieces, which are not shown in the drawing, reach the walking grate furnace A on the feed roller conveyor 2, which conveys them to the fixed beams 4 and the walking beams 5. The workpieces are conveyed intermittently through the furnace A by the walking beams 5 to the delivery roller conveyor 3. To bring this about, the walking beams 5 lift the workpieces from the supporting upper surfaces of the fixed beams 4, convey them horizontally forwards through a certain distance, determined by the stroke of the piston in the cylinder 6, and then lower them again onto the surfaces of the fixed beam 4. This operation is repeated, step by step, until the workpieces reach the delivery roller conveyor 3, which takes them away. The movements of the walking beams follow an approximately rectangular path, or a distorted rectangular path somewhere between a rectangle and a circle. The shape of this path can be varied within wide limits by suitably adjusting the controls for the vertical and the horizontal movements of the walking beams.

The horizontal movements of the walking beams are determined by the sliding crank system, shown in FIG. 4. Assuming that the crank 17 is rotating at constant speed the oscillating arm 19 performs a sine-wave oscillation. The horizontal oscillations of the walking beam 5 therefore take place smoothly and evenly, that is to say without any abrupt changes in velocity. The length of the stroke of this horizontal oscillation can be adjusted steplessly by stepless vertical adjustment in position of the bearing block 20, that is to say by stepless adjustment of the amplitude of oscillation of the oscillating arm.

On the other hand, the lifting and lowering movements of the walking beams 5 are produced by the movements of the lifting carriage 8. The lifting carriage 8 moves horizontally and at the same time vertically, due to the slope of the upper surface of the wedge-shaped rail 10, with the result that the lifting carriage 8 lifts and lowers the walking beams 5. In the present example the vertical movements of the walking beams 5 are directly proportional to the horizontal movements of the lifting carriage 8, and consequently the forces applied by the pistons of the driving cylinder and 16 are applied as lifting forces to the walking beams 5 after being increased or reduced by a factor which depends on the slope of the wedge-shaped rail 10.

The vertical movements of the walking beams 5 take place in several stages. In the first stage the walking beams 5 are accelerated upwards, the driving mechanism, including the tension rods 11, being accelerated from their initial positions. In the second stage of the movement the workpiece is accelerated upwards from the supporting surfaces of the fixed beams 4, the driving mechanism also being accelerated. In the third stage of the movement the workpiece is lowered again onto the fixed beams 4 and in the fourth stage the walking beams 5 move downwards again to their initial positions.

During the initial acceleration of the walking beams and of the driving mechanism, including the tension rods 11 from their initial positions, that is to say from their positions of rest, the energy which has to be supplied to effect the accelerations is reduced in that some of the pistons in the cylinders 16 constantly apply a thrust which largely compensates for the weight of the walking beams 5, the energy for this thrust being derived from a hydraulic accumulator as shown in FIG. 5. In the present example approximately 90 percent of the weight of the walking beams is supported in this way. Consequently the walking beams 5 are lifted quite gently upwards by the piston in the lifting cylinder 15 until they come into contact with the workpiece resting on the fixed beams 4. The effect obtained is that when the walking beams 5 make contact with the workpieces, the impact produced is negligibly small. As soon as the walking beams 5 come into contact with the workpieces the walking beams are immediately brought to a standstill, because the lifting cylinder 15 applies only a small amount of thrust. As soon as this occurs, that is to say as soon as the walking beams have been brought to a standstill, by coming into contact with the workpieces, pressure builds up in the lifting cylinder 15, actuating a pressure sensitive switch 27 and further excess pressure is then released by an over pressure release valve 26. The pressure sensitive switch 27 delivers a control pulse which opens successively a series of valves 28 connecting the accumulator 25 to the remaining thrust cylinders 16 which have not hitherto been used for compensating the weight of the walking beams 5. The valves 28 are opened one after the other to the effect that the lifting thrust applied to the walking beams is increased only gradually and almost continuously until the workpiece is lifted from the supporting surfaces of the fixed beams 4.

The valves 28 can be opened in the desired sequence by various devices. The sequence can be determined electrically by using switching relays. Alternatively, using a mechanical device, the pressure sensitive switch 27 opens the first valve 28, bringing the first piston into movement in its thrust cylinder 16. This piston actuates mechanically a simple limit switch, which opens the next valve 28. On the other hand if desired the simultaneous movements of the other pistons in the cylinders 16 can be utilized. All the pistons move with the transverse beam 12a. Each piston can therefore trip its own limit switch. The sequence in which the valves 28 are opened depends of course on the pressure characteristic curve of the accumulator 25.

In other examples of the invention, not shown in the drawings, each thrust cylinder 16 has its own accumulator. Moreover if desired any number of accumulators can be used, the cylinders 16 being connected together and the accumulators connected in sequence with interposed control valves. Finally each cylinder 16 can if desired have several accumulators, connected in sequence with interposed control valves. This arrangement has the advantage that the decreasing pressure in an accumulator, resulting from the movement of the piston in the cylinder 16, is compensated by bringing in a further accumulator.

In the present example there are enough thrust cylinders 16 to handle the highest workpiece load for which the conveyor is designed. When a smaller workpiece load is being conveyed only some of the thrust cylinders 16 are brought into operation. This can be done for example by the operator by switching off some of the valves 28 by remote control on the basis of a program. Alternatively the thrust cylinders 16 can be selected automatically. For this purpose each thrust cylinder 16 is equipped with a pressure sensitive switch which responds to an upper limiting pressure and a lower limiting pressure and these switches bring the thrust cylinders 16 into operation successively at brief intervals until the pressure in the thrust cylinders 16 no longer rises to the upper limiting pressure of the pressure sensitive switch.

During the lifting operation, only those thrust cylinders 16 are in action which are just necessary to allow the lifting cylinder 15 to lift the existing workpiece load. To lower the workpiece back onto the fixed beams 4 it is therefore merely necessary to release the pressure in the lifting cylinder 15. The weight of the workpiece load, plus the weight of the walking beams, is then sufficient to expel fluid from the thrust cylinders 16 back into the accumulator 25, the walking beams 5 gently lowering the workpieces onto the surfaces of the fixed beams. In this operation the pressure in the accumulator 25 increases back again to its initial value. After the workpieces have come to rest on the fixed beams the walking beams continue to move downwards, because the lifting thrust applied by the trust cylinders 16 which are still in operation is a little less than the .weight of the walking beams. Consequently the walking beams move downwards to their initial positions, hydraulic fluid being expelled from the remaining thrust cylinders 16 back into the accumulator 255. Finally the pressure in the accumulator 25 returns to its initial value and the walking beams 5 return to their initial positions.

In the case where frictional resistances impede the lowering of the workpieces onto the fixed beams, the downward movement of the walking beams 5 can be power assisted. For this purpose, in the present example, the lifting cylinder 15 is made double-acting. During the lifting movement hydraulic fluid admitted to the cylinder chamber behind the piston drives the piston outwards, whereas during the lowering movement, for example after the workpieces have been deposited on the fixed beams, fluid is admitted to the cylinder chamber in front of the piston and is exhausted from the cylinder chamber behind the piston, so that the walking beams 5 are lowered to their initial positions under power.

The control valves which connect the accumulator 25 to the lifting cylinders 15 are preferably program controlled slide valves the reversal period of which can be steplessly adjusted by a throttle, so that the vertical movements of the walking beams are smooth and gentle when the workpieces are being lifted from the fixed beams 4 and lowered back onto them.

I claim:

1. In a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beams in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders and drive pistons, means operatively connecting saidcylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, the force of the accumulator-driven drive pistons before the impact of the walking beam onto the work piece on the conveyor being at a maximum equal to the weight of the walking beam, including means operatively connecting said hydraulic accumulator means to a plurality of said some cylinders, said connecting means including a plurality of control valves and means connecting said valves individually to said cylinders and means for independently actuating said control valves, the latter means including means responsive to a workpiece load on said walking beams and means for actuating said valves to operate said cylinders in sequence in dependence upon the magnitude of said load.

2. ln a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beam in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders, means operatively connecting said cylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, said drive mechanism for moving said walking beam in said horizontal reciprocating movement including at least one hydraulic fluid pressure operated cylinder, a piston in said cylinder, means connecting said piston to said walking beams, and means for controlling the operation of said cylinder to cause said piston to perform a reciprocating movement, said controlling means including a sliding crank mechanism and means for causing said piston to follow movements of said sliding crank mechanism.

3, A walking beam conveyor as claimed in claim 2, wherein said means for causing said piston to follow movements of said sliding crank mechanism include an electrical potentiometer bridge circuit, two variable resistors in said circuit, means connecting one of said variable resistors to said sliding crank mechanism and means connecting the other of said variable resistors to said cylinder to bring about movements of said piston.

4. A walking beam conveyor as claimed in claim 3, wherein said variable resistors are electric sliding contact resistances, the sliding contacts of which are actuated by said sliding crank mechanism and said piston,

5. A walking beam conveyor as claimed in claim 2, wherein said sliding crank mechanism includes a rotary crank, an oscillating arm operatively connected to said crank, means pivotally mounting one end of said oscillating arm and means for adjusting said pivotal mounting means, said adjusting means including means for moving said pivotal mounting means towards and away from said crank to adjust the length of the oscillating movement of said arm.

Claims

1. In a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beams in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders and drive pistons, means operatively connecting said cylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, the force of the accumulator-drIven drive pistons before the impact of the walking beam onto the work piece on the conveyor being at a maximum equal to the weight of the walking beam, including means operatively connecting said hydraulic accumulator means to a plurality of said some cylinders, said connecting means including a plurality of control valves and means connecting said valves individually to said cylinders and means for independently actuating said control valves, the latter means including means responsive to a workpiece load on said walking beams and means for actuating said valves to operate said cylinders in sequence in dependence upon the magnitude of said load.

2. In a walking beam conveyor including a plurality of stationary beams, a plurality of walking beams, means mounting said walking beams for upward and downward movement relative to said stationary beams and reciprocating longitudinal movement relative to said stationary beams, driving mechanism for moving said walking beam in said upward and downward movement and driving mechanism for moving said walking beams in said reciprocating longitudinal movement, the improvement wherein said driving mechanism for moving said walking beams in said upward and downward movement includes a plurality of hydraulic fluid pressure operated cylinders, means operatively connecting said cylinders to said walking beams, means for supplying hydraulic fluid under pressure to some of said cylinders and independent means for supplying hydraulic fluid under pressure to one other of said cylinders, said means for supplying hydraulic fluid to said some of said cylinders including hydraulic accumulator means and means operatively connecting said hydraulic accumulator means to at least one of said some cylinders, said drive mechanism for moving said walking beam in said horizontal reciprocating movement including at least one hydraulic fluid pressure operated cylinder, a piston in said cylinder, means connecting said piston to said walking beams, and means for controlling the operation of said cylinder to cause said piston to perform a reciprocating movement, said controlling means including a sliding crank mechanism and means for causing said piston to follow movements of said sliding crank mechanism.

3. A walking beam conveyor as claimed in claim 2, wherein said means for causing said piston to follow movements of said sliding crank mechanism include an electrical potentiometer bridge circuit, two variable resistors in said circuit, means connecting one of said variable resistors to said sliding crank mechanism and means connecting the other of said variable resistors to said cylinder to bring about movements of said piston.

4. A walking beam conveyor as claimed in claim 3, wherein said variable resistors are electric sliding contact resistances, the sliding contacts of which are actuated by said sliding crank mechanism and said piston.