GB2042453A - Conveyor belt take-up device - Google Patents

Abstract

Take-up device for maintaining or regulating conveyor belt tension has a fluid pressure actuator (8) which acts on the bearing housing 5 of the belt pulley, the bearing housing being movable along a fixed guide 6. Locking elements 12 in the form of ratchet elements are provided along the guide and cooperate with the actuator 8 and bearing housing 5. In operation a plate 1 on the actuator 8 engages the ratchet 12 as the piston of the actuator is advanced to push the housing along the guide. Further tensioning may be applied by depressuring the actuating whereupon the housing engages a ratchet 12, the piston is drawn into the actuator by a spring and the plate 10 engages a further ratchet, repressuring of the actuator moving the housing further along the guide. <IMAGE>

Description

SPECIFICATION Improvements in and relating to conveyor belt take-up devices This invention relates to a conveyor belt takeup device.

Endless conveyor belts are commonly provided with take-up devices for the purpose of maintaining a desired tension in the conveyor belt so that the drive pulley acting upon the belt can impart maximum tractive effort to the belt. A further purpose of such conveyor belt take-up devices is to remove the accumulated slack in the conveyor belt which exists at starting up or during momentary overloads.

Known types of conveyor belt take-up devices generally fall into two categories: (a) the screw or winch type, in which a belt tensioning pulley is supported by shaft bearings mounted on slides which are displaceable in the direction of the belt tension by screwadjustable rods or by steel cables wound onto a winch; (b) the floating or gravity type, in which a tension pulley with its shaft bearings is mounted in vertical slides and weights are suspended from the shaft bearings to apply tension to the belt passing over the pulley.

The above mentioned types of known conveyor belt take-up devices are prone to maladjustment, particularly where a screw or winch tensioning device is used. Moreover, a screw device is prone to contamination by foreign matter and debris and can become clogged by accumulations of dust and moisture. A further object of the invention is to avoid the use of suspended belt tensioning weights, which can present a danger in prolonged use, particularly as they are usually relatively inaccessible for maintenance.

According to the invention there is provided a conveyor belt take-up device comprising a belt-tensioning pulley supported rotatably by bearings which are displaceable in a direction perpendicular to the pulley axis and generally parallel to the belt tension acting upon the pulley by means of at least one fluid pressure actuator, each bearing having a housing which cooperates with and is movable relative to a respective fixed guide with which the or each actuator also cooperates, and means for selectively locking the or each actuator and each bearing housing relative to the guide so that the bearing and the actuator can be advanced along the guide by operation of the actuator.

In one embodiment of the invention the selective locking means comprise respective fluid pressure actuated catches fixed relative to the or each actuator and its associated bearing housing and operable to engage locking surfaces on the associated guide. As a failsafe measure each catch is preferably springloaded into a position of locking engagement with the associated guide, actuation of the catch disengaging the latter from the guide.

In an alternative embodiment of the invention the means for selectively locking the or each actuator and each bearing housing relative to the guide comprise respective ratchet catches arranged to permit movement of the actuator and the bearing housing relative to the guide only in the sense which increased the belt tension.

The device of the present invention, by using fluid pressure, preferably hydraulic, actuators, is reliable in use and easy to maintain. Moreover, the use of fluid pressure actuators enables shock loads in a conveyor belt, for example on start-up or during momentary overloads, to be absorbed, thereby extending the working lifetime of the conveyor belt.

The invention also provides a conveyor belt take-up device comprising a belt-tensioning pulley supported rotatably by bearings which are displaceable in a direction perpendicular to the pulley axis and generally parallel to the belt tension acting on the pulley by means of at least one fluid pressure actuator which acts upon the bearings in a sense to increase the belt tension, each bearing having a housing which is movable relative to a fixed guide, and cooperates with the latter through a ratchet mechanism which permits displacement of the bearing housing relative to the guide in the sense which increases the conveyor belt tension but prevents displacement of the bearing under the influence of the conveyor belt tension upon retraction of fluid pressure actuator or actuators.

According to another aspect the invention further provides an actuator unit for adjusting the position of a bearing in a direction transverse the axis of rotation of the bearing for the purpose of displacing a conveyor belt tensioning pulley supported by the bearing perpendicularly to the axis of the pulley and generally parallel to the belt tension acting upon the pulley, the unit comprising a fluid pressure actuator acting upon the bearing to move the latter relative to a fixed longitudinal guide, both the bearing and the actuator cooperating with the guide through respective locking means which are selectively operable to lock the bearing and the actuator respectively relative to the guide.

In one embodiment of the invention the fluid pressure actuator is interposed between a stop member carried at one end of the actuator and the bearing housing which is connected to the other end of the actuator, the stop member engaging the longitudinal guide through respective locking means arranged to permit movement of the stop member towards the bearing housing upon retraction of the actuator but to prevent movement of the stop member away from the bearing housing upon extension of the actuator. The stop member can thus be moved towards the bearing housing upon retraction of the actua tor, without displacement of the bearing housing itself, and without, therefore, reducing the tension in the belt.Accordingly, it is possible to move the actuator progressively along the guide to maintain a desired tension in a belt as the belt stretches over a prolonged period of use, without having to employ an expensive actuator with a long working stroke.

In one arrangement the locking means comprise ratchet catches spaced apart along the guide and resiliently loaded into positions in which they are engageable by the bearing housing and by the stop member of the actuator. The ratchet catches may be located in respective apertures spaced apart longitudinally in opposite parallel walls of a channel section guide within which the bearing housing and the actuator stop member are located.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of part of a conveyor belt provided with a takeup device according to one embodiment of the inventior.

Figure 2 is a side elevation of the part of the conveyor belt and take-up device shown in Fig. 1; Figure 3 is a partial longitudinal section, taken on line Ill-Il in Fig. 1, showing one of the conveyor belt-up devices according to the invention; Figure 4 is a cross-section on line IV-IV in Fig. 3; Figure 5 is a side elevational view of part of a conveyor belt take-up device according to another embodiment of the invention; Figure 6 is a diagrammatic cross-sectional view taken on line VI-VI of Fig. 5, and Figure 7 is a diagrammatic side elevational view of part of a conveyor belt installation provided with a belt take-up device of the kind shown in Figs. 5 and 6.

The same reference numerals are used throughout the drawings to designate the same or corresponding component parts.

Referring first to Figs. 1 and 2, part of an endless conveyor belt installation is shown, in which a conveyor belt 1 passes over a take-up pulley or drum 2 which is supported on a shaft 3 freely rotatable at opposite ends in respective bearings 4. The bearings 4 are supported in respective bearing housings 5 which are displaceable in a direction perpendicular to the axis of the pulley shaft 3 and generally parallel to the belt tension acting upon the drum 2 along respective longitudinal guides 6 which are supported by fixed supports 7 on opposite sides of the take-up drum 2. Each bearing block 5 is displaceable longitudinally along the respective guide 6 by means of a fluid pressure actuator, in this case a single-acting hydraulic cylinder 8 which is supplied with hydraulic fluid (oil) under pressure through a common supply line 9.

Referring now to Figs. 3 and 4, one of the hydraulic actuator cylinders 8 is shown, with its mechanical connection to the associated bearing block 5; it will be understood that an identical mechanism is associated with the other hydraulic actuator cylinder 8 on the other side of the take-up drum 2.

The end of the hydraulic cylinder 8 opposite the bearing block 5 is provided with a stop plate 10 which engages the respectively longitudinal guide 6 through selective locking means.

In the embodiment of Figs. 1 to 4 the locking means are in the form of automatically acting ratchet catches. Thus the guide 6 comprises a channel section member of pressed steel (Fig. 4) in which the actuator cylinder 8 and the bearing block 5 are accommodated, the take-up drum shaft 3 projecting from the bearing block 5 through the open side of the chennel, section guide 6. The opposite parallel side walls of the channel section guide 6 are provided with a number of apertures 11 spaced apart longitudinally, and respective spring loaded ratchet catches 1 2 are located in each of the apertures 11 for selective engagement with the stop plate 10.

The ratchet catches 1 2 have portions which project laterally into the channel of the guide 6, the catches being urged into these projecting positions by respective leaf springs 1 3 which are supported by a respective channel section spring carrier 1 4 extending longitudinally externally of the side walls of the guide 6 (Fig. 4).Each ratchet catch 1 2 has an inclined face which slopes towards the internal surface of the respective side wall of the guide 6 in a direction away from the bearing block 5, so that the stop plate 10 can move longitudinally along the guide 6 towards the bearing block 5, displacing the ratchet catches 12, movement of the stop plate 10 in the opposite direction, away from the bearing housing 5, being prevented by engagement of the stop plate 10 with a pair of ratchet catches 1 2 in opposite walls of the guide 6, as shown in Fig. 3.

The actuator cylinder 8 has a piston rod 1 5 which is connected through a clevis coupling 1 6 to a guide rod 1 7 which in turn is fixed to the bearing housing 5. The bearing housing 5 is a rectangular block having opposite parallel walls which slide along the internal surfaces of the side walls of the channel section guide 6 (Fig. 3). The opposite sides of the bearing housing engage the ratchet cataches 1 2 and displace the catches into retracted positions flush with the side walls of the guide 6. The ratchet catches 1 2 permit longitudinal displacement of the bearing block 5 in a direction which increases the belt tension, indicated by arrow A in Fig. 3, but prevent longitudinal displacement of the bearing block 5 beyond the first pair of ratchet catches 1 2 encountered by the bearing block 5 in its longitudinal movement opposite to the direction of arrow A.

The hydraulic actuator cylinder 8 incorporates a return spring 18, shown diagrammatically, and in addition a helical thrust spring 1 9 is interposed between the cylinder 8 and the facing end surface of the bearing housing 5. The thrust spring 1 9 is enclosed in a telescopic housing 20 attached at opposite ends to a flange 21 on the cylinder 8 and to the bearing housing 5.

The hydraulic actuator unit illustrated in Figs. 3 and 4 may be operated manually by means of an hydraulic hand pump which supplies hydraulic fluid to the cylinder 8, or alternatively may be power-operated, for example by means of an electric motor driving a hydraulic pump which supplies hydraulic fluid to the cylinder 8.

The operation of one of the hydraulic actuator units is as follows. Upon installation of the take-up device the stop plate 10 of the cylinder 8 is engaged with a pair of ratchet catches 1 2 near one end of the channel section guide 6, as shown in Fig. 3. The cylinder 8 is then pressurised to advance the bearing block 5 longitudinally along the guide 6, simultaneously with the bearing block 5 of the other actuator unit, so that the take-up drum 2 is displaced in the direction of arrow A, to tension the conveyor belt 1. The desired tension in the belt will be correlated to the pressure in the cylinder 8, so that pressurisation of the cylinder 8 may be stopped when a predetermined pressure, corresponding to a desired belt tension, is reached.

If the maximum travel of the bearing housing 5 corresponding to the full stroke of the hydraulic actuator be insufficient to produce the desired tension in the conveyor belt 1, the pressure in the cylinder 8 is released. This causes the cylinder 8 to be displaced longitudinally by the action of the internal return spring 1 8 in the direction of arrow A, the piston rod 15 remaining stationary by virtue of engagement of the bearing housing 5 with one of the pairs of opposed ratchet catches 1 2. This displacement of the cylinder 8 causes the stop plate 10 to advance in the direction of arrow A, passing over some of the ratchet catches 12, until the piston is fully retracted in the cylinder 8.The cylinder 8 is then again pressurised, causing further movement of the bearing housing 5, until the required belt tension is reached, successive depressurisations of the cylinder 8 resulting in progressive displacement of the stop plate 10 towards the bearing housing 5.

It will be appreciated that by successively depressurising and pressurising the single acting hydraulic actuator 8 it is possible to adjust the position of the bearing housing 5 over the full extent of the longitudinal guide 6, without employing an expensive hydraulic actuator of long stroke.

The helical spring 1 9 interposed between the cylinder 8 and the bearing housing 5 will have a spring rate such that in normal operation under the normal tension in the belt 1 the bearing housing 5 "floats" longitudinally and is spaced from the immediately adjacent pair of ratchet catches 12, as shown in Fig. 3. The spring 1 9 is then able to absorb shock loads on the bearing housing 5, for example upon start up and in the event of momentary overloads, the spring 1 9 effectively transmitting the belt load to the hydraulic cylinder 8.

As an alternative to the shock absorbing spring 1 9 it may be advantageous to provide a pressure accumulator in the hydraulic circuit, possibly spring loaded or pneumatically pressurised, to allow shock-absorbing movement of the piston rod 1 5 within the cylinder 8.

In a fully automatic actuator unit in which the actuator cylinder is pressurised by a power-driven hydraulic source, the hydraulic pump or the motor which drives the pump may be controlled by pressure sensors which maintain a desired working pressure in the actuators 8 of the actuator units, maintaining this working pressure, corresponding to a desired belt tension, by automatic advancement of the actuator stop plate 10 as necessary.

Limit switches may be provided to detect the maximum and minimum extensions of the piston within the actuator cylinder, to effect an automatic cycle of adjustment of the stop plate 10 along the guide 6. Thus when the piston rod 15 is fully extended from the actuator cylinder 8 a first limit switch may be operated to relieve the hydraulic pressure in the cylinder 8, causing retraction of the piston within the cylinder 8 until a second limit switch is operated, after the stop plate 10 has advanced towards the bearing housing 5, when the pressure in the hydraulic cylinder 8 will be reinstated.

Maintenance of the actuator unit as illustrated is simple, since the ratchet catches 1 2 may be removed bodily by removing the external channel sections carriers 14.

To protect the interior of the channel section guide 6, and therefore the actuator 8 and the associated mechanism from the ingress of dust and debris a pair of resiliently flexible sealing elements in the form of rubber strips 22 are attached to opposite sides of the channel section guide 6, projecting towards each other and covering the open side of the channel section guide 6, while deflecting sufficiently to allow the take-up drum shaft 3 to pass between the strips.

Figs. 5 and 6 illustrate an alternative embodiment of the invention in which each bearing housing 5 and associated actuator cylinder 8 are selectively engageable with the longitudinal guide 6 through respective hydraulically operated catches. In this embodi ment each guide 6 comprises two parallel channel section members 6A, 6B between which the bearing housing 5 slides longitudinally. A double-acting hydraulic actuator cylinder 8 is located between the guide members 6A and 6B and is connected at one end through a front mounting plate 30 to the bearing housing 5 and at its other end to a rear mounting plate 31.

The front and rear mounting plates 30 and 31 are each in the form of U-shaped members with lateral walls 30A, 30B, and 31A, 31B which have grooved outer faces in sliding engagement with the respective guide members 6A, 6B, as shown in Fig. 6. A first pair of fluid-pressure operated catches 32A, 32B are carried by the front mounting plate 30, the catches 32A, 32B being arranged coaxially for lateral movement perpendicularly to the guide members 6A, 6B, which are each formed with a series of regularly spaced-apart apertures 33A, 33B (Fig. 6) in which the catches 32A, 32B may engageselectively to lock the front mounting plate 30, and therefore the bearing housing 5, relative to the guide 6.The rear mounting plate 31 carries a second pair of fluid-pressure operated catches 34A, 34B arranged coaxially for lateral movement perpendicularly to the guide members 6A, 6B. The catches 34A, 34B are, like the catches 32A, 32B, engageable selectively in respective said apertures 33A, 33B in the guide members 6A, 6B to lock the actuator cylinder 8 relative to the guide 6.

The catches 32A, 32B and 34A, 34B are operated by respective single-acting hydraulic actuators 35A, 35B and 36A, 36B each of which is internally spring-loaded towards its extended or engaged position, the application of hydraulic pressure operating the respective actuator to retract the associated catch. In this way the catches are rendered fail-safe in operation in the event of an hydraulic power failure.

The hydraulic actuator 8, which may have a short stroke, can be operated to 'walk' the mounting plates 30, 31 along the guide 6, in the manner previously described, to increase the tension in a conveyor belt passing around a take-up drum rotatably supported by the bearing 4. In normal operation the actuator 8 is not fully extended, the front hydraulic catches 32A, 32B are retracted, and the rear hydraulic catches 34A, 34B are extended and engaged in respective apertures 33A, 33B in the guide members SA, 6B. Since the hydrau lic circuit of the actuator 8 includes a springloaded accumulator (not shown) the actuator 8 can absorb shocks and sharp belt tension fluctuations due, for example, to starting of the conveyor belt under load.

As the tension in the belt decreases, the actuator 8 extends automatically, advancing the bearing block 5 along the guide 6 to effect a compensating increase in the belt tension. It is arranged that when the actuator 8 reaches the limit of its extension the hydraulic catches 32A, 32B are in register with a respective pair of apertures 33A, 33B and are extended into these apertures to lock the front mounting plate 30 and the bearing block 5 relative to the guide 6. The rear catches 34A, 34B are then retracted hydraulically, and the actuator 8 then retracted, drawing the rear mounting plate 30, until the catches 34A, 34B are in register with appropriately located apertures 33A, 33B in the guide members 6A, 6B.The rear catches 34A, 34B are then extended by relieving the hydraulic pressure supplied thereto, engaging the catches 34A, 34B in the said apertures and locking the rear mounting plate 31. The front catches 32A, 32B are then retracted and the actuator 8 extended to increase the belt tension to the required value. If the actuator 8 extends through its full stroke without tensioning the belt sufficiently the front catches 32A, 32B are again extended to lock the front mounting plate 30 and the above-described sequence is repeated to 'walk' the actuator unit further along the guide 6.

The sequential operation of the actuator 8 and the hydraulic catches 32A, 32B; 34A, 34B may be controlled automatically by an electronic control circuit including solenoid valves controlling the operation of the various actuators 8, 35A, 35B, 36A and 36B. Proving contacts, not shown, may be associated with the front and rear mounting plates 30, 31 to be operated when the respective front and rear catches 32A, 32B; 34A, 34B or one of each pair of said catches, are positively located in respective apertures 33A, 33B in the guide members 6A, 6B.

The above-described sequence of operations may be reversed in order to reduce the conveyor belt tension, for example to facilitate belt maintenance.

The actuator unit described with reference to Figs. 5 and 6 can be installed at any angle to the horizontal or vertical, irrespective of the angle of the conveyor belt. Fig. 7 shows an installation in which the actuator unit is vertical and is indicated generally by reference numeral 37, the conveyor belt 1 being inclined to the horizontal and passing over fixed freely rotatable guide drums 38, 39 upstream and downstream of the take-up drum 2, the shaft 3 of which is rotatably supported at opposite ends by bearings 4. The bearings 4 are movable vertically to adjust the belt tension by the actuator unit 37 according to the invention, the vertical movement of the bearings 4 being guided by guide rods 40 which are guided by guide rollers 41 carried by a vertical fixed frame 42 which supports the guide 6.

Claims (12)

1. A conveyor belt take-up device compris ing a belt-tensioning pulley supported rotatably by bearings which are displaceable in a direction perpendicular to the pulley axis and generally parallel to the belt tension acting upon the pulley by means of at least one fluid pressure actuator, each bearing having a housing which cooperates with and is movable relative to a respective fixed guide with which the or each actuator also cooperates, and means for selectively locking the or each actuator and each bearing housing relative to the guide so that the bearing and the actuator can be advanced along the guide by operation of the actuator.

2. A device as claimed in Claim 1, in which the selective locking means comprise respective fluid pressure actuated catches fixed relative to the or each actuator and its associated bearing housing and operable to engage locking surfaces on the associated guide.

3. A device as claimed in Claim 2, in which each catch is spring-loaded into a position of locking engagement with the associated guide, actuation of the catch disengaging the latter from the guide.

4. A device as claimed in any one of the preceding claims, in which the or each fluid pressure actuator is connected to a manually operable pump.

5. A device as claimed in Claim 2 or Claim 3, in which each bearing housing and the associated actuator are associated with respective pairs of said fluid pressure actuated catches engageable selectively with apertures in opposite walls of the fixed guide.

6. A device as claimed in any one of Claims 1 to 5, in which the or each actuator and the fixed guide extend in a direction inclined to the direction of travel of the conveyor belt, the belt passing over guide pulleys upstream and downstream of the tensioning pulley.

7. A device as claimed in Claim 1, in which the means for selectively locking the or each actuator and each bearing housing relative to the guide comprise respective ratchet catches arranged to permit movement of the actuator and the bearing housing relative to the guide only in the sense which increases the belt tension.

8. A conveyor belt take-up device comprising a belt-tensioning pulley supported rotatably by bearings which are displaceable in a direction perpendicular to the pulley axis and generally parallel to the belt tension acting on the pulley by means of at least one fluid pressure actuator which acts upon the bearings in a sense to increase the belt tension, each bearing having a housing which is movable relative to a fixed guide, and cooperates with the latter through a ratchet mechanism which permits displacement of the bearing housing relative to the guide in the sense which increases the conveyor belt tension but prevents displacement of the bearing under the influence of the conveyor belt tension upon retraction of the fluid pressure actuator or actuators.

9. An actuator unit for adjusting the position of a bearing in a direction transverse the axis of rotation of the bearing for the purpose of displacing a conveyor belt tensioning pulley supported by the bearing perpendicularly to the axis of the pulley and generally parallel to the belt tension acting upon the pulley, the unit comprising a fluid pressure actuator acting upon the bearing to move the latter relative to a fixed longitudinal guide, both the bearing and the actuator cooperating with the guide through respective locking means which are selectively operable to lock the bearing and the actuator respectively relative to the guide.

1 0. An actuator unit according to Claim 9, in which the locking means comprise respective ratchet catches which permit movement of the bearing and the actuator relative to the guide in the sense which increases the belt tension acting upon the bearing in use of the unit.

11. An actuator unit according to Claim 10, in which the longitudinal guide is provided with a number of spaced apart ratchet catches which are resiliently loaded into positions in which they are engageable by a housing of the bearing and by the actuator to prevent movement thereof in the direction of the belt tension acting upon the bearing in use of the unit.

12. An actuator unit according to Claim 11, in which the ratchet catches are located in respective apertures spaced apaprt longitudinally in opposite parallel walls of a channel section guide within which the bearing housing and at least a stop member carried by the actuator are located.

1 3. An actuator unit according to Claim 12, in which the ratchet catches are acted upon by respective leaf springs supported externally of the said walls of the guide by respective longitudinally extending carriers.

1 4. An actuator unit according to Claim 1 2 or Claim 13 in which the bearing housing supports one end of a rotatable pulley shaft the axis of which is perpendicur to the base of the channel section guide, said shaft passing through the open side of the guide.

1 5. An actuator unit according to Claim 12, Claim 1 3 or Claim 14, in which resiliently flexible sealing elements extend longitudinally along the opposite edges defining the open side of the channel section guide to seal the interior of the guide against the ingress of dirt or spillage material.

1 6. An actuator unit according to any one of Claims 9 to 15, in which a return spring acts between the actuator and the bearing to move the actuator away from the bearing when the pressure in the actuator is relieved.

1 7. A conveyor belt take-up device substantially as herein described with reference to and as shown in Figs. 1 to 4 or Figs. 5 to 7 of the accompanying drawings.