GB2346663A

GB2346663A - Belt or chain tensioner

Info

Publication number: GB2346663A
Application number: GB0002941A
Authority: GB
Inventors: Jens Titschert; Arno Breimhorst
Original assignee: DBT Automation GmbH
Current assignee: Caterpillar Global Mining Europe GmbH
Priority date: 1999-02-12
Filing date: 2000-02-09
Publication date: 2000-08-16
Anticipated expiration: 2020-02-09
Also published as: DE19905946A1; DE19905946B4; GB2346663B; AU1528100A; PL338315A1; PL195648B1; GB0002941D0; AU782008B2

Abstract

At least one driving station I or II is provided with a hydraulic piston and cylinder tensioning unit 4 to adjust the tension in a chain or belt 3 by moving the associated drive wheel 2 or 6. The pressure in the working chamber of the tensioning unit 4 and the power consumption of the associated drive station I or II are measured by corresponding sensors. The pressure in the working chamber of the tensioning unit 4 is then adjusted to a set value dependent on the sensed power consumption.

Description

2346663 Process for adjusting the initial tension of belts or chains and

apparatus for carrying out the process The invention relates to a process for adjusting the tension in an endless traction member, in particular a chain, entrained around wheels of spaced-apart stations and to apparatus for carrying out the process.

The preferred field of application of the invention is the adjustment of initial tension in chains of longwall and gate conveyors used in the mining industry. Such conveyors have an endless scraper-chain assembly with one or more chains carrying scrapers which circulates in upper and lower runs and is entrained over the driving wheels of a main driving station and an auxiliary driving station. Both driving stations are equipped with drive means and both stations can be provided with a hydraulic piston and cylinder tensioning unit which displaces the drive wheels relative to one another. Frequently however there is no tensioning unit at the main driving station as the expenditure on adjustment is extremely high if two tensioning units working in opposite directions are used. Furthermore, some conveyors only have drive means at the main driving station while the scraper-chain assembly at the auxiliary station only undergoes a change of direction. Although the expression "driving station" may be used hereafter, this is not intended to be limitive and stations without drive means are intended to be encompassed by the term.

One problem often encountered during operation of conveyors is the creation from time to time of sections of slack chain.

2 In the case of very heavy loads or in the case of obstructions of the longwall conveyor and also when the longwall faces are very long, the main drive station may be loaded to full capacity and the auxiliary drive station brings up to 40% of the output into the upper run. Slack chain is not then created on the lower run. However, in the upper run near the auxiliary drive station the case is different. In this region slack chain can occur. To avoid slack chain it has proved advantageous to vary the distance between the chain-engaging wheels arranged at the main and auxiliary drive stations with the aid of the tensioning unit or units. The occurrence of slack chain can be visually monitored by operators and eliminated by manual adjustment of the chain-engaging wheel spacing. However, monitoring by constant observation by operators is inappropriate during continuous operation. Nowadays, therefore, the chain is pretensioned to avoid slack chain. As the required chain pretensioning constantly changes during operation of the longwall conveyorst adjustment processes for altering the pretensioning have been developed.

With a first process the occurrence of slack chain is monitored by sensors. For this, chain spacing sensors are required with which the chain link spacing is measured. Sensor equipment of this type is expensive and has a very short service life due to the assembly location directly on the drives.

A second process is known from 1'GlUckauf" 122 (1986) No. 13 as a theoretical contribution according to which the chain pretensioning adjustment is to be achieved by measuring of the support power of the chain wheel and also of the initiated torque. For this purpose, the support power should be I 3 determined with a load cell and the torque with a measuring device. On the assumption that the support power corresponds to the sum of the ingoing and outgoing chain power and the torque corresponds to the difference between the ingoing and outgoing chain power, the chain power of the outgoing run should be determined by an evaluating unit and should then form the controlled variable for adjustment of the or each tensioning unit. Testing and implementation of this process has not yet taken place.

Another process and apparatus is known from DE 44 13 321. This known process is used in a longwall face conveyor in which a scraper-chain assembly circulates and is entrained over the drive wheels of drive stations. At least one of the drive stations has a hydraulic piston and cylinder tensioning unit for pretensioning the chain. The tensioning unit is provided with a pressure measuring device with which the total pressure in the working chamber of the hydraulic cylinder is measured. The pretensioning is then adjusted by a pressure differential method. For this purpose the tensioning unit has a path sensor in addition to the pressure sensor. Control of the tensioned state of the chain takes place in that the piston stroke of the tensioning unit is continuously hydraulically adjusted around a defined part stroke and that simultaneously both the pressure change and the path change are measured. When there is a great change in pressure during the defined piston movement, i.e. when there is a strong rise or fall in pressure in the working space dependent on the direction of movement of the piston, an evaluating unit detects that the chain is already highly tensioned. On the other hand if there is no significant change in pressure, the evaluating unit detects that there is slack chain and additional tension can be 4 applied. For this purpose, compensation via the defined piston stroke is continued until a pressure change is achieved which is stored in the evaluating unit as a set value. As the adjustment process only adjusts according to changes in pressure, the adjustment is relatively slow and the variation of the adjustment parameters is complicated particularly in the case of very short conveyors.

It is an object of the invention to provide an improved process and apparatus better able to eliminate the occurrence of slack chain in as simple and cost effective manner as possible and with the necessary reliability.

In one aspect the invention provides a process of adjusting the tension in an endless traction member entrained around wheels of spaced apart stations, at least one of the stations being provided with drive means for driving the associated wheel to drive and circulate the traction member and a hydraulic piston and cylinder tensioning unit for adjusting the distance between the wheels of the stations to control the tension in the traction member; said process comprising sensing the pressure in a working chamber of the tensioning unit, sensing the power consumption of the associated drive means and adjusting the pressure in the working chamber to a set value dependent on the sensed power consumption.

The invention is particularly, but not solely, concerned with traction members in the form of machine drive chains or scraper-chain assemblies of conveyors used in mineral mining. The stations are then the main drive and auxiliary drive stations. In such an environment slack chain usually occurs in the upper run issuing from the auxiliary drive station. In I such a case the traction force in the upper run is zero and the pressure which theoretically exists in the tensioning unit is proportional to the output torque of the drive of the auxiliary drive station. Unlike the process known from DE 44 13 321 Al, in the process according to the invention the resulting change in pressure when the path change is constant is not used as a controlled variable, but only the total pressure measured is used as a controlled variable. Thus according to the invention only the pressure in the working chamber (and therefore possibly the stroke of the tensioning unit) is changed until it corresponds to a preset target value which was established for the instantaneous power consumption of the drive of the particular drive wheel on which the tensioning unit is provided. Set values for the various operating conditions of the conveyors are determined by tests and can be stored in the form of a characteristic curve. The tensioning unit is extended or retracted until the pressure in the working chamber corresponds to the instantaneous pressure set value independently of how far the unit has to be extended or retracted for this purpose. If the pretensioning is adjusted in such a way that the pressure in the working chamber is higher than the pressure at which slack chain occurs for the measured power consumption value, chain traction force is reliably created in the upper run adjacent the wheel of the associated station and, as a result, slack chain cannot occur.

The process according to the invention does not require a continuous motion of the tensioning unit, nor is a sensor for measuring the path necessary. With the process according to the invention it is rather the case that the pressure is directly adjusted to the set value dependent on the measured 6 power consumption value. The set value of the total pressure is preferably taken from a characteristic curve in which a total pressure to be adjusted is allocated to each power consumption value. The characteristic curve is preferably entered into an evaluating unit and stored there. Obviously several characteristic curves, for example for various conveyor lengths can be stored in the evaluating unit.

The characteristic curve according to which the chain pretension is adjusted can be determined by calculation. However, the characteristic curve is preferably determined empirically and/or experimentally. The known parameters, for example the loading state, the length of the longwall face or the conveyor, the course of the longwall face, the width of the conveyor etc., can also be accommodated in the characteristic curve. It is advantageous if the total pressure is established in the characteristic curve by adding a minimum additional pressure to a basic pressure value at which slack chain is completely avoided or disappears. Advantageously, the basic pressure can be determined by reducing the total pressure until slack chain just occurs, whereupon the associated power consumption value is stored. In the simplest evaluation of the process a constant minimum additional pressure is assumed for all power consumption values. In the case of a characteristic curve which is complicated to set up, the minimum additional pressure is established for each power consumption value individually or in certain regions.

However, experimental, calculation and empirical methods can also be mixed to establish the characteristic curve. Thus, the characteristic curve can, for example, be set up by determining only two points of the characteristic curve I 7 experimentally, the characteristic curve itself being a straight line. For this purpose, the conveyor can, for example, be operated without a load, on the one hand, and fully loaded, on the other hand, and the power consumption values and the pressure values thus derived are stored. The straight line connecting the two points then determines the total pressure values for further intermediate power consumption values.

In order to determine the set pressure value for tensioning away the slack chain, a proportionality factor by which the measured power consumption or the basic pressure value determined for it is multiplied, can be provided instead of a characteristic curve. In this proportionality factor the known parameters such as, for example, the loading state, the length of conveyor, the course of the longwall face, the width of the conveyor etc., can also be accommodated.

In another aspect the invention provides apparatus for adjusting the tension in an endless traction member entrained around wheels of spaced apart stations at least one of which has drive means for driving the associated wheel to drive and circulate the traction member and a hydraulic piston and cylinder tensioning unit operable to adapt the distance between the wheels to control the tension in the traction member said apparatus comprising means for sensing the pressure in a working chamber of the tensioning unit and for generating a signal proportional to the sensed pressure, means for sensing the power consumption of the associated drive means and for generating a signal proportional to the sensed power consumption and an evaluating and control unit which receives the signals from the pressure and power consumption 8 sensing means and which adjusts the pressure in the working chamber to a set value in dependence on the sensed power consumption. As, according to the invention, only one sensing means is provided for measuring power consumption in addition to the pressure sensing means, the cost of maintenance and susceptibility to faults is lower than that of apparatus known from the state of the art.

The invention may be understood more readily, and various other aspects and features of the invention may become apparent, from consideration of the following description.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

Figure 1 is a schematic simplified representation of a chain drive mechanism equipped with tensioning devices for tensioning the chain; Figure 2 is a schematic simplified representation of apparatus constructed in accordance with the invention for adjusting the tension in the chain shown in Figure 1 and Figure 3 is a graphical representation of pressure and power consumption pertaining to the apparatus shown in Figure 2 with characteristic curves for adjusting the chain pretension applicable to a process in accordance with the invention.

In the schematic representation of Figure 1, an endless traction member in the form of a chain 3, is entrained around wheels 1, 2 and is driven in a circulating path in upper and I 9 lower runs. The chain 3 may be used in a scraper-chain conveyor in which case the chain 3 may be a single or double chain which carries scrapers which move along a conveyor channel of a scraper-chain conveyor in known manner. Alternatively the chain 3 may drive a mineral winning machine such as a plough. In the case of a scraper-chain conveyor used in a longwall working, the chain wheel 1 is formed as a chain drum in a machine frame with drive means of the conveyor at the so-called main drive station I, while the chain wheel 2 is f ormed as a chain drum in a machine frame with drive means at the other end of the conveyor at the so- called auxiliary drive station II. The actual chain wheel drive means at the main drive station I and at the auxiliary drive stations II are not shown.

In order to control the tension in the chain 3, at least the main drive station I, but preferably each of the drive stations I and II is provided with a tensioning device which is in the form of at least one hydraulic piston and cylinder unit 4 by means of which the rotational axes of the associated chain wheels 1, 2 can be adjusted in the direction of the double arrow 5, allowing optimum chain tensioning. To permit such adjustment the chain wheels 1, 2 can be displacably mounted in the respective machine frames for movement in the direction of the arrows 5, as is known. Alternatively the machine frames accommodating the chain wheels 1, 2 can be designed as telescopic frames with sections displaced relative to one another as the tensioning units 4 operate as is also known.

There is an optimum dynamic chain tension when, during operation, the chain 3, independently of the various operational influences, is neither too highly tensioned nor does it sag around the chain wheels 1 and 2. In order to achieve this optimum dynamic chain tension during operation, apparatus, described hereinafter, is provided for continuous adjustment of the chain tension by corresponding control and adjustment of at least one of the tensioning units 4.

In Figure 1 the rotational direction of the chain wheels 1 and 2 is shown by the arrows 6. It can be seen that a so-called slack chain section 3 can occur at the chain wheel 1 of the main drive station I where the chain 3 is fed off this chain wheel 1 in the lower run, while another slack chain section 311 can occur at the chain wheel 2 of the auxiliary drive station II where the chain 3 is fed off this chain wheel 2 in the upper run. When the slack chain section 3'' forms in the upper run the traction force in the chain 3 directly after the chain has been reeled off the wheel 2 at the auxiliary drive station II is practically zero, so where there is an equilibrium of forces the traction force of the chain 3 in the lower run and therefore the pressure measured in the tensioning unit 4 is proportional to the power output of the chain drive at the auxiliary drive station II. Consequently, the traction force of the chain 3 or the pressure prevailing in the tensioning unit 4 is also proportional to the power consumption of this drive. The power consumption of the auxiliary drive II can be measured in a simple manner. As the piston area of the tensioning unit is known, the following equation applies during operation with the formation of the slack chain section 311:

I - PTOT x A I wherein PTOT: is the total pressure in the tensioning unit 4 I: is the power consumption of the associated chain drive A: is the piston area of the tensioning unit.

The power consumption values and total pressure values at which slack chain section 311 is completely avoided in the top run (increase in chain wheel spacing 1-2) or where slack chain occurs (decrease of the chain wheel spacing 1-2) are determined experimentally, empirically or by calculation. The resulting base pressure value PB is different in each case for the various loading conditions of the conveyor. In the case of the drive motors used in the mining industry such as asynchronous motors, the measured power consumption value changes according to various loading conditions of the conveyors. In order to be sure of avoiding the slack chain section 3' 1 in the top run in every operating condition, the basic pressure value PB required according to the measured power consumption is not used, but a set value is used which is higher than the basic pressure value PB by a minimum additional pressure. This set value is determined in advance as explained in more detail below.

Figure 2 shows on an enlarged scale and in schematic simplification an individual tensioning unit 4 with its cylinder 7 and working chamber 14, a piston 8 slidably guided therein and a piston rod 9. The tensioning cylinder 7 is fixed onto a hydraulic high pressure inlet line Z and the hydraulic return line R. Electromagnetic valves 10 are provided in the lines Z, R which can be controlled by an electronic evaluating 12 and control unit 11 via electric lines 12 and 13. The valves 10 can be mounted directly on the tensioning unit 4 but also arranged separately from the tensioning unit 4 elsewhere in the hydraulic lines Z and R. The working chamber 14 of the unit 4 can be charged with hydraulic fluid f rom a pump 15 connected to the inlet line Z and the piston 8 loaded with the hydraulic pressure. The evaluating unit 11 is connected to the pump 15 via an electric signalling line 16 in order to be able to adjust the pump output and the pressure in the hydraulic inlet line Z. A pressure sensor 17 is integrated into the cylinder 7 to sense the pressure in the working chamber 14. The sensor 7 can be located as shown at the base of the cylinder 7 or elsewhere. Hydraulic piston and cylinder units equipped with an in-built pressure sensors are well known in the mining industry so further detail with regard to the formation and arrangement of this sensor is not necessary. The sensor 17 provides electric signals proportional to the pressure in the chamber 14 and these signals are fed to the evaluating and control unit 11 via a signal line 18.

The evaluating and control unit 11 is connected via a further electric signal line 19, to a measuring device 20 which serves to measure the power consumption I of the drive 21 of the corresponding drive station II or I. One of the chain wheels 1, 2 would be drivably connected to the drive 21, if necessary with interposed gearing.

The adjustment of the tensioned state of the chain 3 follows a characteristic curve B, K or K', as shown in Figure 3. Possibilities for defining these characteristic curves B, K, KI and the adjustment of the pretensioning with regard to these characteristic curves B, K, KI will now be explained.

I 13 According to experience, slack chain still occurs with empty conveyors and a pressure of about 50 bar in the issuing run. By increasing the pressure by about 10 bar this slack chain can be eliminated. In order to avoid excessive pretensioning force and the excessive wear of the chain 3, the pressure of the hydraulic fluid in the working space 14 of the tensioning unit 4 when the conveyor is empty is decreased with the valve 10 open, starting from about 60 bar, until the slack chain section 3' ' occurs at the auxiliary drive station II in the top run. The associated base pressure PB1 and the corresponding power consumption Iempty are measured and both measurements are stored. The conveyor is then operated fully loaded. The pressure in the working space 14 of the tensioning unit 4 is not increased until the moment when no slack chain section 31, occurs at the auxiliary drive station II. The measured base pressure is designated by PB2 at the corresponding power consumption Ifull in Figure 3. The two pressure values PB1, PB2 measured by the pressure sensors 17 are connected by the straight line B so that on a first attempt every pressure value to be adjusted can be determined at a power consumption value between Iepty and Ifull. To be certain, however, the adjustment is preferably not undertaken according to the established base pressure value PB1, PB2 but according to one of the characteristic curves K, K' in which a minimum additional pressure Pmi, PM2 is added to the base pressure values PB1, PB2In the characteristic curve K the added minimum additional pressure Pm, is constant for all operating conditions, while the minimum additional pressure PM2 increases with the increased loading state in the characteristic curve K'. Adjustment can also be made according to the characteristic curve B. 14 In view of the above description of preferred embodiments of the invention various modifications and changes will be readily appreciated by those skilled in the art. It is therefore understood that within the spirit and scope of the appended claims the invention may be practiced in other ways than specifically as described above.

I

Claims

Claims

1. A process of adjusting the tension in an endless traction member entrained around wheels of spaced apart stations, at least one of the stations being provided with drive means for driving the associated wheel to drive and circulate the traction member and a hydraulic piston and cylinder tensioning unit for adjusting the distance between the wheels of the stations to control the tension in the traction member; said process comprising sensing the pressure in a working chamber of the tensioning unit, sensing the power consumption of the associated drive means and adjusting the pressure in the working chamber to a set value dependent on the sensed power consumption.

2. A process according to claim 1, wherein the set value is determined from a pre-determined characteristic curve established by plotting values of sensed pressure and power consumption.

3. A process according to claim 2, wherein the characteristic curve is input into an evaluating and control unit and stored.

4. A process according to claim 2 or 3, wherein the characteristic curve is determined experimentally, by calculation and/or empirically.

5. A process according to claim 2 or 3, wherein the characteristic curve is established by adding a minimum additional pressure to a base pressure at which a slack traction member is just avoided.

16 6. A process according to claim 5, wherein the base pressure is determined by a reduction of pressure in the working chamber until a slack traction member just occurs and the associated power consumption value is then stored.

7. A process according to claim 5 or 6, wherein the minimum additional pressure is constant for all power consumption values.

8. A process according to claim 5 or 6, wherein the minimum additional pressure is determined for each power consumption value.

9. A process according to any one of claims 1 to 8, wherein the traction member is a chain or includes a chain, the stations are main and auxiliary drive stations in a mine working and the tensioning unit is associated with the auxiliary drive station.

10. A process according to claim 1, wherein the set value is determined via a proportionality factor by which the measured power consumption value is multiplied.

11. A process according to claim 1, wherein a base pressure is established by measuring the pressure at which a slack traction member is just avoided and the set value is determined via a proportionality factor by which the measured base pressure is multiplied.

12. A process substantially as described with reference to the accompanying drawings.

I 17 13. Apparatus for adjusting the tension in an endless traction member entrained around wheels of spaced apart stations at least one of which has drive means for driving the associated wheel to drive and circulate the traction member and a hydraulic piston and cylinder tensioning unit operable to adapt the distance between the wheels to control the tension in the traction member; said apparatus comprising means for sensing the pressure in a working chamber of the tensioning unit and for generating a signal proportional to the sensed pressure; means for sensing the power consumption of the associated drive means and for generating a signal proportional to the sensed power consumption and an evaluating and control unit which receives the signals from the pressure and power consumption sensing means and which adjusts the pressure in the working chamber to a set value in dependence on the sensed power consumption.

14. Apparatus according to claim 12, wherein a pump serves to provide hydraulic pressure fluid to the working chamber and the evaluating and control unit controls the pump.

15. Apparatus according to claim 13 or 14, wherein the set value is established by storing several pressure values for different power consumptions in the evaluating and control unit.

16. Apparatus substantially as described with reference to, and as illustrated in, the accompanying drawings.