WO2015090255A1

WO2015090255A1 - A method of the performance control for cyclically operating equipment exposed to varying load, in particular, a scraper conveyor

Info

Publication number: WO2015090255A1
Application number: PCT/CZ2014/000155
Authority: WO
Inventors: Jiří NEUWIRTH
Original assignee: Wista, S.R.O.
Priority date: 2013-12-17
Filing date: 2014-12-12
Publication date: 2015-06-25
Also published as: CZ20131012A3

Abstract

The moving part of cyclically operating equipment performs forward and backward movement between the starting and end dead centre in consecutive cycles, whereas each new cycle starts with initiation of forward movement of the moving part of the cyclically operating equipment. The output of the cyclically operating equipment is controlled by the change of the time of individual cycles, whereas the necessity to change the time of at least one actual cycle is evaluated based on the time of the forward and/or backward movement of the moving part of the cyclically operating equipment in the given cycle or in at least one of the preceding cycles. The time of the actual cycle may be controlled by the change of the speed of the forward or backward movement of the moving part of the cyclically operating equipment or by introduction, cancelling or change of the time delay applied within the given cycle. Whereas the time delay may be included between the forward and backward movement of the moving part of the cyclically operating equipment or after termination of the backward movement of the moving part of the cyclically operating equipment or in the course of the forward and backward movement of the moving part of the cyclically operating equipment. It is convenient that the time delay in the following cycles will be changed, compared to the time delay applied in the preceding cycle by step lenght, which is preset in advance. When a hydraulic or pneumatic drive unit is used, the speed of the forward or backward movement of the moving part of the cyclically operating equipment may be changed by connecting of the pneumatic or hydraulic drive unit to a source of different pressure. When an electric drive unit is used, the speed of the forward and/or backward movement of the moving part of the cyclically operating equipment may be kept in preset limits by the change of the supplied electric input.

Description

A method of the performance control for cyclically operating equipment exposed to varying load, in particular, a scraper conveyor

Technical field

The invention concerns a method of the performance control for cyclically operating equipment exposed to varying load, in particular, a scraper conveyor for transport of loose material. The invention solves optimization of consumption of energy required for operation of equipment, which is unevenly or irregularly loaded. In the case of a scraper conveyor, such situation may occur at workplaces where a scraper conveyor is used for removal of irregularly settled solid particles of loose material, e.g. at workplaces where products are blasted with abrasive material.

Description of prior art

It is well known that linear drive units with a pneumatic, hydraulic, or electric drive are used for operation of cyclically running equipment including scraper conveyors. Pneumatic or hydraulic linear drive units driving a scraper conveyor consist of a piston - a piston connected to one end of a piston rod moves back and forth between two dead centres, while the other end of the piston rod is connected to the frame on which the scrapers of the scraper conveyor are suspended. The inner space of the cylinder is divided by the piston into two areas - the first area is located between the piston and the bottom through which the piston rod protrudes whereas the second area is located between the piston and the opposing cylinder end. In the case of the existing scraper conveyors driven by pneumatic or hydraulic linear drive units, sensors are placed near both piston dead centres indicating presence of the piston at the particular dead centre. Both inner areas are alternately connected via the switching valve to the source of pressure air in the case of a pneumatic linear drive unit or a source of pressure liquid in the case of a hydraulic linear drive unit and to the respective outlet - in the case of a pneumatic linear drive the outlet is into the surrounding atmosphere and in the case of a hydraulic linear drive unit it is an outlet into a storage tank of pressure liquid.

In the case of electrically driven linear drive units, a rod with external thread is used instead of a piston rod and this rod is engaged with the internal thread of a turning nut When the nut is turning, the rod either pushes in or out depending on the rotation direction of the stationary part of the linear drive unit. Sensors are placed near both dead centres of the rod indicating its position. Another established method of driving of a scraper conveyor is using a crank mechanism driven by a pneumatic or electric drive including a gearbox. The crank mechanism is usually placed in the clevis of the scraper conveyor and allows transfer of rotary movement of the crank into the linear movement of the conveyor within the range of me dead centres of me crank mechanism.

It is well known that in the case of cyclically operating equipment using a linear drive a stable input is used for controlling of the linear drive. When such a control method is used, the respective sensor always sends a signal to the switching valve when the piston or the rod reaches one of the dead centres. Based on such signal, the switching valve or electric switch adjusts itself. In the case of a pneumatic or hydraulic drive, the connection of the first area to the source of pressure is replaced by the connection of the second inner area to the pressure source or vice versa. In the case of an electric drive, the rotation direction of the nut is changed.

The disadvantage of this method is that it cannot react to varying load applied to cyclically operating equipment. If such cyclically operating equipment is a scraper conveyor, unnecessary loss of energy occurs in the cycles with decreased load and the piston, rod, or crank mechanism stops in the cycles when the preset output is insufficient. If such cyclically operating equipment is a conveyor, unnecessary loss of energy occurs in the cycles with decreased load. In the case of a pneumatic or hydraulic drive and with constant cylinder volume and stable input, the supplied energy is directly proportional to the pressure of the driving medium. In each cycle in which an inappropriately greater pressure of the medium is used for driving of the piston than would be corresponding to the actual consumption, unnecessary loss of energy occurs, which logically results in less efficient operation. In the case that the constant pressure for driving is selected at a lower level than actually necessary, the equipment has insufficient output in the case of increased loading of the conveyor. In the case of an electric linear or crank drive, energy is lost when direction is changed due to braking and restarting of the frame with scrapers. In the case of continuous operation of conveyors with constant intensity of cycles a relatively large number of cycles with low utilization of the potential driving unit occurs and the result is unnecessary and increased wear due to inexpedient operation. Disclosure of the invention

The stated disadvantages are dealt with by a method of the performance control for cyclically operating equipment exposed to varying load, in particular, a scraper conveyor, according to this invention, whose moving part performs forward and backward movement between the starting and end dead centres in consequent cycles whereas each new cycle starts with initiation of forward movement of the moving part of the cyclically operating equipment. The principle of the invention is that the output of the cyclically operating equipment is controlled by the change of the time duration of individual cycles, whereas the necessity to change the time duration of at least one actual cycle is evaluated based on the time of forward and/or backward movement of the moving part of the cyclically operating equipment in the given cycle or in at least one of the preceding cycles. Alternately, the time of the actual cycle is controlled by the change of the speed of the forward or backward movement of the moving part of the cyclically operating equipment. According to other alternatives the time of the actual cycle may be controlled by introduction or increasing of the time delay between the forward and backward movement of the moving part of the cyclically operating equipment or after termination of the backward movement of the moving part of the cyclically operating equipment or in the course of the forward and backward movement of the moving part of the cyclically operating equipment or by cancelling or limiting the time delay introduced in one or several of the preceding cycles. According to the most suitable alternative, the step length by which the time delay will be changed in at least one subsequent cycle, to be compared with the time delay applied in the preceding cycle or cycles, is preset. In the case when a hydraulic or pneumatic drive is used, the speed of the forward and/or backward movement of the moving part of the cyclically operating equipment is alternately changed by connecting of the pneumatic or hydraulic drive unit to a source of different pressure. In the case when an electric drive is used, the speed of the forward and/or backward movement of the moving part of the cyclically operating equipment is alternately kept in preset limits by the change of the supplied electric input.

The advantage of the method according to this invention is that the input of the linear drive unit driving the cyclically operating equipment is continuously changing depending on the actual loading of the cyclically operating equipment, in particular, by changing the input within each cycle or the number of strokes within a certain time interval. Especially in the cases when such cyclically operating equipment is a scraper conveyor, its operation respects the varying load. Thus unnecessary losses of energy during operation are avoided and the operation of a scraper conveyor is optimized in terms of power consumption and fewer cycles of the conveyor are executed, which results in reduced wear.

Description of the drawings Figures 1 to 10 concern the exemplary impementation according to example 1, figures 11 to 20 concern the exemplary impementation according to example 2, and figures 21 to 30 concern the exemplary impementation according to example 3, whereas each figure concerns only one cycle. In each figure the bottom curve represents the degree of protrusion of the moving part of the linear drive unit from the fixed part of the linear drive unit depending on time and the top curve represents the instantaneous supplied input depending on time. The bottom and top curves in each figure mutually correspond in terms of time, i.e. they are synchronous in terms of time. In figures 1 to 20, the positive value of the pressure means its effect when the moving part of the linear drive unit pushes out from the fixed part, whereas a negative pressure value means effect of pressure when the moving part of the linear drive unit is pushed into the fixed part during the return movement. In figures 21 to 30, the positive value of the current represents its consumption when the moving part of the linear drive unit is pushed out of the fixed part and when the moving part of the linear drive unit is pushed into the fixed part during the return movement because an electric linear drive unit is powered by alternate current and the direction of movement is not therefore controlled by the polarity of the supply voltage. Figures 1 to 10 represent the first to tenth cycles according to example 1, whereas figure 1 represents the first cycle, figure 2 second cycle, figure 3 third cycle, figure 4 fourth cycle, figure 5 fifth cycle, figure 6 sixth cycle, figure 7 seventh cycle , figure 8 eighth cycle , figure 9 ninth cycle, and figure 10 tenth cycle. Figures 11 to 20 represent the first to tenth cycle according to example 2, whereas figure 11 represents the first cycle , figure 12 second cycle, figure 13 third cycle, figure 14 fourth cycle, figure 15 fifth cycle, figure 16 sixth cycle, figure 17 seventh cycle , figure 18 eighth cycle , figure 19 ninth cycle and figure 20 tenth cycle. Figures 1 to 30 represent the first to tenth cycle according to example 3, whereas figure 21 represents the first cycle , figure 22 second cycle, figure 23 third cycle, figure 24 fourth cycle, figure 25 fifth cycle, figure 26 sixth cycle, figure 27 seventh cycle , figure 28 eighth cycle , figure 29 ninth cycle and figure 30 tenth cycle.

Examples of impementation

Example 1 The exemplary implementation according to example 1 concerns a method of controlling the input to a pneumatic linear drive unit, which drives a cyclicaly operating scraper conveyor of which it is a part and whose output is adjusted according to the actual load. The scraper conveyor in this example is used for transporting of loose material, in particular, used abrasive material caught by the scraper conveyor, into the outlet hopper. The scraper conveyor is placed under the grating forming the floor of the workstation where products are cleaned by blasting and it contains scrapers suspended on the frame above the base of the scraper conveyor. The pneumatic linear drive unit consists of a fixed and moving part and is connectible via control valves to two sources of pressure air with different constant pressure levels. One of the sources of the pressure air in the example provides pressure air of 0.2 MPa and the other source provides pressure air at 0.5 MPa. The moving part of the linear drive unit consists of a piston which is connected to a piston rod. The other end of the piston rod is connected to the reciprocating frame of the scraper conveyor. The fixed part of the linear drive unit is formed by a body in the shape of a hollow cylinder. The piston of the linear drive unit is sliding inside the fixed part of the linear drive unit. The piston divides the internal space of the fixed part of the linear drive unit into two inner areas, whereas the actual direction of piston movement is controlled by the selection of the inner area into which pressure air is supplied, whereas pressure air is removed from the other inner area. By switching the control valves, the moving part of the linear drive unit cyclically performes a forward and backward movement between two dead centres in consecutive cycles. The loose material which gradually settles during blasting of products on the surface of the conveyor base is gradually transferred along the base towards the outlet hopper placed at the end of the conveyor so that even the loose material settled on the other side of the base opposite the outlet hopper is fully transferred into the outlet hopper in several consecutive cycles. Scrapers of the conveyor are provided with segments allowing tilting of the scrapers in one direction of their movement while in the other direction they are relatively firmly strutted, which allows movement of loose material by the scarpers in the desired direction while during the reverse movement they bend and slide over the loose material without transferring it, or more precisely, much smaller amount of loose material is transferred back than is transferred forth with the strutted segment.

When describing the movement of the piston in the exemplary impementation according to this example, we designate the time interval during which the moving part performs forward movement as the push phase because during forward movement the scraper pushes the particles of the loose material towards the outlet hopper. We designate the time interval during which the moving part performs in each cycle backward movement, i.e. towards the outlet hopper, as the return phase. The dead centre, when the piston rod is maximally retracted inside the inner space of the cylinder, is called the starting dead centre and the dead centre when the piston rod is fully extruded out of the cylinder is called the end dead centre. If the scraper conveyor is in operation, then the piston with the piston rod moves back and forth within consecutive cycles between the starting and end dead centres. The phase within one cycle when the piston is moving from the starting to the end dead centre is called the push phase. Within the push phase the piston rod is pushed out of the fixed part of the linear drive unit and scrapers push forward the loose material. When the end dead centre is reached, the movement direction of the piston rod is changed and it starts to move back to the starting dead centre. When the piston starts to move back it is the beginning of the return phase of the cycle. Within the return phase, the piston rod pushes into the fixed part of the linear drive unit and the scrapers return to the initial position. The return phase is less demanding in terms of energy than the return phase because only minimum of the loose material is transferred during the return phase. The beginning of the forward movement of the moving part is regarded as start of each new cycle.

The value of the output required for securing of the operation of the scraper conveyor depends on its actual loading, i.e. the actual intensity of sedimentation of loose material, which determines the amount of loose material that needs to be transferred during one cycle. The actual loading of the scrape conveyor is then ascertained according to this example by measuring the time taken by the forward movement of the moving part in given cycle or in several preceding cycles. We take into consideration the pressure of the used pressure air. The output of the scraper conveyor is controlled by controlling the input of the linear drive unit. The performance of the linear drive unit is changed by the time of each cycle, as it is decreased within each cycle by introducing or increasing of the time delay used in the preceding cycle or in several preceding cycles before or in the course or after termination of the backward movement and it is increased by cancelling or limiting of the time delay used in the preceding cycle or in several preceding cycles. The input of the pneumatic linear drive unit can be also altered by the change of the speed of the forward or bactward movement executed by change of the pressure of the used pressure air, executed by connecting of the pneumatic drive unit to a source of different pressur. In this example it is carried out only in the course of the forward movement or during its start. The return phase is always realized using the pressure at which the preceding push phase ended. The contingent change of length of the time delay is changed in a step manner by adding or deducting of the step lenght, which is preset.. Further, with regard to operating conditions the maximum time for the time limit within one cycle is set in advance and the reason is to prevent situation when the scraper conveyor completely stops due to a too long time delay and fails to react to the increased density of sedimentation due to the absence of the push phase for an extended period of time. With regard to the operating conditions, the time range is also determined in advance for the duration of the push phase corresponding to te individual levels of loading of the scraper conveyor. According to this example the maximum time of Hie time delay was set to 30 seconds and the length of the time interval by which the time delay would be changed when required was set at at two seconds. For the used equipment, the time of the push phase with air pressure at 0.2 MPa is up to 4 seconds in the no load mode, the time of the push phase is within 4 to 6 seconds in the standard operation mode, the time of the push phase is within 6 to 8 seconds in the increased load mode and the time of the push phase is within 8 to 12 seconds in the extreme load mode. If the push phase is longer than 12 seconds, the scraper conveyor gets into a condition when malfunction is indicated. Based on the condition ascertained based on the duration of the push phase the course of the remaining cycle is changed as follows. In the case that the no load mode is ascertained, a time delay is introduced of 2 seconds or if the time delay was used in the preceding cycle, then the value of the time delay is increased by this value. In the case that the standard operation mode is ascertained, the time delay is left as it was used in the preceding cycle without changes. In the case that the increased load operation mode is ascertained, the time delay is shortened by 2 seconds compared to the preceding cycle or it is completely cancelled. In the case that the push phase does not finish within 8 seconds, the linear drive unit switches over to the 0.5 MPa pressure source and the push phase is completed at this pressure. If the increased pressure is not sufficient for completing the push phase within 4 seconds, i.e. if it lasts for more than 12 seconds, then malfunction is indicated and the scraper conveyor completely stops. In the return phase, the linear drive unit is always connected to the same source of pressure air to which it was connected upon termination of the push phase within the same cycle.

The method of this example will be for better clarity illustrated by the description of actions associated with operation of the scraper conveyor installed at a workstation where products are cleaned by blasting by loose abrasive material, in particular, in first ten cycles from starting of the blasting operation during which loose material falls onto the scraper conveyor and it needs to be removed from the workplace. This loose material consists of a mixture of abrasive material and particles blasted off of the surface of products. Within the ten described cycles, the scraper conveyor loading is gradually increased and subsequently decreased again. Prior to the start of the first cycle the scraper conveyor was connected to 0.2 MPa pressure source and the data of the length of time delay used during last operation had been deleted from the control unit. The equipment was set so that contingent time delays in each cycle did not take place until after the end of the return phase. Before the start of the first cycle, the scraper conveyor was slightly clogged with material from previous blasting operations.

The first cycle took place before blasting operation was started and therefore no new loose material settled during the first cycle. In the course of the push phase of the first cycle, only the material remaining there from previous operations was removed from the base of the scraper conveyor. The push phase of the first cycle took 3 seconds which corresponds to the no load mode. The first cycle therefore finished with a newly introduced time delay of 2 seconds. This corresponds to the selected time interval for the possible change of time delay within one cycle.

Within the second cycle, still no new material settled down but the amount of the loose material in the scraper conveyor from previous operations was already smaller and so the push phase was reduced to 2 seconds. The scraper conveyor was still working in the no load mode. Therefore, the time delay was increased to 2 seconds to the overall time of 4 seconds. Blasting was initiated during the third cycle and so loose material started to settle down on the base of the scraper conveyor. Therefore, the time of the push phase increased by 3.5 seconds compared to the previous cycle. However, the scraper conveyor was still in the no load mode. Therefore, the time delay was increased by another 2 seconds to the overall time of 6 seconds. In the course of the fourth cycle, the intensity of settling increased and so the time of the push phase increased likewise. The push phase of the fourth cycle took 5 seconds. This corresponds to the standard operation mode when no correction measures are taken. That is why the same length of the time delay was used in the fourth cycle as in the preceding one, i.e. 6 seconds. The settling intensity further increased in the fifth cycle which resulted in the extension of the push phase to 7 seconds. The scraper conveyor was working in the increased load mode in this cycle. Within this mode, the time delay decreased by 2 seconds is used compared to the preceding cycle. The length of the time delay applied in the fifth cycle was therefore 4 seconds.

High-intensity blasting was carried out in the sixth cycle and so the intensity of settling of the loose material on the base of the scraper conveyor increased as well. The highly intensive settling of loose material in the sixth cycle resulted in such loading of the linear drive unit that the piston did not reach the end dead centre within 8 seconds. It means that the scraper conveyor was working in the extreme load mode in the sixth cycle. Therefore, the linear drive unit was disconnected after eight seconds from the source of 0.2 MPa pressure air and it was connected to 0.5 MPa pressure air. Given the increased pressure, the piston reached the end dead centre within 4 extra seconds. Altogether, the push phase took 12 seconds. Therefore, the time delay was completely cancelled and the return phase took place with increased pressure of 0.5 Mpa within 1 second.

For the beginning of the seventh cycle the linear drive unit was connected again to the source of pressure air with lower pressure but the intensity of settling dropped only slightly and so the situation from the sixth cycle was repeated. Only the time of the push phase at 0.5 MPa was reduced to 3.5 s.

The eighth cycle started again by connecting of the linear drive unit to the source of 0.2 MPa pressure air. However, the intensity of settling of the loose material dropped compared to the seventh cycle and so the length of the push phase was reduced to 7 seconds. The increased load mode was stated during which the time delay is shortened if it is applied in the preceding cycle. In the increased load mode, the linear drive unit is not connected to the source of higher pressure, therefore, the return phase took place at the pressure of 0.2 MPa and took 2 seconds.

Settling intensity further dropped in the ninth cycle and so the length of the push phase dropped to 5 seconds. The scraper conveyor worked in the standard operation mode during which no measures are taken. Therefore, the return phase took place again at the lower pressure and it took 2 seconds again. The time delay duration remained at zero.

Blasting was discontinued and settling of loose material stopped in the course of the tenth cycle. The push phase took 2 seconds, no load mode was stated and the tenth cycle was ended with the time delay of 2 seconds.

In the example described above, the maximum specified time for one cycle of 12 seconds was not exceeded, so the scraper conveyor did not get into situation when malfunction would be stated. Example 2

The exemplary impementation according to example 2 differs from the exemplary application described in example 1 by the fact that the linear drive unit is a hydraulic one and that the scrapers of the conveyor drag the loose material to the outlet hopper while moving back in the course of the return phase, i.e. when the moving part of the linear drive unit executes the backward movement from the end dead centre to the starting dead centre. Further, the exemplary application according to example 2 differs from the exemplary application described in example 1 by the fact that the time delays applied in the course of individual cycles are included not only after completion of the backward movement but also before it starts or during its course. The course of intensity of settling as manifested in individual steps in this example is the same as described in example 1.

In the first cycle the just introduced time delay of 2 s is applied between the push phase and the return phase, so that the return phase of the first cycle does not immediately follow the push phase of the second cycle. In the second cycle, the length of the time delay increases by 2 s. The time delay of 2 s before the start of the return phase remains but in the second cycle the time delay increases by 2 extra seconds, which are applied after the completion of the return phase.

In the third cycle, the length of time delay is increased by two extra seconds, which are applied in the course of the return phase so that the movement of the return phase stops for 2 seconds when reaching the half of its travel.

The course of the fourth cycle is the same as the course of the third one.

In the fifth cycle, the length of the time delay applied in this cycle is reduced by two seconds compared to the preceding cycle, which is implemented by cancelling the time delay in the course of the return phase.

Sixth, seventh, eighth, ninth, and tenth cycle occur in the same way as described in example 1.

Example 3

The exemplary impementation according to example 3 differs from the exemplary application described in example 1 by the fact that the linear drive unit is an electric actuator. The electric actuator works with a constant preset speed of movement of the moving part of the linear drive unit, whose open end is connected to the reciprocating frame of the scraper conveyor. During a change of scraper conveyor load, the amount of consumed electric current changes as the actuator automatically adjusts its input so that the moving part of the linear drive unit may move at a constant speed, and so it covers in each cycle the distance from the starting dead centre to the end dead centre within the same time. Therefore, in order to be able to monitor the actual intensity of settling of the loose material on the scraper conveyor base, the course of the consumed electric current is recorded during the forward movement. The recorded course of current consumption in each cycle is evaluated with the objective to specify the mode in which the scraper conveyor operates. The length of the time delay is then increased or decreased as necessary in each cycle according to the ascertained mode.

If the average value of the consumed current ranges between 0 to 10% of the maximum permitted current value for the given electric linear drive, then such mode is the no load mode. The average value of the consumed current between 10 and 45 % of the maximum permitted current value represents the standard operation mode. The average value of the consumed current between 45 and 85 % represents the increased load mode and between 85 and 100% it represents the extreme load mode. If the current exceeds the value of the permitted load, malfunction is indicated as the drive unit may be operated only for a short time with such current consumption.

The course of settling of the loose material in the cycles 1 to 9 described below corresponded to the course of intensity of settling as described in examples 1 and 2. Unlike the situations described in examples 1 and 2 the speed of travel of the moving part of the electric linear drive unit in the extreme load mode is the same as in the other modes. The exemplary application according to example 3 further differs from the exemplary applications described in example 1 or 2 by the fact that after a decrease in settling intensity in the ninth cycle an increase in settling followed to such an extent that the current consumed in the push phase increased above the critical value, the exceeding of which might cause defect of the linear drive unit. That is why the linear drive unit was stopped in the tenth cycle and malfunction was indicated by the controller.

Before the start of the first cycle the scraper conveyor was slightly clogged with material from previous blasting operations as was the case described in example 1. The actuator was set for all phases to a constant speed of pushing in and out of the fixed part of the linear drive unit, which was the same for the push phase as for the return phase, in particular, 0.4 m/s. Unless any malfunction occurred the end part of the moving part of the linear drive unit covered the distance between the start dead centre and the end dead centre in the push phase of each cycle in 2.5 s. The end part of the moving part of the linear drive unit covered the distance between the end dead centre and the start dead centre in the return phase of each cycle also in 2.5 s.

The first cycle took place before blasting operation was started and no new loose material settled during the first cycle. In the course of the push phase of the first cycle, only the material remaimng there from previous operations was removed from the base of the scraper conveyor. Based on the evaluation of the amount of the consumed current it was stated that the scraper conveyor worked in the no load mode. The first cycle therefore finished with a newly introduced time delay of 2 seconds, which corresponds to the selected time interval for the possible change of the time delay within one cycle.

In the second cycle, still no new loose material was settling down. Based on the evaluation of the consumed electric current in the push phase it was stated that the scraper conveyor was still working in the no load mode. That is why the time delay was extended by another 2 seconds to the overall time of 4 seconds, whereas the first two seconds of the time delay took place before the beginning of the return phase and the other two seconds after completion of the return phase.

Blasting of a product was initiated during the third cycle and so loose material started to settle down on the base of the scraper conveyor. Settling of the loose material was not too intensive so the no load mode was ascertained again. Therefore, the time delay was increased by another 2 seconds to the overall time of 6 seconds. The first part of the time delay 2 seconds long took place before the beginning of the return phase and the second part 4 seconds long took place after completion of the return phase.

In the course of the fourth cycle, the intensity of settling increased and so current consumption increased to a level corresponding to the standard operation mode. In the standard operation mode, no correction measures are taken, therefore, the same course of the time delay was selected for the fourth cycle as in the preceding cycle with the same overall length of the time delay of 6 seconds.

Settling intensity further increased in the fifth cycle which resulted in further increase of electric current consumption in the course of the push phase. The scraper conveyor was working in the increased load mode in the fifth cycle. The time delay was reduced by 2 seconds in this cycle compared to the time delay applied in the previous cycle. The length of the time delay applied in the fifth cycle was then 4 seconds - two seconds before the start of the return phase and two seconds after its completion.

High-intensity blasting was carried out in the sixth cycle and so the intensity of settling down of the loose material on the base of the scraper conveyor further increased. Very intensive settling of loose material in the course of the sixth cycle resulted in such load that based on the evaluation of the consumed current in the course of the push phase of the sixth cycle the extreme load mode was stated. That is why the time delay was cancelled altogether.

The intensity of settling in the seventh cycle compared to the intensity of settling in the seventh cycle slightly dropped. However, this reduction was not sufficient for stating that the increased load mode had been reached. The scraper conveyor was working in the extreme load mode again in the seventh cycle. As no time delay was applied in the preceding cycle, the remaining part of the seventh cycle went also without any time delay.

Settling intensity of the loose material dropped significantly in the eighth cycle compared to the seventh cycle, so based on the evaluation of electric current values, the increased load mode was stated. The time delay is shortened in the increased load mode if it is applied in the preceding cycle. The remaining section of the eighth cycle went in this case without any time delay.

Settling intensity dropped even further in the ninth cycle, so the scraper conveyor was working in the standard operation mode, during which no measures are taken. Therefore the return phase was implemented without any time delay again.

In the course of the tenth cycle, blasting of an extremely polluted part of a product started. In the course of the push phase, such great amount of loose material gradually settled on the base of the scraper conveyor that the actuator in an effort to maintain the speed provided ever greater amount of current until the current exceeded the safe limit, which occurred before the end part of the extending part of the linear drive unit reached the end dead centre. Defect was stated and the linear drive unit was disconnected from the power supply. Blasting had to be interrupted and the scrapers had to be manually released.

Industrial applicability

The invention may be used for all periodically working equipment with uneven loading - even for equipment provided with rotary drives.

Claims

C L A I M S

A method of the performance control for cyclically operating equipment exposed to varying load, in particular, a scraper conveyor, whose moving part performs a forward and backward movement between the starting and end dead centres in consecutive cycles. whereas each new cycle starts by forward movement of the moving part of the cyclically operating equipment, characterized in that the output of the cyclically operating equipment is controlled by the change of time of each cycle, whereas the necessity to carry out a change of the time of at least one actual cycle is evaluated based on the time taken by the forward and/or backward movement of the moving part of the cyclically operating equipment in the given cycle or in at least one of the preceding cycles.

The method according to claim 1 characterized in that the time of the actual cycle is controlled by the change of the speed of the forward or backward movement of the moving part of the cyclically operating equipment.

The method according to claim 1 characterized in that the time of the actual cycle is controlled by introduction or increasing of the time delay between the forward and backward movement of the moving part of the cyclically operating equipment or after termination of the backward movement of the moving part of the cyclically operating equipment or in the course of forward or backward movement of the moving part of the cyclically operating equipment.

The method according to claim 1 characterized in that the time of the actual cycle is controlled by canceling or limiting of the time delay introduced in one or in several preceding cycles.

The method according to claim 3 or 4 characterized in that the step length by which the time delay will be changed in at least one subsequent cycle, to be compared with the time delay applied in the preceding cycle or cycles, is preset. The method according to claim 2 characterized in that case when a hydraulic or pneumatic drive unit is used, the speed of the forward or backward movement of the moving part of the cyclically operating equipment is changed by connecting of the pneumatic or h draulic drive unit to a source of different pressure.

The method accordmg to claim 3 or 4 characterized in that case when an electric drive unit is used, the speed of the forward or backward movement of the moving part of the cyclically operating equipment is kept in preset limits by the change of the supplied electric input.