Chain hoist control

Abstract

A method is disclosed that includes: detecting the onset of resonance when a chain hoist moves a load; determining a new speed of rotation of a sprocket of the chain hoist to avoid the resonance; and controlling the chain hoist to use the new speed.

Description

Technical Field

[0001] The invention relates to a chain elevator and control thereof. Background Art

[0002] A chain hoist is an example of a device that can lift loads of various sizes. A chain hoist may be designed, for example, for industrial use, or a chain hoist may be designed for use in the entertainment industry, for example for realizing stage productions. When a load is attached to the device, for example by means of a chain of the device, it is important that the load can be lifted and lowered safely. It is therefore advantageous that the load does not swing or bounce freely supported by the lifting chain, but rather remains as stable as possible during lifting and lowering.

[0003] The chain hoist may include a sprocket that can be rotated by an electric motor and pulls the chain, wherein a load attached to the chain can be lifted and lowered. The chain includes links, via which forces can be transmitted in the longitudinal direction of the chain. The links may include alternating links attached to each other vertically or horizontally, and along the contact surface of the alternating links, recesses in the sprocket are shaped to correspond to these links. Due to the recesses, the effective diameter of the sprocket changes, and when the sprocket rotates, for example, at a constant angular velocity, a variable speed is applied to the chain in a pulsating manner. The regular alternating speed in the chain motion can also be regarded as an alternating force of the chain. Therefore, the operation of the chain may produce pulsations, which may cause resonance in the chain. When the resonance is strong, the resonance causes the chain hoist to vibrate, which may be transmitted to the supporting structure and may also cause a dangerous situation in an actual lifting event. Summary of the invention

[0004] An apparatus comprising a chain, a sprocket, a motor and a control unit, wherein the apparatus further comprises: means for determining the onset of resonance when a chain hoist moves a load; means for determining a new speed of rotation of the sprocket of the chain hoist to avoid resonance; and means for controlling the chain hoist to use the new speed.

[0005] A lift comprising: means for determining the onset of resonance when the chain lift moves a load; means for determining a new speed of rotation of a sprocket of the chain lift to avoid resonance; and means for controlling the chain lift to use the new speed.

[0006] A method for controlling a chain hoist, the method comprising: determining the onset of resonance when the chain hoist moves a load; determining a new speed of rotation of a sprocket of the chain hoist to avoid the resonance; and controlling the chain hoist to use the new speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1a , Figure 1b and Figure 1c An example of a chain lift structure is shown.

[0008] Figure 2 An exemplary embodiment is shown with the aid of a block diagram.

[0009] Figure 3 Graphs 312 , 322 , 332 , 314 , 324 , and 334 are included and illustrate measurement results of exemplary embodiments. DETAILED DESCRIPTION

[0010] The device that can lift the load can be, for example, a chain hoist. The chain hoist may include a chain, a device that can clamp the load and is attached to the end of the chain, a sprocket, a motor, and a brake. Some exemplary embodiments may also include a transmission and a control unit that can control the motor. The control unit may also refer to a logic unit, and its implementation may vary. The control unit may include, for example, a variable frequency drive. In addition, the chain hoist may have a user interface, by means of which the operation of the chain hoist can be controlled by its operator. In some exemplary embodiments, the user interface may also be present in a separate device connected to the chain hoist by a wired or wireless connection.

[0011] The chain hoist may be used in some examples such that the chain hoist is part of a lifting system which in addition to the chain hoist may include, for example, an overhead mobile crane, a light lift system, or a jib crane.

[0012] Figure 1a A simplified example of a chain hoist 100 is shown. The chain hoist 100 comprises a chain 120, which may be, for example, a link chain or a roller chain. The chain is connected to a clamping device, by means of which a load 130 may be attached to the chain so that the load is suspended at the end of the chain. The clamping device may be one or more attachment mechanisms. For example, a hook may be used as a clamping device.

[0013] The housing 110 of the chain hoist comprises a sprocket to which a chain 120 is attached and by means of which the chain can be moved so that the load is lowered or lifted. The sprocket can be rotated by means of a motor, i.e. the motor is then functionally attached to the sprocket. The motor can be an electric motor, such as, for example, an adjustable speed motor. The motor can be controlled, for example, by a variable frequency drive. The housing of the chain hoist can also comprise a transmission and a brake.

[0014] The operation of the chain hoist can be controlled, for example, by a controller coupled to the hoist, the controller comprising buttons for controlling the operation of the chain hoist. Using the buttons, the load can be, for example, raised and lowered so that the length of the chain can be rolled up shorter or unrolled longer by the sprocket. This can be performed, for example, by rotating the sprocket, wherein the load attached to the chain is raised or lowered and at the same time the length of the chain between the sprocket and the load changes. In addition, the chain hoist can include a control unit, which can control the operation of the hoist, such as, for example, the direction of travel and / or the speed of travel. The chain hoist can also include a variable frequency drive, which can be part of the control unit or which can be connected to the control unit.

[0015] The chain lift can be attached by means of bracket 115. In some exemplary embodiments, the attachment can also be performed in any other suitable manner. The chain lift can lift loads of various sizes. For example, the load can be in the weight range of 100 kg to 2,500 kg, but loads in other weight ranges can also be lifted and lowered. The maximum load can be, for example, 5,000 kg or 10,000 kg.

[0016] Figure 1b A sprocket 140 is shown. The sprocket 140 has a polygonal shape and it may include teeth, whereby the chain 120 can attach itself around the sprocket. The free, unloaded end of the chain (the end not coupled to the load to be lifted) can then be lowered into a chain bag or housing not shown in the figure. Thus, the rotation of the sprocket 140 (which can then be provided by means of an electric motor) causes the chain 120 to move upward or downward depending on the direction of rotation of the sprocket 140. Thus, the load 130 can be lifted or lowered.

[0017] Due to its polygonal shape, when the sprocket rotates, its angular velocity remains constant or substantially constant, but its linear velocity changes. This so-called polygonal phenomenon causes vibrations in the chain 120 and the load 130 attached thereto, which together form a spring-mass system. The spring-mass system has a natural vibration frequency that depends on both the length of the chain 120 and the mass of the load 130. Since the free length of the chain 120 and the mass of the load 130 may vary in different lifting steps and when the hook load is selected, the natural vibration frequency, which can be called the characteristic frequency, also varies.

[0018] If the natural vibration frequency of the spring-mass system is close to the operating frequency, this can lead to resonance. This resonance can be detrimental because it causes the load to oscillate in an undesirable manner, which can also be dangerous. For example, in the event of difficult vibration phenomena, the chain hoist must be slowed down and the hook load may fall, or the hook load may fall with the chain hoist. It is therefore desirable to be able to prevent the development of such resonances.

[0019] The generation of resonance can be avoided in a variety of ways. In some exemplary embodiments, resonance can be reduced by installing a damper connected to the electric motor, which controls the operation of the electric motor so that the generation of resonance can be avoided. Such a damper can be, for example, part of the control unit, or alternatively can be its own unit.

[0020] In some exemplary embodiments, the development of resonance can be prevented by back coupling, where the speed is continuously adjusted based on force measurement so that the force changes caused by uneven rotation due to changes in chain speed are minimized. However, this requires a fast response so that the minimization can be performed effectively. In order to have a fast response to the back coupling, the device requires more fully effective components, which may increase the cost and size of the required device.

[0021] The chain hoist may further comprise a filter unit, which may be a separate unit or a part of some other unit, such as for example a control unit and / or a variable frequency drive. Figure 1c This is explained so that it shows an example of a control unit 150, which includes a variable frequency drive 152, a measuring unit 154 and a filter unit 156. The filter unit 156 can, for example, perform a high-pass filtering so that the vibration caused by the sprocket can be compared with the force signal F L Separation, the force signal describes the force caused by the load on the chain. In order to receive the force signal F L Any suitable measuring method may be used. The signal describing the vibration obtained from the filter unit 156 may be analyzed in the filter unit 156 or in some other suitable unit, so that the minimum value F of one vibration period may be determined from the filtered signal of the part of the force affecting the chain. min and the maximum value F max The difference F can be calculated based on the minimum and maximum values PeakToPea□ =F max -F min .

[0022] The filter unit 156 can measure the minimum and maximum values ​​of the part of the force affecting the chain for several different vibration cycles, thereby making it possible to observe how the difference between the minimum and maximum values ​​of the force develops during several vibration cycles. This observation can be performed, for example, in the filter unit 156 or in the control unit 150, and it can be implemented, for example, by means of software and memory and one or more processors. If the difference F is observed PeakTiPeak If F starts to increase, it can be inferred that resonance has begun. This inference can be based on, for example, F PeakTiPeak has increased beyond a predetermined limit.

[0023] To avoid the onset of resonance, the control of the motor is adjusted so that the control unit 150 adjusts the speed command of the motor to run the chain hoist. The control unit 150 may also include a variable frequency drive 152. This can be achieved by adding a correction term f to the speed command. corr The speed command thus determines the speed at which the sprocket rotates with the aid of the motor and thus the chain hoist operates. This speed is preferably an angular velocity. When an increased resonance is observed, the correction term f is used to adjust the speed command. corr The speed is adjusted in the negative direction. In other words, avoiding resonance can also be understood as an attempt not to completely damp the vibrations, but as the resonance increases, the operating speed is changed so that when running upwards the speed can, for example, be slowed down, while on the other hand when running downwards the speed can be accelerated. It should still be noted that the increase in speed must be controlled and that acceleration may mean a marginal increase in speed. Avoiding resonance can therefore be understood as either completely avoiding resonance or damping the resulting resonance. An uncontrolled or excessive increase in speed may lead to operating problems. In addition, the chain hoist and its components have a limit speed that must not be exceeded under any circumstances, so the increase in speed must be controlled within the characteristics of the chain hoist. In this way, the change in speed can overcome the resonance. The polygon phenomenon itself is not something that can be avoided, but rather the resonance occurs in each length of the free chain. By using the correction term f added to the speed command corr The advantage obtained is that no separate return coupling device is required, which naturally generates more delays and increases the size of the required device. In addition, the delay of the return coupling weakens the damping effect. There is no such delay for the speed change, because the purpose is not to damp a single vibration, but to change the speed to a speed range where the chain and the load resonate less. In addition, by means of this arrangement, when passing through the resonance point, the movement of the chain can continue at a changed speed, whereby in other words, the system state and the vibration trend change simultaneously due to the change in the free length of the chain. In practice, the correction term may have to be negative. For safety reasons, the correction of increasing speed should probably not be used.

[0024] As mentioned above, the increase in resonance can be based on, for example, F PeakToPeak The limit value may be F on , which is a parameterizable limit value and when this limit value is exceeded, the variable frequency drive (which may be, for example, part of the control unit) starts integrating, for example, in the negative direction. PeakToPeak Again below the parameterizable limit value F off , the variable frequency drive starts integrating in a positive direction, for example.

[0025] Therefore, the correction term f corr This can be determined by:

[0026]

[0027] In the above equation, ja is the gain of the variable frequency drive, t s is the program's operating cycle, and f maxcorr The maximum correction allowed by the correction item. The program operation cycle can be understood as the time describing the time point when the correction item is used.

[0028] Figure 2 An example of an embodiment is shown with the aid of a block diagram. The first box S1 of the block diagram shows a measurement signal, which may also be referred to as a force signal, which describes the force caused by the load on the chain. The measurement may be performed using any suitable measurement method. For example, a device that may be part of or connected to a chain hoist may be used, and the device may include a device for performing the measurement. The device for measuring the force is preferably connected to the measuring unit 154. For example, a variable frequency drive may be a device including a device for measuring the force. The force may be measured, for example, such that the chain hoist includes a separate force sensor, such that the static force of the load suspended in the chain due to gravity is applied to the force sensor. The force sensor is also capable of measuring dynamic forces caused by vibrations. In addition, in some exemplary embodiments, the variable frequency drive may measure the electrical load during lifting according to the magnitude of the rotational torque controlled on the motor shaft by the current through the motor. The load is proportional to the lifting force. The electric motor is preferably an AC motor.

[0029] In box S2, high pass filtering may be performed on the signal. High pass filtering may be performed by any suitable device, which may also include program code and means for executing the program code. The device may be part of some other device and / or part of a chain hoist. Alternatively, the device may be connected to the chain hoist. High pass filtering may be performed in, for example, a variable frequency drive. High pass filtering is from an exemplary embodiment, the purpose of which is a method that can substantially cut equal shares of quantities with different variable values.

[0030] Box S3 shows the minimum and maximum values ​​of the force determined from the vibration period according to the high-pass filtered signal. Based on these values, it is determined in box S4 whether resonance has begun. These determinations can be completed by equipment and program codes suitable for them. The program code can be stored in a memory, and it can be executed by means of one or more processors. The equipment utilized can be part of a chain hoist, part of some other equipment, or connected to another equipment or a chain hoist. The equipment can include, for example, a variable frequency drive.

[0031] If it is determined that resonance has not started, it is possible to move to box S1 again and detection can be continued during lifting or lowering. If it is detected that resonance has started, it is possible to move to box S5. Box S5 shows the determination of the operating speed of the motor causing the sprocket of the chain hoist to rotate. This determination can be done in the control unit or in a separate unit, and it can be done at least in part with the help of program code. If the determination is made in a separate unit, the unit can be part of the chain hoist or it can be connected to the chain hoist. The determination can be performed in a variable frequency drive, for example.

[0032] Figure 3 The results of the measurements as a function of time between 0 seconds and 29 seconds according to an exemplary embodiment are shown, when the chain hoist transmits the load so that the speed does not change (charts 312, 322, 332, marked as "off"), and then so that the speed changes (charts 314, 324, 334, marked as "on"), when it has been determined that resonance has begun. It should be noted that in the measurements and the examples shown ("off / on"), the guidance speed wref is the same before the vibration is detected, and the load mass m is the same. Graph 312 shows the angular velocity of the motor at different points in time. As shown, the speed remains constant or almost constant. Graph 322 shows the chain length at corresponding points in time when the motor causes the sprocket to rotate so that the length of the chain is shortened and the load is thus lifted. Graph 332 shows how the resonance is generated and how the resonance increases at a point of about 20 seconds, whereby, in the vibration system of the chain and the load caused by gravity, the frequency caused by the polygonal chain sprocket is sufficiently close to the characteristic frequency of the vibration system, and the system begins to resonate. This resonance causes the load to oscillate and become unbalanced, which can lead to a hazardous situation and is therefore undesirable.

[0033] Graph 314 again shows the angular velocity of the motor at different points in time when the speed of the motor changes with the onset of resonance. Graph 324 shows the length of the chain when the motor causes the sprocket to rotate so that the length of the chain is shortened and the load is lifted as a result. Graph 334 shows how resonance starts. As can be seen from graphs 314 and 334, when resonance starts, the angular velocity of the motor changes simultaneously or substantially simultaneously. Graph 324 shows the effect of a small change in the angular coefficient at the time point 18-22 seconds due to a reduction in speed. When in other words in graph 314 the speed has been reduced from level 500 to level 400, which is equivalent to a change of approximately -20%, no very significant change occurs in the lifting operation of the chain hoist. Even if the vibration is significantly reduced, this change does not significantly impair the lifting capacity. Therefore, the minimum and maximum points of the vibration remain more moderate than when the speed does not change with the onset of resonance. In the diagrams 312, 322 and 332, the "off" condition is described by the following values: lifting speed wref = 2.46 pu, load mass m = 106 kg, maximum force fp2p during vibration = 5060 N, when the load is 2.45 m above the ground. In other words, in the diagrams 314, 324 and 334, the "off" condition is described by the following values: lifting speed wref = 2.46 pu, load mass m = 106 kg, maximum force fp2p during vibration = 2520 N, when the load is 0.58 m above the ground. In these exemplary embodiments, a halving of the maximum vibration force has been achieved. In addition, the length of the vibration chain moves to different points of length during the maximum vibration, which also shows the good functionality of the exemplary embodiment. In this example, the predetermined limit value is selected so that the difference between the maximum and minimum values ​​of the force is below 2,520, and the regulation is not activated. Of course, setting different parameters for the regulation system will enable damping, even for such a vibration amount. Furthermore, when utilizing this approach, the highest amplitude vibrations may occur in a different chain length than in the "off" state.

[0034] It should also be noted that if the spring constant of the spring-mass system formed by the chain and the load is known in advance, this information can be used and thus a continuously avoidable resonant frequency can be determined based on the chain length and the load. In such an exemplary embodiment, the detection of the onset of resonance based on the difference between the maximum and minimum values ​​of the force during the vibration period can therefore be omitted.

[0035] In some exemplary embodiments, it is not always possible to know in advance the spring constant of the spring-mass system formed by the chain and the load. This may be due to, for example, that the mass of the load varies in different situations, or that the mass is unknown, or that the available chains differ, for example, in their size and / or stiffness. In addition, the chain may wear during use, which may change its characteristics. If the mass of the load being lifted changes during lifting, which may be very unusual, the characteristics and characteristic vibration frequencies of the vibration system may change. For example, when the load being lifted includes a leaking container, the mass of the load being lifted may change. When the chain length is long, the mass of the free chain above the hook load may also have an impact on the total mass being lifted.

[0036] By means of the exemplary embodiment described above, resonances can thus be avoided without requiring further devices for return coupling. In addition, the speed can be changed sufficiently quickly so that resonances can be effectively avoided. By reducing the vibration dynamic forces, the life of the chain hoist can be extended and the lifting load can be prevented from falling. In addition, the load on the overhead structure to which the chain hoist is attached is smaller. It should be noted that the chain hoist can be easily replaced with a new one, but if the overhead structure is damaged, higher repair or reinforcement requirements are required.

[0037] It is also obvious to those skilled in the art that, even though some exemplary embodiments are described above, the present invention can be implemented in various ways, and the present invention is therefore not limited to the examples of the above-described embodiments.

Claims

1. A device, comprising: means for measuring a signal describing the force caused by the load on the chain; means for performing high pass filtering on said signal and for determining a maximum force and a minimum force affecting said chain of a chain hoist during a vibration period, and determining the onset of resonance based on said maximum force and said minimum force; means for detecting the onset of resonance when moving a load via a chain hoist; means for determining a new speed of rotation of a sprocket of the chain hoist such that resonance is avoided, wherein the new speed is determined by adding a correction term to a speed command, and the speed command determines the speed at which the sprocket rotates by means of a motor; and Means for controlling said chain hoist to use said new speed. 2 . The apparatus of claim 1 , wherein resonance is determined to have started when a difference between the maximum force and the minimum force of the vibration period exceeds a predefined limit value.

3. Apparatus according to any one of the preceding claims, wherein the new speed is determined such that the speed is decelerated if the chain lift is travelling upwards and the speed is accelerated if the chain lift is travelling downwards.

4. A chain hoist comprising the device according to any one of claims 1 to 3.

5. A lift, which is an overhead mobile crane, a light lifting system or a jib crane, and which comprises the chain lift according to claim 4.

6. A method comprising: measuring a signal describing the force caused by the load on the chain; high pass filtering the signal and determining the maximum and minimum forces affecting the chain of the chain hoist during a vibration cycle, and determining a start of resonance based on the maximum force and the minimum force; Determine the onset of resonance when moving a load via a chain hoist; determining a new speed of rotation of a sprocket of the chain elevator such that resonance is avoided, wherein the new speed is determined by adding a correction term to a speed command, and the speed command determines the speed at which the sprocket rotates by means of a motor; as well as The chain hoist is controlled to use the new speed. 7 . The method of claim 6 , wherein resonance is determined to have started when the difference between the maximum force and the minimum force of the vibration period exceeds a predefined limit value.

8. The method according to any one of claims 6 to 7, wherein the new speed is determined such that the speed is decelerated if the chain lift is running upwards and the speed is accelerated if the chain lift is running downwards.

9. The method according to any one of claims 6 to 7, wherein the method is performed continuously during raising or lowering of the chain lift.

Images