Chain hoist control

Abstract

A method comprising: detecting the onset of resonance as a chain hoist moves a load; determining a new speed of rotation of a chain wheel of the chain hoist to avoid the resonance; and controlling the chain hoist to use the new speed.

Description

[Technical field]

[0001] The present invention relates to a chain hoist and its control. [Background technology]

[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 may be designed for use in the entertainment industry, for example to realize stage performances. When a load is attached to a device, for example by the device's chain, it is important that the load can be raised and lowered safely. For this reason, it is advantageous that a load supported freely by a hanging chain does not sway or bounce, but remains as stable as possible during the raising and lowering.

[0003] The chain hoist may comprise a chain wheel that may be rotated by an electric motor, which pulls the chain and allows the load attached to the chain to be raised and lowered. The chain comprises links through which forces can be transmitted in the longitudinal direction of the chain. The chain links may include alternating links attached to each other either vertically or horizontally, according to the contact surfaces of the alternating links, recesses in the chain wheel are shaped accordingly. The recesses change the effective diameter of the chain wheel, which imposes a pulsating variable speed on the chain when the chain wheel rotates, for example, at a constant angular speed. The regularly alternating speed of the chain motion can also be seen as an alternating force on the chain. This causes the chain motion to pulsate, which may cause resonances in the chain. If the resonance is strong, it may cause vibrations in the chain hoist, which may be transmitted to the support structure and may cause a dangerous situation during the actual lift. Summary of the Invention

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

[0005] 1. A chain hoist comprising: means for determining the onset of resonance as the chain hoist moves a load; means for determining a new speed of rotation of a chain wheel of the chain hoist to avoid resonance; and means for controlling the chain hoist to use the new speed.

[0006] A method for controlling a chain hoist, the method including determining an onset of resonance as the chain hoist moves a load, determining a new speed of rotation of a chain wheel 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] An example of a chain hoist structure is shown. [Figure 1b] An example of a chain hoist structure is shown. [Figure 1c] An example of a chain hoist structure is shown. [Diagram 2] An exemplary embodiment is illustrated by a block diagram. [Diagram 3] Graphs 312, 322, 323, 314, 324 and 334 are included and show measurement results for an exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The device capable of lifting a load may be, for example, a chain hoist. The chain hoist may comprise a chain, a means allowing to grip the load and attached to the end of the chain, a chain wheel, a motor, and a brake. Some exemplary embodiments may also include a transmission and a control unit capable of controlling the motor. The control unit may also refer to a logic unit, the implementation of which may vary. The control unit may include, for example, a variable frequency drive. Additionally, the chain hoist may have a user interface, by which the operation of the chain hoist may 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.

[0009] The chain hoist may be used such that in some instances it is part of a lifting system that may include, in addition to the chain hoist, for example, an overhead traveling crane, a light lifting system, or a rotating boom crane.

[0010] Figure 1a shows a simplified example of a chain hoist 100. 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 gripping means by which a load 130 may be attached to the chain such that it is suspended from the end of the chain. The gripping means may be one or more attachment mechanisms. For example, a hook may be used as the gripping means.

[0011] The chain hoist housing 110 includes a chain wheel to which a chain 120 is attached, which moves the chain to raise and lower a load. The chain wheel may be rotated by a motor, i.e., a motor is operatively attached to the chain wheel. The motor may be an electric motor, such as, for example, a variable speed motor. The electric motor may be controlled, for example, by a variable frequency drive. The chain hoist housing may also include a transmission and a brake.

[0012] The operation of the chain hoist may be controlled, for example, by a controller coupled to the hoist, the controller comprising buttons for controlling the operation of the chain hoist. The buttons may be used, for example, to raise and lower a load so that a length of chain can be wound up shorter or unwound longer by the chain wheel. This may be done, for example, by rotating the chain wheel, in which case the length of chain between the chain wheel and the load is changed while the load attached to the chain is raised and lowered. Furthermore, the chain hoist may comprise a control unit capable of controlling the operation of the hoist, for example the direction of operation and / or the speed of operation. The chain hoist may also comprise a variable frequency drive, which may be part of the control unit or may be connected to the control unit.

[0013] The chain hoist may be attached by bracket 115. In some exemplary embodiments, the attachment may be by any other suitable method. The chain hoist is capable of lifting loads of various sizes. The loads may be in the weight range of, for example, 100-2,500 kg, although other weight ranges of loads may be lifted and lowered. At a maximum, the loads may be, for example, 5,000 kg or 10,000 kg.

[0014] FIG. 1b shows a chain wheel 140. The chain wheel 140 may be polygonal in shape and include teeth, around which the chain 120 may be attached. The free, unloaded end of the chain, which is not connected to the load to be lifted, may then be lowered into a chain bag or housing, not shown. Thus, the rotation of the chain wheel 140, which may be provided by an electric motor, causes the chain 120 to move upwards or downwards, depending on the direction of rotation of the chain wheel 120. Thus, the load 130 can be either raised or lowered.

[0015] Due to its polygonal shape, when the chain wheel rotates, its angular velocity remains constant or essentially constant, but its linear velocity changes. This so-called polygonal phenomenon induces vibrations in the chain 120 and the attached load 130, which together form a spring-mass system. This spring-mass system has a natural frequency that depends on both the length of the chain 120 and the mass of the load 130. As the free length of the chain 120 at different climbs and the mass of the load 130 when selecting the hook load may change, the characteristic frequency, which may be called the natural frequency, also changes.

[0016] If the natural frequency of the spring-mass system is close to the operating frequency, this can cause resonance. This resonance can be harmful as it causes the load to swing in ways that are undesirable and can be dangerous. For example, in difficult vibration events, the use of a chain hoist must be slowed down, the hook load may fall, or the hook load may fall along with the chain hoist. It is therefore desirable to be able to prevent such resonance from occurring.

[0017] The occurrence of resonances can be avoided in a number of ways. In some exemplary embodiments, resonances may be reduced by placing a damper in association with the electric motor, which controls the operation of the electric motor such that the generation of resonances may be avoided. Such a damper may be, for example, part of the control unit, or alternatively may be a unit in its own right.

[0018] In some exemplary embodiments, the occurrence of resonance may be prevented by a back coupling, where the speed is continuously adjusted based on the 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 in order to be able to perform the minimization effectively. To have a fast response for the back coupling, the device requires more fully effective components, which may increase the cost and size of the device required.

[0019] The chain hoist may also comprise a filter unit, which may be a separate unit or may be part of other units, such as for example a control unit and / or a variable frequency drive. Fig. 1c illustrates this by showing an example of a control unit 150 including a variable frequency drive 152, a measurement unit 154 and a filter unit 156. The filter unit 156 may for example perform high pass filtering, so that the vibrations caused by the chain wheels are filtered out of the force signal F, which represents the force caused by the load on the chain. L The force signal F L Any suitable measurement method can be used to receive F . The signal representative of 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 from the filtered signal is determined for the portion of the force acting on the chain. min and maximum value F max It is possible to determine the difference F PeakToPeak =F max -Fmin may be calculated from the minimum and maximum values.

[0020] The filter unit 156 can measure the minimum and maximum values ​​of the force portion affecting the chain for several different vibration periods, so that it is possible to observe what kind of evolution occurs in the difference between the minimum and maximum force values ​​during several vibration periods. This observation can be performed for example in the filter unit 156 or in the control unit 150, and can be implemented for example by software and a memory and one or more processors. The difference F PeakToPeak If it is observed that F begins to increase, it can be inferred that resonance has begun. This inference can be made, for example, by PeakToPeak may be based on an increase in the

[0021] To avoid initiated resonance, the control of the motor is adjusted such that the control unit 150 adjusts the command for the speed at which the chain hoist is operated by the motor. The control unit 150 may also include a variable frequency drive 152. The command includes a correction term f that is added to the speed command. corr The speed command is thus a determination of the speed at which the chain wheel is rotated by the motor and thus the chain hoist is operated. The speed is preferably an angular velocity. When resonance is observed to intensify, i.e. to increase, the speed is adjusted by a correction term f corrIn other words, the avoidance of resonance can also be understood as not trying to completely damp the vibrations, but rather that as the resonance increases, the operating speed is modified so that when operating upwards the speed can for example be slowed down, while when operating downwards the speed can be accelerated. It should also be noted that the increase in speed must be controlled, and that an acceleration can mean a slight increase in speed. The avoidance of resonance can therefore be understood as either completely avoiding resonance or damping the resonance that occurs. An uncontrolled or excessive increase in speed can cause problems in operation. Furthermore, the chain hoist and its components have limit speeds that cannot be exceeded under any circumstances, and therefore the increase in speed must be controlled within the characteristics of the chain hoist. In this way, it is possible to overcome the resonance by a change in speed. The polygon phenomenon itself is not avoided, but the resonance occurring in each length of the free chain is avoided. The correction term f added to the speed command corr The advantage of using is that a separate return link device is not needed, which naturally creates more delay and increases the size of the device required. Additionally, delays in the return link weaken the effect of damping. There is no such delay in the change of speed, since the objective is not to damp a single vibration, but instead to shift the speed to a speed range where the chain and load are less resonant. Additionally, this configuration allows the chain motion to continue at a modified speed as it passes through the resonance point, thereby equivalently changing the state of the system and the vibration tendency at the same time with the change in the free length of the chain. In practice, the correction term may have to be negative. A correction that increases the speed may not be used for safety reasons.

[0022] As mentioned above, an increase in resonance may occur, for example, when F increases beyond a certain limit. PeakToPeak This limit may be determined based on F onF , which is a parameterizable limit value beyond which, for example, a variable frequency drive, which may be part of the control unit, starts to integrate, for example, negatively. PeakToPeak is again a parameterizable limit value F off If the input voltage Vcc falls below 0.5 V, the variable frequency drive may begin to integrate, for example, in a positive direction.

[0023] Correction term f corr may therefore be determined as follows:

[0024]

number

[0025] In the above formula,

[0026]

number

[0027] FIG. 2 shows an exemplary embodiment by means of a block diagram. The first block S1 of the block diagram indicates measuring a signal, which may be called a force signal, which represents the force caused by the load on the chain. This measurement may be performed with the aid of any suitable measurement method. For example, it is possible to use a device that may be part of the chain hoist or that may be connected to the chain hoist, which device may comprise the means for performing the measurement. The means for measuring the force are preferably connected to the measurement unit 154. For example, a variable frequency drive may be the device that comprises the means for measuring the force. The force may be measured, for example, if the chain hoist includes a separate force sensor, such that the static force of the load suspended by the chain by gravity is applied to it. The force sensor may also be capable of measuring dynamic forces caused by vibrations. Furthermore, the variable frequency drive may, in some exemplary embodiments, measure the electric load during the lift from the magnitude of the rotational moment controlled on the motor shaft from the motor's current. This load is proportional to the lift force. The electric motor is preferably an AC motor.

[0028] In block S2, high pass filtering may be performed on the signal. The high pass filtering may be performed by any suitable device, which may also include a program code and a means for executing the program code. This device may be part of another device and / or part of the chain hoist. Alternatively, the device may be connected to the chain hoist. The high pass filtering may be performed for example in a variable frequency drive. The high pass filtering is from an exemplary embodiment, the purpose of which is a way to be able to substantially cut off equal shares of the amount with different values ​​of the variable.

[0029] Block S3 shows determining minimum and maximum force values ​​from the vibration period from the high pass filtered signal. Based on these, in block S4 it is determined whether resonance has started. These determinations may be made by suitable apparatus and program code. The program code may be stored in a memory and executed by one or more processors. The apparatus utilized may be part of a chain hoist, part of another apparatus, or may be connected to another apparatus or to a chain hoist. The apparatus may comprise, for example, a variable frequency drive.

[0030] If it is determined that resonance has not started, it is possible to move to block S1 again, and detection may be performed continuously during ascent or descent. If it is detected that resonance has started, it is possible to move to block S5. Block S5 illustrates determining the operating speed of a motor that rotates a chain wheel of the chain hoist. The determination may be performed in the control unit or a separate unit, and may be performed at least in part by program code. If the determination is performed in a separate unit, the unit may be part of the chain hoist or may be connected to the chain hoist. The determination may be performed, for example, in a variable frequency drive.

[0031] FIG. 3 shows measurements from an exemplary embodiment as a function of time from 0 to 29 seconds as the chain hoist transports a load with the speed unchanged (charts 312, 322, 332, note off) and then with the speed changed when it is determined that resonance has begun (charts 314, 324, 334, note on). Note that in the measured and shown example (off / off), the guideline speed wref is the same as before detecting vibration and the load mass m is the same. Chart 312 shows the angular velocity of the motor at different times. As can be seen, the speed remains constant or nearly constant. Chart 322 shows the chain length at the corresponding times as the motor rotates the chain wheel such that the length of the chain is shortened and therefore the load is lifted. Graph 332 shows how resonance occurs and increases at about 20 seconds, whereby in the gravity induced vibration system of the chain and load, the frequency produced by the chain wheel of the polygonal shaped chain becomes close enough to the characteristic frequency of the vibration system that the system begins to resonate, which can cause the load to swing out of balance, creating a dangerous situation and is therefore undesirable.

[0032] Chart 314 again shows the angular velocity of the motor at different times when the speed is changed due to the onset of resonance. Chart 324 shows the chain length as the motor rotates the chain wheel such that the length of the chain is shortened and therefore the load is lifted. Chart 334 shows how resonance begins. As can be seen from charts 314 and 334, the angular velocity of the motor changes at or substantially the same time as resonance begins. Chart 324 shows the effect of the speed reduction as a small change in the angular coefficient at time 18-22 seconds. Similarly, in chart 314, when the speed is reduced from level 500 to level 400, which equates to a change of about -20%, no significant change occurs in the lifting behavior of the chain hoist. This change does not significantly weaken the lifting ability even though the vibration is significantly reduced. Thus, the vibration minima and maxima remain more gradual than if the speed was not changed as resonance begins. In charts 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 during vibration fp2p=5060 N, when the load is at a height of 2.45 m above the ground. Similarly, in charts 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 during vibration fp2p=2520 N, when the load is at a height of 0.58 m above the ground. In these exemplary embodiments, a halving of the maximum vibration force is achieved. Additionally, the length of the vibrating chain is shifted to a different point in length at maximum vibration, which also shows the good functionality of the exemplary embodiment. The predetermined limit value was selected in this example such that the difference between the maximum and minimum force values ​​is less than 2,520 N and the regulation is not activated. Of course, by setting different parameters in the regulation system, damping can also be produced for this vibration amount. Furthermore, the maximum amplitude of vibration may occur at a different chain length when utilizing this method than in the OFF state.

[0033] 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 utilized and thus the avoidable resonant frequency can be determined continuously based on the chain length and the load. Thus, in such an exemplary embodiment, it is possible to omit the detection of the onset of resonance based on the difference between the maximum and minimum force values ​​during the vibration period.

[0034] 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, for example, to the mass of the load changing in different situations, or the mass being unknown, or the available chains having, for example, different sizes and / or stiffness. Additionally, the chain may wear during use and change its characteristics. If the mass of the load being lifted changes during the lift, which is very unusual, the characteristics and characteristic frequencies of the vibration system may change. The mass of the load being lifted may change, for example, when the load being lifted includes a leaking container. With long chain lengths, the mass of the free chain above the hook load may also create a variable factor that affects the total mass being lifted.

[0035] Therefore, by the above exemplary embodiment, it is possible to avoid resonance without needing additional devices for return coupling. Additionally, the speed may be changed quickly enough so that resonance can be effectively avoided. By reducing the oscillating dynamic forces, it is possible to extend the life of the chain hoist and avoid the drop of the load being lifted. Furthermore, the overhead structure to which the chain hoist is attached is subjected to a smaller load weight. It is noted that the chain hoist can be replaced with a new one very easily, whereas the overhead structure requires more effort to repair or reinforce if damaged.

[0036] In addition, although several exemplary embodiments have been described above, it will be apparent to those skilled in the art that the present invention can be implemented in various ways, and therefore the present invention is not limited to the example embodiments described above.

Claims

1. An apparatus comprising: means for measuring a signal representative of a force caused by a load on the chain; means for performing high pass filtering on the signal to determine maximum and minimum forces acting on the chain of a chain hoist during a period of oscillation and for determining an onset of resonance based on the maximum and minimum values; means for detecting the onset of resonance as a load is moved by the chain hoist; means for determining a new speed of rotation of a chain wheel of the chain hoist such that resonance is avoided, the new speed being determined by adding a correction term to a speed command and such that the speed is decreased when the chain hoist is operated upward and the speed is increased when the chain hoist is operated downward, the speed command determining the speed at which the chain wheel is rotated by the electric motor; and means for controlling the chain hoist to use the new speed.

2. 2. The apparatus of claim 1, wherein resonance is determined to have begun when the difference between the maximum and minimum values ​​of the vibration period exceeds a predetermined limit value.

3. A chain hoist comprising a device according to claim 1 or 2.

4. A hoist, which is an overhead traveling crane, a light lifting system, or a rotating boom crane, comprising the chain hoist of claim 3.

5. 1. A method comprising: Measuring a signal representative of a force caused by a load on the chain; performing high pass filtering on the signal to determine maximum and minimum forces acting on the chain of a chain hoist during a period of oscillation and determining an onset of resonance based on the maximum and minimum values; determining an onset of said resonance when a load is moved by a chain hoist; determining a new speed of rotation of a chain wheel of the chain hoist such that resonance is avoided, the new speed being determined by adding a correction term to a speed command and such that the speed is decreased when the chain hoist is operated upward and the speed is increased when the chain hoist is operated downward, the speed command determining the speed at which the chain wheel is rotated by the electric motor; and controlling the chain hoist to use the new speed.

6. 6. The method of claim 5, wherein the onset of resonance is determined when the difference between the maximum and minimum values ​​of the vibration period exceeds a predetermined limit value.

7. The method according to claim 5 or 6, wherein the method is implemented continuously during raising or lowering of the chain hoist.

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