EP0841298B1 - Control arrangement with detection of the weight of the load - Google Patents

Description

In the case of hoists, extremely dangerous situations can occur for people and material if the hook or the load hanging from it gets stuck on any fixed parts when lifting the hoist. The process is abruptly fast and the crane operator's reaction time is not enough to prevent this from causing dramatic system overloads. For this reason, the hoist is equipped with sensors and a control device, which should automatically stop the lifting movement as soon as such a danger is detected.

The longer the reaction time of the system as a whole, ie the more time passes between the recognition that a certain load limit is exceeded, and the stoppage of the drive motor, the greater is the additional force increase occurring after exceeding the load limit. More detailed considerations show that at the normal stroke speed the largest energy of the system is stored as kinetic energy in the armature of the drive motor. The there after switching off the motor current contained energy is up to 80% of the total kinetic energy in the system. To prevent this, the speed should be reduced as quickly as possible when a stuck hook threatens. For this purpose, it is necessary to know the weight of the load incl. The weight of the rope to have a variable limit, which allows early decision.

From DE-20 58 712 C3, which represents the closest prior art, an overload protection for a hoist is known, which is effective only when lifting the load from the pad. When the crane operator or operator of the hoist wants to lift the load off the ground at the main hoisting speed, the hoist first moves at the rated hoisting speed to quickly tighten the rope. As soon as the measuring device detects a cable force of about 20% of the rated load on the hoist, it automatically switches over from the main course to the feeder and blocks the main hoisting speed. The blocking of the main lifting speed remains available until it is ensured that there is no overloading of the hoist. If there is any snagging during the lifting of the load or the load is heavier than the allowable rated load, the cable force will exceed a second limit, which is approximately 110% of the rated load, and the hoist will be shut down. It can then be set in motion only in the direction of sinks.

By using the fine stroke after the rope tightening, dramatic overloading of the hoist can only be avoided when starting the load because the kinetic energy is small. However, should the load become caught during the lifting movement, the machine will operate at the main lifting speed, ie at high speed, which will cause the problems described above. A variable limit is not described.

The known from DE-29 30 439 C2 method for controlling a hoist uses the time derivative of the cable force to determine whether an overload can occur when lifting the load. As soon as the increase in the cable power is too great, it is switched over to the feeder when lifting.

A time-derivative system is very sensitive to disturbances, both to perturbations that seem to simulate too fast a rise and perturbations that simulate the opposite direction.

Based on this, it is an object of the invention to provide a drive and control system for lifting equipment, which is able to determine when lifting a load extremely fast their weight, if necessary, plus the weight of the rope.

This object is achieved by the drive and control system with the features of claim 1.

The new drive and control system is able to detect very quickly whether the load is raised and what weight it has. This quick response is made possible because the new drive and control system is self-adaptive and automatically adjusts a variable upper limit as the cable force increases. Descending or adjusting the upper variable limit stops automatically when the load hangs freely on the rope, even if longitudinal vibrations in the rope have been induced by the tearing of the load. Thus, the limit is available almost simultaneously with the floating state of the load. It There is no need to use timers that push the load far into the future to make sure that even a long rope has been tightened and the vibrations have subsided.

If, in a purely temporally operating method, no sufficiently long pause would be provided between the switching on of the drive motor and the determination of the load signal, induced vibrations could lead to errors. It only needs to be assumed that the pause has expired at a time when the load on the free rope is swinging straight up, resulting in a smaller load signal. The control system would read this value, which is below the true weight of the load, and thus immediately fall into the overload case at the next half wave of the oscillation leading to the emergency shutdown.

To avoid this, in a purely temporal system, the length of the break would have to be set for the worst case scenario. This most unfavorable case is at maximum length of the rope and the rated load. In these conditions, the swinging or lulling of the load takes the longest time, measured from the initial tightening of the rope to the sufficient decay of the rope vibrations.

In the new method, such a long dead time does not occur. The system already operates safely if, after the last time the variable limit has been exceeded and its tracking has been passed, a time has elapsed which is slightly longer than one oscillation period of the rope oscillation. This time span is significantly shorter than the aforementioned required break in time-dependent systems. It suffices, this maximum oscillation period to wait to decide that now the load is raised and in the future no load signals will appear which are greater than this now reached variable upper limit. Unless the load gets stuck somewhere.

Depending on how the hoist is dimensioned and which vibration amplitudes are to be expected, it is sufficient to record the upper variable limit thus determined and to use it as a future reference value for overload measurements.

However, if the expected vibrations have a larger amplitude and an exact match is needed between the upper variable limit and the true weight of the load, it may be necessary to additionally introduce a variable lower limit. This is adjusted upwards as long as the variable upper limit is exceeded. Only if no exceeding of the variable upper limit value takes place can the lower value of the lower variable limit value be evaluated in the sense of a reduction of both the lower variable limit value and the upper variable limit value. Thus, with some delay, the upper and lower limits follow the oscillating load signal until the amplitude of the oscillations fall within the band set between the upper and lower variable limits.

The system can not know whether, after the last correction of either limit, it is very close to the current magnitude of the load signal. In order to avoid disturbances here, it may be expedient, after the expiry of the specified time, to increase or decrease the variable upper limit value and / or the variable lower limit value by a small incremental value expand, ie slightly increase the distance between the two limits.

Moreover, further developments of the invention are the subject of dependent claims.

• Fig. 1 einen Seilzug gemäß der Erfindung, in einer perspektivischen Schemazeichnung,
• Fig. 2 das elektrische Blockschaltbild.für die Steuerungseinrichtung des Seilzugs nach Fig. 1 und
• Fig. 3 einen Ausschnitt aus einem Flußdiagramm des Steuersystems nach Fig. 2 und
• Fig. 4 ein Diagramm zur Veranschaulichung des Kraftverlaufs und der Änderung der variablen Grenzwerte mit der Zeit.

In the drawing, an embodiment of the object of the invention is shown. Show it:

• 1 is a cable according to the invention, in a perspective schematic drawing,
• Fig. 2 shows the electrical Blockschaltbild.für the control device of the cable according to Fig. 1 and
• Fig. 3 is a detail of a flowchart of the control system of FIG. 2 and
• 4 shows a diagram for illustrating the course of force and the change of the variable limit values with time.

Fig. 1 shows a schematic perspective view of a cable 1 with a stored in a frame 2 cable drum 3. From the cable drum 3 runs from a rope 4, which leads to a hook block 5 and from there back to an anchoring point 6 in the frame. On the hook block 5 hangs a load. 7

In order to set the cable drum 3 in turns, an electric motor 8 is flanged to the frame 2, which is preferably a three-phase motor with squirrel-cage rotor. The control of the motor 8 is done via a schematically indicated control arrangement 9, which is housed in a unfolded drawn control box 11. On the control device 9, a handset or hanging button 13 is connected via a suspension cable 12, which serves as an input device.

The hanging button 13 has two manually operated push buttons 14 and 15, which serve to control the movement of the cable drum 3. For example, by slightly depressing the push button 14 to a pressure point, the cable drum 3 in the sense of raising the load 7 at a slow speed (Feingang) set in motion. If the push button 14 is actuated beyond the pressure point, the lifting of the load 7 takes place at an increased speed (main lifting speed). The same applies mutatis mutandis to the push button 15, which controls the downward movement.

As shown in FIG. 2, the control arrangement 9 is based on a microprocessor 16, ie with the push buttons 14 and 15 are not controlled motor contactors directly, but the coming of these push buttons 14, 15 signals enter the microprocessor 16, which in turn according to switching or Motor contactors of a power supply 17 is driving. The microprocessor 16 takes over the entire function monitoring of the hoist. 1

The power connections to the network or the power supply for the microprocessor 16 are not shown in Fig. 2 for the sake of clarity, since they contribute nothing to the understanding of the invention.

To an input 18 of the microprocessor 16 via the control cable 12, the pendant switch 13 is connected. An output 19 of the microprocessor 16 is connected to a control input 21 of the power supply device 17. This includes in the simplest case motor contactors to set the drive motor 8, which is connected via lines 22 to an output 23 of the power supply device 17, either in the two directions of rotation with different speeds in motion. The drive motor 8 is a pole-changing three-phase motor with squirrel cage rotor, which has the property of braking electrically when switching from the low number of poles to the high number of poles, ie when switching from the high speed to the low speed.

Instead of the combination of contactors and a pole-changing asynchronous motor, a frequency converter can be used in conjunction with a three-phase asynchronous motor with a fixed number of pole pairs. When the engine speed is reset, the same braking effect will occur if the frequency converter is set up accordingly. In this case, either the energy is fed back into the power grid or destroyed in braking resistors.

An armature shaft 24 of the drive motor 8 is coupled to a mechanical brake device 25 and drives the cable drum 3 via a housed in the cable drum 3 Planetary gear.

To the mechanical braking device 25 includes a rotatably coupled to the armature shaft 24 brake disk 26 and a pair of pliers on this attacking brake shoes 27 which can be applied via a schematically indicated actuator 28 to the brake disc 26 and with the aid of the brake shoes 27 can be released. The brake actuator 28 has a control input 29 which is connected via a line 31 to an output 32 of the microprocessor 16.

In order to prevent that a mechanical overload of the hoist 1 is due to an excessive hook load, a cable force sensor 33 is provided which emits an electrical signal proportional to the cable force at its output 34.

The rope force sensor 33 can be designed in different forms. It may be a load cell, which is arranged at the fixed anchoring point 6 between the traction cable 4 and the frame 2. However, the cable force sensor 33 can also be arranged in the suspension of the hoist 1 in order to measure or weigh the weight of the hoist 1 together with the load hanging thereon. Finally, it is also conceivable to use as a cable force sensor 33, a force measuring device which measures an axial force on an axis within the reduction gear between the drive motor 8 and the cable drum 3 and makes use of it that with helical gears a dependent on the transmitted torque axial force. In all cases, the rope force sensor 33 provides at its output 34 a signal indicative of the value of the load 7 hanging on the hook 5. Specifically, this value also includes the variable weight of the extended one Rope, which is generally negligible. This electrical load signal passes through a connecting line 35 directly and thus virtually unswept and instantaneously in an input 36 of the microprocessor 16th

Fig. 3 illustrates in the form of a flow chart that program part which runs in the microprocessor 16 and serves to determine the hook load or the weight of the lifted load 7, including the weight of the cable 4.

The program section shown in Fig. 3 is only passed through the first time a load, but not when the already floating load is stopped and restarted, regardless of whether up or down.

The program is reached at 41 from the main program. Next, it is next checked at 42 whether the load signal F supplied by the load sensor 33 is greater than a lowest fixed reference value Ref ₁ . This reference value Ref ₁ is set very low and corresponds to the newly tightened cable 4. It is about 10% of the rated load of the hoist 1. If the program determines that the load signal F is below the limit value Ref ₁ , becomes a block instruction 43th branches, in which an upper variable limit value Ref ₂ and a lower variable limit value Ref _{3 are set} to their respective lowest values K1 and K2. Then the program piece according to FIG. 4 at 44 is again left in the direction of the main program until it is jumped back from the main program at 41. The drive motor 8 runs with the speed selected by the user via the pendant button.

If it is found at the branch point 42, however, that the load signal F is greater than the lower limit value Ref ₁ , it is concluded from a tightening of the rope 4 and the lifting process for the load begins. In order to avoid unnecessary vibrations in the cable 4 and the Aufglager for the hoist 1 when loosening the load 7 and to stop very quickly in the event of an overload again, irrespective of the input via the pendant switch 13 desire for lifting speed inevitably in a subsequent instruction block 45 at the power supply device 17 is given a command that resets the speed of the drive motor 8 to the Feinhubgeschwindigkeit or lowest stroke speed v _fine . This ensures that now the further tightening of the rope 4 is continued at the lowest speed.

Then it is checked at a branch point 46, whether the load signal F is greater than the current value of the upper variable limit value Ref ₂ . If so, in a subsequent instruction block 47, both the variable upper limit value Ref ₂ and the variable lower limit value Ref _{3 are} respectively increased by an incremental value Δ. Furthermore, a clock is started on its start value.

The instruction block 47 is not executed when the load signal remains smaller than the upper variable limit value Ref ₂ .

In any case, it is then checked at a branch point 48 whether the load signal F is above or below the lower variable limit value Ref ₃ . If the lower limit value is undershot, in the instruction block 49 the upper variable limit value Ref ₂ and the lower variable limit value Ref ₃ are reduced by the incremental value Δ. In addition, the clock is reset to the initial value and restarted.

The program then proceeds to a branch point 51, at which it is checked whether the clock, because the instruction blocks 47 and 49 were skipped, meanwhile displays a time value which is greater than t _G. This time period t _G is slightly greater than the worst case period of oscillation of the load 7 on the cable 4. If this time limit t _{G is} not exceeded, the program returns to the input of the instruction block 45 to resend the checks at the branching points 46 and 48, so that the variable limit values Ref ₂ and Ref ₃ are corrected as the case may be.

If the test at branch point 51 is positive, ie the clock has not been reset for a time greater than t _G , the program interprets this as meaning that the cable oscillations have decayed so far that the resulting fluctuations in the load signal F within the band, which is bounded above by the current value of the upper variable upper limit Ref ₂ and down by the current value of the lower variable limit Ref ₃ .

Since it may be that, for example, the currently achieved value of the upper variable value Ref _{2 is} only slightly above the true value of the load signal F at static load, it is expedient if, following the branch point 51 in the instruction block 52 then the upper variable Limit value Ref _{2 is} increased by a fixed small incremental value a. The upper limit now reached after the instruction block 52 may be referred to as Reference value are used in order to decide on further operation, whether an operating situation has occurred, which makes it advisable to switch to safety for reasons in the low speed.

In the event that the lower limit is used to detect excessive vibrations that make it seem advisable to switch the operation of the hoist, for example, because very large vibration amplitudes have been created by jogging, the lower variable limit Ref ₃ by a small Increment a be reduced, so that under unfavorable conditions, a sufficient distance to the idle state of the load signal F is achieved.

When the instruction block 52 is reached, it is clear that the load 7 is swinging freely on the hook, so that now, when there are no other conditions prohibiting switching to the higher speed, it can be upshifted to the user desired speed. For this purpose, it is checked at a branching point 53 whether the desired stroke speed v _soll desired by the user _is equal to the fast stroke speed v _fast . If so, in a block 53, the stroke speed V is _quickly switched to the fast stroke speed v. After leaving the instruction block 53 or in the case of a negative exit of the check at the branch point 52, the program part is left at 54 in the main program.

The program section shown shows the parts essential for understanding. Any required holding patterns and the check for exceeding the overload limit have been omitted for the sake of clarity.

The behavior of the program is explained below with reference to FIG. 4:

It is assumed that at time t _0, the load 7 is attached to the floppy rope 4 and the user via the button 14, the fast lifting speed v _quickly request the cable 1. The rope 4 is tightened very quickly and then stretched with a steep gradient.

At time t ₁ , the load signal F delivered by the load sensor 63 exceeds the lower fixed limit value Ref ₁ , which is interpreted as an indication that a sufficient tension has built up in the cable 4 and further operation with the fast main lift speed is not appropriate. At the time t ₁ , the control circuit 9 therefore switches the power supply device 17, so that subsequently the motor 8 only works _fine with the slow fine lifting speed v.

Since previously the condition F <Ref _{1 was} not met, the two variable limits Ref ₁ and Ref ₂ were respectively reset to their initial values K1 and K2. Because of the switch back to the slow speed, the load signal F will rise less steeply from the time t ₁ .

At the instant t ₂ , the load signal F will for the first time become greater than the upper variable limit value Ref ₂ still sitting at its start value, which is then increased by Δ at the instant t ₂ as well as the lower variable limit value Ref ₃ . This process of exceeding Ref ₂ and increasing Ref ₂ and Ref ₃ will be repeated several times until time t ₈ . Until then, the program will execute the instruction block 47, but skip the instruction block 49. At the same time, the clock is always reset to the initial value.

What the control circuit 9 can not know yet, but results from the further course of the load signal F, a situation had already occurred here in which the load 7 had lifted off the ground and a rope oscillation was induced. Accordingly, at time t _9, the check at 46 is negative, ie the instruction block 47 is skipped. On the other hand, the check at instruction block 48 is positive, because the load signal F is now for the first time smaller than that in synchronism with the variable upper limit value Ref ₂ with the upper limit value Ref _{3 set} higher. Therefore, the instruction block 49 is executed, and both the lower variable limit value Ref ₃ and the upper variable limit value value Ref ₂ are decreased by Δ. This means that in the course of the load signal F, although no longer falls below the currently set value of the variable lower limit Ref ₃ , but at time t ₁₀ the opposite at time t ₈ reduced upper variable limit Ref ₂ . The result of this in the program is that the instruction block 47 is no longer executed, but rather the instruction block 47 is executed. In the case of the selected course of F, this leads to the fact that the upper variable limit value Ref _{2 is} again set to the value that it once had at time t ₈ . The same applies to the lower variable limit Ref ₃ .

Since the oscillation has not yet decayed sufficiently, the lower variable limit value Ref _{3 is again} undershot even at time t ₁₁ , with the result that the two variable limit values Ref ₂ and Ref _{3 are} again reduced by Δ in the instruction block 49.

After the time t ₁₁ , the value of F remains smaller than the now-tracked upper variable limit value Ref _{2, in} spite of the vibrations still present F remains greater than the current value of the lower variable limit Ref ₃ . The result is that the clock is no longer reset and the loop between the instruction block 45 and the instruction block 52 is no longer run until F becomes smaller again than the reference value Ref ₁ which corresponds to the discontinuation of the load 7.

As can be seen, the upper variable limit value Ref _{2 is} adjusted practically simultaneously with the sufficient decay of the cable vibrations after lifting the load 7. As mentioned, for safety reasons, the values of the two variable limit values Ref ₂ and Ref ₃ can now be changed in the sense of increasing the bandwidth. The system does not need to work with a break time that takes into account the worst case load and is decidedly too long for normal operation. The system is able to work very fast again with the full lifting speed, because the steady state is a maximum of one period after the last time one of the limit values Ref ₂ , Ref _{3 is} also exceeded in steady state stability.

How exactly the upper or lower variable limit Ref ₂ or Ref ₃ agrees with the true weight F depends on how large the distance between these two variable limits Ref ₂ and Ref _{3 is} selected. The smaller the bandwidth, the more accurate the two variable thresholds Ref ₂ and Ref ₃ coincide with the true signal F. In practice, it has been found that a distance between the two variable limits Ref ₂ and Ref ₃ of about 3-4% of the rated load allows a very accurate measurement.

A hoist is provided with a control system at during the lifting of the load of the pad dynamically retraced an upper limit until the detected by the control system load signal for the first time does not exceed this stepwise increased limit. Subsequently, it is checked whether, as a result of vibrations, a stepwise entrained lower limit value is undershot. If this is not the case, the limit values remain at the current value, otherwise they are gradually reduced and increased again until the load signal remains between the two limits. Thus, the system can adjust very quickly to any load and is practically in the steady state with the lifting of the load and the subsequent decay of the rope oscillation, which means that the limits are reliably set and can be trusted.

Claims (13)

1. Drive and control system (9) for a hoist (1) having a load suspension means (4, 5),
   with a drive motor (8) for moving the load suspension means (4, 5),
   with a power supply means (17) for the drive motor (8), to which the drive motor (8) is connected and which has control inputs (21),
   with a sensor arrangement (33) to detect force acting on the load suspension means (4, 5) and to emit a load signal (F) identifying the magnitude of the force,
   with an input device (19) for controlling the drive motor (8) and
   with a control circuit (16) connected to the input device (13), into which the load signal (F) from the sensor arrangement (33) is fed,
   characterized in that the control circuit (16) contains control programm
   in which a variable upper limit (Ref₂) for the load signal is made available,
   which (i) compares the load signal (F) with the variable upper limit (Ref₂),
   which (ii) increases the upper limit (Ref₂) when the variable upper limit (Ref₂) is exceeded by the load signal (F) and
   which repeats steps (i) and (ii) until the load signal (F) remains smaller than the variable upper limit (Ref₂) for a fixed time (t_G).
2. Drive and control system according to Claim 1, characterised in that the variable upper limit (Ref₂) is respectively increased by a constant amount.
3. Drive and control system according to Claim 1, characterised in that a fixed limit (Ref₁) is made available in the program, and that steps (i) and (ii) are only performed once the load signal (F) has fallen below the fixed limit (Ref₂) after the fixed time (t_G) has elapsed.
4. Drive and control system according to Claim 1, characterised in that a variable lower limit (Ref₃) is made available in the program for the load signal (F), and that each time the variable upper limit (Ref₂) limit is increased, the variable lower limit (Ref₃) is also increased.
5. Drive and control system according to Claim 1, characterised in that the variable lower limit (Ref₃) is respectively increased by a fixed amount (Δ).
6. Drive and control system according to Claim 1, characterised in that the variable lower limit (Ref₃) and the variable upper Limit (Ref₂) have a fixed interval between them.
7. Drive and control system according to Claim 1, characterised in that the fixed interval between the variable lower limit (Ref₃) and the variable upper limit (Ref₂) lies between 2% and 20% of the nominal load of the hoist (1).
8. Drive and control system according to Claim 4, characterised in that (iii) the load signal (F) is compared with the variable lower limit (Ref₃), that (iv) when the load signal (F) falls below the variable lower limit (Ref₃) the lower limit (Ref₃) is reduced, and that steps (iii) and (iv) are repeated until the load signal (F) remains larger than the variable lower limit (Ref₃) for a fixed time (t_G).
9. Drive and control system according to Claim 1 or 8, characterised in that the fixed time (t_G) amounts to between 0.2 seconds and 5 seconds.
10. Drive and control system according to Claim 1, characterised in that after the fixed time (t_G) has elapsed, the upper variable limit (Ref₂) is increased by a given value and/or the lower variable limit (Ref₃) is reduced by a given value.
11. Drive and control system according to Claim 1 or 8, characterised in that the drive motor (8) can be operated at at least one high and at least one low speed.
12. Drive and control system according to Claim 11, characterised in that the program blocks the high speed irrespective of the input via the input device (13) at least until the fixed time (t_G) has elapsed.
13. Drive and control system according to Claim 11, characterised in that when a movement of the load suspension means (4, 5) is called for via the input device (13), the program automatically switches over the drive motor (8) to a low speed after the variable upper limit (Ref₂) has been exceeded by the load signal (F).

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