A crane grab control method in poor visibility environment

Abstract

The present invention discloses a crane grab control method in an environment with poor visibility, including: S1. opening the lifting mechanism, the grab descends at the same speed, and the grab continues to descend if it does not touch the material surface; S2. During the grab's descent process, the grab automatically stops descending if it has touched the material surface; S3. When the grab contacts the material surface, the lifting mechanism is automatically stopped, and the grab is controlled to automatically sink; S4. After the bucket is closed, the lifting mechanism is opened, the grab rises at the same speed, and unloading is completed after it rises to the right position. The present invention realizes the control of the crane grab in an environment with poor visibility. It only needs to utilize the characteristics of the permanent magnet synchronous motor. The existing grab crane does not need to be modified, and no additional detection devices are required (there is no need to add absolute value encoders, torque sensors, high-precision electronic scales, high-echo laser scanners, fog-penetrating cameras and other devices that traditional solutions need to add). By judging the output current of the lifting and opening and closing frequency converters, the automatic lowering function is realized if the material surface is not touched, the automatic stopping function is realized if the material surface is touched, the grab amount is controlled, the automatic deceleration and stop of the descent is realized, the automatic sinking of the grab is controlled, and the automatic load balancing of the grab is controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of grab cranes, and in particular relates to a crane grab bucket control method in an environment with poor visibility. Background Art

[0002] Grab cranes are often used for transporting and loading bulk materials in mine material yards, dock shipping, etc., as well as for grabbing slag in blast furnace filter pools, etc.

[0003] When manually operating a grab bucket, the lifting and opening and closing of two sets of wire ropes must be controlled at different times during each step, making clear observation of the grab bucket and wire ropes crucial. The laser scanner, acting as the eyes of the intelligent grab crane, also needs to clearly scan the contours and height of the material surface during operation.

[0004] However, on-site conditions, such as docks, are often subject to heavy rain and fog. In mine material yards and blast furnace filter pools, high-temperature water condenses in winter, forming thick fog, severely impacting visibility and laser scanning. Operators cannot clearly see the status of the wire rope and grab bucket, such as whether it is touching the material surface or whether the tilt angle is excessive. This can lead to bucket tipping, rope tangling, and empty grabs. Because intelligent grab cranes fail to accurately capture the real-time material pile height, the resulting grab height is inaccurate. If the height is too high, the grab bucket will close in mid-air. If the height is too low, the wire rope will be lowered too much, causing the rope to tangle on the drum or become entangled in the grab bucket. Summary of the Invention

[0005] To address the above problems, the present invention proposes a crane grab control method for environments with poor visibility. A permanent magnet synchronous motor does not require excitation, and the current output by the inverter is used to control the grab to perform active work, overcome the gravity of the grab and other friction forces, and accurately reflect the current wire rope tension.

[0006] The present invention provides a crane grab bucket control method in a poor visibility environment, comprising:

[0007] S1. Open the lifting mechanism, and the grab bucket descends at the same speed, so that it can continue to descend without touching the material surface;

[0008] S2. During the descent of the grab bucket, it automatically stops descending when it touches the material surface;

[0009] S3. When the grab bucket contacts the material surface, the lifting mechanism automatically stops and the grab bucket is controlled to sink automatically;

[0010] S4. After the bucket is closed, the lifting mechanism is opened and the grab bucket rises at the same speed. After it rises to the right position, unloading is completed.

[0011] In step S1, during the descending process of the grab bucket, in order to avoid empty grabbing, it is necessary to realize the function of continuing to descend automatically when the grab bucket does not touch the material surface, specifically:

[0012] When the grab bucket descends to grab the material, it must be in an empty bucket state, which can be obtained by formula (1):

[0013]

[0014] In formula (1), I0 is the total current of the current hoisting opening and closing, m0 is the weight of the empty bucket, u is the friction coefficient, k is the linear transformation coefficient, and g is the acceleration of gravity;

[0015] That is, the current fluctuates around I0. According to the on-site situation, a judgment current I1 is set when the material surface is not touched. If the current current I≥I1, the grab should continue to descend.

[0016] In a specific embodiment, it is set that I1=0.4I0, that is, it is determined that the weight m1=0.4m0, then the current i≥I1, and the grab bucket should continue to descend.

[0017] The above logic judgment is added to the programmable controller (PLC). When the grab bucket continues to descend without touching the material surface, even if the PLC receives the instruction to close the bucket and grab the material, it will still control the grab bucket to continue descending until it touches the material surface and then executes the closing bucket and grabbing operation.

[0018] In step S2, during the descent of the grab bucket, in order to avoid excessive lowering, it is necessary to realize the function of automatically stopping the descent when the grab bucket touches the material surface, specifically:

[0019] When the grab bucket descends to grab the material, it must be in an empty bucket state. Substituting it into formula (1) yields:

[0020]

[0021] That is, the current fluctuates around I0. According to the on-site situation, a current I2 is set to judge whether the material surface has been touched. That is, the current current i≤I2, and the grab should stop descending.

[0022] In a specific embodiment, I2=0.2I0 is set, that is, the weight m2=0.2m0 is judged, that is, the current I≤I2, and the grab bucket should stop descending.

[0023] Add the above logic judgment to the programmable controller (PLC). When the grab bucket has touched the material surface, it should stop descending. At this time, even if the PLC receives a descending instruction, it will control the grab bucket to stop descending instead of continuing to descend and loosening the rope.

[0024] In a specific embodiment, the above two functions can be enabled separately, and I1 and I2 can be modified according to actual needs.

[0025] Furthermore, by setting I2 in the interval [0, I0], the grab weight can be controlled to any value between the empty bucket and the full bucket, thus achieving the purpose of automatic loading.

[0026] There are two extreme cases: 1) The grab bucket is completely on the ground, current I = 0, and the two sets of wire ropes are completely relaxed and no longer exert tension. The grab bucket is subjected to the full gravity m0g and sinks to grab a full bucket. 2) The grab bucket is not in contact with the ground, current I = I0. The gravity of the grab bucket is offset by the tension of the wire ropes, leaving it suspended in mid-air. Without gravity, it cannot sink and can only grab an empty bucket. Therefore, I2 can take any value in the interval [0, I0].

[0027] Furthermore, the grab bucket can be automatically decelerated to achieve a quick and smooth landing. Specifically:

[0028] Add more judgment points, such as I3=0.8I0, m3=0.8m0;

[0029] I4=0.6I0,m4=0.6m0;

[0030] I5=0.4I0,m5=0.4m0;

[0031] During the descent process, the grab bucket should gradually slow down from contact with the material surface to complete landing;

[0032] When I<0.8I0, the descending deceleration is 60% of the rated speed;

[0033] When I<0.6I0, the descent deceleration is 40% of the rated speed;

[0034] When I<0.4I0, the descent deceleration is 20% of the rated speed;

[0035] When I<0.2I0, decelerate to a complete stop;

[0036] The above judgment points can be increased or decreased, and can be set to different values ​​according to the site to achieve fast and smooth landing, and prevent large impacts from causing wire rope skipping, inclined bucket inversion, etc.

[0037] In step S3, the grab bucket is controlled to automatically sink and grab, thereby increasing the full bucket rate, specifically:

[0038] In order for the grab bucket to sink, the hoisting rope must be lowered simultaneously when the bucket is closed. Because the grab bucket sinks by its own weight, the height gradually decreases, and the hoisting rope will gradually be tightened to prevent the grab bucket from descending.

[0039] Add two judgment currents I of the lifting rope q1 , I q2 And the descent speed V1, V2, where I q2 >I q1 , V2>V1;

[0040] When the output current of the lifting inverter I'>I q1When , it means that the hoist rope is being tightened. At this time, the PLC sends a speed instruction to the inverter to control the grab bucket to descend at the speed of V1.

[0041] When the output current of the lifting inverter I'>I q2 When the lifting rope is lowered, it means that the lowering speed is not fast enough and it is still being tightened. At this time, the PLC sends a speed instruction to the inverter to control the grab bucket to descend at a faster speed of V2.

[0042] When the output current of the lifting inverter I'≤I q1 When the lifting rope is lowered to the appropriate height, it means that the tension is kept at this small level so that it does not become loose.

[0043] When the grab bucket finally sinks, the hoisting rope follows and descends, realizing the sinking of the grab bucket and keeping the wire rope in a pre-tightened state to prevent the wire rope from being scraped off or the rope on the drum from being tangled.

[0044] Furthermore, the grab bucket is controlled to automatically complete load balancing. During the bucket closing operation, the opening and closing wire ropes are gradually tightened and reach the maximum tension, while the lifting wire ropes are still in a pre-tightened or relaxed state. At this time, the bucket is closed and starts to lift. The lifting wire ropes must be tightened first to share the load of the opening and closing wire ropes before they can rise synchronously.

[0045] In step S4, the load balance or the motor torque balance can be directly expressed in terms of current, i.e., the inverter output current balance;

[0046] During the ascent, the faster the rope is reeled in, the faster the wire rope becomes tighter, and the purpose is achieved by controlling the ascent speed.

[0047] Further, calculate the output current I of the switching inverter k And the lifting inverter output current I q The difference and absolute value: I abs =|I k -I q |;

[0048] The current difference I abs The goal is to reduce the speed of the inverter to a minimum, and use it as feedback for closed-loop control, using the PI proportional integral algorithm to automatically adjust the output speed of the two inverters;

[0049] Set the scale parameter K p and the integration parameter K i , with I abs The deviation signal is used to control the lifting and opening and closing speed, and finally the load can be balanced at the balance value I' abs It can be completed quickly and accurately within 2 seconds.

[0050] The present invention has the following advantages:

[0051] 1. The present invention provides a crane grab bucket control method in an environment with poor visibility, which realizes crane grab bucket control in an environment with poor visibility. It only needs to utilize the characteristics of a permanent magnet synchronous motor. The existing grab crane does not need to be modified, and no additional detection devices are required (there is no need to add absolute value encoders, torque sensors, high-precision electronic scales, high-echo laser scanners, fog-penetrating cameras, and other devices required by traditional solutions).

[0052] 2. The present invention realizes the automatic lowering function when the material surface is not touched, the automatic stopping function when the material surface is touched, the control of the grab amount, the automatic deceleration and stop of the descent, the automatic sinking of the grab, and the automatic load balancing of the grab by judging the output current of the lifting and opening and closing frequency converters.

[0053] 3. The present invention is applicable to various environments with poor visibility and is not limited to another medium, such as water.

[0054] 4. During operation, you only need to manually open the bucket in the air and then close it, and the grab crane can automatically complete the steps of descending, touching the bottom, sinking, and load balancing. This solves the problem of poor visibility and inability to clearly observe the status of the grab bucket and wire rope, and can still easily complete the grab operation. In particular, it solves the problem caused by the inability of the intelligent grab crane to obtain the actual material surface height. The present invention has high economic benefits and large optimization space. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is the force analysis diagram of the grab bucket;

[0056] Figure 2 Flowchart of the control method of the present invention. DETAILED DESCRIPTION

[0057] The present invention will be further described below with reference to the accompanying drawings and embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments, as all technologies implemented based on the present invention fall within the scope of the present invention.

[0058] The principle of this invention is that a permanent magnet synchronous motor (PMSM) requires no excitation. The inverter output current is used to control the grab bucket to perform active work, overcoming the bucket's gravity and other frictional forces. This accurately reflects the current wire rope tension (total gravity), indicating a linear relationship between the grab bucket weight and current. The inverter output current is read by a programmable controller (PLC) via a bus or analog input.

[0059] 1) When the grab bucket descends at a constant speed, the wire rope tension = grab bucket gravity - friction force, that is:

[0060] F d =I d *k=m*gm*g*u, where F dis the wire rope tension during descent, I d is the total current of the current hoisting switch, k is the linear conversion coefficient, m is the weight of the grab bucket, g is the acceleration of gravity, and u is the friction coefficient. Figure 1 shown.

[0061] Perform the following calibration:

[0062] When the grab bucket is empty, the process of uniform descent is completed and the I d1 , will I d1 Substituting the empty bucket weight m0 into the equation, we can get: d1 *k=m0*g-m0*g*u.

[0063] When the grab bucket is loaded with fixed weight material, the process of uniform descent is completed and the I d2 , will I d2 Substituting the weight m1 (empty bucket weight plus fixed weight material) into the equation, we can get: I d2 *k=m1*g-m1*g*u. k and u can be calculated from these two sets of equations.

[0064] 2) When the grab bucket rises at a constant speed, the wire rope tension = grab bucket gravity + friction force, that is:

[0065] F u =I u *k'=m*g+m*g*u', where F u is the wire rope tension during ascent, I u is the total current of the current hoisting switch, k' is the linear conversion coefficient, m is the weight of the grab, g is the acceleration of gravity, and u' is the friction coefficient. Figure 1 shown.

[0066] The calibration process is the same as 1), but with a uniform ascent. k' and u' can be calculated from the two sets of equations.

[0067] Therefore, when descending at a constant speed, we can calculate: Conversely, the current I value can also be calculated. When the current rises at a constant speed, it can be calculated: Conversely, the current I value can also be calculated. Among them, m is the total weight of the grab bucket, and I is the total current of the current lifting switch.

[0068] Example 1

[0069] A crane grab bucket control method in a poor visibility environment comprises the following steps:

[0070] (1) During the descent of the grab bucket, in order to avoid empty grabbing, it is necessary to realize the function of continuing to descend automatically when not touching the material surface. When descending to grab the material, the grab bucket must be in an empty bucket state. Given the empty bucket weight m0, we can substitute it into the formula to get:

[0071]

[0072] That is, the current fluctuates around I0. At this time, a non-contact material surface judgment current I1 can be set according to the on-site situation. If I1=0.4I0 (i.e., the judgment weight m1=0.4m0), the current I≥I1 should continue to decrease.

[0073] The above logic judgment is added to the programmable controller (PLC). When the grab bucket continues to descend without touching the material surface, even if the PLC receives the instruction to close the bucket and grab the material, it will still control the grab bucket to continue descending until it touches the material surface and then executes the closing bucket and grabbing operation.

[0074] (2) During the descent of the grab bucket, in order to avoid excessive lowering, it is necessary to realize the function of automatically stopping the descent when it touches the material surface. When descending to grab the material, the grab bucket must be in an empty bucket state. The parameter of the empty bucket weight m0 is known, and it is substituted into the formula to obtain:

[0075]

[0076] That is, the current fluctuates around I0. At this time, a material surface judgment current I2 can be set according to the on-site situation. If I2 = 0.2I0 (i.e., the judgment weight m2 = 0.2m0), the current I≤I2 should stop decreasing.

[0077] Add the above logic judgment to the programmable controller (PLC). When the grab bucket has touched the material surface, it should stop descending. At this time, even if the PLC receives a descending instruction, it will control the grab bucket to stop descending instead of continuing to descend and loosening the rope.

[0078] Above, the two functions can be enabled separately, and I1 and I2 can be modified according to actual needs.

[0079] Furthermore, the grab volume can be controlled. By setting the value of I2, the force applied to the grab bucket, and thus the weight of the material being grabbed, can be controlled. There are two extreme cases: 1) The grab bucket is completely on the ground, current I = 0, and the two sets of wire ropes are completely relaxed, no longer exerting tension. The grab bucket is subjected to the full gravity force m0g, and after sinking, it can grab a full bucket. 2) The grab bucket is not in contact with the ground, current I = I0. The gravity of the grab bucket is offset by the tension of the wire ropes, causing it to float in mid-air. Without gravity, it cannot sink, and can only grab an empty bucket. Therefore, by setting I2 in the range [0, I0], the grab weight can be controlled to any value between an empty and full bucket, achieving the goal of controlling the grab volume in situations such as automatic loading.

[0080] Furthermore, the grab can be controlled to automatically decelerate and land quickly and smoothly. More judgment points can be added, such as I3=0.8I0 (or m3=0.8m0), I4=0.6I0 (or m4=0.6m0), and I5=0.4I0 (or m5=0.4m0). During the descent process, the grab should gradually decelerate from the time it gradually contacts the material surface to the time it completely lands. When I<0.8I0, the descent deceleration is 60% of the rated speed; when I<0.6I0, the descent deceleration is 40% of the rated speed; when I<0.4I0, the descent deceleration is 20% of the rated speed; when I<0.2I0, the deceleration is to a complete stop. The above judgment points can be increased or decreased, and can be set to different values ​​on site to achieve fast and smooth landing, and prevent large impacts from causing wire rope skipping, inclined bucket inversion, etc.

[0081] (3) The grab bucket can be controlled to sink automatically and improve the full bucket rate. To achieve sinking, the lifting rope must be lowered synchronously when the bucket is closed. Because the grab bucket sinks by its own weight, the height gradually decreases, and the lifting rope will gradually be tightened to prevent the grab bucket from falling. Increase the two judgment currents I of the lifting rope q1 , I q2 And the descent speed V1, V2, where I q2 >I q1 , V2>V1. When the output current of the lifting inverter I'>I q1 When the lifting rope is tightened, the PLC sends a speed command to the inverter, which controls the grab bucket to descend at a speed of V1. When the output current of the lifting inverter I'>I q2 When the lifting rope is lowered too slowly, it is still being tightened. At this time, the PLC sends a speed command to the frequency converter, which controls the grab bucket to descend at a faster speed of V2. When the output current of the lifting frequency converter I'≤I q1 When the grab bucket is sunk, the hoist rope is lowered to the appropriate height and the tension is kept at this small level so that it does not become loose. When the grab bucket sinks, the hoist rope follows the drop and the grab bucket sinks, while the wire rope is kept in a pre-tensioned state to prevent the wire rope from being scraped off or the rope on the drum from becoming tangled.

[0082] Furthermore, the grab bucket can be controlled to automatically balance the load. During bucket closing, the opening and closing wire ropes gradually tighten and reach maximum tension, while the lifting wire ropes are still pre-tensioned or relaxed. At this point, when the bucket closes and begins to lift, the lifting wire ropes must be tightened to share the load of the opening and closing wire ropes before a synchronous rise can resume.

[0083] (4) The balance of load or the balance of motor torque can be directly expressed in terms of current, i.e. the balance of inverter output current. During the ascent process, the faster the rope is retracted, the faster the wire rope is tightened, which means that the purpose can be achieved by controlling the ascent speed. Specifically, the output current I of the inverter is calculated. k And the lifting inverter output current I qThe difference and absolute value: I abs =|I k -I q |. With the current difference I abs The goal is to reduce the speed of the inverter and use it as feedback for closed-loop control. The PI proportional integral algorithm is used to automatically adjust the output speed of the two inverters. Set the proportional parameter K p and the integration parameter K i , with I abs The deviation signal is used to control the lifting and opening and closing speed, and finally the load can be balanced at the balance value I' abs It can be completed quickly and accurately within 2 seconds.

[0084] Features of this invention: 1. Old grab cranes do not need to be modified, and there is no need to add devices such as absolute encoders, torque sensors, high-precision electronic scales, high-echo laser scanners, fog-penetrating cameras, etc. that traditional solutions require. 2. During manual operation, the grab crane only needs to manually open and close the bucket in the air, and it will automatically complete the steps of descending, bottoming out, sinking, and load balancing. In particular, it solves the problem of poor visibility and the inability to clearly observe the status of the grab bucket and wire rope, and can still easily complete the grab operation. 3. It solves the problem caused by the intelligent grab crane's inability to obtain the actual material surface height.

[0085] Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A crane grab control method in a poor visibility environment, characterized in that include: S1. The lifting mechanism is activated, and the grab bucket descends at the same speed, allowing it to continue descending even when it is not touching the material surface. S2. During the descent process, the grab bucket automatically stops when it touches the material surface; S3. When the grab bucket contacts the material surface, the grab bucket is automatically controlled to sink and grab; S4. After the bucket is closed, the lifting mechanism is activated, and the grab bucket rises at the same speed, completing the unloading process once it reaches its designated position. In step S1, during the descending process of the grab bucket, in order to avoid empty grabbing, it is necessary to realize that the surface not touching the material continues to descend, specifically: When the grab bucket is in an empty state when it descends to grab the material, the relationship between current and weight is established: （1） In formula (1), is the total current of current hoisting and closing, is the empty bucket weight, is the friction coefficient, is the linear transformation coefficient, is the acceleration due to gravity; Set a current to judge whether the material surface is not touched ,set up , that is, to judge the weight , current , the grab bucket should continue to descend; Add logic judgment to the programmable controller (PLC). When the grab bucket continues to descend without touching the material surface, even if the PLC receives the command to close the bucket and grab the material, it will still control the grab bucket to continue descending until it touches the material surface and then close the bucket and grab the material. In step S2, specifically: During the grab bucket's descent, in order to avoid excessive lowering, it is necessary to automatically stop descending when it touches the material surface. Specifically: Set a current to judge whether the material surface has been touched ,set up , that is, to judge the weight , current , the grab bucket should stop descending; Add the above logic judgment to the programmable controller PLC. When the grab bucket touches the material surface, it should stop descending. At this time, even if the PLC receives a descending instruction, it will control the grab bucket to stop descending instead of continuing to descend and loosening the rope. By controlling the grab bucket to automatically decelerate, a quick and smooth landing can be achieved. Specifically: Add more judgment points, , ; ， ； ， ； During the descent process, the grab bucket should gradually slow down from contact with the material surface to complete landing; when When the descent speed is reduced to the rated speed ; when When the descent speed is reduced to the rated speed ; when When the descent speed is reduced to the rated speed ; when When the vehicle is running, slow down to a complete stop; The judgment points can be increased or decreased, and can be set to different values ​​according to the site to achieve a quick and smooth landing and prevent the wire rope from skipping due to large impacts; In step S3, specifically: In order for the grab bucket to sink, the hoisting rope must be lowered simultaneously when the bucket is closed. Because the grab bucket sinks by its own weight, the height gradually decreases, and the hoisting rope will gradually be tightened to prevent the grab bucket from descending. Add two judgment currents of the lifting rope and descent speed ,in , ; When the output current of the inverter is raised When the lifting rope is tightened, the PLC sends a speed command to the inverter to control the grab bucket to Speed ​​decreases; When the output current of the inverter is raised When the lifting rope is lowered too fast, it means that the lifting rope is still being tightened. At this time, the PLC sends a speed instruction to the inverter to control the grab bucket to move faster. Speed ​​decreases; When the output current of the inverter is raised When the lifting rope is lowered to the appropriate height, it means that the tension is kept at this small level so that it does not become loose. When the grab bucket finally sinks, the hoisting rope follows and descends, achieving sinking of the grab bucket and keeping the wire rope pre-tightened to prevent the wire rope from being scraped off or the rope on the drum from becoming tangled. In step S4, the load balance or the motor torque balance can be directly expressed in terms of current, i.e., the inverter output current balance; During the ascent, the faster the rope is reeled in, the faster the wire rope becomes tighter, and the purpose is achieved by controlling the ascent speed; Calculate the output current of the switching inverter And the output current of the lifting inverter The difference and take the absolute value: ; Current difference The goal is to reduce the speed of the inverter to a minimum, and use it as feedback for closed-loop control, using the PI proportional integral algorithm to automatically adjust the output speed of the two inverters; Set scale parameters and integral parameters ,by The deviation signal is used to control the lifting and opening and closing speed, and finally the load is balanced at the equilibrium value. It can be completed quickly and accurately within 2 seconds.

2. The crane grab bucket control method in a poor visibility environment according to claim 1, characterized in that: The grab bucket is controlled to automatically complete load balancing. When the bucket is closed, the opening and closing wire ropes are gradually tightened and reach the maximum tension, while the lifting wire rope is still in a pre-tightened or relaxed state. At this time, the bucket is closed and begins to lift. The lifting wire rope must be tightened first to share the load of the opening and closing wire ropes before it can rise synchronously.

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