Electric grab device

Abstract

To provide a grab device capable of avoiding unnecessary additional gripping movement.SOLUTION: An electric grab device 1 includes a girder 3 connected to a crane 2, a plurality of buckets 4 provided rotatably with respect to the girder 3, a slide bar 5 rotatably connected to each of the buckets 4, a ball screw 6 moving the slide bar 5 to rotate each bucket 4, a servomotor 7 driving each bucket 4 to open / close by driving the ball screw 6, and a motor control part 16 for controlling the driving of the servomotor 7. The motor control part 16 drives the servomotor 7 by torque control when performing the closing drive.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electric grab device that opens and closes a bucket by a servo motor.

Background Art

[0002] Conventionally, a hydraulic grab device is known that includes a center frame suspended by a crane, a pair of buckets pivotally supported on the center frame so as to be openable and closable, a hydraulic cylinder that drives the opening and closing thereof, a hydraulic generating mechanism, and a control mechanism that supplies the generated hydraulic pressure to the hydraulic cylinder to control the expansion and contraction operation (see, for example, Patent Document 1).

[0003] In the hydraulic grab device of Patent Document 1, a sensor for detecting the stroke of the hydraulic cylinder is provided on the hydraulic cylinder, and an arithmetic unit that calculates the opening and closing degree of the bucket from the stroke information of the hydraulic cylinder detected by the sensor, and a display unit that displays the opening and closing degree of the bucket calculated by the arithmetic unit are provided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a grab device that is driven to open and close by a hydraulic cylinder like the hydraulic grab device of Patent Document 1, when gripping an object, when the bucket is driven to close and the pressure switch is turned on, it is determined that the bucket is closed.

[0006] After that, when the grab device is suspended by a crane, in order to prevent the object from falling, a catching operation is performed to apply a load to the hydraulic cylinder so as to drive the bucket further in the closing direction. Since this catching operation is performed regardless of whether the object falls or not, power may be wasted.

[0007] An object of the present invention is to provide a grab device capable of avoiding an unnecessary catching operation in view of the problems of such prior art.

Means for Solving the Problems

[0008] The grab device of the present invention is a girder connected to a crane, a plurality of buckets rotatably provided with respect to the girder, a link member rotatably connected to each bucket, a ball screw that moves the link member to rotate each bucket; a servo motor that performs an opening drive to rotate each bucket in an opening direction to open it and a closing drive to rotate each bucket in a closing direction to grip an object after the opening drive by driving the ball screw; a motor control unit that controls the drive of the servo motor and drives the servo motor by torque control during the closing drive; the motor control unit includes: a desired amount input unit to which a desired value corresponding to a desired gripping amount by the bucket is input; an opening amount setting unit that sets an opening amount of the bucket by the opening drive based on the desired value; a weight measurement unit that measures the weight of the electric grab device when the bucket grips an object and the girder is suspended by the crane; when the weight measured by the weight measurement unit when gripping the object with the opening amount of the bucket set based on the desired value is not within a predetermined range of the weight corresponding to the desired value, the object is gripped again with the opening amount of the bucket reset so that the weight measured by the weight measurement unit approaches the weight corresponding to the desired value It is characterized by the above.

[0010] According to the present invention, when the motor control unit drives the bucket to close in order to grasp the object, the servo motor is driven by torque control, so that the generated torque of the servo motor is maintained at a constant level within the set torque range.

[0011] Meanwhile, if an object is pinched between the buckets during this process and the buckets cannot be driven further in the closing direction within the set torque range, the servo motor stops rotating but continues to apply a certain torque to the buckets in the closing direction. After that, if the girder is lifted by the crane and the pinched object drops, the servo motor can drive the buckets in the closing direction within the set torque range, so the servo motor additionally drives the buckets in the closing direction. That is, the object is automatically grabbed again.

[0012] On the other hand, if the object is not pinched between the buckets during the closing drive, the servo motor directly drives the buckets to the closed position, continues to apply a certain torque in the closing direction, and is lifted by the crane. In this case, the re-grabbing as described above is not performed.

[0013] After the closing drive is completed in this way, the crane can transport the girder to the position where the buckets should open (the position to release the object). Therefore, unlike the case of the conventional hydraulic grab device, it is not necessary to always perform re-grabbing regardless of whether the object is pinched between the buckets, so unnecessary re-grabbing operations can be avoided and the power required for this can also be saved.

[0014] Also, in the electric grab device of the present invention, different from the case of the hydraulic grab device, the grab is driven by a servo motor without relying on a hydraulic pump. For this reason, the degree of limitation of tilting is less than that of the hydraulic grab device, where tilting is considerably limited to prevent air suction of the hydraulic pump.

[0015] In addition, in the case of the hydraulic grab device, it stops when the hydraulic pressure becomes high, but in the case of the electric grab device of the present invention, there is no such cause for stopping. Also, in the case of the hydraulic grab device, there is a risk of oil leakage, but in the case of the electric grab device of the present invention, such a situation does not occur.

[0017] Also, Corresponding to the desired grasping amount at the desired amount input partdesired value By inputting , the bucket can be opened to a corresponding opening amount, and the object can be grasped with a desired grasping amount. For example, when a larger bucket is adopted and the grasping amount is large, a value corresponding to a smaller grasping amount can be input so as to obtain a desired grasping amount.

[0019] Also, when gripping an object with the opening amount of the bucket set based on the desired value input to the desired amount input unit Since the weight measured by the weight measuring unit corresponds to the actual grasping amount of the object by the bucket, by referring to this actual grasping amount, the opening amount setting unit can more accurately correspond to the desired value input by the desired amount input unit. grip the object with the reset opening amount of the bucket The opening amount of the bucket can be set.

[0022] In the present invention, the ball screw is rotatably supported by the girdle along the vertical direction, the link member is constituted by a slide bar provided at the central portion of the link member and moved vertically via a ball screw nut screwed with the ball screw, the upper end portion of the ball screw is connected to the rotation shaft of the servo motor, and each bucket with the central axis fixed to the girder may be rotatably provided by the girdle via a fulcrum shaft and rotatably connected to the slide bar via a force point shaft on the base end side of the fulcrum shaft.

[0023] According to this, when the servo motor rotates the ball screw in one direction or the other direction, the slide bar moves upward or downward, and a force for rotating the bucket in the closing direction or the opening direction around the fulcrum shaft is applied to each bucket via the force point shaft. Therefore, the motor control unit can drive each bucket to close or open by controlling the servo motor.

[0024] In the present invention, the link member, the ball screw, and the servo motor may be provided for each bucket, and the motor control unit may control each servo motor individually.

[0025] According to this, since a link member, a ball screw, and a servo motor are provided for each bucket, each bucket can be driven at different timings or at synchronized timings. Therefore, the operation patterns of the buckets can be increased, and the degree of freedom of operation of the electric grab device by the operator can be improved. Further, by driving each bucket synchronously, inconveniences such as driving in order from the bucket with a small load as in the case of a hydraulic grab device can be avoided.

[0026] In this case, the ball screw constitutes a ball screw cylinder that drives the rod portion forward and backward, the link member is constituted by the rod portion, the ball screw cylinder and the servo motor are provided for each bucket, and the base end portion of the ball screw cylinder is rotatably supported by the girdle together with the corresponding servo motor. Each bucket with the central axis fixed to the girder may be rotatably supported by the girdle via a fulcrum shaft and rotatably connected to the tip end portion of the rod portion via a force point shaft on the tip end side of the fulcrum shaft.

[0027] According to this, by driving the ball screw cylinder with the servo motor corresponding to each bucket, each bucket can be driven individually or simultaneously. Therefore, an object remaining at a corner can be scraped off by driving only the bucket located at the corner.

[0028] In the present invention, the motor control unit may include a load measurement unit that measures the load of the servo motor when performing the closing drive in an idling operation where the object is not grasped. According to this, based on the load (load torque) measured by the load measurement unit, it is possible to predict the breakage and replacement timing of each component constituting the electric grab device.

[0029] In the present invention, the motor control unit may include a load factor display unit that measures and displays the load factor of the servo motor. According to this, by referring to the load factor of the servo motor displayed by the load factor display unit, it becomes possible to confirm the aging deterioration of the electric grab device and perform predictive maintenance (a maintenance method of grasping or predicting the deterioration state and replacing or repairing parts).

[0030] In the present invention, the bucket has a mesh or lattice-like portion, and the motor control unit may include a bucket vibration unit that controls the servo motor so that the bucket vibrates when the bucket is lifted by the crane.

[0031] According to this, by vibrating the bucket with the bucket vibration unit, it is possible to shake off the ash in the object remaining in the bucket from the mesh of the bucket, or to shake off only the small particles from the object in which large and small particles are mixed in the bucket through the mesh of the bucket to classify the particles by size.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an electric grab device according to an embodiment of the present invention.

[0034] As shown in FIG. 1, this electric grab device 1 includes a girder 3 connected to a crane 2, a plurality of buckets 4 rotatably provided with respect to the girder 3, a slide bar 5 as a link member rotatably connected to each bucket 4, a ball screw 6 for moving the slide bar 5, and a servo motor 7 that performs an opening drive for driving the bucket 4 in the opening direction to open before grasping an object and a closing drive for closing the bucket 4 to grasp the object after the opening drive by driving the ball screw 6, and a control unit 8 (see FIG. 2) for controlling the operation of each part of the device.

[0035] The servo motor 7 has an electromagnetic brake and is fixed to the girder 3. The ball screw 6 is rotatably supported by the girder 3 along the vertical direction. That is, the lower end and the upper end of the ball screw 6 are radially supported by a bearing 9 and a bearing 10 fixed to the girder 3, respectively. The upper end of the ball screw 6 is connected to the rotation shaft of the servo motor 7 by a coupling 11.

[0036] The slide bar 5 is provided with a ball screw nut 12 that engages with the ball screw 6 at its central portion and is raised and lowered by the ball screw 6. Each bucket 4 is supported by the girder 3 so as to be rotatable between an open position and a closed position around a fulcrum shaft 13. In FIG. 1, each bucket 4 located at the closed position is shown by a solid line, and each bucket 4 located at the open position is shown by a two-dot chain line.

[0037] The end of each bucket 4 on the side opposite to the tip side of the fulcrum axis 13 is connected to the slide bar 5 so as to be rotatable via the force point axis 14. That is, the bucket 4 is configured to be driven to open and close according to the elevation of the slide bar 5 by the ball screw 6. Note that although two buckets 4 are shown in FIG. 1, the number is not limited to two and may be three or more.

[0038] FIG. 2 shows the configuration of the control unit 8. The control unit 8 is composed of a microcomputer, a memory, a program, etc. As shown in FIG. 2, the control unit 8 includes a crane control unit 15 that controls the drive of the crane 2 and a motor control unit 16 that controls the drive of the servo motor 7.

[0039] When driving the bucket 4 to close, the motor control unit 16 drives the servo motor 7 by torque control. That is, the servo motor 7 detects its output torque and feeds back this detected value to the current command for driving the servo motor 7, so that the output torque is held at a constant value.

[0040] The motor control unit 16 includes a desired amount input unit 17 to which a value corresponding to a desired grasping amount by the bucket 4 is input, and an opening amount setting unit 18 that sets the opening amount by driving the bucket 4 to open based on the value input to the desired amount input unit 17. Examples of the value corresponding to the desired grasping amount input to the desired amount input unit 17 include the opening amount by driving the bucket 4 to open, the weight of the object to be grasped, and the volume.

[0041] When driving to open, the motor control unit 16 drives the servo motor 7 so as to reach the opening amount set by the opening amount setting unit 18. The input of the value corresponding to the grasping amount to the desired amount input unit 17 is performed by an input device 19 such as a keyboard or a tablet.

[0042] Further, the motor control unit 16 includes a weight measurement unit 20 that measures the weight of the electric grab device 1 when the bucket 4 grabs the object and the girder 3 is lifted by the crane 2. In this case, the opening amount setting unit 18 may set the opening amount by the opening drive of the bucket 4 based on the weight measured by the weight measurement unit 20 in addition to the value input by the desired amount input unit 17.

[0043] Further, the motor control unit 16 may include an opening / closing repetition unit 21 that controls the servo motor 7 so that the bucket 4 repeats opening and closing within a certain opening / closing range until the weight measured by the weight measurement unit 20 becomes the weight corresponding to the value input by the desired amount input unit 17.

[0044] FIG. 3 shows a fixed mode process as an example of the control process by the control unit 8. However, before the start of the process, the electric grab device 1 is positioned above the object by the crane 2. When the process starts, in step S1, the control unit 8 receives, from the desired amount input unit 17, the input of a value corresponding to the desired grasping amount by the bucket 4 from the input device 19.

[0045] Next, in step S2, the opening amount setting unit 18 sets the opening amount of the bucket 4 by the opening drive based on the value input to the desired amount input unit 17.

[0046] Next, in step S3, the bucket 4 is driven by the servo motor 7 so as to have the opening amount set by the opening amount setting unit 18.

[0047] Next, in step S4, the crane control unit 15 lowers the girder 3 with the crane 2 and positions the bucket 4 above the object.

[0048] Next, in step S5, the motor control unit 16 drives the servo motor 7 under torque control to drive the bucket 4 in the closing direction to grasp the object. At this time, if the object is sandwiched between the buckets 4 and the bucket 4 cannot be driven further in the closing direction within the set torque range, the servo motor 7 stops rotating but continues to apply a certain torque in the closing direction to the bucket.

[0049] Next, in step S6, the crane control unit 15 raises the girder 3 with the crane 2 to lift the bucket 4 that has grasped the object. At this time, if the sandwiched object falls, the servo motor 7 can drive the bucket 4 in the closing direction within the set torque range, so the servo motor 7 additionally drives the bucket 4 in the closing direction. That is, automatic re-grasping is performed.

[0050] On the other hand, if the object is not sandwiched between the buckets 4 during the closing drive in step S5, the servo motor 7 directly drives the bucket 4 to the closed position (the position of the bucket 4 shown by the solid line in FIG. 1), continues to apply a certain torque in the closing direction, and is lifted by the crane 2. In this case, the above-mentioned re-grasping is not performed.

[0051] Next, in step S7, the crane control unit 15 transports the girder 3 with the crane 2 to the position where the grasped object is discharged.

[0052] Next, in step S8, the motor control unit 16 drives the bucket 4 to open and close with the servo motor 7. Thereby, the grasped object is discharged.

[0053] Thereby, the process in the fixed mode of the control unit 8 is completed. If it is felt that the amount of the object grasped in step S5 is large, when performing the fixed mode process in FIG. 3 next, the value corresponding to the desired grasping amount input in step S1 can be set smaller to optimize the grasping amount.

[0054] For example, the grasping amount with the normal opening amount is 10m3 Adopt the bucket 4. If the grasping amount is too large, the value input in step S1 is set to a value corresponding to a grasping amount of 9m 3 or 8m 3 By setting it to a value corresponding to the grasping amount, the grasping amount can be optimized.

[0055] Fig. 4 shows the automatic adjustment mode A process as another example of the process by the control unit 8. However, before the start of the process, the electric grab device 1 is positioned above the object by the crane 2. When the process starts, steps S11 to S16 are the same as steps S1 to S6 in the fixed mode process of Fig. 3.

[0056] Next, in step S17, the weight below the girder 3 being suspended by the crane 2 is measured by the weighing unit 20. This measurement can be performed using a load meter provided on the crane 2.

[0057] Next, in step S18, it is determined whether the measured value measured in step S17 is appropriate. This determination is made by comparing the measured value with the weight corresponding to the value corresponding to the desired grasping amount input in step S11. If the measured value is within a predetermined range of the weight, it is determined to be appropriate.

[0058] If it is determined to be appropriate in step S18, then in step S19, the crane control unit 15 transports the girder 3 by the crane 2 to the position where the object grasped in step S15 is discharged.

[0059] Next, in step S20, the motor control unit 16 drives the bucket 4 to open and close with the servo motor 7. Thereby, the object grasped in step S15 is discharged, and the automatic adjustment A process in Fig. 4 ends.

[0060] On the other hand, if it is determined in step S18 that it is not appropriate, the process returns to step S12, and the opening amount setting unit 18 sets the opening amount of the bucket 4 by opening drive based on the value input to the desired amount input unit 17. However, in this case, in addition to the value input by the desired amount input unit 17, the opening amount of the bucket 4 by opening drive is set based on the weight measured by the weighing unit 20.

[0061] That is, the weight of the object corresponding to the value input by the desired amount input unit 17 is compared with the weight of the object corresponding to the weight measured by the weighing unit 20, and the opening amount is set again so that the latter approaches the former.

[0062] Next, the processes from step S13 to S18 are performed. If it is determined in step S18 that it is appropriate, the processes of steps S19 and S20 are performed in the same manner as above, and the automatic adjustment A process in FIG. 4 ends. That is, the processes of steps S12 to S18 are repeatedly performed until it is determined in step S18 that it is appropriate.

[0063] Note that the process of step S18 may be moved after step S20, and the opening amount of the bucket 4 in step S12 may be reset every time an object is discharged.

[0064] FIG. 5 shows an automatic adjustment mode B process as still another example of the process by the control unit 8. However, before the start of the process, the electric grab device 1 is positioned above the object by the crane 2. When the process starts, until steps S21 to S27, the same processes as steps S11 to S17 in the automatic adjustment mode B process in FIG. 4 are performed.

[0065] Next, in step S28, it is determined whether the measured value measured in step S27 is appropriate. In this determination, the measured value is compared with the weight corresponding to the value corresponding to the desired gripping amount input in step S21, and if the measured value is within a predetermined range of the weight, it is determined to be appropriate.

[0066] If it is determined to be appropriate in step S28, then in step S30, the crane control unit 15 uses the crane 2 to transport the girder 3 to the position where the object grasped in step S25 is discharged.

[0067] Next, in step S31, the motor control unit 16 drives the servo motor 7 to open and close the bucket 4. As a result, the object grasped in step S15 is discharged, and the automatic adjustment process in FIG. 5 ends.

[0068] On the other hand, if it is determined in step S28 that it is not appropriate, then in step S29, the bucket 4 is opened and closed within a certain opening and closing range, and the process returns to step S27. The certain opening and closing range is set so that a part of the object grasped by the bucket 4 drops and the measured value measured in step S27 decreases by an appropriate amount.

[0069] The processes of steps S27 to S29 constitute an opening and closing repetition unit 21 that is repeated until it is determined in step S28 that the measured value measured in step S27 is appropriate. If it is determined in step S28 that it is appropriate, the processes of steps S30 and S31 are performed as described above, and the automatic adjustment B process in FIG. 5 ends.

[0070] As described above, according to the present embodiment, when an object is not pinched between the buckets 4 during the closing drive, no chasing grasping is performed when the crane 2 is lifted, so unnecessary chasing grasping operations can be avoided, and the power required for this can be reduced. In addition, since the bucket 4 is driven by the servo motor 7, compared with the case of a hydraulic grab device, the degree to which it is restricted from tilting to prevent air suction of the hydraulic pump is less.

[0071] Further, according to the present embodiment, there is no possibility that the hydraulic pressure becomes high and stops or the oil for the hydraulic pressure leaks as in the case of a hydraulic grab device, so the operation of the electric grab device 1 can be improved.

[0072] Also, according to the fixed mode process of FIG. 3, by inputting a value corresponding to a desired grasping amount into the desired amount input unit 17, the bucket 4 is opened so as to have a corresponding opening amount, and the object can be grasped with the desired grasping amount.

[0073] Also, according to the automatic adjustment mode A process of FIG. 4, in addition to the value input to the desired amount input unit 17, based on the weight measured by the weighing unit 20, the opening amount setting unit 18 sets the opening amount by driving the bucket 4 to open, so that the object can be automatically grasped with the desired grasping amount.

[0074] Also, according to the automatic adjustment mode B process of FIG. 5, until the weight measured by the weighing unit 20 becomes the weight corresponding to the value input by the desired amount input unit 17, the bucket 4 is repeatedly opened and closed within a certain opening and closing range by the opening and closing repetition unit 21, so that the object can be grasped more quickly with the desired grasping amount.

[0075] FIG. 6 shows an electric grab device according to another embodiment. As shown in FIG. 6, this electric grab device 1b includes a girder 3b connected to the crane 2, a plurality of buckets 4b rotatably provided with respect to the girder 3b, a ball screw cylinder 22 for each bucket 4b that individually drives each bucket 4b, a servo motor 7b for each ball screw cylinder 22 that individually drives each ball screw cylinder 22, and a control unit that controls the operation of each part of the device.

[0076] The base end portion of the ball screw cylinder 22 is rotatably supported by the girder 3b together with the corresponding servo motor 7b. Each bucket 4b is supported by the girder 3b so as to be rotatable between an open position and a closed position around the fulcrum shaft 13b.

[0077] On the tip side and outside of each bucket 4b with respect to the fulcrum shaft 13b, the tip end portion of the rod portion 23 driven to advance and retreat of the corresponding ball screw cylinder 22 is connected so as to be rotatable via the force point shaft 14b. That is, the rod portion 23 functions as a link member in the present invention.

[0078] Therefore, each servo motor 7b can individually open and close the corresponding bucket 4b by means of the corresponding ball screw cylinder 22. Note that although two buckets 4b are shown in FIG. 6, the number is not limited to two, and three or more may be used. In that case, a ball screw cylinder 22 and a servo motor 7b for driving each bucket 4b are provided for each bucket 4b.

[0079] The control unit of the electric grab device 1b includes a crane control unit and a motor control unit similar to those of the control unit 8 in FIG. 2 of the electric grab device 1, except that the motor control unit individually drives and controls each servo motor 7b, and performs the fixed mode process shown in FIG. 3, the automatic adjustment mode A process shown in FIG. 4, and the automatic adjustment mode B process.

[0080] According to the present embodiment, since the ball screw cylinder 22 and the servo motor 7b are provided for each bucket 4b, and each bucket 4b can be driven individually or in synchronization with all the buckets 4b, the operation pattern of the bucket 4b can be increased, and the degree of freedom of operation of the electric grab device 1b by the operator can be improved.

[0081] For example, an object remaining in a corner can be scraped off by driving only the bucket 4b located at that corner. Also, by driving each bucket 4b in synchronization, it is possible to avoid inconveniences such as driving in order from the bucket 4b with a small load, as in the case of a hydraulic grab device.

[0082] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto. For example, when the bucket 4 has a mesh or lattice portion, a bucket vibration unit may be provided that controls the servo motor 7 so that the bucket 4 vibrates when the bucket 4 grabs an object and the girder 3 is lifted by the crane 2.

[0083] According to this, by vibrating the bucket with the bucket vibrating part, the ash in the object remaining in the bucket can be shaken off from the mesh of the bucket, or only the small particles can be shaken off from the object in which large and small particles are mixed in the bucket from the mesh of the bucket to sort the particles by size.

[0084] Further, the motor control unit 16 may include a load measurement unit that measures the load of the servo motor 7 when performing the closing drive in the no-load operation where the object is not grasped. According to this, based on the load (load torque) measured by the load measurement unit, it is possible to predict the breakage and replacement timing of each component constituting the electric grab device 1.

[0085] For example, FIG. 7 is a graph showing a measurement example of the load of the servo motor 7 measured by the load measurement unit. The horizontal axis is the elapsed time when performing the closing drive from the open position to the closed position of the bucket 4, and the vertical axis is the load of the servo motor 7. The range T indicated by the broken line is the allowable load range. The graph curve G shows the variation of the load with the passage of time.

[0086] When performing the closing drive in the no-load operation and as a result of measuring the load by the load measurement unit, if a load variation as shown by the graph curve G is measured, the portion enclosed by the one-dot chain line in the graph curve G deviates from the allowable range T of the load of the servo motor 7. From this, it is suspected that the ball screw 6 or the like is damaged, and it can be understood that it is the replacement timing of components such as the ball screw 6.

[0087] Further, the motor control unit 16 may include a load rate display unit that measures and displays the load rate of the servo motor 7. According to this, by referring to the load rate of the servo motor displayed by the load rate display unit, it is possible to confirm the aging deterioration of the electric grab device and perform predictive maintenance (a maintenance method of grasping or predicting the deterioration state and replacing or repairing parts).

[0088] Further, the grab is not limited to the bucket grab and may be a comb-tooth grab.

Explanation of Reference Numerals

[0089] 1, 1b... Electric grab device, 2... Crane, 3, 3b... Girder, 4, 4b... Bucket, 5... Slide bar, 6... Ball screw, 7... Servo motor, 8... Control unit, 9... Bearing, 10... Bearing, 11... Coupling, 12... Ball screw nut, 13... Fulcrum shaft, 14... Force point shaft, 15... Crane control unit, 16... Motor control unit, 17... Desired amount input unit, 18... Opening amount setting unit, 19... Input device, 20... Weight measurement unit, 21... Opening and closing repetition unit, 22... Ball screw cylinder, 23... Rod part, T... Allowable range, G... Graph curve.

Claims

1. A girder connected to a crane, A plurality of buckets rotatably provided with respect to the girder, A link member rotatably connected to each bucket, A ball screw that moves the link member to rotate each bucket, A servo motor that performs an opening drive to rotate each bucket in the opening direction to open by driving the ball screw, and a closing drive to rotate each bucket in the closing direction to grasp an object after the opening drive, A motor control unit that controls the drive of the servo motor and drives the servo motor by torque control during the closing drive, The motor control unit includes: A desired amount input unit to which a desired value corresponding to a desired grasping amount by the bucket is input, An opening amount setting unit that sets the opening amount of the bucket by the opening drive based on the desired value, A weight measurement unit that measures the weight of the electric grab device when the bucket grasps an object and the girder is suspended by the crane, When the weight measured by the weight measurement unit when grasping an object with the opening amount of the bucket set based on the desired value is not within a predetermined range of the weight corresponding to the desired value, the object is grasped again with the opening amount of the bucket reset so that the weight measured by the weight measurement unit approaches the weight corresponding to the desired value. The electric grab device is characterized by this.

2. The ball screw is rotatably supported along the vertical direction by the girder, The link member is constituted by a slide bar provided at the central portion of the link member and moved in the vertical direction via a ball screw nut that engages with the ball screw, The upper end portion of the ball screw is connected to the rotation shaft of the servo motor, Each bucket is rotatably supported by the girder via a fulcrum shaft with a central axis fixed to the girder, and is rotatably connected to the slide bar via a power point shaft on the proximal end side of the fulcrum shaft. The electric grab device according to claim 1, characterized in that.

3. The link member, the ball screw, and the servo motor are provided for each bucket, and the motor control unit controls each servo motor individually. The electric grab device according to claim 1, characterized in that.

4. The ball screw constitutes a ball screw cylinder for driving the rod portion to advance and retreat. The link member is constituted by the rod portion. The ball screw cylinder and the servo motor are provided for each bucket. The proximal end portion of the ball screw cylinder is rotatably supported by the girder together with the corresponding servo motor. Each bucket is rotatably supported by the girder via a fulcrum shaft with a central axis fixed to the girder, and is rotatably connected to the distal end portion of the rod portion via a power point shaft on the distal end side of the fulcrum shaft. The electric grab device according to claim 3, characterized in that.

5. The motor control unit includes a load measurement unit that measures the load of the servo motor when performing the closing drive in an idling operation where the object is not grasped. The electric grab device according to any one of claims 1 to 4, characterized in that.

6. The motor control unit includes a load factor display unit that measures and displays the load factor of the servo motor. The electric grab device according to any one of claims 1 to 5, characterized in that.

7. The bucket has a mesh or lattice-like portion, and the motor control unit includes a bucket vibration unit that controls the servo motor so that the bucket vibrates when the bucket is lifted by the crane. The electric grab device according to any one of claims 1 to 6, characterized in that it is provided.

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