JP3390512B2 - Excavator drive controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for an excavator which excavates a ground by rotating an excavation shaft by an electric motor. 2. Description of the Related Art Generally, as shown in FIG. 1, an excavator for excavating a pit in a ground has a driving unit 4 along a guide rail 3 on a side surface of a leader mast 2 supported upright on a working machine 1. The drive unit 4 is suspended by a wire 5 and is lifted and lowered by a winch 6 mounted on the work machine 1 so that the drive unit 4 can be moved up and down. The drilling shaft 8 such as an auger screw, a casing auger, etc., connected to an output shaft that rotates through the shaft is rotationally driven to bore the ground. [0003] The electric motor 7 of the above-mentioned excavator is rotated at a constant rotational speed by a normal drive circuit using a commercial power supply or the like, or at two different rotational speeds by pole number conversion. However, when excavating the ground with the excavation shaft 8, it is necessary to secure the torque required for excavation and to increase the rotation speed as much as possible. Although desirable in terms of increasing efficiency, the above-mentioned conventional one cannot excavate efficiently. In view of the foregoing, the present invention provides an efficient excavation method in which the number of revolutions is increased steplessly as much as possible while securing the torque required for excavation without overloading the electric motor for driving the excavation shaft. It is an object of the present invention to provide a drive control device for an excavator that enables the operation. [0006] As a means for solving the problems of the prior art, the present invention relates to an excavator for excavating a ground by rotating an excavation shaft by an electric motor. A driving circuit, an inverter circuit provided separately from the driving circuit and having a frequency converter attached thereto, and a circuit switching device for selectively switching between the two circuits and connecting to the electric motor of the excavator. And a current detector for detecting a load current of the electric motor; a driving method discriminating device for the electric motor; and an inverter speed setting device, wherein the driving method discriminating device includes a load detected by the current detector. The circuit switches to an inverter circuit when the current is within a predetermined set current value, and switches to a normal drive circuit when the load current value exceeds the set current value. The inverter speed setting device has a function of controlling a switching device, the inverter speed setting device increases the frequency of the inverter when the load current value is within a set value at a set frequency when the inverter circuit is driven, and the load current value is at the frequency. It has a function of maintaining the inverter frequency constant when the set value is exceeded. When digging with a light load or a normal load as in the early stage of digging, the electric motor is driven by an inverter circuit,
The frequency is gradually increased, and until the frequency reaches the rated frequency of the electric motor (for example, 50 Hz), the ratio of the current value to the rated current value of the electric motor is small (about 90%).
%), The current frequency is maintained as it is, when it is substantially equal (about 90 to 120%), the current frequency is maintained, and when it is larger (about 120% or more), the drive switching device operates to activate the commercial power supply circuit. The operation is switched to. When the frequency reaches the rated frequency, if the ratio of the current current value to the rated current value of the electric motor at that time is small (less than about 70%), the frequency is increased as it is and substantially equal (about 70%). When the current frequency is higher (about 120% or more), the drive circuit switching device is activated to switch to the commercial power supply circuit and operate. Until the maximum frequency is reached, the ratio of the current value to the rated current value of the electric motor is small (about 70%).
The frequency is increased during the period, the current frequency is maintained when the frequency is about 70 to 90%, and the frequency is lowered when the frequency reaches about 90%. The fluctuation of the current value at this time is dealt with by increasing or decreasing the frequency. When entering a commercial power supply circuit, about 90%
If it is less than the value, the operation is switched to the inverter circuit. The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 2 is a block diagram showing one embodiment of a drive control device for controlling the electric motor 7 in the drive unit 4 of the excavator. A normal drive circuit 9 (commercial power supply drive circuit) for driving the electric motor 7 is shown in FIG. ), An inverter circuit 10 provided separately from the drive circuit 9 and having a frequency converter added to a normal drive circuit, and a circuit switch for selectively switching these two circuits 9 and 10 to connect to the electric motor 7 of the excavator. Device 11,
A current detector 12 for detecting a load current of the electric motor 7
And a drive method determining unit 13 for the electric motor 7 and an inverter speed setting unit 14. When the load current detected by the current detector 12 is within a predetermined set current value, the drive method determining unit 13 switches to the inverter circuit 10 and the load current value exceeds the set current value. The inverter speed setting unit 14 has a function of controlling the circuit switching device 11 to switch to the normal drive circuit 9 when the load current value is within a set value at a predetermined set frequency when the inverter circuit is driven. And the function of keeping the inverter frequency constant when the load current value exceeds the set value at the above frequency. FIG. 3 shows a flow chart. In the case of excavation with a light load or a normal load (flow A (main flow)), as in the early stage of excavation, the electric motor 7 outputs the operation signal 1
In response to the input of 01, the inverter circuit 10 starts a low speed operation (step 102). As a result, a large current does not flow when the electric motor is started, so that power saving is achieved. Then, gradually increase the frequency (step 10).
3) Until the frequency reaches the rated frequency of the electric motor 7 (50 Hz in the Kanto area), the ratio of the current value to the rated current value of the electric motor 7 is compared (step 104), and the ratio is less than 90%. In this case, the frequency is increased until the rated frequency is reached, and when the frequency is 90 to 120%, the current frequency is maintained (step 105) and the operation is performed.
If it is 20% or more, the drive circuit switching device 11 operates to switch to the commercial power supply circuit 9 (step 106), and the flow B
Move to. In addition, according to the commercial power supply circuit 9, although the rotation is constant, it can withstand a high load current. When the frequency reaches the rated frequency, the current value with respect to the rated current value of the electric motor 7 at that time is compared (step 107). If the ratio is less than 70%, the frequency is increased as it is. (Step 108),
When the frequency is 70% to 120%, the current frequency is maintained (step 109). When the frequency is 120% or more, the drive circuit switching device 11 operates to switch to the commercial power supply circuit (step 1).
06), the flow proceeds to flow B. Here, the lower limit is set to 70% smaller than 90% in Step 104 because the torque of the electric motor decreases when the rated frequency is exceeded, and the load current value increases significantly to compensate for the torque. This is because there is a risk of doing so. When the frequency is further increased in step 108, the ratio of the current value to the rated current value of the electric motor 7 is compared again (step 110). Then, while the ratio is less than 70%, it is determined whether or not the frequency has reached the highest frequency (step 111).
Returning to step 108, the frequency is further increased, and when the maximum frequency is reached, the process returns to step 110 to continue comparing the current value with the rated current value. When the ratio of the current value to the rated current value is 70 to 90%, the current frequency is maintained (step 112). When the current value reaches 90% or more, the flow shifts to flow C to reduce the frequency. It goes (step 113). At this time, even if the ratio of the current value to the rated current value of the electric motor 7 exceeds the upper limit of 90%, the reason for not switching to the commercial power supply circuit 9 as in other cases is that
This is because, when the frequency is increased and the frequency is increased, the torque gap is large when switching to the commercial power supply. In the flow C, the ratio of the load current to the rated current value of the electric motor is compared (step 114) while decreasing the frequency of the inverter. If the ratio is less than 70%, the flow returns to the main flow A, and the frequency is increased again. (Step 108), the frequency is maintained at 70 to 90% (Step 115), and at 90% or more, it is determined whether the current frequency has reached the rated frequency (Step 116).
If the rated frequency is not reached, the frequency is further decreased (return to step 113). If the rated frequency is reached, the process returns to the main flow A. When the operation is switched to the commercial power supply circuit 106 in the flow B, the ratio of the load current to the rated current is compared (step 117). When the ratio is less than 90%, the operation is switched to the inverter circuit 10 (step 118). , 90% or more, the operation is performed with the current status maintained. The frequency gap at the time of switching to the inverter circuit 10 may be covered by providing a time lag (about 2 seconds). Further, when excavating the ground where the load is expected to be larger than at the beginning of the excavation, the commercial power supply circuit 9 may be started from the beginning (flow B). As described above, according to the present invention, the driving circuit for the electric motor of the excavator is driven by switching between the normal driving circuit (commercial power supply circuit) and the inverter circuit. As a result, when driving by the inverter circuit, it is possible to increase the rotation speed as much as possible after securing the torque necessary for excavating the ground, to perform efficient excavation, and to apply a high load unsuitable for driving by the inverter circuit. When the ground is reached, it is possible to switch to the normal drive circuit to protect the inverter circuit and perform excavation with high torque, and to increase the number of revolutions while obtaining the torque required for excavation without overloading the electric motor. You can excavate as high as possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view showing an example of an excavator to which the present invention is applied. FIG. 2 is a circuit block diagram showing one embodiment of a drive control device according to the present invention. FIG. 3 is a flowchart of the same. [Description of Signs] 2 Leader mast 4 Drive unit 7 Electric motor 8 Drilling shaft 9 Normal drive circuit 10 Inverter circuit 11 Circuit switching device 12 Current detector 13 Driving method determination unit 14 Inverter speed setting unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-178098 (JP, A) JP-A-7-158056 (JP, A) JP-A-59-204490 (JP, A) 71284 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) E21B 7/00 E21B 3/02 E02F 5/02

Claims (1)

(57) [Claim 1] In an excavator for excavating a ground by rotating a digging shaft by an electric motor, a normal drive circuit for driving the electric motor and a drive circuit separately provided from the drive circuit An inverter circuit having a frequency converter attached to the normal drive circuit, a circuit switching device for selectively switching between the two circuits and connecting to the electric motor of the excavator, and a current detector for detecting a load current of the electric motor. A driving method discriminating device for the electric motor, and an inverter speed setting device, wherein the driving method discriminating device controls the inverter circuit when the load current detected by the current detector is within a predetermined set current value. Switching, and has a function of controlling the circuit switching device to switch to a normal drive circuit when the load current value exceeds the set current value. Increasing the frequency of the inverter when within a set value in the setting frequency load current value at the time of inverter circuit driving a defined,
An excavator drive control device having a function of maintaining an inverter frequency constant when a load current value exceeds a set value at the frequency.