JP3100045B2 - Core drill automatic feeder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic feeder for a core drill used for cutting and drilling an object to be cut such as reinforced concrete, concrete, and rock.

[0002]

2. Description of the Related Art Conventionally, a core drill of this type includes a rotary drive for rotating a core bit, a feed mechanism for moving the core bit forward and backward, a feed drive for driving the feed mechanism, a support for supporting these, and a support. And a gantry used for fixing the pedestal. Further, in the core drill, operations of cutting and drilling are automatically controlled by a control device. This control device has an operation panel and an electronic control circuit inside. In addition, in a wet core drill, cooling water is guided to the core bit in order to cool the core bit, and supply / stop of the cooling water can be adjusted by a cooling water supply valve.

[0003] As a prior art, Japanese Patent Application Laid-Open No. 3-27908 is disclosed. This is a cutting target value that provides an optimum rotation speed for the core bit in accordance with the information on the size of the core bit, and the motor for rotating the core bit (hereinafter referred to as a main motor) in which the peripheral speed of the cutting edge of the core bit is constant regardless of the size of the core bit. (Referred to as a motor)), and controls the current value to be constant. This purpose is based on the data that the drilling speed of the core drill is maximum when the peripheral speed of the core bit is constant and appropriate (about 180 m / min). Further, a condition satisfaction means for outputting a release signal when a condition in which the core bit hits the workpiece and cutting is started and the core bit safely rotates, a main motor and a feed motor (hereinafter referred to as a feed motor) from the start. )) To a fixed low speed,
After the restriction is released by a release signal from the condition satisfaction means, the constant current control is performed by the cutting target current value of the main motor. The purpose is that the feed motor and main motor rotate at high speed just before the start of cutting,
It is stated that a large impact is applied to the core drill body at the moment when the cutting edge of the core bit hits the object to be cut, and the cutting position is apt to be shifted, so that the cutting and drilling accuracy is deteriorated. However, even if the speed is reduced at the start, the commutator motor has a problem in that there is a limit in the characteristic of the motor speed, and it is difficult to perform a low-speed rotation (for example, 50 m / min) without danger. Was. Also,
With the constant current value control of the main motor to keep the cutting edge peripheral speed of the core bit constant, it is difficult to realize the proper load of the core drill due to the characteristics of the commutator motor, and the reduction in cutting efficiency due to insufficient load torque is avoided. There was a problem that it was not. Furthermore, the commutator motor needs to perform a constant current value control at the same set current in the cutting of the reinforcing bar and the concrete portion due to the relationship between the rated current and the limiting value of the rated current. There is a problem that the cutting efficiency is reduced due to the shortage, and it is conceivable that the load torque is increased by changing the speed ratio at the reinforcing bar portion, but there is a problem that the structure becomes complicated.

On the other hand, a method of detecting the number of rotations of a motor from an encoder attached to the motor and controlling the frequency so that a predetermined motor rotation can be obtained efficiently is that a predetermined torque can be obtained even at a low speed. An example of such a device is a driving device for a core drill including a high-speed induction motor of a variable frequency inverter driven by slip frequency control and a speed reducer thereof, as disclosed in Japanese Patent Application Laid-Open No. H8-2247.
No. 27, published by the present applicant. This is to solve the above-mentioned problem in the characteristics of the single-phase 100 V commutator motor, which has been mainly used in the conventional core drill driving device. That is, this is a speed detector that detects the speed of the induction motor, a slip frequency calculator that determines the torque characteristics, a frequency setter that sets the frequency of the maximum speed, and a frequency calculator that determines the frequency of the inverter. V / f where the motor gap magnetic flux number is always constant
Has a voltage calculator previously input into the circuit, adds the slip frequency calculated by the slip frequency calculation from the motor speed and the motor speed converted to the frequency, and adds the added value and the frequency setter. The frequency of the set maximum speed is input to the frequency calculator and the voltage calculator, and the high-speed rotation induction driven by the variable frequency inverter having these calculation outputs as the frequency command value and the voltage command value of the inverter is input. An object of the present invention is to provide a core drill driving device including an electric motor and a speed reducer. FIG. 9 shows a specific example of the characteristic curve of the present invention. In the figure, the number of rotations of the core bit for each size of 1 to 6 inches is almost constant irrespective of the variation of the load torque, and the proper peripheral speed (about 180 m / min) of the cutting surface of the core bit at the time of actual cutting is It has the feature that it can be maintained at the point of use. Furthermore, if an optimum rotation speed is selected for each core bit size, a predetermined load can be realized by setting one cutting current target value (inverter input current). Also,
As a soft starter for this core drill, Jpn.
No. 581 is disclosed by the present applicant. This relates to the manual feeder of the core drill,
Low-speed rotation with almost no chatter at no load (for example, 50 to
80 r / min) can be realized.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the problem of an automatic feeder for a core drill using a commutator motor as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 3-27908. Utilizing the core drill drive disclosed in Japanese Patent Application Laid-Open No. 224727/1995, a proper cutting surface peripheral speed and a predetermined load torque for each bit can be easily obtained, so that the cutting efficiency is good. It is an object of the present invention to provide a core drill automatic feeder capable of low-speed operation with little chatter or the like of a core drill soft starting device disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-15064.

[0006]

SUMMARY OF THE INVENTION The present invention provides a speed detector for detecting the speed of an induction motor, a slip frequency calculator for determining a torque characteristic, a frequency setting device for setting a frequency of a maximum speed, and an inverter. It has a frequency calculator for determining the frequency, and a voltage calculator for which the V / f value at which the motor gap magnetic flux number is always constant is previously input into the circuit, and is calculated from the motor speed by the slip frequency calculator. The slip frequency and the motor speed converted into the frequency are added together, and the added value and the frequency of the maximum speed set by the frequency setting device are input to the frequency calculator and the voltage calculator, and their calculation outputs are output. A rotation drive unit for rotating a core bit composed of a high-speed induction motor driven by a variable frequency inverter having a frequency command value and a voltage command value of the inverter and a speed reducer thereof A core bit automatic feeder having a control device for controlling the operation of a core drill having a feed drive unit for driving a feed mechanism for moving the core bit forward and backward, a rotation speed setting means for setting an optimum rotation speed for the core bit; Current value setting means for setting a predetermined load current at the inverter inlet, which is a cutting target current value at the inverter inlet for applying a predetermined load torque to the core drill; and a cutting target current value from the current value setting means and the inverter inlet. Motor control means for comparing the load current detected by the current detection means for detecting the load current, and controlling the number of revolutions of the motor of the feed drive unit so that the load current at the inverter entrance becomes the cutting target current value. Is provided.

The rotation speed setting means is a main motor rotation speed setting circuit for outputting a bit signal to the inverter via a main motor rotation speed determination circuit when a bit size is selected. Time, soft start,
And a target input current setting circuit for storing a target current value at the time of cutting through and outputting the target current value to a comparison circuit, wherein the motor control means outputs the deviation signal from the comparison circuit to the feed motor of the feed drive unit such that the deviation signal becomes zero. It is preferable to use a feed motor control circuit.

[0008]

The present invention also provides a speed detector for detecting the speed of an induction motor, a slip frequency calculator for determining a torque characteristic, a frequency setting device for setting a frequency of a maximum speed,
It has a frequency calculator for determining the frequency of the inverter, and a voltage calculator for which the V / f value at which the motor gap magnetic flux number is always constant is previously input into the circuit, and calculates the slip frequency calculator from the motor speed. The calculated slip frequency and the motor speed converted into the frequency are added together, and the added value and the frequency of the maximum speed set by the frequency setting device are input to the frequency calculator and the voltage calculator, and these calculations are performed. A rotation drive unit for rotating a core bit composed of a high-speed rotation induction motor driven by a variable frequency inverter whose output is a frequency command value and a voltage command value of an inverter and its speed reducer, and a feed for moving the core bit forward and backward A core drill automatic feeder having a control device for controlling the operation of a core drill having a feed drive unit for driving a mechanism; The number of setting conditions distinguished by cutting conditions during cutting, the establishment of each setting condition, is characterized in that it has a function of determining the detection of the inverter inlet current.

Further, the present invention is characterized in that it has a function of judging the establishment of the core bit rotation speed setting condition by detecting a core bit feed speed.

[0011]

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of an automatic feeder for a core drill according to the present invention. In the figure, a core drill 1 and a control device 2 controlled by a variable frequency inverter 38 described later are configured, and both are connected via a cable 3. The core drill 1 includes a main motor 4 and a speed reducer 5, a bit rotation driving unit 7 for rotating a core bit 6, a feed mechanism 8 for moving the core bit 6 forward and backward, and a feed mechanism 8 including a feed motor 9 and a speed reducer 10.
And a support 12 for supporting the same.
And a gantry 13 used when mounting each of the above members and fixing it to a workpiece. In addition, the gantry 13 is fixed to a workpiece by an anchor bolt 14. The core bit 6 is connected to an output shaft of the speed reducer 5 via a tube 15. The cooling water is supplied to the core bit 6 after passing through a water cooling jacket (not shown) of the main motor 4 via a supply hose 16 to be cooled.
In the passage of the cooling water supply means, a flow control valve 17 and a cooling water amount detector 37 are provided.

FIG. 2 shows the operation panel 18 of the control device 2, and FIGS. 3 and 4 show sequence diagrams for explaining the configuration and operation. In FIG. 2, 19 is a power switch, 2
0 is a cutting distance indicator, 21 is a cutting distance setting device, 23 is an operation mode selection switch, 22 is a bit size selection switch, and 24 and 25 are used at the time of manual selection, for selecting the current value and rotation speed of the main motor, respectively. Switch. Reference numeral 26 denotes a forward / reverse switch of the feed motor 9 which is used at the time of manual selection. 27 is a distance setting switch, 2
8 is a distance setting reset switch, 29 is an abnormality display reset switch, 30 is a main motor abnormality display, 31 is a cutting impossible display, 32 is a cutting completion display, 33 is an operation start switch, and 34 is an operation stop switch. Show.

Next, the configuration and basic operation of the control circuit 2 will be described with reference to FIGS.

First, the main motor speed setting means 43 will be described. The setting of the number of revolutions of the main motor 4 is selected according to the bit size and the respective cutting conditions at the time of cutting the concrete portion, the reinforcing bar portion, the soft start, and the cutting penetration. That is, the set value in the case of cutting the concrete portion is set to an appropriate value of the bit peripheral speed (about 180 m / min). Since the cutting efficiency does not significantly affect the peripheral speed of the bit, the setting at the time of cutting the rebar portion is preferably used (for example, reduced by 30%) by increasing the load torque as compared with the time of cutting the concrete portion, as long as the bit strength is not affected. Therefore, the setting of the number of revolutions is also set lower. The setting at the time of soft start and at the time of cutting penetration is a safe low rotation (for example, 50 r /
min). These details will be described with reference to FIG. That is, when the bit size is selected by the main motor rotation speed setting circuit 39 as the rotation speed setting means, the bit size signal 391 is sent to the main motor rotation speed determination circuit 392. When the cutting of the concrete portion is completed and the steel reaches the reinforcing bar portion, the feed speed is rapidly reduced (for example, 1/5). At this time, the detection signal 401 detected by the feed speed detector 40 of the feed motor 9 is sent to the cutting speed classification circuit 402, and a signal 424 indicating that the rebar cutting has been started is sent to the main motor speed determination circuit 392. send. When the cutting progresses and passes through the rebar and starts cutting the concrete portion, the feed speed rapidly increases (for example, by a factor of 5), and a signal 425 indicating the start of concrete cutting is sent to the main motor rotation speed determination circuit 392 in the same manner.
Sent to Thus, the main motor speed determination circuit 392
Determines whether concrete cutting or reinforcing bar cutting is being performed based on the above signal, and is output as signals 393 and 394, respectively, and is input to the variable frequency inverter 38 as a main motor speed command signal 396, and the main motor 4 It is configured to output a control signal 397 for controlling. Here, instead of the feed speed detector 40, the detection signal 422 of the input current detector 42 of the inverter 38 is sent to the input current determination circuit 4
23 to determine whether the current is excessive current when the reinforcing bar arrives or passes through the reinforcing bar, and may be sent to the main motor rotation speed determining circuit 392 as a reinforcing bar cutting start signal 424 and a concrete cutting start signal 425, respectively. At the time of soft start and at the time of cutting through, the main motor rotational speed determination circuit 392 sends the signal 395 to the main motor 4 via the variable frequency inverter 38, which will be described in detail later.

Next, the target input current setting means 44 of the inverter will be described. The setting of the target input current is performed separately from the setting of the bit rotation speed, and is performed at the time of cutting the concrete part and the reinforcing bar part (for example, 25A) and at the time of soft starting (for example,
15A) and three types of cutting (for example, 5A). These relationships will be described with reference to FIG. The target input current setting circuit 41, which is current value setting means, stores the above target current values in advance. Each of the selected target current value signals 411 and the load input current detector 42, which is current detection means, are stored. A comparison circuit 412 that forms a deviation signal by comparing the detection signal 421 detected by the above-described steps, and the deviation signals 413 to 415 from the comparison circuit 412 at the time of cutting a concrete part and a reinforcing bar, at the time of soft starting, and at the time of cutting through become zero. And a feed motor control circuit 416 which is a motor control means for outputting a control signal 417 for controlling the feed motor 9.

Next, the soft start control means 45 will be described. When the start signal 331 is inputted by pressing the operation switch 33, the rotation speed of the main motor 4 is set by the operation state judgment circuit 441 (FIG. 4) for outputting the soft start signal 332 and the soft start signal 332 from the operation state judgment circuit 441. Then, it is input to the variable inverter 38 and controls the main motor 4. Further, a target input current value of the inverter is set and input to the feed motor control circuit 416 to control the feed motor 9. The soft start control means 45 is configured to measure the time by a soft start signal 332 at the time of starting, and to release the time by a soft start release timer 333 that outputs a release signal 334 after a set time period has elapsed. Further, the target point arrival detecting means 46 detects a bit moving distance detector 35 for detecting the moving distance of the core bit 6, a cutting distance setting device 21 for setting a cutting moving distance, and a cutting distance setting device 21 after starting.
Is determined that the core bit 6 has reached the target cutting point on the basis of the distance setting signal 211 and the moving distance signal 351 from the bit moving distance detector 35, and the soft start release signal 35
And a cutting determination circuit 352 that outputs a signal No. 3.

Next, a bit origin position detector 3 for detecting the original position of the core bit 6 before starting, detecting that the core bit 6 has reached a target point, and outputting a target point arrival signal 361.
6, a target point reaching signal 354 from the target point reaching detecting means 46 and a current drop signal 355 at the time of cutting through the input current judging circuit 423 are sent to a motor forward / reverse judging circuit 357 to reverse the feed motor 9. A start / stop signal 443 for outputting a control signal 358 and stopping the main motor 4 when the bit origin position detector 36 detects that the core bit 6 has returned to the original position, and a control signal for stopping the feed motor 9. Operation determination circuit 441 that outputs 442
It is composed of

Next, a flow control valve 17 and a cooling water detector 37 are provided in a passage of a supply means for supplying cooling water to the main motor 4 and the core bit 6, and the control valve 17 is opened at the time of starting.
A circuit for closing the control valve 17 after the cutting is completed is configured. Also, a cooling water amount decrease signal 371 from the cooling water amount detector 37
To close the control valve 17 and stop the device.

Next, the flow of the operation of the entire automatic feeder will be described with reference to the flowcharts of FIGS. 5 to 8 and FIGS. In FIG. 5, first, the bit origin position 101 and the cutting target position 124 are set by the cutting distance setting device 21 of the operation panel 18, and the predetermined main motor speed and the inverter input current which are the soft start conditions 102 are set. ,
If the start button 33 of the automatic feeder is turned on (10
0), main motor 4 (103), feed motor 9 (10
4), inverter 38 (105) and cooling water supply valve 17
(106) is simultaneously turned ON, and the core bit 6 is lowered by the feed mechanism 8 to the concrete cutting surface. During that time, the rotation speed of the main motor 4 is maintained at a constant low speed (for example, 50 r / min) regardless of the load, so that the landing can be performed safely without chattering or other problems. After landing, control 107 for increasing / decreasing the feed motor 9 is performed to keep the input current constant, so that the main motor 4 is not overloaded due to overcurrent. After the start, the elapsed time is counted by the timer 110, and the above soft start condition release 111 is performed. Normally, the soft start ends about 5 mm after landing, but can be adjusted with the timer 110 according to environmental conditions.

If the soft start condition release 111 is satisfied,
A new normal operation (concrete cutting) condition 112 and a reinforcing bar operation condition 113 are newly set, and the process automatically shifts to full-scale cutting of reinforced concrete. Concrete part
In the rebar cutting, control is performed to increase the speed 120 and reduce the speed 119 of the feed motor 9 in order to keep a predetermined input current constant (118 to 121). However, when cutting concrete, the appropriate peripheral speed (approximately 18
(0 m / min), a different value is selected for the set rotation speed for each bit size. On the other hand, when cutting the rebar,
Since the cutting efficiency has little effect on the bit peripheral speed, it is effective on the cutting efficiency to reduce the rotation speed within the range of the rated current and increase the torque within the range of the allowable stress of the bit peak. Even with the same bit size, the number of rotations is set to be lower (for example, about 30% lower) than during concrete cutting. Therefore, it is necessary to judge between concrete cutting and reinforcing bar cutting. This method will be described with reference to FIGS. 7 and 8.

In the method shown in FIG. 7, the setting conditions of the number of revolutions of the core bit are distinguished by the difficulty of cutting the workpiece, and the setting of each setting condition is determined by detecting the excessive current at the entrance of the inverter. In other words, when the concrete part is being cut, when it arrives at the rebar part, or when it arrives at the concrete part while the rebar part is being cut, an excessive current that is too large or too small is detected. Thus, it is a method of determining whether to transfer to the concrete part or the rebar part. During concrete cutting, when the input current is 114 A, the rotation speed of the main motor 4 is set to the target set rotation speed 1 of the reinforcing bar.
This is a method in which the operation is lowered to 16A, and conversely, in the case of the input current of 115A, the rotation speed of the main motor is increased to the target set rotation speed of 117A for the concrete part, and the operation is automatically switched during the rebar cutting.

In the method of FIG. 8, in another embodiment, the satisfaction of the condition for setting the rotation speed of the core bit is determined by the feed speed of the core bit. That is, since the feed speed at the time of cutting the concrete portion and the reinforcing bar portion is significantly different (for example, about 5 times faster than the reinforcing bar portion in concrete), the shift to the concrete portion and the reinforcing bar portion is determined by detecting this feed speed. How to Feed rate 114B during concrete cutting
In the case of (1), the rotation speed of the main motor is reduced to the target set rotation speed of 116B for the reinforcing bar, and conversely, during the cutting of the reinforcing bar, when the feed speed is 115B, the rotation speed of the main motor is set to the target of the concrete portion. This is a method of automatically switching the operation by increasing the rotation speed to 117B.

In this way (returning to FIG. 6), during the full-scale rebar concrete, the input current is equal to or less than the no-load set current.
When the number of revolutions decreases to 21, the number of revolutions 123 of the main motor 4 is decreased to the number of revolutions set in the no-load condition setting 122 (the same at the time of soft starting). Next, after it is confirmed by the signal of the arrival at the cutting target position 124 that the penetration has been made, the main motor 4 (126), the feed motor 9 (127), the inverter 38 (128), the cooling Water supply valve 17 (129) is OF
It becomes F. Then, the feed motor reverse rotation 130 is performed, and when the bit arrives at the origin 131, the operation of the feed motor 132 is also stopped, and the cutting 133 is completed.

[0026]

The automatic feeder for a core drill according to the present invention comprises:
Compared to the conventional core drill automatic feeder that uses a commutator motor, the load torque is only one point in order to maintain the proper rotation speed of the core bit, which requires complicated constant current value control. Once is set, the load torque hardly changes, so that a predetermined load torque can be easily obtained by setting the current value, and the control is simplified, and
When the cutting characteristics of the workpiece change, a desired load torque can be obtained even if the current value is constant, and the cutting efficiency can be improved. In addition, it is possible to easily realize the control of the soft start operation that enables safe low-speed rotation without chatter at the start.

[Brief description of the drawings]

FIG. 1 is an overall perspective view of an automatic core drill feeder according to an embodiment of the present invention.

FIG. 2 is a front view of an operation panel according to the embodiment.

FIG. 3 is a sequence diagram for explaining a configuration and a basic operation.

FIG. 4 is a continuation of the sequence diagram of FIG. 3;

FIG. 5 is a flowchart for explaining the flow of operation.

FIG. 6 is a continuation of A in the flowchart of FIG. 5;

FIG. 7 is a continuation of B in the flowchart of FIG. 5;

FIG. 8 is another embodiment of a flowchart for explaining the flow of operation.

FIG. 9 is a characteristic diagram of a conventional driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core drill 2 ... Control device 3 ... Cable 4 ... Bit rotation electric motor (main motor) 5 ... Reduction gear 6 ... Core bit 7 ... Bit rotation drive part 8. ..Feed mechanism 9 ... Electric motor (feed motor) for bit feed 10 ... Reducer 11 ... Feed drive unit 12 ... Post 13 ... Base 14 ... Anchor bolt 15 ... Tube Reference Signs List 16 supply hose 17 flow control valve 18 operation panel 19 power switch 20 cutting distance display 21 cutting distance setting device 22 bit size selection switch 23 ... Operation mode selection switch 24 ... Main motor current value changeover switch 25 ... Rotation speed selection changeover switch 26 ... Feed motor forward / reverse rotation switch 27 ... Distance setting changeover switch 28 ... Release setting reset switch 29: Abnormality display reset switch 30: Main motor abnormality display 31: Cutting not possible display 32: Cutting completion display 33: Operation start switch 34: Operation Stop switch 35 ・ ・ ・ Bit moving distance detector 36 ・ ・ ・ Bit origin position detector 37 ・ ・ ・ Cooling water detector 38 ・ ・ ・ Variable frequency inverter 39 ・ ・ ・ Main motor speed setting circuit 40 ・ ・ ・ Feed Speed detector 41 ・ ・ ・ Target input current setting circuit 42 ・ ・ ・ Load input current detector 43 ・ ・ ・ Main motor speed setting means 44 ・ ・ ・ Target input current setting means 45 ・ ・ ・ Soft start control means 46 ・..Target moving distance setting means

Continuation of the front page (56) References JP-A-8-224727 (JP, A) JP-A-7-323419 (JP, A) JP-A-3-213246 (JP, A) JP-A-6-226734 (JP) JP-A-7-314226 (JP, A) JP-A-4-141307 (JP, A) JP-A-10-58436 (JP, A) JP-A-6-79716 (JP, A) 6-31512 (JP, A) JP-A-9-300338 (JP, A) JP-A-4-17698 (JP, U) Registered utility model 3043121 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28D 1/14 B23B 47/02 H02P 5/46

Claims (3)

(57) [Claims] 1. A speed detector for detecting a speed of an induction motor, a slip frequency calculator for determining a torque characteristic, a frequency setter for setting a frequency of a maximum speed, and a frequency calculator for determining a frequency of an inverter. A voltage calculator in which the V / f value at which the motor gap magnetic flux number is always constant is previously input into the circuit, and the slip frequency calculated by the slip frequency calculator from the motor speed and the motor converted into the frequency. The sum is added to the speed and the frequency of the highest speed set by the frequency setting device is input to the frequency calculator and the voltage calculator. A rotary drive unit that rotates a core bit composed of a high-speed rotation induction motor driven by a variable frequency inverter and a speed reducer, and moves the core bit forward and backward A rotation speed setting means for setting an optimum rotation speed for a core bit, and a predetermined load on the core drill. Current value setting means for setting a predetermined load current at the inverter entrance, which is a cutting target current value at the inverter entrance for applying torque, and detecting the cutting target current value from the current value setting means and the load current at the inverter entrance. Motor control means for comparing the load current detected by the current detection means and controlling the number of revolutions of the motor of the feed drive unit so that the load current at the inverter inlet becomes the cutting target current value. Core drill automatic feeder. 2. A speed detector for detecting a speed of an induction motor, a slip frequency calculator for determining a torque characteristic, a frequency setter for setting a frequency of a maximum speed, and a frequency calculator for determining a frequency of an inverter. A voltage calculator in which the V / f value at which the motor gap magnetic flux number is always constant is previously input into the circuit, and the slip frequency calculated by the slip frequency calculator from the motor speed and the motor converted into the frequency. The sum is added to the speed and the frequency of the highest speed set by the frequency setting device is input to the frequency calculator and the voltage calculator. A rotary drive unit that rotates a core bit composed of a high-speed rotation induction motor driven by a variable frequency inverter and a speed reducer, and moves the core bit forward and backward In a core drill automatic feeder having a control device for controlling the operation of a core drill having a feed drive unit for driving a feed mechanism to be driven, a setting condition of a rotation speed of a core bit is distinguished by a cutting condition at the time of cutting, and each setting is performed. An automatic feeder for core drills, characterized in that it has a function of determining whether the condition is satisfied by detecting an inverter inlet current. 3. The automatic feeder for a core drill according to claim 2, further comprising a function of judging the establishment of the rotation speed setting condition of the core bit by detecting a feed speed.