Magnetic attraction type tapping device

Abstract

To provide a magnetic attraction type tapping device that can perform processing of a small screw hole in a thin processed object as well as processing of a large screw hole in a thick processed object while preventing performance of tapping in a state in which a magnet possibly falls from the object.SOLUTION: A magnetic attraction type tapping device 1 comprises a tool body 10, a tap size selection switch 30 for inputting the size of a mounted tap T, an electromagnet 40 for magnetically attracting and fixing the tool body 10 to an object, and a magnetic sensor 42 measuring magnetic flux density in a circumference of the electromagnet 40. The magnetic attraction type tapping device 1 sets a normal magnetic flux density range according to the size of the tap input with the tap size selection switch 30 (S14), and does not drive an electric motor 20 (S18) when the magnetic flux density (S16) measured by the magnetic sensor 42 deviates from the normal magnetic flux density range.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a magnetic adsorption type tapping device for performing tapping on a workpiece while being fixed to the workpiece with a magnet.

Background Art

[0002] There is known a magnetic adsorption type tapping device in which, when the workpiece is a magnetic material such as iron, the tapping device is fixed to the workpiece by a magnetic adsorption force generated by an electromagnet or a permanent magnet, and tapping is performed. For example, the tapping device disclosed in Patent Document 1 includes a magnet on the bottom surface portion, and is configured to be fixed to a workpiece that is a magnetic material by the magnetic adsorption force of this magnet. This tapping device is configured to automatically rotate and drive a tapping bolt (tap) with a tapping motor to perform tapping.

[0003] In this tapping device, the load of the tapping motor is measured, and when the load deviates from a predetermined range, the tapping motor is rotated reversely to pull out the tap from the processing hole. For example, when the tap reaches the bottom surface of the pilot hole, or when some problem occurs such as the tap becoming inclined with respect to the pilot hole, the load related to the tapping motor increases. When the load thus deviates from the predetermined range in this way, the tapping motor is rotated reversely. By stopping the forward rotation drive of the tapping motor when the load deviates from the predetermined range in this manner, it is considered possible to prevent the processed screw hole from being crushed or the tap from being damaged. The predetermined range of the load of this tapping motor is set such that the maximum value increases as the diameter of the pilot hole for performing tapping, that is, the size of the tap to be used, increases.

[0004] In addition, Patent Document 2 discloses a portable machine tool in which the main body of the machine tool is fixed by an electromagnet. In this portable machine tool, the magnetic flux around the electromagnet is measured by a magnetic sensor, and the plate thickness of the object to which the electromagnet is magnetically adsorbed is estimated from the output value of the magnetic sensor. When the output value of the magnetic sensor is not within a predetermined range, this portable machine tool determines that the plate thickness is too thin to obtain sufficient magnetic adsorption force, and does not start driving the electric motor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the tapping device disclosed in the above-mentioned Patent Document 1, when the load of the tapping motor deviates from a predetermined range, the forward rotation drive of the motor is stopped. Therefore, it is possible to prevent the tapping device from receiving a reaction force of a certain magnitude or more from the tap. Thus, it is considered that it is possible to prevent the tapping device from coming off the object due to the reaction force to some extent. However, when tapping is performed with a relatively large-sized tap, since the maximum value of the predetermined range of the load is set to a large value, when tapping is performed on a relatively thin object with a large-sized tap, even if the load of the motor is within the set predetermined range, a reaction force exceeding the magnetic adsorption force may act and the magnet may come off the object.

[0007] In the portable machine tool disclosed in Patent Document 2 described above, when a predetermined magnetic adsorption force is not obtained, the driving of the electric motor is not started, and thus machining cannot be performed. Therefore, it is possible to prevent the electromagnet from coming off due to the reaction force received by the tool when machining is performed in a state where a sufficient magnetic adsorption force is not obtained. By the way, in tapping, as the diameter of the screw hole to be formed, that is, the size of the tap to be used, increases, the reaction force received by the tap increases. Therefore, when performing tapping with this portable machine tool, the range of the magnetic adsorption force that allows the start of machining needs to be set to a magnitude that can withstand the reaction force received when performing tapping using the largest-sized tap assumed in the device. The minimum plate thickness with respect to the diameter D of the screw hole to be formed is usually 1 / 2D (preferably D) or more. For example, when machining a relatively large M20 screw hole, the plate thickness of the workpiece is usually 10 mm or more, which is relatively large, so a sufficient magnetic adsorption force can be obtained. However, a relatively small M6 screw hole may be formed in a material with a thin plate thickness of about 4 mm. In that case, not much magnetic adsorption force can be obtained. That is, the magnetic adsorption force actually obtained with a thin plate thickness where a small screw hole can be formed may not reach the range of the magnetic adsorption force set based on the reaction force received by the largest-sized tap assumed. Then, with a device such as Patent Document 2 with such a setting, it becomes impossible to form a screw hole in a thin material.

[0008] Therefore, an object of the present invention is to provide a magnetic adsorption type tapping device that can perform tapping from machining a small screw hole in a thin workpiece to machining a large screw hole in a thick workpiece while preventing tapping from being performed in a state where the magnet may come off from the object.

Means for Solving the Problems

[0009] That is, the present invention A tool body having a tap holder capable of mounting taps of various sizes and an electric motor for rotationally driving the tap holder, Tap size input means for inputting the size of the tap attached to the tap holder, A magnetic fixing part attached to the tool body for magnetically adsorbing to an object to fix the tool body to the object, A magnetic sensor configured to measure the magnetic flux density around the magnetic fixing part that changes in correlation with the magnetic adsorption force when the magnetic fixing part magnetically adsorbs to the object, A control unit that sets a normal magnetic flux density range according to the size of the tap input by the tap size input means, and does not drive the electric motor when the magnetic flux density measured by the magnetic sensor is outside the normal magnetic flux density range, Provided is a magnetic adsorption type tapping device comprising:

[0010] In the magnetic adsorption type tapping device, an appropriate normal magnetic flux density range can be set according to the tap size. Thereby, during tapping with a small-sized tap that generates only a relatively small load torque, the electric motor is driven even with a relatively small magnetic adsorption force, enabling tapping on a thin object where it is difficult to obtain a large magnetic adsorption force. On the other hand, during tapping with a large-sized tap that generates a relatively large load torque, the electric motor is driven only when a relatively large magnetic adsorption force is generated, preventing the fixation by the magnetic fixing part from being released due to the load torque in advance.

[0011] Further, the control unit can set a normal load torque range according to the size of the tap input by the tap size input means, and stop the driving of the electric motor when the torque applied to the tap is outside the normal load torque range.

[0012] Thereby, when the torque applied to the tap becomes excessively large due to some malfunction, the driving of the electric motor can be stopped to prevent breakage of the tap or collapse of the screw hole.

[0013] Further, the normal magnetic flux density range can be set such that a magnetic adsorption force of a magnitude that prevents the magnetic fixing portion from coming off due to the reaction force received by the tool body from the tap when the torque applied to the tap is the maximum torque within the normal load torque range.

[0014] This makes it possible to prevent the electromagnet from coming off due to the reaction force received by the tap when the torque applied to the tap becomes excessively large due to some defect.

[0015] Furthermore, the control unit can be configured to stop driving the electric motor when the magnetic flux density measured by the magnetic sensor deviates from the normal magnetic flux density range during driving of the electric motor.

[0016] During tapping, an external force may be unexpectedly applied to the tool body, or the feed of the tap may be made too fast, etc., causing the magnetic fixing portion to lift up. In such a case, a gap is generated between the magnetic fixing portion and the object to which it is magnetically adsorbed, resulting in a sharp decrease in the magnetic adsorption force. Then, the magnetic flux density measured by the magnetic sensor deviates from the normal magnetic flux density range. By stopping the driving of the electric motor at that time, it is possible to prevent the tool body from being swung around or falling down.

[0017] Hereinafter, an embodiment of the magnetic adsorption type tapping device according to the present invention will be described based on the accompanying drawings.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiment for Carrying Out the Invention

[0019] The magnetic adsorption type tapping device 1 according to an embodiment of the present invention includes a tool body 10 and a magnetic fixing portion 12 attached below the tool body 10 as shown in FIGS. 1 and 2. As will be described later, the magnetic adsorption type tapping device 1 is configured to perform tapping in a state where the tool body 10 is fixed to the workpiece by magnetically adsorbing the magnetic fixing portion 12 to the workpiece which is a magnetic material.

[0020] The tool body 10 has a base portion 14 to which the magnetic fixing portion 12 is fixed, and a movable portion 16 attached to the base portion 14 so as to be movable in the vertical direction as viewed in the figure. The movable portion 16 moves up and down by rotating a handle 18 attached to the base portion 14. The movable portion 16 has, inside thereof, an electric motor 20, a gear mechanism 22, and a tap holder 24 that is drivingly connected to the electric motor 20 via the gear mechanism 22. The tap holder 24 is rotationally driven by the electric motor 20. Various sizes of taps T can be detachably attached to the tap holder 24.

[0021] On the upper surface 16a of the movable part 16, as shown in FIG. 3, a power switch 26, a forward / reverse switching switch 28, a tap size selection switch (tap size input means) 30, and an LED display unit 32 for displaying the operating state are arranged. The base part 14 and the movable part 16 are electrically connected by a wiring 34 (FIGS. 1 and 2), and the power switch 26, the forward / reverse switching switch 28, and the tap size selection switch 30 are connected to a control circuit 36 (FIG. 2) arranged in the base part 14 via the wiring 34. A power cord 38 for supplying power to the magnetic adsorption type tapping device 1 is provided in the base part 14.

[0022] As shown in FIG. 2, the magnetic fixing part 12 includes an electromagnet 40 and a magnetic sensor 42 arranged above the electromagnet 40. The magnetic sensor 42 is arranged at a position where it can measure the magnetic flux density of the magnetic field generated around the electromagnet 40. More specifically, the magnetic sensor 42 is arranged so as to measure the magnetic flux density around the electromagnet 40 that changes in correlation with the magnetic adsorption force when the electromagnet 40 is magnetically adsorbed to a magnetic body. In this embodiment, the magnetic sensor 42 is arranged at a position where the magnetic flux density increases when the electromagnet 40 is arranged on a thicker magnetic body and a larger magnetic adsorption force is generated. That is, the magnetic flux density measured by the magnetic sensor 42 increases as the magnetic adsorption force increases. The arrangement of the magnetic sensor 42 is not limited to this, and for example, it can also be arranged at a position where the magnetic flux density decreases when the electromagnet 40 is arranged on a thicker magnetic body and a larger magnetic adsorption force is generated. In that case, the magnetic flux density measured by the magnetic sensor 42 decreases as the magnetic adsorption force increases.

[0023] As shown in FIG. 4, a microcomputer (control unit) 44 is arranged in the control circuit 36 within the base portion 14. The control circuit 36 further includes a rectifier 48 that converts the alternating voltage supplied from an external AC power source 46 into a direct current voltage, and a step-down circuit 50 that steps down the direct current voltage of the rectifier 48 to 5V according to the microcomputer 44. Within the movable portion 16, there are arranged a motor drive circuit 52 for driving the electric motor 20 and a motor current detection resistor 54 for detecting the magnitude of the current flowing through the electric motor 20. Further within the movable portion 16, a Hall IC 56 for detecting the rotation of the electric motor 20 is arranged in proximity to the electric motor 20. When a direct current voltage is supplied from the step-down circuit 50, the microcomputer 44 starts up and begins the control described later. The microcomputer 44 mainly controls the rotational drive of the electric motor 20 by the motor drive circuit 52 based on the states and outputs of the forward / reverse switching switch 28, the tap size selection switch 30, the magnetic sensor 42, the motor current detection resistor 54, and the Hall IC 56.

[0024] An exemplary operation of the magnetic adsorption type tapping device 1 according to the present embodiment will be described below with reference to FIGS. 5 and 6. Prior to starting the operation of the magnetic adsorption type tapping device 1, a tap T of an appropriate size is attached to the tap holder 24 according to the machining content, and the tap size selection switch 30 is switched according to the attached tap T. For example, when performing M6 screw hole machining, an M6 machining tap is attached to the tap holder 24, and the tap size selection switch 30 is switched to the M6 position.

[0025] With the power cord 38 connected to an external AC power supply 46, turn on the power switch 26 (S10). Then, a 5V DC voltage is supplied to the microcomputer 44 via the rectifier 48 and the step-down circuit 50, causing the microcomputer 44 to start up and begin control. At the same time, a DC voltage is also supplied to the electromagnet 40 via the rectifier 48, driving the electromagnet 40 (S12). If the magnetic adsorption type tapping device 1 is placed on a magnetic body, the magnetic adsorption type tapping device 1 is fixed to the magnetic body by the magnetic field generated by the electromagnet 40. Next, the microcomputer 44 checks the state of the tap size selection switch 30 and sets the normal load torque range and the normal magnetic flux density range according to the size of the tap T selected by the tap size selection switch 30 (S14). The tap size selection switch 30 in this embodiment can select the tap size from among M6, M8, M10, M12, M16, and M20. The normal load torque range and the normal magnetic flux density range set by the microcomputer 44 when each size is selected are set by determining the upper limit value of the normal load torque range and the lower limit value of the normal magnetic flux density range, respectively. The upper limit value of the normal load torque range and the lower limit value of the normal magnetic flux density range for each tap size are pre-stored in the memory of the microcomputer 44.

[0026] In this embodiment, by taking advantage of the fact that the load torque of the tap and the load on the motor are correlated, and that the load on the motor and the magnitude of the current flowing through the electric motor 20 are correlated, the value of the current flowing through the electric motor 20 is used as a value indirectly representing the magnitude of the load torque in the control of this embodiment. The upper limit value of the normal load torque range is set to a value that is larger than the load torque acting on the tap during appropriate tapping using taps of each size, and smaller than the load torque at which taps of each size start to break. Therefore, as long as the tapping is being performed appropriately, the current flowing through the electric motor 20 basically does not exceed the motor current value set as the upper limit value of the normal load torque range. As the size of the tap T increases, the load torque during tapping and the load torque that the tap can withstand increase, so the motor current value, which is the upper limit value of the normal load torque range, is set to be a larger value as the tap size increases. In this embodiment, the load torque is indirectly indicated by the current value flowing through the electric motor, but a torque sensor may be arranged on the rotating shaft of the electric motor, the tap holder, etc. to directly measure the load torque. In that case, the normal load torque range is set as the output value of the torque sensor or a value corresponding to the torque value indicated by it.

[0027] The lower limit value of the normal magnetic flux density range is set to a value at which a magnetic adsorption force sufficient to withstand, with a certain margin, the load torque acting on the tap during appropriate tapping using taps of each size can be obtained. In the present embodiment, the lower limit value of the normal magnetic flux density range is set to a value at which a magnetic adsorption force of a magnitude that prevents the magnetic fixing portion 12 from coming off even when the maximum torque within the normal load torque range acts on the tap during tapping with taps T of each size is obtained. The lower limit value of the normal magnetic flux density range can be determined with reference to the plate thickness generally considered necessary when forming screw holes of each size. For example, when forming an M6 screw hole, it becomes difficult to form a screw hole with sufficient strength when the plate thickness is less than 4 mm, and thus it is generally rare to form an M6 screw hole in a material with a thinner plate thickness. Therefore, when M6 is selectively input, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 4 mm can be used as the lower limit value of the normal magnetic flux density range. Similarly, when it is M8, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 5 mm, when it is M10, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 6 mm, when it is M12, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 7 mm, when it is M16, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 9 mm, and when it is M20, the magnetic flux density obtained when magnetically adsorbing to a magnetic body with a plate thickness of 10 mm can be used as the lower limit value of the normal magnetic flux density range. However, when the magnetic flux density obtained when magnetically adsorbing to a magnetic body with the minimum required plate thickness for each tap size is smaller than the value of the magnetic flux density at which a magnetic adsorption force sufficient to withstand, with a certain margin, the load torque acting on the tap during appropriate tapping can be obtained, it is not appropriate to use such a magnetic flux density value as the lower limit value of the normal magnetic flux density. The value of the magnetic flux density determined based on the required plate thickness can be adopted only when narrowing the normal magnetic flux density range (increasing the lower limit value). When the magnetic sensor 42 is arranged such that the measured magnetic flux density decreases as the magnetic adsorption force increases, the normal magnetic flux density range can be set by determining its upper limit value.

[0028] When the microcomputer 44 sets the normal load torque range and the normal magnetic flux density range based on the size of the tap T selectively input by the tap size selection switch 30 (S14), it then acquires the output value of the magnetic sensor 42 (S16). Then, it checks whether the magnetic flux density indicated by the acquired output value of the magnetic sensor 42 is within the normal magnetic flux density range (S18). In this embodiment, this means checking whether the measured magnetic flux density is equal to or greater than the lower limit value of the normal magnetic flux density range. When the magnetic flux density measured by the magnetic sensor 42 is within the normal magnetic flux density range, the microcomputer 44 checks the state of the forward / reverse switching switch 28 (S20). When the forward / reverse switching switch 28 is not ON, that is, when it is OFF, the above S14 to S18 are repeated and waiting is performed until the forward / reverse switching switch 28 becomes ON. When the forward / reverse switching switch 28 becomes ON, it is checked whether the forward / reverse switching switch 28 is ON on the forward side or ON on the reverse side (S22). When the forward / reverse switching switch 28 is on the forward side, the microcomputer 44 controls the motor drive circuit 52 to rotate the electric motor 20 forward (S24), and when the forward / reverse switching switch 28 is on the reverse side, it controls the motor drive circuit 52 to rotate the electric motor 20 in reverse (S26). In S18, when the measured magnetic flux density is outside the normal magnetic flux density range, the control after S20 is not advanced. Therefore, even if the forward / reverse switching switch 28 is turned ON, the driving of the electric motor 20 is not started and tapping cannot be performed.

[0029] When the electric motor 20 is driven forward or backward, next, as shown in FIG. 6, the microcomputer 44 acquires the output value of the magnetic sensor 42 (S28). Further, it is confirmed whether the tap size selection switch 30 has been switched (S30). If the size of the input tap T has changed, the normal load torque range and the normal magnetic flux density range are reset to ranges corresponding to the size of the newly input tap T (S32). Note that it is not normal to switch the tap size selection switch 30 at this stage. However, for example, if it is noticed that the tap size selection switch 30 has selected an incorrect tap size, the correct tap size is selectively input here. The magnetic flux density measured by the magnetic sensor 42 is compared with the set normal magnetic flux density range (S34). If the magnetic flux density measured by the magnetic sensor 42 is within the normal magnetic flux density range, the microcomputer 44 acquires the motor current value flowing through the electric motor 20 (S36). Specifically, the microcomputer 44 acquires the voltage value at the position between the motor drive circuit 52 and the motor current detection resistor 54, and obtains the value of the current flowing through the electric motor 20 from that value and the resistance value of the motor current detection resistor 54. The microcomputer 44 then checks whether the acquired motor current value is within the normal load torque range (S38). The motor current value increases as the load applied to the electric motor 20, that is, the load torque acting on the tap holder 24 and the tap T, increases. When the tap T mounted on the tap holder 24 is not in contact with the object to be processed, that is, when tapping is not being performed, the load applied to the electric motor 20 is very small, so the motor current value also becomes small. When the handle 18 is operated to insert the tap T into the counterbore formed in the object to be processed and start tapping with the tap T, the load applied to the tap T and the electric motor 20 increases, and accordingly the motor current also increases. When the size of the tap T is appropriately input by the tap size selection switch 30 and tapping is also appropriately performed, the motor current value should be within the set normal load torque range.When the motor current value is within the normal load torque range, specifically when the motor current value is equal to or less than the upper limit value of the normal load torque range, the above steps S28 to S38 are repeated until the forward / reverse switching switch 28 turns OFF (S40). When the forward / reverse switching switch 28 turns OFF, the microcomputer 44 stops driving the electric motor 20 (S42). In normal tapping, when the tap T reaches a predetermined position in the pilot hole or when tapping is performed on the entire pilot hole that has been penetrated, the forward / reverse switching switch 28 is turned OFF to temporarily stop the electric motor 20. After the driving of the electric motor 20 is stopped, the control returns to S14 in FIG. 5. Thereafter, the forward / reverse switching switch 28 is set to the reverse side (S22), the electric motor 20 is reversed (S26), and the tapping is completed by pulling out the tap T from the pilot hole.

[0030] When the magnetic flux density deviates from the normal magnetic flux density range in S34 above, the microcomputer 44 stops the electric motor 20 (S44). Also, when the motor current value deviates from the normal load torque range in S38 above, the microcomputer 44 also stops driving the electric motor 20 (S44). When tapping is properly performed, the motor current value does not exceed the upper limit value of the normal load torque range. However, when some problem occurs during tapping, the load increases and the motor current value may deviate from the normal load torque range. Such problems include, for example, when the position of the tap T is displaced or inclined with respect to the pilot hole, or when the chip is clogged so that it adheres to the groove of the tap. Thus, after the electric motor 20 is forcibly stopped because the magnetic flux density deviates from the normal magnetic flux density range or the motor current value deviates from the normal load torque range, no other operation is performed until the forward / reverse switching switch 28 turns OFF (S46). When the forward / reverse switching switch 28 turns OFF, the control returns to S14 in FIG. 5.

[0031] In this embodiment, a single forward / reverse changeover switch 28 is used to implement a switch for turning the drive of the electric motor 20 on and off and a switch for selecting forward / reverse rotation, but they may be separate switches. In that case, in S40 described above, when the switch for selecting forward / reverse rotation is switched, the process may return to S14 without stopping the electric motor 20. Then, in S22 to S26, the electric motor 20 may be driven in a direction opposite to the previous driving direction. Also, in S46, the process may wait until the switch for turning the drive on and off is turned off.

[0032] In the magnetic adsorption tapping device 1, a normal magnetic flux density range is set according to the size of the tap selectively input by the tap size selection switch 30. When the magnetic flux density measured by the magnetic sensor 42 deviates from the set normal magnetic flux density range, the electric motor 20 is prevented from driving (S14 to S18). Therefore, it becomes possible to prevent tapping from being performed in a state where the electromagnet 40 may be detached from the workpiece due to the load torque assumed to be applied to the tap T during tapping. On the other hand, since the normal magnetic flux density range is set according to the size of the selected tap, tapping can be performed even in a state where only a relatively small magnetic adsorption force is generated when machining a small-sized screw hole that generates only a relatively small load torque, and tapping can be performed only in a state where a relatively large magnetic adsorption force is generated when machining a large-sized screw hole that generates a relatively large load torque. This makes it possible to prevent an excessive magnetic adsorption force from being required, particularly when tapping a small screw hole, so that tapping can be performed even on a thin object that cannot obtain a very large magnetic adsorption force. Further, if the normal magnetic flux density range for each tap size is set as the range of the magnetic flux density obtained when the thickness of the workpiece is equal to or greater than the minimum thickness normally required for the screw hole formed by that tap, it is also possible to prevent tapping from being performed on an excessively thin workpiece. For example, a plate thickness of 10 mm or more is usually required for an M20 screw hole. However, when the electromagnet 40 is magnetically adsorbed on a workpiece having a thickness of less than 10 mm when an M20 tap is selected, the magnetic flux density measured by the magnetic sensor 42 at that time becomes less than the lower limit value of the normal magnetic flux density range set based on the plate thickness. Therefore, it is possible to prevent tapping from being performed on a workpiece having a thickness of less than 10 mm with an M20 tap.

[0033] Also, in the magnetic adsorption type tapping device 1, a normal load torque range is set according to the tap size selectively input by the tap size selection switch 30, and when the motor current value flowing through the electric motor 20 deviates from the set normal load torque range, the drive of the electric motor 20 is stopped. Therefore, it is possible to prevent the tap from being damaged due to an excessive load torque acting on the tap. Further, the maximum load torque that can occur in the tap T within this normal load torque range is smaller than the load torque (holding torque) that the electromagnet 40 can withstand within the normal magnetic flux density range. In other words, the normal magnetic flux density range is set such that the magnetic adsorption force generated by the electromagnet 40 is of a magnitude that the electromagnet 40 does not come off due to the reaction force received from the tap T when the load of the electric motor 20 reaches the maximum torque within the normal load torque range. Therefore, even if an excessive load torque occurs in the tap, since the drive of the electric motor 20 is stopped before a load torque exceeding the holding torque of the electromagnet 40 acts on the tap T, it is possible to prevent the load torque from exceeding the holding torque and the electromagnet 40 from coming off.

[0034] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the magnetic fixing portion for fixing the magnetic adsorption type tapping device may be constituted by a permanent magnet instead of an electromagnet. In the above embodiment, it is assumed that taps from M6 to M20 are attached and they can be selectively input by the tap size selection switch. However, it may be possible to selectively input smaller taps and larger taps. Also, the normal load torque range and the normal magnetic flux density range do not necessarily have to be set to different values for each tap. The tap sizes may be divided into several groups (for example, large, medium, small), and the normal load torque range and the normal magnetic flux density range may be set for each group. That is, the same normal load torque range and normal magnetic flux density range may be set for several tap sizes. Whether to set the normal load torque range is optional. The tap size input means for selectively inputting the tap size may be configured to selectively input the tap size by a button type switch, directly input the tap size by a touch panel type input device, or input the tap size by a signal from an external device connected by wire or wirelessly, etc., and can be in any form. Furthermore, in the above embodiment, the movable part is moved by manually operating the handle, but it may be configured to be automatically moved by an electric motor or the like.

Explanation of Signs

[0035] 1 Magnetic adsorption type tapping device 10 Tool body 12 Magnetic fixing portion 14 Base portion 16 Movable part 16a Upper surface 18 Handle 20 Electric motor 22 Gear mechanism 24 Tap holder 26 Power switch 28 Forward / reverse switching switch 30 Tap size selection switch (tap size input means) 32 LED display section 34 Wiring 36 Control circuit 38 Power cord 40 Electromagnet 42 Magnetic sensor 44 Microcomputer (control unit) 46 AC power supply 48 Rectifier 50 Step-down circuit 52 Motor drive circuit 54 Motor current detection resistor 56 Hall IC T tap

Claims

1. A tool body having a tap holder capable of mounting taps of various sizes, and an electric motor for rotationally driving the tap holder, tap size input means for inputting the size of the tap mounted on the tap holder, a magnetic fixing portion attached to the tool body for magnetically adsorbing to an object to fix the tool body to the object, a magnetic sensor configured to measure the magnetic flux density around the magnetic fixing portion that changes in correlation with the magnetic adsorption force when the magnetic fixing portion magnetically adsorbs to the object, a control unit that sets a normal magnetic flux density range according to the size of the tap input by the tap size input means, and does not drive the electric motor when the magnetic flux density measured by the magnetic sensor deviates from the normal magnetic flux density range, A magnetic adsorption type tapping device comprising the above.

2. The control unit sets a normal load torque range according to the size of the tap input by the tap size input means, and stops driving the electric motor when the torque applied to the tap deviates from the normal load torque range. The magnetic adsorption type tapping device according to Claim 1.

3. The normal magnetic flux density range is a range in which a magnetic adsorption force of a magnitude that does not cause the magnetic fixing portion to come off due to the reaction force received by the tool body from the tap when the torque applied to the tap reaches the maximum torque within the normal load torque range. The magnetic adsorption type tapping device according to Claim 2.

4. The control unit stops driving the electric motor when the magnetic flux density measured by the magnetic sensor during driving of the electric motor deviates from the normal magnetic flux density range. The magnetic adsorption type tapping device according to Claim 1.

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