JP2012139786A - Screwing tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screwing tool capable of performing zero point adjustment and gain adjustment of a strain gage after assembling of housing to reduce a manufacture man-hours.SOLUTION: The screwing tool includes an electric motor, a power transmission mechanism for driving an output shaft mounting an edge tool with the motor, a control part for controlling the rotation of the motor, a torque sensor 12 for detecting generation of tightening torque on the output shaft, and a detection circuit 70b for detecting an output signal from the torque sensor 12 and outputing it to the control part. The control part is provided with a microcomputer 60 having an A/D port, and the detection circuit 70b is provided with digital potentiometers 83, 84 for electrically performing adjustment of a zero point and/or the maximum amplitude of output of the detection circuit. The zero point and/or the maximum amplitude of the output of the detection circuit 70b is adjusted so as to be within an input voltage range of the A/D port contained in the microcomputer 60 by adjusting the digital potentiometers 83, 84.

Description

  The present invention relates to a screw tightening tool that is rotationally driven by a motor and tightens a screw or the like with a predetermined tightening torque, and more particularly to a screw tightening tool that is improved so as to easily adjust a torque detection device in a manufacturing stage.

  As a screw tightening tool for tightening screws, bolts, etc., an apparatus using an oil pulse unit that generates a striking force by using hydraulic pressure is known. A tool using an oil pulse unit has a feature that operation noise is low because there is no collision between metals. As an example of such a device, there is, for example, Patent Document 1, an air motor or a DC motor is used as power for driving the oil pulse unit, and the output shaft of the motor is directly connected to the oil pulse unit. Pulling the trigger switch to activate the device drives the motor. The external control box (external connection device) detects whether the tightening has been performed with the specified tightening torque using the output from the torque detection means or angle detector. Stop rotation.

  In recent years, brushless DC motors have come to be used as drive sources for portable screw tightening tools. A brushless DC motor has the advantages of being able to control rotation with high accuracy, maintenance-free, long life, low loss, and increased workload. A brushless DC motor is a DC motor without a brush (rectifying brush), which uses a winding on the stator side and a permanent magnet on the rotor side, and sequentially energizes a predetermined coil with power driven by an inverter. To rotate the rotor. In a screw tightening tool using a brushless DC motor, for example, a switching element for turning on / off the energization of a stator winding and a control circuit for generating a control signal for turning on / off the switching element are provided in a housing. It is necessary to mount on a circuit board provided inside.

  On the other hand, in the method of sending the output from the torque detection means and the angle detector to the control box provided outside as in Patent Document 1, the weak output signal from the detector is sent through the cable, so that the attenuation The length of the cable that can be disposed is limited, for example, about 3 m. Therefore, in order to eliminate this cable length limitation, there is a demand for processing the output from the torque detection means and the angle detector inside the screw tightening tool and sending the detection result to the external connection device. It was.

  In order to satisfy such a demand, a torque detection means is provided in a screw tightening tool using a brushless DC motor, and the rotation of the motor is controlled using the output from the torque detection means. In a conventional screw tightening tool, as shown in Patent Document 2, a strain gauge is provided on an output shaft as torque detection means, and an output from the strain gauge is provided by a rotary transformer to transmit to a torque detection means (torque detection circuit). The output signal of the torque detection means is sent to the external connection device.

Japanese Patent Laid-Open No. 2007-30056 Japanese Examined Patent Publication No. 6-24713

  The output signal transmitted from the strain gauge to the outside via the rotary transformer is a weak analog signal, and this output must be detected by the detection circuit and transmitted to the external connection device. Since the weak signal detected by this detection circuit needs to be analog / digital converted (hereinafter referred to as “A / D conversion”), it is important to adjust the gain with high accuracy. Therefore, in order to match the range of the analog waveform from the detection circuit to the measurement range of the A / D converter, it is necessary to provide a variable resistor in the detection circuit and adjust by rotating the volume of the variable resistor during product assembly was there. Adjustment of such a variable resistor (mechanical adjustment work) is complicated, leading to an increase in manufacturing cost.

  The present invention has been made in view of the above background, and its object is to provide a screw tightening tool that is inexpensive and highly reliable by reducing the number of steps required for adjusting the torque detection circuit to reduce the manufacturing cost. There is to do.

  Another object of the present invention is to use an electronic semi-fixed resistor as a variable resistor included in the detection circuit of the torque detection circuit, and to adjust the resistance value electrically from a control unit or an external connection device. It is to provide a screw tightening tool.

  Still another object of the present invention is not to use a dedicated A / D converter but a control microcomputer (referred to as a “microcomputer” for short) in A / D converting the output signal of the detection circuit of the torque detection circuit. An object of the present invention is to provide a screw tightening tool that uses the included A / D conversion function to reduce the number of parts.

  The characteristics of representative ones of the inventions disclosed in the present application will be described as follows.

  According to one aspect of the present invention, a motor, a power transmission mechanism that drives an output shaft on which a tip tool is mounted by the motor, a control unit that controls rotation of the motor, and generation of tightening torque on the output shaft are generated. In a screw tightening tool having a torque detection means for detecting and a detection circuit for detecting an output signal from the torque detection means and outputting the detected signal to the control section, a microcomputer having an A / D port is provided in the control section, An adjusting means for electrically adjusting the zero point or / and the maximum amplitude of the output of the detection circuit is provided, and by adjusting the adjusting means, the zero point or / and the maximum amplitude of the output of the detection circuit is set to A / A of the microcomputer. It is adjusted to fall within the input voltage range of the D port. The torque detection means includes a strain gauge provided on the output shaft, and a rotary transformer that transmits the output signal of the strain gauge to the detection circuit, and the adjustment means is an electronic semi-fixed resistor.

  According to another feature of the invention, the electronic semi-fixed resistor is a digital potentiometer and includes three input terminals: chip select (CS), increment (INC), and up / down (U / D). The resistance value of the digital potentiometer is electrically set by a microcomputer via an input terminal. The power transmission mechanism includes a striking mechanism having an oil pulse unit, and the microcomputer calculates the tightening torque value by the oil pulse unit using the signal detected by the detection circuit, and when the set torque value is reached, the motor is turned on. I stopped it. The screw tightening tool has a transmission / reception device for communicating with the external connection device via the communication path, and the control unit is configured to control the digital potentiometer based on the setting instruction signal of the digital potentiometer sent from the external connection device via the communication path. Change the setting value.

  According to still another aspect of the present invention, a motor, an output unit driven by the motor, a tip tool connected to the output unit, a housing that houses the motor, a sensor that is housed in the housing, and a sensor And a screw tightening tool having an adjusting means for adjusting the gain of the output signal, wherein the adjusting means can be electrically adjusted from the outside of the housing. The adjusting means is, for example, an electronic semi-fixed resistor. The adjustment is performed by an external connection device that can be connected to a screw tightening tool. A torque measuring device for detecting the torque of the output unit is connected to the external connection device, and adjustment is performed by a signal from the torque measuring device.

  According to the first aspect of the present invention, the detection circuit is provided with adjusting means for electrically adjusting the zero point or / and maximum amplitude of the output, and the zero point or / and maximum amplitude of the output is adjusted by adjusting the adjusting means. Since it is adjusted to be within the input voltage range of the A / D port of the microcomputer, the zero point and / or the maximum amplitude can be adjusted before and after the assembly of the screw tightening tool. It is possible to realize a screw tightening tool that can reduce labor costs and improve the adjustment accuracy.

  According to the invention of claim 2, the torque detecting means includes a strain gauge provided on the output shaft and a rotary transformer for transmitting the output signal of the strain gauge to the detection circuit, and the adjusting means is an electronic semi-fixed resistor. It can be electrically controlled from a microcomputer included in the screw tightening tool or an external connection device connected to the screw tightening tool.

  According to the invention of claim 3, since the electronic semi-fixed resistor is a digital potentiometer, the set resistance value can be easily changed only by sending a command signal to the input terminal of the digital potentiometer.

  According to the invention of claim 4, the power transmission mechanism includes an impact mechanism having an oil pulse unit, and the microcomputer calculates and sets a tightening torque value by the oil pulse unit using a signal detected by the detection circuit. Since the motor is stopped when the torque value is reached, a screw tightening tool that can be securely tightened with a specified tightening torque can be realized.

  According to the invention of claim 5, since the control unit changes the setting value of the digital potentiometer based on the setting instruction signal of the digital potentiometer sent from the external connection device via the communication path, the external connection device is used. The screw tightening tool can be adjusted accurately and easily.

  According to the invention of claim 6, since the adjusting means for adjusting the gain of the signal output from the sensor in the screw tightening tool is configured to be electrically adjustable from the outside of the housing, the zero point or / and the maximum The amplitude can be adjusted regardless of before and after the assembly of the screw tightening tool, and the labor cost for assembly can be reduced, and a screw tightening tool with improved adjustment accuracy can be realized.

  According to the seventh aspect of the present invention, since the adjusting means is an electronic semi-fixed resistor, the set resistance value of the semi-fixed resistor can be electrically controlled.

  According to the invention of claim 8, since the adjustment is performed by an external connection device that can be connected to the screw tightening tool, the external connection device can be used without preparing a control program necessary for the adjustment in the screw tightening tool in advance. It becomes possible to control from the side.

  According to the ninth aspect of the present invention, the torque measuring device for detecting the torque of the output unit is connected to the external connection device, and the adjustment is performed according to the signal from the torque measuring device. It is possible to realize a screw tightening tool with high accuracy.

  The above and other objects and novel features of the present invention will become apparent from the following description and drawings.

It is sectional drawing which shows the whole screw fastening tool 1 which concerns on the Example of this invention. It is sectional drawing of the AA part of FIG. It is a block diagram which shows the circuit structure of the drive control system of the motor 3 of the screw fastening tool 1 which concerns on the Example of this invention. It is a figure which shows the whole circuit structure of the screw fastening tool 1 which concerns on the Example of this invention. FIG. 5 is a block diagram showing a detailed configuration of a detection circuit 70b in FIG. FIG. 6 is a block diagram showing a detailed configuration of the electronic semi-fixed resistor 83 in FIG. 5. It is the schematic for demonstrating the method of the zero point adjustment and gain adjustment of the screw fastening tool 1 which concerns on the Example of this invention. It is a block block diagram of the connection apparatus at the time of gain adjustment of the screw fastening tool 1 which concerns on the Example of this invention. It is a flowchart which shows the procedure of the zero point adjustment of the screw fastening tool 1 which concerns on the Example of this invention. It is a flowchart which shows the procedure of the gain adjustment of the screw fastening tool 1 which concerns on the Example of this invention. It is a block diagram which shows the detailed structure of the detection circuit 170b which concerns on a prior art. It is the schematic for demonstrating the procedure which performs the zero point adjustment and gain adjustment of the detection circuit 170b single-piece | unit based on a prior art. It is the schematic for demonstrating the output waveform figure of the detection circuit 170b based on a prior art, and the adjustment method of the zero point and gain. It is the schematic for demonstrating the method of the gain adjustment (secondary adjustment) after the assembly of the screw fastening tool 201 which concerns on a prior art. It is a wave form diagram for demonstrating the correction method by the gain adjustment (secondary adjustment) of the screw fastening tool 201 which concerns on a prior art.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the present specification, the impact-type screw tightening tool 1 will be described as an example of the screw tightening tool. Moreover, the up-down and front-back directions of the screw tightening tool 1 will be described as directions shown in FIG.

  FIG. 1 is a diagram illustrating the entire screw tightening tool 1, a power supply box 30 connected thereto, and an external connection device 40 according to the present embodiment, and the screw tightening tool 1 is shown in a sectional view. The screw tightening tool 1 drives the motor 3 using the electric power supplied from the power supply box 30 through the cable 2, drives the oil pulse unit 4 by the motor 3, and outputs to the output shaft 5 connected to the oil pulse unit 4. By applying the rotational force and the striking force, the rotational striking force is transmitted continuously or intermittently to a tip tool (not shown) such as a hexagon socket to perform operations such as nut tightening and bolt tightening.

  The power supplied by the cable 2 is, for example, DC 140V, and is generated from a commercial power supply 29 such as AC100V in a power supply box 30 provided outside the tool body. In the power supply box 30, a DC 12V power supply is further generated from the commercial power supply 29 for the control system power supply and supplied to the screw tightening tool 1 through the cable 2. Although not shown, the cable 2 is configured to include a power cord for DC 140V and a power cord for DC 12V, and the cable 2 and the screw tightening tool 1 and / or the power box 30 have connectors not shown. It may be configured to be detachable by use, or may be configured to be detachable.

  The motor 3 is a brushless DC motor including a rotor 3b having a permanent magnet on the inner peripheral side and a stator 3a having a winding wound around an iron core on the outer peripheral side, and includes two bearings 10a and 10b. Thus, the rotary shaft 20 is fixed and accommodated in the cylindrical body 6a of the housing. The housing is composed of three parts, a body part 6a, a grip part 6b, and a circuit board housing part 6c, and is integrally manufactured from plastic or the like as an insulator. Further, the housing can be divided into left and right on the plane including the longitudinal axis of the body portion 6a and the longitudinal axis of the grip portion 6b, that is, the cross-sectional portion of FIG. 1, and the detachable housing is fixed by a plurality of screws (not shown). Is done. A drive circuit board 7b for driving the motor 3 is disposed on the rear side of the motor 3, and an inverter circuit composed of a semiconductor element such as an FET and the rotation position of the rotor 3b are arranged on the circuit board. A rotational position detecting element 42 for detecting is mounted. As the rotational position detection element 42, for example, a Hall element or a Hall IC can be used. A cooling fan 17 for cooling the motor 3 and the oil pulse unit 4 is provided at the rearmost end inside the body portion 6a of the housing.

  A trigger switch 14a is disposed in the vicinity of the attachment portion of the grip portion 6b extending downward at a substantially right angle from the body portion 6a of the housing, and is proportional to the amount of the trigger switch 14a pulled by the switch circuit board 14b provided immediately below the trigger switch 14a. The signal is transmitted to the motor control board 7a. Inside the circuit board housing part 6c on the lower side of the grip part 6b, the three circuit boards of the motor control board 7a, the sensor board 8 and the communication board 9 are arranged in a direction substantially perpendicular to the dividing surface of the housing. Arranged in parallel. Guide grooves 21a, 21b, and 21c serving as portions for holding the circuit board are formed on the inner wall of the circuit board housing portion 6c of the housing. These guide grooves 21a, 21b, and 21c are similarly formed on the other side of the housing that can be divided. When assembling, the guide grooves 21a, 21b, and 21c are placed on the work table so that the inner surface of the housing on one side is up, The three circuit boards can be easily fixed by simply inserting them into the guide grooves 21a, 21b, 21c of the housing and overlapping the other housing so that the three circuit boards are fitted into the guide grooves of the other housing.

  The communication board 9 is provided with a plurality of light emitting diodes (LEDs) 18, and the light from the light emitting diodes 18 is arranged so that it can be identified from the outside through a transmission window of a housing (not shown) or through a through hole. The light-emitting diode 18 is turned on when normal tightening is completed and the motor 3 is stopped, flashed as an alarm when it is determined that tightening is abnormal, or turned on when communication abnormality occurs.

  As the oil pulse unit 4 built in the body 6a of the housing, a known unit can be used. The oil pulse unit 4 is mainly synchronized with the drive portion that rotates in synchronization with the motor 3 and the output shaft 5 to which the tip tool is attached. Thus, the output part is composed of two parts that rotate. The drive portion that rotates in synchronization with the motor 3 includes a liner plate 23 that is directly connected to the rotary shaft 20 of the motor 3 and a liner 22 that has a substantially cylindrical outer diameter that is fixed so as to extend forward on the outer peripheral side thereof. . The output portion that rotates in synchronization with the output shaft 5 includes a main shaft 24 and a blade (not shown) that is attached to a groove formed 180 degrees apart on the outer peripheral side of the main shaft 24 via a spring. Is done. The main shaft 24 is penetrated by the integrally molded liner 22 and is held so as to be able to rotate in a closed space formed by the liner 22 and the liner plate 23, and oil for generating torque is generated in the closed space. (Hydraulic oil) is filled.

  When the trigger switch 14 a is pulled to start the motor 3, the rotational force of the motor 3 is transmitted to the oil pulse unit 4. When the oil pulse unit 4 is filled with oil and no load is applied to the output shaft 5 or when the load is small, the output shaft 5 is nearly rotated by the motor 3 only by the resistance of the oil. Rotate synchronously. When a strong load is applied to the output shaft 5, the rotation of the output shaft 5 and the main shaft 24 stops, and only the liner 22 on the outer peripheral side of the oil pulse unit 4 continues to rotate. The oil pressure rapidly rises to generate a shock pulse, and the main shaft 24 is rotated by a strong spire-like torque, and a large tightening torque is transmitted to the output shaft 5. Thereafter, the same striking operation is repeated several times, and the tightening target is tightened with the set torque. The output shaft 5 is held at the rear end by the bearing 10 c and the front is held by the case 15 by the metal 16.

  The diameter of the output shaft 5 is thin on the front side of the bearing 10c, and a strain gauge 12 as a torque detection sensor is attached to the thinned portion. On the front side of the location where the strain gauge 12 is attached, the diameter of the output shaft 5 is thick, and the input transformer 11a for supplying voltage to the strain gauge 12 at that location and the output from the strain gauge 12 are transmitted. An output transformer 11b is provided. The input transformer 11a and the output transformer 11b include coils disposed on the inner peripheral side and the outer peripheral side, respectively. The inner peripheral side coil is fixed to the output shaft 5, and the outer peripheral side coil is fixed to the case 15. Input / output voltages to the input transformer 11a and the output transformer 11b are transmitted to the sensor substrate 8 via the connector 11c. Each part mentioned above attached to the output shaft 5 is integrated in the cylindrical case 15, and the case 15 is attached to the front side of the trunk | drum 6a of a housing. In addition, a wiring cover 19 for covering connection wiring and the like is provided at the lower portion of the case 15.

Next, the mounting structure of the rotational position detection sensor and the torque detection sensor will be described with reference to FIG.
FIG. 2 is a cross-sectional view taken along a line AA in FIG. The output shaft 5 on the inner side of the case 15 has a narrow diameter only at a position where the strain gauge 12 is attached in the cylindrical output shaft 5 and has a substantially square cross section. And the strain gauge 12 is provided in each of four planes located in the outer periphery of a cross section. Thereby, the detection accuracy of torque can be improved. The strain gauge 12 is a sensor that detects a minute change (strain) in mechanical dimensions as an electrical signal, and is fixed to the surface of the structure by bonding or the like. A commercially available general-purpose product can be used as the strain gauge 12, but a gauge lead that is a lead wire is attached from the strain sensing part of the strain gauge 12. The wiring cover 19 is a cover for forming a space through which a wiring for detecting a rotational position and a wiring for a torque detection sensor, which will be described later, pass.

  Next, the configuration and operation of the drive control system of the motor 3 will be described with reference to FIG. FIG. 3 is a block diagram showing a circuit configuration of the drive control system of the motor 3. In this embodiment, the motor 3 is a three-phase brushless DC motor. This brushless DC motor is a so-called inner rotor type, and includes a rotor (rotor) 3b including a plurality of sets of permanent magnets (magnets) including N and S poles, and a star-connected three-phase motor. In order to detect the rotational position of the stator 3a (stator) composed of the stator windings U, V, and W and the rotor 3b, three rotations arranged at predetermined intervals in the circumferential direction, for example, at an angle of 60 ° A position detection element 42 is provided. Based on the position detection signals from these rotational position detection elements 42, the energization direction and time to the stator windings U, V, W are controlled, and the motor 3 rotates.

  The drive circuit substrate 7b is configured to include an inverter circuit including six switching elements Q1 to Q6 such as FETs (Field Effect Transistors) connected in a three-phase bridge form. The gates of the six switching elements Q1 to Q6 that are bridge-connected are connected to the rotation control circuit 51, and the drains or sources of the six switching elements Q1 to Q6 are star-connected stator windings U. , V, W. As a result, the six switching elements Q1 to Q6 perform a switching operation according to the switching element drive signals (drive signals H1 to H6) input from the rotation control circuit 51, and the 140V DC applied to the inverter circuit is three-phased. (U phase, V phase and W phase) Electric power is supplied to the stator windings U, V and W as voltages Vu, Vv and Vw.

  Of the switching element drive signals (three-phase signals) for driving the gates of the six switching elements Q1 to Q6, the three negative power supply side switching elements Q4, Q5, Q6 are converted into pulse width modulation signals (PWM signals) H4, The operation amount (stroke) of the trigger switch 14a is detected by the applied voltage setting circuit 49, and a setting signal based on the operation amount is output to the first microcomputer 50 for motor control. The microcomputer 50 adjusts the amount of power supplied to the motor 3 by changing the pulse width (duty ratio) of a PWM (Pulse Width Modulation) signal, and controls the start / stop of the motor 3 and the rotation speed.

  Here, the PWM signal is supplied to any one of the positive power supply side switching elements Q1 to Q3 or the negative power supply side switching elements Q4 to Q6 of the inverter circuit, and the switching elements Q1 to Q3 or the switching elements Q4 to Q6 are switched at high speed. As a result, the power supplied to each stator winding U, V, W is controlled by 140V DC. In this embodiment, since the PWM signal is supplied to the negative power supply side switching elements Q4 to Q6, the electric power supplied to the stator windings U, V, W by controlling the pulse width of the PWM signal. Can be adjusted to control the rotation speed of the motor 3.

  Although not shown, the first microcomputer 50 temporarily stores a central processing unit (CPU) for outputting a drive signal based on the processing program and data, a ROM for storing the processing program and control data, and data. It includes a RAM for storing, a timer having a clock function, and the like.

  Next, the overall circuit configuration of the screw tightening tool 1 according to the present embodiment will be described with reference to FIG. In this embodiment, the motor system power source that serves as the power source for the motor 3 and the motor control circuit and the control power source for other control devices are divided into two systems, the motor system power source being a non-insulated power source and the control system power source being insulated. Two direct currents are supplied via a cable 2 from a power supply box 30 provided outside. The 140 V direct current is generated by the full-wave rectifying / smoothing circuit 31 in the power supply box 30. The full-wave rectifying / smoothing circuit 31 is, for example, a combination of a rectifying circuit in which four rectifying elements are connected in a bridge shape and a smoothing circuit using a capacitor. The 12V direct current is generated by an AC / DC converter 32 disposed in the power supply box 30.

  In the circuit 1A, 140V direct current is supplied to the drive circuit board 7b of the motor 3. Drive power is supplied to a stator winding of a predetermined motor 3 by an inverter circuit mounted on the drive circuit board 7b. The 140V direct current is also supplied to the 18V constant voltage circuit 53. The 18V constant voltage circuit 53 may be configured by a known chopper circuit, or may be configured by a known constant voltage circuit in which a Zener diode and a transistor are combined. The 18V DC output from the 18V constant voltage circuit 53 is input to the second constant voltage circuit 52, and the second constant voltage circuit 52 operates the operating voltage Vcc for operating the microcomputer 50, for example, 5V DC and 3. 3V direct current is generated.

  The direct current generated by the power supply box 30 is input to a portion other than the control circuit for the motor 3. First, 12V DC is input to the constant voltage circuit 64, where a voltage for operating the microcomputer 60, for example, 5V, 3.3V, is generated and input to the microcomputer 60. Also. Input to ± 12 V power supply 71. The ± 12V power supply 71 generates a voltage of −12V in addition to + 12V. −12V is used for driving the strain gauge 12. Note that the power supply line from the ± 12 V power supply 71 to the strain gauge 12 is not shown. The 12 V direct current is also supplied to the cooling fan 17. The cooling fan 17 is ON / OFF controlled by the drive circuit 72 under the control of the microcomputer 60.

  The first microcomputer 50 and the second microcomputer 60 are connected via a signal line to exchange data between them, but the signal line is connected via a photocoupler 65 in order to maintain the insulation relationship between the two. . Signals sent from the second microcomputer 60 to the first microcomputer 50 are a signal 68 for setting the rotational driving force of the motor 3 and a signal 69 for ON / OFF control for turning off the rotation of the motor 3. is there. The data sent from the first microcomputer 50 to the second microcomputer 60 is an acknowledge signal 67 for a signal 66 indicating whether the trigger switch 14 a is turned on and a signal 68 for setting the rotational driving force of the motor 3. . Of course, the type of signal is not limited to this, and the exchange of other signals is arbitrary.

  A transmission signal from the transmission circuit 70a of the torque detection circuit 70 is supplied to the strain gauge 12 via the input transformer 11a. At the same time, the reference amplitude from the transmission circuit 70a is also sent to the microcomputer 60. This is because the microcomputer 60 cannot detect distortion from the torque waveform without inputting the reference amplitude. When tightening torque is generated by the oil pulse unit 4 on the output shaft 5, the resistance value of the strain gauge 12 changes, and the reference amplitude signal changed by the change in resistance value is transmitted to the detection circuit 70b via the output transformer 11b. It is detected. Since a signal for offset adjustment is sent from the microcomputer 60 to the detection circuit 70b, the detection signal corrected for offset is output to the microcomputer 60.

  In this embodiment, a torque detection circuit 70 including a detection circuit 70b is provided inside the screw tightening tool 1. Further, the microcomputer 60 is configured to calculate how much torque value (tightening torque) is used by using the output value of the strain gauge 12. Normally, the reference amplitude signal deformed by the change in the resistance value of the strain gauge 12 has a very small signal level and is easily influenced by external noise. However, in this embodiment, since the distance from the strain gauge 12 to the detection circuit 70b is short, detection can be performed while suppressing the influence of noise as much as possible. Furthermore, since the output of the detection circuit 70b is input to the microcomputer 60 and digitized using an A / D converter included in the microcomputer 60, there is no need to prepare a separate A / D converter. The number of parts can be reduced.

  Next, the operation | movement at the time of the bolt fastening using the screw fastening tool 1 of a present Example is demonstrated. First, the operator operates an operation button (not shown) of the main body, and the operator who sets the tightening torque value sets a bolt or the like on the tip tool and positions the material to be tightened, and then pulls the trigger switch 14a. The microcomputer 50 controls the motor 3 to rotate in accordance with the drawn stroke. At this time, the microcomputer 60 may limit the rotation speed of the motor 3 according to the set tightening torque. For example, when the tightening torque is low, the microcomputer 60 corresponds to the microcomputer 50 with a low tightening torque. The maximum rotation number of the motor 3 is instructed. When the rotation speed of the motor 3 is limited as described above, the microcomputer 50 is instructed to rotate the motor 3 even when the stroke of the trigger switch 14a corresponds to a higher rotation speed. Control to be kept at.

  Next, the microcomputer 60 monitors the output of the strain gauge 12 to monitor whether the tightening has been performed with a predetermined tightening torque. If the microcomputer 60 determines that the tightening has been normally completed with the set tightening torque value, the microcomputer 60 sends a signal for turning off the motor 3 to the microcomputer 50 via the signal line 69. When the microcomputer 50 receives the instruction to turn off the motor, the microcomputer 50 stops the rotation of the motor 3 even though the trigger switch is turned on. The operator can recognize that the work is completed by the automatic stop of the motor 3.

  The microcomputer 60 can exchange various data with the external connection device 40 via the RS422 transceiver 61. In this case, the RS422 transceiver 61 and the external connection device 40 are connected using the signal line 44. The cable 2 including the signal line 44 is detachably connected by the connector 43 and is connected to the power supply box 30 and the external connection device 40. The communication using the signal line 44 may use a known wireless communication system instead of a wired communication system.

  In the screw tightening tool 1 described above, it is important to accurately detect the tightening torque value by the strain gauge 12 in order to manage the tightening torque. Therefore, in the process of manufacturing and assembling the screw tightening tool 1, adjustment of the torque detection circuit 70, particularly adjustment of the detection circuit 70b, is carefully performed.

  Before explaining the embodiment of the present invention, a conventional method for adjusting a detection circuit will be described with reference to FIGS. FIG. 11 is a block diagram showing a detailed configuration of the detection circuit 170b according to the prior art. A signal output from the strain gauge 12 via the output transformer 11 b is detected by the torque waveform extraction circuit 180. This detected signal is an analog output and varies in a range of −12 V to +12 V due to individual differences of the strain gauges 12. In order to enable the input of this varying signal to the second microcomputer 60, the output signal from the detection circuit 170b is adjusted to be in the range of 0V to 5V.

  There are two adjustment points. One is the output voltage of the strain gauge 12 when the impact torque is 0, and the mechanical semi-fixed resistor 183 (VR_1) included in the zero point adjustment circuit 181 so that the output voltage becomes 0V. ) To adjust. Further, the mechanical semi-fixed resistor 184 (VR_2) included in the gain adjustment circuit 182 is used so that the maximum value of the output signal after the zero point adjustment (the maximum tightening torque, for example, the output waveform at the time of impact of 40 Nm) becomes 5V. adjust. The mechanical semi-fixed resistors 183 and 184 are, for example, chip-type cermet film ceramic semi-fixed variable resistors, and the resistance value can be changed within a predetermined range by a mechanical operation such as turning the slot portion with a screwdriver or the like. it can.

  FIG. 12 is a diagram for explaining how to adjust the mechanical semi-fixed resistors 183 and 184. This adjustment is performed before the case 15 containing the input transformer 11a and the output transformer 11b is assembled in the housing, and is adjusted in a state where the case 15 and the sensor substrate 208 are connected. First, the output shaft 5 protruding from the case 15 is fitted into the hole of the fixture 186. The cross-sectional shape of the hole of the fixture 186 is substantially the same as the cross-sectional shape of the output shaft 5, thereby holding the output shaft 5 so that it cannot rotate.

  Next, the output shaft 185 of the torque application device (not shown) is fitted into the fitting groove (see the output shaft 5 in FIG. 1) at the rear end of the output shaft, and before applying the torque, the mechanical semi-fixed resistor 183 is applied. The zero point is adjusted by mechanically turning the slot portion of the screw with a screwdriver or the like. Next, a predetermined torque value (for example, 40 Nm) is applied by a torque application device, and the slot portion of the mechanical semi-fixed resistor 184 is mechanically rotated with a screwdriver or the like so that the output waveform at that time becomes + 5V. Adjust by.

  FIG. 13 is an output waveform diagram of the detection circuit 170b and a schematic diagram for explaining a method for adjusting the zero point and gain. The left side of FIG. 13 shows output waveforms 191 to 193 of the detection circuit 170b when a torque of 40 Nm is applied to the output shafts 5 of the bodies a to c to be adjusted. Here, the output waveform of the detection circuit 170b varies in a range from −12V to + 12V, and as shown by the output waveform 191 in the airframe “a”, the zero point output 191a is about 2V and 40 Nm output (40 Nm 191b is a little over 10V. By adjusting the mechanical semi-fixed resistors 183 and 184, such a waveform is adjusted so that the output value falls within the range of 0V to + 5V as in the adjusted output waveform 195 as shown on the right side of FIG. To. In other words, the mechanical semi-fixed resistor 183 is adjusted so that the zero point output 191a of slightly over 2V becomes 0.5V like the adjusted zero point output 195a. Next, the mechanical semi-fixed resistor 184 is adjusted so that the 40Nm output 191b of slightly over 10V becomes 4.5V like the adjusted 40Nm output 195b. If necessary, the adjustment of the mechanical semi-fixed resistors 183 and 184 is repeated to adjust the output waveform 195 on the right side of FIG. By adjusting in this way, the adjusted output waveform can be input to the A / D conversion port of the microcomputer 60, and the subsequent processing can be performed using the A / D converter built in the microcomputer 60. it can.

  Similarly, the output waveform 192 of the machine body b is adjusted so that the zero point output 192a of about −2.5V becomes 0.5V like the adjusted zero point output 195a, and the 40Nm output 192b of about 1.2V is obtained. After adjustment, the output voltage is adjusted to 4.5V, such as 40Nm output 195b. Further, the output waveform 193 of the machine body c is adjusted so that the zero point output 193a of about 3.6V becomes 0.5V like the adjusted zero point output 195a, and the 40Nm output 193b of about 6V is adjusted to 40Nm output. It is adjusted to be 4.5V as in 195b.

  Here, the zero point output 195a after adjustment is set to 0.5V instead of 0V because the adjustment point may be shifted after the case 15 and the sensor substrate 208 are incorporated. This is so that the microcomputer 60 can electrically correct. The reason why the adjusted 40 Nm output 191b is set to 4.5 V instead of 5 V is to provide a detection margin of about 10% from the assumed maximum torque value.

  FIG. 14 is a schematic diagram for explaining a method of gain adjustment (secondary adjustment) after assembly of the screw tightening tool 201 after the case 15 and the sensor substrate 208 are assembled. After the assembly of the housing, the screw tightening tool 101 is connected to the torque measuring device 95 in the configuration as shown in FIG. 14, the display value of the torque measuring device 95 is compared with the display of the external connection device 40, and a constant torque is applied. Is calculated as a correction coefficient α, and this correction coefficient is written from an external connection device to a nonvolatile memory in the communication board. The torque measuring device 95 has a main body 95a of a torque measuring device 95 having an input portion (not shown) for inputting a striking torque from the output shaft 5 of the screw tightening tool 201, and a display for displaying the measured torque value. It is comprised by the device 95b. The person who performs the adjustment work reads the torque value displayed by the display 95b, calculates the correction value to be stored in the screw tightening tool 201, and sends the obtained correction value to the screw tightening tool 201 via the external connection device 40. Remember me.

  FIG. 15 is a waveform diagram for explaining a correction method by gain adjustment (secondary adjustment) of the screw tightening tool 201 according to the related art. In the configuration shown in FIG. 14, the peak value of the output waveform 196 of the detection circuit 170b of the screw tightening tool 201 when the output torque is detected to 40 Nm by the torque measuring device 95 should ideally be + 4.5V. . However, the accuracy during single-unit adjustment cannot be maintained 100% even after assembly, and the peak value of the output waveform 196 may not match +4.5 V as shown in FIG. Therefore, the correction coefficient α is obtained based on the deviation Vd from +4.5 V, and the correction coefficient α is stored in the EEPROM 62 (see FIG. 4) connected to the microcomputer 60. In the detection of the actual torque value by the screw tightening tool 201, the tightening torque value is calculated using this correction coefficient α and output to the external connection device 40. During the actual tightening operation, the external connection device 40 or the screw tightening tool 201 calculates the tightening torque value using the correction coefficient α, so that an accurate torque value without variations can be obtained.

  11 to 15 described above are the zero point adjustment and gain adjustment method of the detection circuit 170b in the conventional screw tightening tool 201, but the following matters to be improved by the inventors' examination are as follows. It turned out to be.

  From the viewpoint of cost reduction, the analog output of the strain gauge 12 is converted using the A / D converter built in the microcomputer 60. Therefore, the analog output is converted to A to make the best use of the resolution of the A / D converter. It is necessary to match the input range (0V to + 5V) of the / D converter. This operation is achieved by adjusting the zero point and adjusting the gain (maximum amplitude), and this adjustment is performed at the manufacturing stage. These adjustments are made by a method in which mechanical semi-fixed resistors 183 and 184 are manually adjusted by an operator, and cannot be adjusted after the housing is assembled so that the user cannot adjust. For example, after adjustment, VR_1 and VR_2 are applied with a coating material for preventing loosening and sent to the housing assembly process. The inventors have verified that the use of a mechanical semi-fixed resistor is low in cost as a part, but the man-hours required for adjustment are enormous and the total cost is rather high. In addition, after the adjusted case 15 and the sensor substrate 208 are assembled in the housing, if the mechanical semi-fixed resistors 183 and 184 need to be adjusted for some reason, it is necessary to disassemble the housing. I found it annoying.

  Therefore, in this embodiment, the zero point adjustment and gain adjustment of the detection circuit 70b are configured to be electrically adjustable after the housing is assembled. FIG. 5 is a block diagram showing a detailed configuration of the detection circuit 70b of FIG. The detection circuit 70b includes a torque waveform extraction circuit 80 for extracting an output signal from the output transformer 11b, a zero point adjustment circuit 81, and a gain adjustment circuit 82. An electronic semi-fixed circuit is used for adjustment of the zero point adjustment circuit 81. A resistor 83 is connected, and an electronic semi-fixed resistor 84 is connected for adjustment of the gain adjustment circuit 82. As the electronic semi-fixed resistors 83 and 84, for example, digital potentiometers can be used, and the resistance values can be electrically adjusted by the control lines 85 and 86 from the microcomputer 60.

  FIG. 6 is a block diagram showing a detailed configuration of the electronic semi-fixed resistor 83. The electronic semi-fixed resistor 83 is a component for setting the wiper of the analog variable resistor 83b (trimmer or volume) from the outside with a digital signal from a microcomputer or the like. The whole is configured as a single IC, and includes a variable resistor 83b and a control / memory 83a. Wiper settings for determining the resistance value are stored in an EEPROM included in the control / memory 83a. .

  The wiper position is controlled through three input lines. The control line 85 of the electronic semi-fixed resistor 83 includes three chips: a chip select (CS) 85a, an increment (INC) 85b, and an up / down (U / D) 85c. When the chip select (CS) 85a is set to low, the wiper position can be adjusted using the signals of the increment (INC) 85b and the up / down (U / D) 85c. When the chip select (CS) 85a is set high and the direction is determined by the up / down (U / D) 85c, the value of the internal register included in the control / memory 83a is 1 in synchronization with the clock applied to the increment (INC) 85b. Increase or decrease each time. Thus, by changing the value of the register, the wiper position of the electronic semi-fixed resistor 83 can be controlled by the microcomputer.

  Next, how to adjust the zero point and the gain of the screw tightening tool 1 according to the embodiment of the present invention will be described with reference to FIG. In the conventional screw tightening tool described with reference to FIGS. 11 to 15, the zero point adjustment and the gain adjustment are performed before the case 15 in which the input transformer 11 a and the output transformer 11 b are accommodated is incorporated into the housing. However, in this embodiment, these are adjusted after being incorporated into the housing. After the assembly of the housing as shown in FIG. 7, the output shaft 5 of the screw tightening tool 1 is set on the main body 95 a of the torque measuring device 95. In this state, zero point adjustment and gain adjustment are performed while the screw tightening tool 1 is stopped or driven with a predetermined torque. FIG. 8 is a block diagram of the connected device at this time.

  In FIG. 8, the second microcomputer 60 mounted on the communication board 9 is connected to the external connection device 40 via the signal line 44. Although not shown in FIG. 7, the external connection device 40 is also connected to the torque measuring device 95 so that data can be exchanged between the external connecting device 40 and the torque measuring device 95.

  FIG. 9 is a flowchart showing a procedure of zero point adjustment of the screw tightening tool 1 according to the embodiment of the present invention. This adjustment is performed in a state where the output shaft 5 of the screw tightening tool 1 is set on the main body 95a of the torque measuring device 95 and the trigger switch is not pulled as shown in FIG. It is realized by software by executing a computer program using a computer.

First, in step 101, it is determined whether the trigger switch 14a is turned off. If it is not off, the zero point cannot be adjusted and the system waits (step 101). When the trigger switch 14a is turned off, the external connection device 40 gives an instruction to measure the output voltage V ₀ which the detection circuit 70b to the microcomputer 60, receives the measurement result (step 102). Next, the external connection device 40 determines whether the output voltage V ₀ is within a specified range, here 0.4V or more and 0.6V or less (step 103). Here, when the output voltage V ₀ is within the specified range, the zero point adjustment process is completed.

If the output voltage V ₀ deviates from the specified range in step 103, the external connection device 40 determines whether the output voltage V ₀ is larger than 0.6V (step 104). When the output voltage V ₀ is larger than 0.6 V, the chip select (CS) 85a is set high with respect to the electronic semi-fixed resistor 83 to shift the zero point downward, and the up / down (U / D ) In 85c, one pulse is sent so as to be added to the increment (INC) 85b in the down direction (step 105). Such an operation is signaled from the microcomputer 60 to the electronic semi-fixed resistor 83 when the external connection device 40 instructs the microcomputer 60. When step 105 is completed, the process returns to step 101.

If the output voltage V ₀ is smaller than 0.6 V in step 104, the chip select (CS) 85a is set high for the electronic semi-fixed resistor 83 to shift the zero point upward, and the up / down (U / D) Ascending in 85c, one pulse is sent to be added to increment (INC) 85b (step 106). Such an operation is performed by the microcomputer 60 with respect to the electronic semi-fixed resistor 83 when the external connection device 40 instructs the microcomputer 60. When step 105 is completed, the process returns to step 101.

  Next, when the zero point adjustment is completed, the procedure proceeds to the gain adjustment procedure described in FIG. FIG. 10 is a flowchart showing a procedure of gain adjustment of the screw tightening tool 1 according to the embodiment of the present invention. This adjustment is performed by setting the output shaft 5 of the screw tightening tool 1 on the main body 95a of the torque measuring device 95 and pulling the trigger switch as shown in FIG. 7, and a microcomputer (not shown) included in the external connection device 40 is used. This is realized by software by executing a computer program.

First, the external connection device 40 sets the adjustment mode to the gain adjustment mode. In the gain adjustment mode, data is exchanged not only with the screw tightening tool 1 but also with the torque measuring device 95. Next, the external connection device 40 sets a motor applied voltage at which a peak torque of about 40 Nm is generated for the microcomputer 60 and instructs the microcomputer 60 of the screw tightening tool 1 to apply this applied voltage to the motor 3 (step) 112). The microcomputer 60 that has received the instruction issues the instruction to the microcomputer 50 (see FIG. 4), so that the motor 3 is activated (step 113). If the motor 3 is not started in step 113, the external connection device 40 stands by, and when it is started, the peak torque Vp sent from the torque measuring device 95 is measured. The maximum value V _pm of the peak torque Vp is simultaneously displayed on the display unit 40a of the external connection device 40 (step 114), whereby the operator can confirm the adjustment level.

Next, the microcomputer 60 stops the rotation of the motor 3 by turning off the trigger switch 14a (step 115). Next, the external connection device 40 compares the maximum value V ′ _pm and V _pm of V ′ _p during motor start-up measured by the torque measuring device 95. And the difference ( _Vpm - _V'pm ) is displayed on the display part 40a of the external connection apparatus 40 (step 116). Next, it is determined whether or not the calculated difference (V _pm −V ′ _pm ) is within the range of −0.1 Nm or more and +0.1 Nm, and if it is within the range, the process is terminated (step 117). . If it is not more than −0.1 Nm and not more than +0.1 Nm in step 117, the chip select (CS) 85 a is set high from the external connection device 40 to the electronic semi-fixed resistor 84, and up / down (U / D) A signal count is instructed, a pulse is sent in increment (INC) (step 118), and the process returns to step 113. The operation of step 118 is electrically controlled by the microcomputer 60 with respect to the electronic semi-fixed resistor 84 when the external connection device 40 gives an instruction to the microcomputer 60.

  As described above, in this embodiment, the zero point adjustment and gain adjustment of the torque detection circuit 70b are electrically performed after the housing is assembled using the two electronic semi-fixed resistors 83 and 84. Therefore, since adjustment before assembling the housing can be omitted, it is possible to realize a screw tightening tool that greatly reduces the assembling cost. Even when the zero point and gain of the detection circuit 70b are readjusted after the product is shipped, it can be easily performed without disassembling the housing.

As mentioned above, although demonstrated based on the Example which shows this invention, this invention is not limited to the above-mentioned form, A various change is possible within the range which does not deviate from the meaning. For example, in the above-described embodiment, an example of an impact tool having a torque sensor has been described. However, the present invention is not limited to this, and any screw tightening tool that detects a tightening torque using a strain gauge may be used as a driver drill or other rotation tool. The same applies to tools.

DESCRIPTION OF SYMBOLS 1 Screw tightening tool 1A Whole circuit 2 (Internally incorporated) 2 Cable 3 Motor 3a (Motor) Stator 3b (Motor) rotor 4 Oil pulse unit 5 Output shaft 6 Housing 6a (Housing) Body 6b (Housing) Grip part 6c (Housing) circuit board storage part 7a Motor control board 7b Drive circuit board 8 Sensor board 9 Communication board 10a, 10b, 10c Bearing
11a Input transformer 11b Output transformer 11c Connector 12 Strain gauge 14a Trigger switch 14b Switch circuit board 15 Case 16 Metal 17 Cooling fan 18 Light emitting diode 19 Wiring cover 20 Rotating shaft 21a, 21b, 21c Guide groove 22 Liner 23 Liner plate 24 Main Shaft 29 Commercial power supply 30 Power supply box 31 Full wave rectification smoothing circuit 32 AC / DC converter 40 External connection device 40a Display unit 42 Rotation position detecting element 43 Connector 44 Signal line 49 Applied voltage setting circuit 50 Microcomputer 51 Rotation control circuit 52 Constant voltage circuit 53 18V constant voltage circuit 60 microcomputer 61 RS422 transceiver 62 EEPROM 64 constant voltage circuit 65 photocoupler 66, 67, 68, 69 signal line 70 torque detection circuit 70a (torque Transmission circuit 70b (in the output circuit) Detection circuit 71 (in the torque detection circuit) 71 ± 12V power supply 72 Drive circuit 80 Torque waveform extraction circuit 81 Zero point adjustment circuit 82 Gain adjustment circuit 83 Electronic semi-fixed resistor 83a Memory 83b Variable resistance Part 84 Electronic semi-fixed resistor 85 Control line 95 Torque measuring device 95a Main body 95b Display 101 Screw tightening tool 170b Detection circuit 180 Torque waveform extraction circuit 181 Zero point adjustment circuit 182 Gain adjustment circuit 183, 184 Mechanical semi-fixed resistor 185 Output shaft 186 Fixing tool 191, 192, 193, 195 Output waveform 191a, 192a, 193a, 195a Zero point output 191b, 192b, 193b, 195b 40Nm output 196 Output waveform 201 Screw tightening tool 208 Sensor substrate

Claims (9)

A motor,
A power transmission mechanism for driving an output shaft on which a tip tool is mounted by the motor;
A control unit for controlling rotation of the motor;
Torque detecting means for detecting occurrence of tightening torque in the output shaft;
In a screw tightening tool having a detection circuit that detects an output signal from the torque detection means and outputs the detected signal to the control unit,
The control unit is provided with a microcomputer having an A / D port,
The detection circuit is provided with adjusting means for electrically adjusting the zero point or / and the maximum amplitude of the output of the detection circuit,
A screw tightening tool characterized in that by adjusting the adjusting means, the zero point or / and the maximum amplitude of the output of the detection circuit are adjusted to fall within the input voltage range of the A / D port of the microcomputer. The torque detection means includes a strain gauge provided on the output shaft, and a rotary transformer that transmits an output signal of the strain gauge to the detection circuit,
The screw tightening tool according to claim 1, wherein the adjusting means is an electronic semi-fixed resistor. The electronic semi-fixed resistor is a digital potentiometer, and includes three input terminals of chip select (CS), increment (INC), and up / down (U / D),
The screw tightening tool according to claim 2, wherein a resistance value of the digital potentiometer is electrically set by the microcomputer through the input terminal. The power transmission mechanism includes a striking mechanism having an oil pulse unit,
4. The microcomputer calculates a tightening torque value by an oil pulse unit using a signal detected by the detection circuit, and stops the motor when reaching a set torque value. A screw tightening tool according to any one of the above. The screw tightening tool has a transmission / reception device for communicating with an external connection device via a communication path,
5. The screw according to claim 4, wherein the control unit changes a setting value of the digital potentiometer based on a setting instruction signal of the digital potentiometer sent from the external connection device via the communication path. Fastening tool. A motor,
An output unit driven by the motor;
A tip tool connected to the output unit;
A housing for housing the motor;
A sensor housed in the housing;
A screw tightening tool having adjusting means for adjusting the gain of the signal output from the sensor,
A screw tightening tool characterized in that the adjusting means can be adjusted electrically from the outside of the housing.   The screw tightening tool according to claim 6, wherein the adjusting means is an electronic semi-fixed resistor.   The screw tightening tool according to claim 6 or 7, wherein the adjustment is performed by an external connection device connectable to the screw tightening tool. A torque measuring device for detecting the torque of the output unit is connected to the external connection device,
The screw tightening tool according to claim 7 or 8, wherein the adjustment is performed by a signal from the torque measuring device.

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