JP2006281364A - Automatic screw tightening machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic screw tightening machine which suppresses increase of working hour required for screw tightening and accurately determines whether the screw tightening state is good or bad. <P>SOLUTION: The automatic screw tightening machine has a driver bit 31 engageable with a screw head, an AC servo motor 30 driving to rotate the driver bit 31, and a control unit 4. The control unit 4 obtains a tightening torque at each position in the screwing process of the screw which is screwed in a workpiece by being engaged with the driver bit 31 to receive a rotation transmission. The control unit 4 compares the tightening torque with an ideal torque value at the position where the tightening torque is obtained, and determines the quality. The ideal torque value is selected from a series of the ideal torque value from the initial stage of screwing till the completion of screwing when the screw is normally screwed and tightened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an automatic screw tightening machine that determines whether or not a screw is tightened by comparing and determining characteristic waveform information such as torque and rotation angle when a screw is tightened on a workpiece.

  An automatic screw tightening machine that has a driver bit that rotates in response to the drive of a rotational drive source such as a motor, engages the driver bit with a screw drive unit, transmits rotation to the screw, and thereby tightens the screw on the workpiece. Is conventionally known. Conventionally, in this type of automatic screw tightening machine, as shown in Japanese Patent Application Laid-Open No. H10-228707, whether or not the screwing is good is determined using a torque method, an angle method, a torque rate method, or the like.

  In the torque method, a target tightening torque value is set in advance, and the screw tightening is terminated when the tightening torque in the screwing process reaches the target tightening torque. In the angle method, a target screw rotation angle is set in advance, and the screw tightening is terminated when the screw rotation angle in the screwing process reaches the target rotation angle. Further, the torque rate method compares the amount of change in the tightening torque with respect to the amount of change in the rotation angle between the start point and end point of a certain section in the screwing process of the screw with an ideal value to determine pass / fail.

Japanese Patent No. 2697240

  In the above conventional screwing quality judgment method, screwing quality judgment is performed only at a limited screwing position. Therefore, even if an abnormal tightening torque or the like is generated at a screwing position other than the judgment position. The problem of not being able to be detected has occurred.

  Since the Toccull rate method uses the information in the section with screwing as the target of pass / fail judgment, it is possible to perform pass / fail judgment with higher accuracy than the torque method and angle method. There is a problem that accurate pass / fail judgment cannot be made unless the section is after the seating of the screw head seating surface where the torque increases proportionally. In the invention described in Patent Document 1, the screw is temporarily tightened to a temporary tightening torque, and then the screw is loosened, and the problem in the conventional torque rate method is solved with the torque rate at this time. However, this method requires a work to loosen the screw once tightened to the temporary tightening torque, which causes problems such as a very long working time for the screw tightening work.

  The present invention was created in view of the above problems, and an object of the present invention is to provide an automatic screw tightening machine that suppresses an increase in work time required for screw tightening work and performs accurate screw tightening determination. It is. In order to achieve this object, the present invention provides an automatic screw tightening machine having a driver bit engageable with a screw head and a rotational drive source for rotationally driving the driver bit. By receiving the rotation transmission, the tightening torque at each position in the screwing process of the screw to be screwed into the workpiece is obtained, and the screwing is completed from the beginning of screwing when the screw is screwed normally and tightened. It has a control unit that makes a comparison with a corresponding ideal torque in the series of ideal torques described above.

  It is preferable that the control unit acquires position information of the screwed position where the tightening torque is acquired, and compares and determines the ideal torque value corresponding to the screwed position information and the acquired tightening torque. Moreover, in the said structure, it is desirable to comprise so that the area which compares and determines a fastening torque and an ideal torque value can be set. The control unit further includes a display unit that displays a tightening torque waveform in the screw tightening operation and an ideal torque value waveform used in the comparison determination process in the screw tightening operation after the screw tightening operation is completed. It is desirable to have it. In this case, the display unit is preferably configured to display the waveform of the upper limit value and the lower limit value of the ideal torque value together with the waveforms of the tightening torque and the ideal torque value.

  The automatic screw tightening machine of the present invention acquires a tightening torque at each position in the screwing process of the screw, compares this with a preset ideal torque value at the position, and determines pass / fail. . For this reason, it is possible to continuously monitor the fluctuation of the tightening torque from the beginning of screwing to the completion of one screw. If any abnormality occurs in the tightening torque during the screwing process, this can be detected immediately. There is an advantage that it is possible to judge the screw tightening quality with extremely high accuracy, such as stopping the work. Further, unlike the prior art, there is no need to loosen the screw once tightened to the temporary tightening torque, and there is an advantage that the work efficiency can be maintained and improved by preventing an increase in the screw tightening operation time. Furthermore, after the completion of the screw tightening operation, the display unit displays the waveforms of the ideal torque value and the tightening torque, so that the operator can visually confirm the progress of the screw tightening operation. When an abnormality occurs, it is possible to easily estimate the position where the abnormality occurs and the degree of influence due to the abnormal torque.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an automatic screw tightening machine, which is a reciprocating drive unit 2, a tool unit 3 connected to the reciprocating drive unit 2, a control unit 4 for controlling the tool unit 3, and the reciprocating drive unit 2. And a control unit 5 for controlling.

  The reciprocating drive unit 2 includes a ball screw mechanism 21 connected to an AC servo motor 20 (hereinafter simply referred to as a motor 20) having an encoder 20a, and a tool table 22 connected to a nut member 21a of the ball screw mechanism 21. It consists of and. The tool unit 3 is installed on the tool table 22. A dedicated ASIC circuit (not shown) is incorporated in the motor 20 of the reciprocating drive unit 2 so that the number of pulse signals generated by the encoder 20a can be measured.

  The tool unit 3 includes an AC servomotor 30 (hereinafter simply referred to as a motor 30) as a rotation driving unit. The motor 30 is provided with an encoder 30a which is an example of rotation detection means. When the motor 30 is driven and its drive shaft 30b rotates, a pulse signal is generated from the encoder 30a as a rotation signal corresponding to this. It is done. Further, the lower part of the motor 30 is a speed reducer 30c, and the drive shaft 30b rotates at the number of rotations decelerated by the speed reducer 30c.

  A driver bit 31 is connected to the drive shaft 30b of the motor 30 so as to rotate integrally. The driver bit 31 has a tip shape that engages with a cross-shaped drive hole recessed in the head of the screw. Further, one end of a thin cylindrical strain generating member 32 is connected to the lower portion of the speed reducer 30 b of the motor 30 so as to include the driver bit 31. The other end of the strain generating member 32 is fixed to a flange member 33 for installing the tool unit 3 on the tool table 22. Further, as an example of a strain detecting means for generating a signal corresponding to the amount of elastic deformation of the strain generating member 32, four strain gauges 34. It is. These strain gauges 34 change the output voltage signal in accordance with the amount of elastic deformation of the strain generating member 32, and as shown in FIG. 2, they constitute a Wheatstone bridge circuit, and an amplifier 35 and analog / digital conversion. The control unit 4 is connected to a later-described measurement unit 47 via a unit 36 (hereinafter referred to as an A / D conversion unit 36).

  The control unit 4 stores a control unit 40, a motor drive unit 41 that controls a load current value to the motor 30, and various programs and parameters necessary for controlling the tool unit 3, and various information can be written therein. A storage unit 42 having a sufficient capacity, an operation unit 43 for inputting various types of information and signals, a display unit 44 including a liquid crystal screen and LEDs that can display various types of information, and a display unit 44 A display control unit 45 that performs display control, a pulse measurement unit 46 that is built into the motor 30 and can measure the number of pulse signals generated by the encoder 30a, and a lift that performs drive control of the motor 20 of the reciprocating drive unit 2 It is comprised from the control part 47 and the torque detection part 48 which calculates | requires fastening torque from the output voltage signal of the said strain gauge 34 ....

  When the motor drive unit 41 receives a drive command signal from the control unit 40, the motor drive unit 41 controls a current value (load current value) applied to the motor 30 according to a load torque applied to the drive shaft of the motor 30. The drive shaft 30b is controlled to rotate at a predetermined speed (number of rotations). That is, the load current value to the motor 30 increases or decreases in proportion to the load torque applied to the drive shaft 30b. Further, the storage unit 42 stores in advance the angle measurement reference torque value, the target torque value, the target torque upper limit value, the target torque lower limit value, and the characteristic waveform information for each screw to be tightened as parameters for executing the screw tightening control. Has been.

  The angle measurement reference torque value is a tightening torque value used as a reference for starting measurement of the rotation angle in the process of screw tightening, and a desired value may be input from the operation unit 43 and stored. it can. As the angle measurement reference torque value, for example, a torque value generated when the screw tip of the screw begins to bite into the female screw of the work, or a tightening that starts to increase when the head seating surface of the screw contacts the work. If it is the same screw, such as the torque value, the torque value that can be reproduced almost stably according to the tightening state and position and can be clearly distinguished from the tightening torque value for the previous rotation angle, This is preferable in comparing and determining the ideal torque value in the characteristic waveform information and the actual tightening torque value on the basis of the rotation angle.

  Further, the target torque value, the target torque upper limit value, and the target torque lower limit value define a tightening torque that is an index for screw tightening completion and an allowable width thereof, and these are input from the operation unit 43. The maximum value in the specified characteristic waveform information is selected.

  The characteristic waveform information is obtained by adding an ideal tightening torque value (hereinafter referred to as an ideal torque value) when a screw is screwed into a work and adding an upper limit width set in advance to the ideal torque value. An ideal torque upper limit value and an ideal torque lower limit value obtained by subtracting a preset lower limit value from the ideal torque value are associated with the rotation angle of the screw at the time of screwing. Are summarized in the above). The maximum value of these ideal torque values, the ideal torque upper limit value, and the ideal torque lower limit value corresponding thereto are the target torque value, the target torque upper limit value, and the target torque lower limit value. This characteristic waveform information is provided for each type of screw. By operating the operation unit 43 and selecting the type of screw displayed on the display unit 44, the characteristic waveform information corresponding to the screw is identified. An identification code for this purpose is written in a predetermined area in the storage unit 42 that is referred to when the control program is executed, and the characteristic waveform information is selected in the screw tightening control.

  The storage unit 42 is also provided with a work table for storing an actual screw rotation angle during screw tightening (hereinafter referred to as an actual rotation angle) and a corresponding tightening torque.

As shown in FIG. 3 to FIG.
S01: Waiting for input of a screw tightening start command signal from the operation unit 43.
S02: The flag is set to “0”.
S03: A work code is generated and held.
S04: With reference to the identification code of the characteristic waveform information in the storage unit 42, the target torque value, the target torque upper limit value, and the target torque lower limit value are set from the characteristic waveform information characteristic table corresponding to this identification code.
S05: The record in which the ideal torque value corresponding to the angle measurement reference torque value is registered is selected from the characteristic table, and the rotation angle of this record is set as the rotation angle initial value.
S06: A descending command signal is given to the elevation control unit 47.
S07: A drive command signal is given to the motor drive unit 41.
S08: The tightening torque is read from the torque detector 48.
S09: Check whether the tightening torque has reached the angle measurement reference torque value, and if not, jump to S08.
S10: A pulse measurement start signal is given to the pulse measurement unit 46.
S11: The tightening torque is read from the torque detector 48.
S12: The integrated value of the pulse signal is read from the pulse measuring unit 46, and the rotation angle obtained from this is added to the rotation angle initial value to obtain the actual rotation angle.
S13: The tightening torque and the actual rotation angle are associated with each other and written in the work table of the storage unit 42.
S14: The ideal torque value, the ideal torque upper limit value, and the ideal torque lower limit value corresponding to the actual rotation angle are read from the storage unit 42.
S15: If the ideal torque value is equal to the target torque value, the process jumps to S17.
S16: It is checked whether the tightening torque is within the range of the ideal torque lower limit value or more and the ideal torque upper limit value or less. If it is off, the process jumps to S18, and if it falls, the process jumps to S11.
S17: It is checked whether the tightening torque is within the range of the target torque lower limit value or more and the target torque upper limit value or less. If so, jump to S19.
S18: The flag is set to “1”.
S19: A stop command signal is given to the motor drive unit 41.
S20: The identification code and the work table are stored in the storage unit 42 using the work code as a key.
S21: If the flag is “0”, jump to S23.
S22: An abnormal end signal with the work code added is given to the display control unit 45, and the process jumps to S24.
S23: A normal end signal with a work code added is given to the display control unit 45.
S24: An ascending command signal is given to the elevation controller 47.
S25: Execute screw tightening control as an end.

The display control unit 45 receives the normal end signal or the abnormal end signal sent from the control unit 40 and performs the screw tightening display control shown in FIG.
S30: Wait for a normal end signal or an abnormal end signal.
S31: The identification code for the work code and the work table are read from the storage unit 42.
S32: Read characteristic waveform information corresponding to the identification code from the storage unit.
S33: If the waveform display command signal is an abnormal end signal, the process jumps to S35.
S34: A normal display command signal is given to the display unit 44, and the process jumps to S36.
S35: An abnormal display command signal is given to the display unit 44.
S36: End.

  In the automatic screw tightening machine 1, when a start switch (not shown) of the operation unit 43 is pressed, a unique work code is generated for each screw tightening operation in the control unit 40. Further, the control unit 40 refers to the identification code set in the reference area of the storage unit 42, and sets the target torque value, the target torque upper limit value, and the target torque lower limit value from the characteristic table in which the characteristic waveform information corresponding to this is written. Is read and set. Furthermore, the control unit 40 selects or calculates a rotation angle at which an ideal torque value corresponding to the angle measurement reference torque value is generated from the characteristic table, and sets this as the rotation angle initial value.

  Subsequently, the motor 20 of the reciprocating drive unit 2 is driven to operate the ball screw mechanism 21. As a result, the nut member 21a and the tool table 22 are lowered, so that the driver bit 31 of the tool unit 3 uses a screw previously held by a holding chuck (not shown) provided on the moving path as a female screw of the workpiece. Extrude. At this time, the motor 30 of the tool unit 3 is also driven, and the driver bit 31 is rotating. As a result, the screw is engaged with the driver bit 31 to receive rotation and is screwed into the female screw of the workpiece.

  The control unit 40 monitors the screw tightening torque detected by the torque detection unit 48 immediately after the start of driving of the motor 30 described above. When this reaches the angle measurement reference torque value, the pulse measurement unit 46 sends a pulse of the encoder 30a. Gives signal integration command. Receiving this, the pulse measurement unit 46 starts integration of the pulse signals emitted by the encoder 30a, and the control unit 40 refers to the pulse integration value of the pulse measurement unit 46 to obtain the rotation angle of the screw each time. . As a result, for example, the time when the tip of the screw thread starts to bite into the female screw inlet of the work, the time when the head seating surface of the screw is seated on the work and the tightening torque is increased, etc. are detected. The rotation angle of the screw from can be known. The control unit 40 selects or calculates a rotation angle at which an ideal torque value corresponding to the angle measurement reference torque value is generated in advance from the characteristic table, and holds this as a rotation angle initial value. Then, the rotation angle obtained from the pulse integrated value is added to the initial rotation angle value, and this is used as the actual screw rotation angle (actual rotation angle). This makes it possible to match the rotation angle information in the characteristic waveform information with the actual rotation angle of the screw that is actually screwed in, and to accurately compare the characteristic waveform information described later and the tightening torque value.

  After the integration of the pulse signals starts, the control unit 40 reads the tightening torque from the torque detection unit 48 at a predetermined sampling time, and calculates the actual rotation angle of the screw from the pulse integration value. Then, the ideal torque value, the same upper limit value, and the same lower limit value corresponding to the calculated actual rotation angle are selected or calculated from the characteristic table, and it is determined whether or not the tightening torque value is within the range defined by these. . By doing so, the screw can be screwed into the workpiece and tightened while comparing the ideal screw tightening torque with the actual screw tightening torque in real time and actual rotation angle. It is possible to detect unauthorized fluctuations in the tightening torque in the process and perform highly accurate screw tightening work.

  The process of comparing and determining the tightening torque and the ideal torque value is repeated until it can be determined that the ideal torque value read from the characteristic table is equal to the target torque value that has already been set (the maximum value of the ideal torque value). If the tightening torque value deviates from the allowable range of the ideal torque in the process, the screw tightening operation is stopped at that time. Further, when it is finally confirmed that the tightening torque is within the allowable range of the target torque value (the range defined by the upper limit value and the lower limit value of the target torque), the screw tightening operation ends normally. . The actual rotation angle and the tightening torque used for the comparison determination process are written and stored in the work table each time. This work table is stored in the storage unit using the work code as a key together with the identification code when the work is stopped or finished. For this reason, it is possible to call and confirm / use the data of the screw tightening work performed before.

  Whether the screw tightening operation is stopped halfway or completed normally, the tightening torque used for the final comparison judgment process is displayed on the liquid crystal screen of the display unit, and the characteristic table The waveforms of the ideal torque value, the ideal torque upper limit value, and the ideal torque lower limit value and the tightening torque waveform recorded in the work table are drawn. FIG. 7 shows an example thereof, and FIG. 7A shows a display state of each torque waveform when the screw tightening is normally performed up to the target torque value. FIG. 7B shows the display state of each torque waveform when the tightening torque exceeds the ideal torque upper limit value during the screwing process due to foreign matter biting, screw portion molding failure, or the like. In this way, by displaying the waveforms of the ideal torque value and the actual tightening torque, the operator can visually check the progress of the screw tightening work, and if an abnormality occurs, the occurrence It becomes possible to easily estimate the position and the degree of influence of abnormal torque. In addition, when the screw tightening operation is stopped in the middle, “Tightening torque abnormality” is displayed on the liquid crystal screen of the display unit, and the abnormality occurrence LED that is attached to the liquid crystal screen is turned on. In addition, when the screw tightening operation is normally completed, “normal end” is displayed on the liquid crystal screen of the display unit, and a screw tightening normal LED provided along with the liquid crystal screen is turned on.

  In either case of normal completion of screw tightening or stop of screw tightening, after the motor drive is stopped, the tool unit returns to the original position by the reciprocation of the reciprocating drive unit, and waits for the next screw tightening operation. .

  In the above description, the screw rotation angle is measured in response to the screw tightening torque reaching the angle measurement reference torque value. However, the screw tip of the screw has reached the female screw inlet of the workpiece. Can be determined from the signal of the encoder of the motor, and this can be used as a trigger for starting the rotation angle measurement. Further, the actual rotation angle of the screw is taken as an example of position information of the screwing position where the tightening torque described in the claims is acquired, and the ideal torque value is read with reference to this, and this is compared with the tightening torque. Judgment of screw tightening was made. However, in addition to this, for example, the same effect can be obtained by comparing the tightening torque and the ideal torque value in time series using the position information of the screwing position as the working time. However, when the time series is used in this way, the screw position varies with time even with the same screw according to the rotational speed of the motor 30, that is, the rotational speed of the driver bit 31. Therefore, when using a time series for the position information of the screwing position, the rotational speed of the motor 30 is matched with the rotational speed when the ideal torque is obtained, or correction according to the rotational speed parameter is performed in the screw tightening control. It is necessary to take measures.

  Further, the angle measurement reference torque value may be set by operating the operation unit 43 to display a desired characteristic table on the display unit 44 and selecting a desired ideal torque value from the desired characteristic table. In addition, two angle measurement reference torques can be set, and the tightening torque is limited only to the rotation angle section defined by these two angle measurement reference torques (or only to the section excluding this section). You may comprise so that a comparison with an ideal torque value may be performed. By doing so, the degree of freedom and convenience in determining whether or not the screw tightening can be improved.

The block explanatory view of the automatic screw fastening machine concerning the present invention. The block explanatory view of the principal part of the automatic screw fastening machine concerning the present invention. The flowchart of the screw tightening control front stage of the automatic screw tightening machine which concerns on this invention. The flowchart of the screw tightening control middle stage of the automatic screw tightening machine which concerns on this invention. The flowchart after the screwing control of the automatic screwing machine which concerns on this invention. The flowchart of the screwing completion | finish display control of the automatic screwing machine which concerns on this invention. Explanatory drawing of the torque waveform display in the automatic screw fastening machine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Automatic screwing machine 2 Reciprocating drive unit 3 Tool unit 4 Control unit 20 AC servo motor 20a Encoder 21 Ball screw mechanism 30 AC servo motor 30a Encoder 31 Driver bit 40 Control part 41 Motor drive part 42 Memory | storage part 43 Operation part 44 Display part 45 Display Control Unit 46 Pulse Measurement Unit 47 Elevation Control Unit 48 Torque Detection Unit

Claims (5)

An automatic screw tightening machine having a driver bit engageable with a screw head and a rotational drive source for rotationally driving the driver bit,
When the tightening torque at each position in the screwing process of the screw to be screwed into the workpiece is acquired by engaging the driver bit and receiving rotation transmission, and this screw is tightened by tightening the screw normally An automatic screw tightening machine comprising a control unit for making a comparison with a corresponding ideal torque in a series of ideal torques from the initial screwing to the completion of screwing.   2. The control unit according to claim 1, wherein the control unit acquires position information of the screwed position where the tightening torque is acquired, and compares and determines an ideal torque value corresponding to the screwed position information and the acquired tightening torque. Automatic screw tightening machine as described.   The automatic screw tightening machine according to claim 1 or 2, wherein a section for comparing and determining a tightening torque and an ideal torque value can be set.   The control unit includes a display unit that displays the waveform of the tightening torque in the screw tightening operation and the waveform of the ideal torque value used for the comparison determination process in the screw tightening operation upon completion of the screw tightening operation. The automatic screw tightening machine according to any one of claims 1 to 3, wherein   The automatic screw tightening machine according to claim 4, wherein the display unit is configured to display waveforms of an upper limit value and a lower limit value of the ideal torque value together with each waveform of the tightening torque and the ideal torque value. .

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