JP5965694B2 - Screw tightening device and control method - Google Patents

Description

  The present invention relates to a screw tightening device and a control method thereof that can realize screw tightening with a simple configuration and high accuracy.

  An electric screwdriver is used to quickly and easily perform the screwing operation. The electric screwdriver includes, for example, a bit whose tip can be fitted into a groove or a hole in the head of the screw, a motor that generates a rotational force, a gear that transmits the rotational force generated by the motor, And a clutch mechanism that transmits and disengages rotational force.

  The electric screwdriver can be tightened with a high torque by including a gear and a clutch mechanism, and the torque is limited at low cost by transmitting and disconnecting the rotational force.

  On the other hand, an electric driver provided with a clutch mechanism has a drawback that the tightening torque is not stable with a small torque of a small screw such as M2 or less. In addition, since the bit is rotated at a high speed, there is a disadvantage that a groove or a hole in the head of the screw is crushed. In addition, when a gear is interposed, there is a problem that even if the motor is torque controlled, there is backlash and friction, the tightening torque is not stable, and the torque control by the clutch mechanism must be relied upon.

  For this reason, the tightening torque may be controlled by the load cell without using the clutch mechanism, but it is expensive and lacks versatility. Therefore, there is a demand for an electric driver that can perform torque control without using these clutch mechanisms and gears.

  For example, a brushless DC motor, a rotation control circuit for controlling the rotation of the motor, an impact unit driven by the motor, an output shaft connected to the shaft of the impact unit and mounted with a tip tool, torque detection means, An electric tool including a microcomputer that controls the tightening of the tip tool using the output of the torque detection means and a storage means has been proposed (see Patent Document 1). This electric tool detects the tightening torque, determines whether or not the specified tightening has been performed, and stores the data in the tool body.

  Although the electric tool provided with such a torque sensor as a torque detecting means can realize highly accurate torque control, it cannot be provided at a low cost because it includes the torque sensor.

  Therefore, a screw tightening device that can realize highly reliable screw tightening without using a torque sensor has been proposed (see Patent Document 2). This screw tightening device is equipped with means for generating a rotation speed detection signal of an electric driver motor that is attached to a blade that can move up and down and rotates at high speed, and a vertical movement detection that is provided on a vacuum suction pipe that can slide up and down on the blade. A means for generating a signal, a circuit for PWM-controlling a power supply and a motor drive circuit while feeding back a current flowing to a predetermined motor from two types of detection signals, and a screw tightening pattern corresponding to a screw and a workpiece from the outside are selected. And a circuit for displaying and outputting screw tightening torque data.

  Since this screw tightening device does not use a torque sensor, it can be provided at a low cost, and by detecting a change in current, a seating detection is performed in a very short time, and a reverse brake circuit including a current limit is provided. Therefore, high-precision screw tightening is realized by avoiding excessive tightening due to inertia (inertia) and instability.

Japanese Patent Application Laid-Open No. 2010-12587 Japanese Patent No. 2682084

  However, the screw tightening device described in Patent Document 2 includes an air cylinder, a vacuum suction pipe, a vertical motion detection sensor, and the like, and thus has a complicated configuration and is still expensive. Further, since the gear is provided, there is a problem that the above-described backlash and friction occur, and the tightening torque is not stable.

  This screw tightening device, after detecting seating by a change in current, passes a brake current for a set time, outputs it as a current value with a low torque according to the type of screw, and tightens further, Since the motor is driven with the set torque current value for a certain period of time, it takes time to tighten the screws. This is not an efficient work.

  By the way, there are stepping motors (also called pulse motors) as well as brushless direct current motors in which the function of the brush is replaced by a semiconductor switch as described in Patent Document 1. The stepping motor is inexpensive, and the rotation angle and rotation speed are determined by the number and period of pulse signals to be applied. As a result, the desired operation can be realized without feedback control within the rated load.

  Therefore, using this stepping motor, it is possible to provide a simple configuration at low cost, improve work efficiency, enable screw reuse, and achieve screw tightening with high accuracy. The provision of such a control method has been desired.

  This invention is made | formed in view of the said subject, The said subject can be solved by providing the screw fastening apparatus of this invention, and its control method.

  The screw tightening device of the present invention includes a bit for fitting to a screw, a stepping motor for supplying power for rotating the bit, and a drive for driving the stepping motor by an input PWM (Pulse Width Modulation) signal. And a torque of the stepping motor is calculated from the current value detected by the driving means, and the screw tightening state is determined using the calculated torque, and the driving means to the driving means is determined according to the determined state. Control means for continuing or blocking input of the PWM signal.

  It is preferable that the stepping motor, the driving unit, and the control unit are accommodated in a casing of the screw fastening device. This is because the number of wirings can be reduced (reduced wiring) by being housed in the housing.

  The stepping motor applies power directly to the bit to rotate the bit. Therefore, there is no clutch mechanism or gear between the bit and the stepping motor.

  The screw tightening device includes storage means for storing a specified number of torques arranged in order from the latest torque each time a new torque is calculated, and the control means is configured to store the latest torque or the latest torque in order. It is determined whether an average torque obtained by averaging a predetermined number of torques arranged is equal to or greater than a set torque. If it is determined that the average torque is equal to or greater than the set torque, it is determined that tightening is completed, and the PWM signal Input can be blocked. Note that the stepping motor stops spontaneously by blocking the input of the PWM signal to the driving means.

  The screw tightening device includes position detection means for detecting a position or rotation angle in the rotation direction of the stepping motor, and the control means has a rotation speed obtained from information on the detected position or rotation angle. Speed control can be performed by controlling the PWM signal so that the rotation speed is set.

  Further, each time a new torque is calculated, the specified number of torques are stored in order from the latest torque, and each time the latest torque is calculated, the torque is calculated using the specified number of torques. An average torque obtained by averaging a predetermined number of torques arranged in order includes storage means for sequentially arranging and storing the latest average torque, and the control means uses the torque stored in the storage means or the average torque to be adjacent to each other. The difference between the matching torque or the average torque is calculated, and the difference is compared to determine whether the screw is in a seated state. After determining that the screw is in the seated state, the position detecting means detects It is determined whether the set position or the rotation angle has reached a set position or rotation angle, It is determined that the completion can be shut off input of the PWM signal.

  Further, each time a new torque is calculated, the specified number of torques are stored in order from the latest torque, and each time the latest torque is calculated, the torque is calculated using the specified number of torques. An average torque obtained by averaging a predetermined number of torques arranged in order includes storage means for sequentially arranging and storing the latest average torque, and the control means uses the torque stored in the storage means or the average torque to be adjacent to each other. The difference between the matching torque or the average torque is calculated, the difference is compared to determine whether or not the screw is seated, and after determining that the seat is in the seated state, the storage means again Using the stored torque or the average torque, calculate the difference between the adjacent torques or the average torque, and compare the differences. To determine if it has reached the yield point of the screw, it is also possible to determine the clamping when it is determined to have reached the yield point has been completed to cut off the input of the PWM signal.

  The storage means further stores the set torque, the set rotation speed, the rotation speed obtained by driving the stepping motor, all torques, and the number of rotations required for screw tightening. Can do.

  The control method of the present invention includes processing executed by the control means of the screw tightening device as processing steps. That is, the step of calculating the torque of the stepping motor from the current value detected by the driving means, the step of determining the screw tightening state using the calculated torque, and the step of calculating the torque to the driving means according to the determined state Continuing or interrupting the input of the PWM signal.

  The screw tightening device includes storage means for storing a designated number of torques arranged in order from the latest torque each time a new torque is calculated, and in the determining step, the latest torque or the latest torque is sequentially ordered. It is determined whether an average torque obtained by averaging a predetermined number of torques arranged is equal to or greater than a set torque. In the step of continuing or shutting down, tightening is completed when it is determined that the torque is equal to or greater than the set torque. Thus, the PWM signal input can be cut off.

  Further, the screw tightening device includes position detection means for detecting a position or rotation angle in the rotation direction of the stepping motor, and the control method sets a rotation speed obtained from information on the detected position or rotation angle. The method further includes controlling the PWM signal so as to achieve the rotated speed.

  Each time a new torque is calculated, the specified number of torques are stored in order from the latest torque, and each time the latest torque is calculated, the specified number of torques are used to calculate the order. An average torque obtained by averaging a predetermined number of torques also includes storage means for sequentially storing them from the latest average torque, and in the step of determining, the torque stored in the storage means or the average torque is used to be adjacent to each other. The difference between the torque or the average torque is calculated, and the difference is compared to determine whether the screw is in a seated state. After determining that the seat is in the seated state, the position detection unit detects the difference. In addition, it is determined whether the position or the rotation angle has reached a set position or rotation angle, and the step of continuing or blocking is determined. So it is possible to cut off the input of the PWM signal is determined to be tightened when it is determined to have reached the position or the rotational angle is set has been completed.

  Each time a new torque is calculated, the specified number of torques are stored in order from the latest torque, and each time the latest torque is calculated, the specified number of torques are used to calculate the order. An average torque obtained by averaging a predetermined number of torques also includes storage means for sequentially storing them from the latest average torque, and in the step of determining, the torque stored in the storage means or the average torque is used to be adjacent to each other. The difference between the torque or the average torque is calculated, and the difference is compared to determine whether or not the screw is in a seated state. After determining that the seat is in the seated state, the difference is stored in the storage means again. The calculated torque or the average torque is used to calculate the difference between the adjacent torques or the average torque, and the respective differences are compared. In the step of determining whether or not the yield point of the screw has been reached, and in the step of continuing or interrupting, it is determined that the tightening has been completed when it is determined that the yield point has been reached, and the PWM signal input is interrupted. Can do.

  Since the screw fastening apparatus of the present invention uses an inexpensive stepping motor and has a simple configuration, it can be provided at low cost. In addition, since the screw tightening device and the control method thereof according to the present invention can directly control the tightening torque of the screw, particularly for the tightening of the fine screw, the high speed and high accuracy can be achieved without crushing the fitting groove. The screw tightening can be realized. Even when the side to be tightened is resin, the screw groove on the side to be tightened is not crushed.

  In addition, it is not necessary to apply a brake or rotate at a low torque during screw tightening, so that the work efficiency can be improved. Since the yield point is not greatly exceeded in the screw tightening operation, the screw can be reused.

  Furthermore, by accommodating the motor, the driving means, and the control means in one housing, it becomes compact and the number of wires can be reduced (wiring saving). Also, by recording the rotation speed, torque, and rotation speed obtained in the storage means, it can be traced afterwards, and when a screw with the wrong length is used, It is possible to detect a tightening abnormality such as when tightening at a small number of rotations. The torque curve can be recorded and traced, and the information can be recorded and managed.

The figure which showed the structural example of the screw fastening apparatus of this invention. The circuit block diagram which showed an example of the drive circuit with which a screw fastening apparatus is provided. The functional block diagram which showed an example of the control circuit with which a screw fastening apparatus is provided. The figure which showed the relationship between the tightening angle of a screw, and a tightening torque. The figure which illustrated the data table with which a screw fastening device is provided. The flowchart which showed the flow of the process in the case of implementing a screw fastening using a torque method. The flowchart which showed the flow of the process in the case of implementing a screw fastening using a rotation angle method. The flowchart which showed the flow of the process in the case of implementing a screw fastening using a torque gradient method.

  FIG. 1 is a diagram showing a configuration example of a screw fastening device of the present invention. Note that the embodiment shown in FIG. 1 is one configuration example, and the present invention is not limited to this embodiment. The screw tightening device of the present invention can be applied to screws of various types and sizes, but can be preferably applied to, for example, fine screws of M2 (nominal diameter of metric screw 2 mm) or less.

  The elements of the screw include the winding direction, the number of threads, the shape of the thread groove, the diameter, the pitch, the number of ridges, and the like. The number of stripes indicates how many screw grooves are cut in one screw. From the information of these elements, it can be assumed how many rotations can be tightened.

  The screw includes a male screw and a female screw, and the male screw has a head, a seating surface, a shaft, and a screw tip. A fitting groove for turning with a tool is formed on the top surface of the head. Examples of the fitting groove include a slit that is a single character, a cross hole that is a crossed hole, and the like.

  As shown in FIG. 1, the screw fastening device includes a bit 10 to be inserted and fitted in the fitting groove, a stepping motor 11 for supplying power for rotating the bit 10, and an input PWM. A drive circuit 12 that drives the stepping motor 11 by a signal, a position detector 13 as position detection means, and a control circuit 14 as control means are configured. The position detector 13 can be provided as necessary.

  Further, in this screw tightening device, it is preferable that the stepping motor 11, the drive circuit 12, the position detector 13, and the control circuit 14 are accommodated in a housing of the screw tightening device, as shown in FIG. It is more preferable that they are integrated. As a result, the screw tightening device can be made compact, and the number of wires can be reduced (wiring saving). In the case of integration, as shown in FIG. 1, a stepping motor 11 is connected to the bit 10, the stepping motor 11, the position detector 12 and the drive circuit 13 are connected, and the position detector 12 and the drive circuit 13 are connected. The control circuit 14 can be connected and integrated.

  The bit 10 is manufactured from carbon steel, stainless steel, or the like similar to the screw, and has a shape in which a tip portion thereof is fitted into the fitting groove of the screw. For this reason, after inserting the bit 10 into the fitting groove of the screw and fitting it, the screw can be rotated and tightened by rotating the bit 10.

  The stepping motor 11 can realize accurate speed control by adding a position detector 13 and configuring the control circuit 14 as shown in FIG.

  The stepping motor 11 includes a rotor connected to a shaft and a stator around which an electric wire provided around the rotor is wound. One end of the shaft is connected to a chuck or the like for attaching and detaching the bit 10 described above, and the bit 10 can be rotated via the shaft and the chuck by the rotation of the rotor. The rotor is magnetized, and when electric current is supplied to the wires wound around the opposing stator and the stator is magnetized to the same magnetic pole, an attractive force and a repulsive force are generated to rotate in a certain direction by a certain angle.

  The stepping motor 11 rotates the rotor by switching the direction of current flow and sequentially generating this attractive force and repulsive force. By the way, there are three types of stepping motor 11: PM (permanent magnet) type, VR (gear-like iron core) type, and HB (composite) type, but VR type produces only an attractive force to rotate the rotor, The PM type and the HB type generate a suction force and a repulsive force to rotate the rotor.

  In the stepping motor 11, one phase is formed by the two magnetic poles of the rotor and the stator facing the rotor. A motor having two sets of these phases is called a two-phase stepping motor, and other stepping motors include a three-phase stepping motor and a five-phase stepping motor. Any phase stepping motor can be employed in the present invention.

  In the present invention, since the start, natural stop, and torque control can be performed by the control circuit 14 to be described later, no gear or clutch mechanism is required, and the stepping motor 11 directly powers the bit 10 to rotate the bit 10, Moreover, it can be stopped naturally.

  The drive circuit 12 drives the stepping motor 11 by the PWM signal generated and input by the control circuit 14. In response to the control circuit 14 blocking the input of the PWM signal, the drive circuit 12 naturally stops the stepping motor 11. In the case of a two-phase stepping motor, the drive circuit 12 includes, for example, eight FETs (field effect transistors) and two coils, and turns on and off the current with the FETs and alternately supplies current to the two coils. By magnetizing the coil, the rotor is rotated and the stepping motor 11 is driven.

  As an example, the drive circuit 12 can be composed of eight FETs 20 to 27 as shown in FIG. 2, two coils 28 and 29, and two current detectors 30 and 31. The control circuit 14 outputs eight FET gate signals and inputs them to the gates of the FETs 20 to 27. The current detectors 30 and 31 detect currents flowing through the coils 28 and 29 and feed back to the control circuit 14 as voltage conversion signals VSa and VSb of currents of the respective phases.

  Referring to FIG. 1 again, the position detector 13 detects the position or rotation angle of the stepping motor 11 in the rotation direction. Therefore, the position detector 13 can detect how much the rotor of the stepping motor 11 has rotated. Specifically, the angle is 1 ° or 2 °. Examples of the device for detecting the position and rotation angle include an encoder and a resolver. The position detector 13 can output as a pulse signal indicating the position or rotation angle.

  The control circuit 14 receives the input of the pulse signal output from the position detector 13, and calculates the rotation speed and the number of rotations of the rotor (hereinafter referred to as the rotation number) from the number of pulses. Then, the control circuit 14 sets the obtained rotation speed to an external PC (not shown) or the like, and sets the rotation speed input from the PC or the like via a cable or the rotation speed preset in the internal memory. Thus, the PWM signal input to the drive circuit 12 is controlled.

  For example, the difference between the set rotation speed and the obtained rotation speed is obtained, and the rotation speed is controlled to be increased or decreased by the difference, so that the set rotation speed is controlled. Can do. Specifically, the voltage applied to the electric wire is controlled by changing the pulse width of the PWM signal input to the drive circuit 12. As a result, the rotation angle of the rotor per unit time changes, and as a result, changes to the set rotation speed. In this way, the control circuit 14 performs rotation speed control.

  The control circuit 14 inputs the PWM signal to the drive circuit 12 while performing the rotation speed control, and calculates the torque of the stepping motor 11 from the current values detected by the current detectors 30 and 31 provided in the drive circuit 12. Then, the screw tightening state is determined using the calculated torque. Then, the control circuit 14 continues or blocks the input of the PWM signal to the drive circuit 12 according to the determined state. When the input of the PWM signal is continued, the control circuit 14 continues the rotation speed control as it is.

  An example of the control circuit 14 is a microcontroller (microcomputer). The microcomputer can include a CPU core, a memory for storing a program for realizing the above processing, a timer, and an I / O interface. The microcomputer may include a communication interface for communicating with a PC or the like. The communication interface may be an interface for performing wired communication or an interface for performing wireless communication. Note that wireless communication can be performed using a wireless LAN or Bluetooth (registered trademark).

  With reference to a functional block diagram illustrating an example of the control circuit 14 illustrated in FIG. 3, a detailed configuration of the control circuit 14 and processing performed by each functional unit will be described. The control circuit 14 includes a speed detector 40, a speed calculator 41, a limit processor 42, a current calculator 43, an A / D converter 44, a first coordinate converter 45, a second coordinate converter 46, and a PWM voltage converter 47. , A limit time counting unit 48, a PWM cutoff processing unit 49, a number detection unit 50, a number determination unit 51, and a warning unit 52.

  The speed detector 40 detects the rotational speed by calculating the rotational speed from the pulse signal input from the position detector 13. When the position detector 13 converts the pulse signal into a pulse signal, the pulse signal is generated so as to generate one pulse at an arbitrary rotation angle. Therefore, the rotation speed can be calculated by using the number of pulses for one rotation.

  The speed calculation unit 41 is detected by the speed detection unit 40 using a rotation speed command value set from an external PC (not shown) or the like, or a rotation speed command value preset in an internal memory. An instruction to increase or decrease a constant current value with respect to the current value currently applied to the coils 28 and 29 so that the rotation speed becomes the rotation speed set to the rotation speed command value. As a result, the data is output to the limit processing unit 42. FIG. 3 shows a case where a rotation speed command value is given from an external PC or the like.

  The limit processing unit 42 receives the result, is set in an external PC or the like, refers to a current limit value given from the PC or the like or a current limit value preset in an internal memory, and the drive circuit 12 It is determined whether or not a value obtained by increasing or decreasing a constant current value to the current values given to 28 and 29 reaches the current limit value. FIG. 3 shows a case where a current limit value is given from an external PC or the like.

  The motor torque TM can be calculated from Equation 1 below. In Equation 1, IM is a current value applied to the coils 28 and 29, and KT is a torque constant of the motor.

  Referring to Equation 1 above, the motor torque TM is proportional to the current value IM, and the torque TM has reached the torque limit value by determining whether or not the current value IM has reached the current limit value. It can be determined whether or not. This determination is made in order to limit the torque of the motor and prevent excessive torque on the screw.

  FIG. 4 shows the relationship between the screw tightening angle and the tightening torque. The tightening torque varies depending on the tightening angle and can generally be divided into six stages. The first stage is a section until the screw is fitted into the screw hole. The torque at this time is considered to coincide with the torque when the motor itself and the bit 10 are idled.

  The second stage is a section from when the screw is fitted into the screw hole until the seating process starts. The seating is a state when the seat surface of the screw is attached to the object to be fastened. Since it is fitted into the screw hole, the torque increases from the first stage, but the increase is considered to be slight.

  The third stage is a section in the seating process, and the torque at this time is called a snag torque. In the first stage and the second stage, the torque was almost constant, but in this third stage, the torque F increases according to the angle θ. The time when dF / dθ obtained by differentiating F by θ becomes a constant value is considered to be when the seating is completed.

  The fourth stage is a section in a normal tightening process and is called an elastic region. Screw tightening increases the axial force by extending the screw, and the axial force increases in proportion to the length of extension. Thus, the torque increases in proportion to the increase in angle. Therefore, dF / dθ is substantially constant in this elastic range.

  The fifth stage is a section where the rate of increase in torque with respect to the angle decreases beyond the yield point of the screw, and is called a plastic zone. The fifth stage is a section where the screw stretched in the fourth stage has escaped from the elastic region where it does not return. If the yield point is greatly exceeded and the plastic zone is entered deeply, the restoring force of the screw is lost and the same screw cannot be reused.

  The sixth stage is a section in which the rate of increase in torque with respect to the angle decreases, and the section in which the increase rate is negative. This section is considered to be a state in which the screw or the object to be fastened is progressing. Therefore, if the tightening is continued as it is, it is considered that the screw will eventually idle.

  In the present invention, since the control circuit 14 can calculate the torque of the stepping motor 11 from the current values detected by the current detectors 30 and 31, the screw tightening state using the calculated torque, that is, which It can be judged whether it is in a stage. The control circuit 14 can continue or block the input of the PWM signal to the drive circuit 12 according to the determined state. For example, input of the PWM signal can be continued until the set torque is reached, or after sitting, until the set position or rotation angle is reached, or until the yield point is reached, and when it is reached, it can be shut off .

  In addition, the torque at the yield point is set as the torque limit, the current value corresponding to the torque limit is set as the current limit value, and the torque is limited so that it does not increase beyond that, and it is possible to reliably prevent screw breakage, etc. It is possible to make it possible. The current limit value can be set to a current value corresponding to the torque at the yield point as described above, but even if the torque exceeds the torque at the yield point, it is within the range where the restoring force of the screw is not lost. It is also possible to set the current value corresponding to a certain torque.

  Referring to FIG. 3 again, when limit processing unit 42 determines that the current limit value has not been reached, it sends the result to current calculation unit 43 as a current command. The A / D converter 44 converts the voltage conversion signal (analog) of the current detected by the current detectors 30 and 31 of the drive circuit 12 into a voltage conversion signal (digital). The first coordinate conversion unit 45 receives these two voltage conversion signals (digital), converts the coordinates from fixed coordinates to rotation coordinates, and converts the coordinates into signals for performing current calculation processing in the current calculation unit 43, and converts the coordinates. Get the value.

  The current calculation unit 43 receives the current command, and calculates a current value to be passed through the coils 28 and 29 by the driving circuit 12 using the obtained coordinate conversion value. When receiving an instruction to increase the current value by a constant current value, the current calculation unit 43 adds the constant current value to the coordinate conversion value to obtain a current value to be passed through the coils 28 and 29. On the other hand, when receiving an instruction to decrease by a constant current value, the current calculation unit 43 subtracts the constant current value from the coordinate conversion value to obtain a current value to be passed through the coils 28 and 29.

The current calculation unit 43 sends the obtained current value information to the second coordinate conversion unit 46, and the second coordinate conversion unit 46 performs a return coordinate conversion process for distributing the voltage commands to the two phases. Specifically, the second coordinate conversion unit 46 performs coordinate conversion to return the rotation coordinate to the fixed coordinate. The PWM voltage converter 47 converts the voltage command received from the second coordinate converter 46 into a pulse voltage, and generates a PWM signal. The PWM signal is supplied to the drive circuit 12 as an FET gate signal referred to as G _{1 to} G ₈ .

  When the limit processing unit 42 determines that the current limit value has been reached, the limit processing unit 42 instructs the current limit value to be the current value, and the current calculation unit 43 sends the current value information to the second coordinate conversion unit 46. The PWM voltage converter 47 generates a PWM signal that gives the current value and inputs the PWM signal to the drive circuit 12. Thereby, it can restrict | limit so that it may not become the torque more than the torque corresponding to the current limit value, and the restoring force of a screw is not lost, A screw can be reused.

  On the other hand, the limit processing unit 42 notifies the limit time counting unit 48 to measure for a certain time. The limit time counting unit 48 measures the set time, and notifies the PWM cutoff processing unit 49 when the time is reached. Immediately after receiving the notification, the PWM cutoff processing unit 49 shuts down the stepping motor 11 by blocking the input of the PWM signal from the PWM voltage conversion unit 47 to the drive circuit 12.

  The number detection unit 50 detects the number of rotations of the stepping motor 11 from the output signal of the position detector 13. In FIG. 3, the signal is branched in the control circuit 14 and input to the speed detector 40 and the frequency detector 50. However, the output signal of the position detector 13 is branched externally, and the speed detector 40 and the frequency detector 50. It may be configured to be input separately. The number detection unit 50 also generates a pulse signal so that one pulse is generated at an arbitrary rotation angle when the position detector 13 converts the pulse signal into a pulse signal. Can be calculated. The number detection unit 50 detects a pulse generated by a pulse signal in a rotation angle method, which will be described later, as a count command signal.

  The number determination unit 51 uses the count value obtained from the number detection unit 50, is set in an external management server or the like, is given by the management server or the like, or is preset in the internal memory. Compare to determine whether the values are the same. As described above, since the number of rotations required to tighten the screw is assumed in advance, the number of rotations is set as a count value, and it is determined whether or not it is the same value as the set count value. It can be judged whether it is tightened correctly.

  Since the number determination part 51 has shown that it has tightened correctly, when both correspond, it can complete | finish a process, without instruct | indicating anything. When the screw tightening device includes a display unit, the number determination unit 51 can display on the display unit that the tightening has been correctly performed. On the other hand, if the number does not match, the number determination unit 51 indicates that the screw is not correctly tightened, such as being inserted obliquely, so the warning unit 52 gives an error sound. When it is sounded or provided with a display unit, the fact that an error has occurred is displayed on the display unit.

  In the present invention, any of the torque method, the rotation angle method, and the torque gradient method known so far can be employed as a method for performing screw tightening. The torque method is a method for managing the tightening torque of the screw, the rotation angle method is a method for managing the rotation angle of the screw after seating, and the torque gradient method is a method of tightening to the yield point of the screw.

  When the screws are tightened using these methods, the control circuit 14 calculates torque, performs calculation using the calculated torque, and determines the screw tightening state using the calculation result. For this reason, the screw tightening apparatus can be provided with a storage means for storing the calculated torque and the calculation result. This storage means stores a set torque, a set rotation speed, a set count value, a current limit value, etc. given from an external PC, etc. The calculated torque or the like can also be stored.

  FIG. 5 is a diagram illustrating a data table stored in the storage unit. The storage means stores three data tables shown in FIGS. The first data table shown in FIG. 5A stores a specified number of torques arranged in order from the latest torque each time a new torque is calculated. In FIG. 5A, a field capable of storing seven torques as torque data is provided, and each time a new torque is calculated, it is stored in the field indicated by D1 at the head. At this time, since the latest torques are stored in order, the data in D1 goes to D2, the data in D2 goes to D3, the data in D3 goes to D4, and the data in D4 goes to D5. The data in D5 is moved to D6, and the data in D6 is moved to D7. Note that the data in D7 is deleted from the first data table.

  The second data table shown in FIG. 5B is provided with a field capable of storing five data, and each time a new torque is calculated, the result calculated using the torque data of the first data table Remember in the field. The second data table stores, as torque data, an average torque obtained by averaging a predetermined number of torques arranged in order in the first data table for the purpose of absorbing torque fluctuations. In FIG. 5B, an average torque obtained by averaging the three torques is stored, and an average torque obtained by averaging the torques D1, D2, and D3 in the first data table is stored in the field indicated by A1. A2 has an average torque of D2, D3, D4, A3 has an average torque of D3, D4, D5, A4 has an average torque of D4, D5, D6, A5 has an average torque of D5, D6, D7 Each is remembered.

  The third data table shown in FIG. 5C is provided with a field capable of storing four data, and each time a new torque is calculated, the result calculated using the average torque of the second data table Remember in the field. The third data table stores torque change rate data, and stores the difference between adjacent average torques in the second data table as change rate data. In FIG. 5C, Δ1 as a difference is a value obtained by subtracting A2 from A1 in the second data table, Δ2 is a value obtained by subtracting A3 from A2, and Δ3 is a value obtained by subtracting A4 from A3. , Δ4 stores values obtained by subtracting A5 from A4.

  In this embodiment, only seven torques are stored and calculation is performed using the seven torques. However, the number of data is not limited to seven, and may be any number. Further, the average torque stored in the second data table is not limited to averaging three torques arranged in the order in the first data table, and it is also possible to store a torque obtained by averaging two or four or more. It is.

  FIG. 6 is a flowchart showing a flow of processing for performing screw tightening control using the above torque method. The processing is started from step 600. In step 605, the PWM signal is controlled so that the set rotational speed is given from an external PC or the like, and the controlled PWM signal is input to the drive circuit 12 to input the stepping motor. 11 starts to rotate.

  In step 610, the control circuit 14 calculates a torque from the current values detected by the current detectors 30 and 31 provided in the drive circuit 12, and stores the calculated torque value in the storage means as an initial torque. In step 615, the control circuit 14 sets the initial torque in all the fields D1 to D7 of the first data table. In step 620, the control circuit 14 uses the initial torque set in the first data table to obtain an average torque for setting in the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table.

  In step 625, when a current value is input from the drive circuit 12, the control circuit 14 calculates the torque, shifts the data in the first data table one by one, and sets the latest torque in the vacant D1 field. To do. Subsequently, in step 630, the control circuit 14 calculates and obtains an average torque for input to the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table.

  In step 635, it is determined whether the average torque set in the field A1 of the second data table is equal to or greater than the set torque. Each time a new current value is detected, the calculation of torque in steps 625 to 635, the setting to the first data table, the calculation of the average torque, the setting to the second data table, and the determination of whether or not the set torque is exceeded Repeatedly.

  If it is determined that the torque is equal to or greater than the set torque, the process proceeds to step 640, where the control circuit 14 cuts off the input of the PWM signal to the drive circuit 12, stops the stepping motor 11 naturally, and ends the process in step 645. To do.

  In the configuration shown in FIG. 3, since the limit processing unit 42 limits the current value, a PWM signal is generated so as to have the same current value as the current limit value, and the PWM signal is input to the drive circuit 12. At the same time, by setting the time set value of the limit time counting unit 48 that starts time measurement to 0, the PWM cutoff processing unit 49 is notified immediately, and the input of the PWM signal to the drive circuit 12 is cut off. The stepping motor 11 can be naturally stopped.

  In the embodiment shown in FIG. 6, the average torque is adopted for the purpose of absorbing fluctuations in the torque data, but the latest torque calculated newly is used and the latest torque is equal to or greater than the set torque. It is also possible to determine whether or not.

  FIG. 7 is a flowchart showing a flow of processing for performing screw tightening control using the above rotation angle method. This processing is started from step 700, and in step 702, the PWM signal is controlled so as to have a set rotational speed given from an external PC or the like, and the controlled PWM signal is input to the drive circuit 12 to perform stepping. The rotation of the motor 11 is started.

  In step 704, the control circuit 14 calculates a torque from the current values detected by the current detectors 30 and 31 provided in the drive circuit 12, and stores the calculated torque value in the storage means as an initial torque. In step 706, the control circuit 14 sets this initial torque in all the fields D1 to D7 of the first data table. In step 708, the control circuit 14 uses the initial torque set in the first data table to obtain an average torque for setting in the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table.

  In this rotation angle method, in step 710, torque change rate data set by the control circuit 14 to Δ1 to Δ4 in the third data table is obtained. Then, the control circuit 14 sets the obtained change rate data in the third data table. Thereafter, in step 712, the control circuit 14 waits until a count command signal indicating that the pulse signal output from the position detector 13 has rotated by a predetermined angle is detected.

  When the count command signal is detected, in step 714, the control circuit 14 calculates torque from the latest current value detected by the drive circuit 12, and shifts the data in the first data table one by one, Set the latest torque in the vacant D1 field. Subsequently, at step 716, the control circuit 14 calculates and obtains an average torque for setting in the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table. Further, in step 718, the control circuit 14 calculates and calculates change rate data for setting in the fields Δ1 to Δ4 of the third data table. Then, the control circuit 14 sets the obtained change rate data in the third data table.

  Thereafter, in step 720, the control circuit 14 compares the change rate data of Δ1 to Δ4, and determines whether or not the inequality of Δ1> Δ2> Δ3> Δ4 holds. This step 720 is to determine whether or not the initial curve in the third stage shown in FIG. 4 corresponds to a position where the curve begins to rise, and is a step to determine whether or not the third stage has been entered.

  If it is determined that the inequality in step 720 is not satisfied, the process returns to step 712, and the control circuit 14 waits for the count command signal to be detected again. On the other hand, if it is determined that the inequality is satisfied, it is possible to proceed to step 724 as it is, but here it cannot be said that the inequality is not satisfied even in the first stage and the second stage. Therefore, in order to prevent an erroneous determination from being made, in step 722, the control circuit 14 determines whether the average torque set in the field A1 of the second data table is four times or more of the initial torque. To do. The value of 4 times is an example, and it may be 2 times or 3 times as long as an erroneous determination can be prevented.

  If it is determined that the value is not four times or more, the determination is incorrect, and the process returns to step 712 to wait for the count command signal to be detected again. On the other hand, when it is determined that the number is four times or more, the process proceeds to step 724, and the control circuit 14 waits for the count command signal to be detected. Thereafter, in step 726, the control circuit 14 calculates the torque from the latest current value detected by the drive circuit 12, shifts the data in the first data table one by one, and updates the empty D1 field. Set the torque.

  Subsequent to step 726, in step 728, an average torque for setting in the fields A1 to A5 of the second data table is calculated and obtained. Then, the control circuit 14 sets the obtained average torque in the second data table. Further, in step 730, the control circuit 14 calculates and obtains change rate data for setting in the fields Δ1 to Δ4 of the third data table. Then, the control circuit 14 sets the obtained change rate data in the third data table.

  In step 732, the control circuit 14 compares the change rate data of Δ1 to Δ4, and determines whether the inequality of Δ1> Δ2> Δ3> Δ4 is not satisfied. In this step 732, the curve changes from the third stage to the fourth stage shown in FIG. 4 to determine whether or not Δ1 and Δ2 become the same value and the above inequality is not satisfied. This is a step of determining a point.

  If it is determined that the inequality holds, the process is still in the middle of the third stage, and the process returns to step 724, and the control circuit 14 waits for the count command signal to be detected again. On the other hand, when it is determined that the inequality is not established, the process proceeds to step 734, and the control circuit 14 stores the determined torque at the seating point in the storage unit as “snag torque”. In step 736, the control circuit 14 starts counting the count command signal from the position detector 13.

  In the rotation angle method, counting can be started from the seating point, and it can be determined whether the tightening has been correctly performed by determining whether the count value has reached the set count value.

  Therefore, in step 738, the number of count command signals detected after the count is started is used as a count value, and the control circuit 14 determines whether or not the count value has reached the set count value. If it is determined in step 738 that the set count value has not been reached, the determination in step 738 is repeated. If it is determined that the count value has been reached, the process proceeds to step 740 where the control circuit 14 outputs the PWM signal to the drive circuit 12. The input is cut off, the stepping motor 11 is naturally stopped, and this processing is terminated at step 742.

  FIG. 8 is a flowchart showing a flow of processing for performing screw tightening control using the above torque gradient method. This process is started from step 800, and in step 802, the PWM signal is controlled so that the set rotational speed given from an external PC or the like is obtained, and the controlled PWM signal is input to the drive circuit 12 to perform stepping. The rotation of the motor 11 is started.

  In step 804, the control circuit 14 calculates a torque from the current values detected by the current detectors 30 and 31 provided in the drive circuit 12, and stores the calculated torque value in the storage means as an initial torque. In step 806, the control circuit 14 sets this initial torque in all the fields D1 to D7 of the first data table. In step 808, the control circuit 14 uses the initial torque set in the first data table to obtain an average torque for setting in the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table.

  In this torque gradient method, in step 810, torque change rate data set by the control circuit 14 to Δ1 to Δ4 in the third data table is obtained. Then, the control circuit 14 sets the obtained change rate data in the third data table. Thereafter, in step 812, the control circuit 14 waits for detection of a count command signal indicating that the pulse signal output from the position detector 13 has rotated by a predetermined angle.

  When the count command signal is detected, in step 814, the control circuit 14 calculates torque from the latest current value detected by the drive circuit 12, shifts the data in the first data table one by one, Set the latest torque in the vacant D1 field. Subsequently, at step 816, the control circuit 14 calculates and obtains an average torque for setting in the fields A1 to A5 of the second data table. Then, the control circuit 14 sets the obtained average torque in the second data table. Further, in step 818, the control circuit 14 calculates and calculates change rate data for setting in the fields Δ1 to Δ4 of the third data table. Then, the control circuit 14 sets the obtained change rate data in the third data table.

  Thereafter, in step 820, the control circuit 14 compares the change rate data of Δ1 to Δ4, and determines whether or not the inequality Δ1> Δ2> Δ3> Δ4 holds. If it is determined that the inequality in Step 820 is not satisfied, the process returns to Step 812, and the control circuit 14 waits for the count command signal to be detected again.

  If it is determined that the inequality is satisfied, it is possible to proceed to step 824 as it is. However, in this case, it cannot be said that the inequality is not satisfied even in the first stage or the second stage. In step 822, the control circuit 14 determines whether the average torque set in the field A1 of the second data table is four times or more of the initial torque. The value of 4 times is an example, and it may be 2 times or 3 times as long as an erroneous determination can be prevented.

  If it is determined that it is not more than four times the above, an erroneous determination has been made, and the process returns to step 812 to wait for the count command signal to be detected again. On the other hand, if it is determined that the number is four times or more, the process proceeds to step 824, and the control circuit 14 waits for the count command signal to be detected. Thereafter, in step 826, the control circuit 14 calculates the torque from the latest current value detected by the drive circuit 12, shifts the data in the first data table one by one, and updates the empty D1 field. Set the torque.

  Subsequent to step 826, in step 828, an average torque for setting in the fields A1 to A5 of the second data table is calculated and obtained. Then, the control circuit 14 sets the obtained average torque in the second data table. Further, in step 830, the control circuit 14 calculates and calculates change rate data for setting in the fields Δ1 to Δ4 of the third data table. Then, the control circuit 14 sets the obtained change rate data in the third data table.

  In step 832, the control circuit 14 compares the change rate data of Δ1 to Δ4, and determines whether the inequality of Δ1> Δ2> Δ3> Δ4 is not satisfied. If it is determined that the inequality holds, the process is still in the middle of the third stage, and the process returns to step 824, and the control circuit 14 waits for the count command signal to be detected again. On the other hand, when it is determined that the inequality is not established, the process proceeds to step 834, and the control circuit 14 stores the determined torque at the seating point in the storage means as “snugging torque”. Up to this point, the rotation angle method is the same as above.

  In step 836, the control circuit 14 waits for the count command signal to be detected. Thereafter, in step 838, the control circuit 14 calculates the torque from the latest current value detected by the drive circuit 12, shifts the data in the first data table one by one, and puts the latest in the empty field D1. Set the torque.

  Subsequent to step 838, in step 840, an average torque for setting in the fields A1 to A5 of the second data table is calculated and obtained. Then, the control circuit 14 sets the obtained average torque in the second data table. Furthermore, in step 842, the control circuit 14 calculates and calculates change rate data for setting in the fields Δ1 to Δ4 of the third data table. Then, the control circuit 14 sets the obtained change rate data in the third data table.

  In step 844, the control circuit 14 compares the change rate data of Δ1 to Δ4, and this time determines whether or not the inequality of Δ1 <Δ2 <Δ3 <Δ4 holds. This step 844 is a step for determining whether or not the torque increase rate at the initial stage of the fifth stage shown in FIG.

  If it is determined that the inequality does not hold, the process is still in the middle of the fourth stage, the process returns to step 836, and the control circuit 14 waits for the count command signal to be detected again. On the other hand, if it is determined that the inequality is established, the process proceeds to step 846, and the control circuit 14 stores the determined torque at the yield point in the storage means as “yield point torque”. In step 848, the control circuit 14 cuts off the input of the PWM signal to the drive circuit 12, stops the stepping motor 11 naturally, and ends this processing in step 850.

  In the embodiment shown in FIGS. 7 and 8, the average torque is adopted for the purpose of absorbing fluctuations in the torque data, but the difference between adjacent torques is changed using the torque in the first data table. It is also possible to calculate as rate data and use the rate of change data to determine the seating point and the yield point.

  When performing screw tightening using the screw tightening apparatus of the present invention, it can be performed at a constant rotational speed from the beginning to the end, or can be performed at a variable speed that changes the rotational speed in the middle. In particular, if it is performed at a variable speed, it can be tightened to a certain degree in a short time, and then the rotational speed can be reduced and tightened slowly at a predetermined speed. It can be tightened without. Even when the side to be tightened is resin, the screw groove on the side to be tightened is not crushed.

  The rotational speed, all torques, rotational speeds, etc. calculated by the control circuit 14 during the control can be stored not only in the storage means provided in the control circuit 14 but also in the storage means provided in the external management server, etc. Then, tracing can be performed, and abnormalities such as a case where a screw having an incorrect length is used or a case where the screw is inserted obliquely and tightened at a rotational speed lower than a predetermined rotational speed can be detected. Also, a torque curve can be recorded, and recording management of these information becomes possible.

  The screw tightening device and the control method thereof according to the present invention have been described in detail with reference to the embodiments shown in the drawings, but the present invention is not limited to the above-described embodiments, and other embodiments are described. It can be modified within the range that can be conceived by those skilled in the art, such as addition, change, deletion, etc., and any embodiment is included in the scope of the present invention as long as the operation and effect of the present invention are exhibited. is there. Therefore, a control program for realizing the control method can be provided, and the control program can be stored in a storage medium or provided in a download form.

DESCRIPTION OF SYMBOLS 10 ... Bit, 11 ... Stepping motor, 12 ... Drive circuit, 13 ... Position detector, 14 ... Control circuit, 20-27 ... FET, 28, 29 ... Coil, 30, 31 ... Current detector, 40 ... Speed detector , 41 ... speed calculation unit, 42 ... limit processing unit, 43 ... current calculation unit, 44 ... A / D converter, 45 ... first coordinate conversion unit, 46 ... second coordinate conversion unit, 47 ... PWM voltage conversion unit, 48 ... limit time counting part, 49 ... PWM cutoff processing part, 50 ... frequency detection part, 51 ... frequency judgment part, 52 ... warning part

Claims (11)

A bit for mating with a screw;
A stepping motor that provides power to rotate the bit;
Driving means for driving the stepping motor by an input PWM (Pulse Width Modulation) signal;
The torque of the stepping motor is calculated from the current value detected by the drive means, the screw tightening state is determined using the calculated torque, and the PWM signal to the drive means is determined according to the determined state. Control means to continue or block input ;
Storage means for storing a specified number of torques arranged in order from the latest torque each time a new torque is calculated;
Have
The control means determines whether or not an average torque obtained by averaging the latest torque or a predetermined number of torques arranged in order from the latest torque is equal to or greater than a set torque. If it is determined that the tightening has been completed, the PWM signal input is shut off.
Screw tightening device.   The screw tightening device according to claim 1, wherein the stepping motor, the driving unit, and the control unit are housed in a housing of the screw tightening device.   The screw tightening device according to claim 1 or 2, wherein the stepping motor directly powers the bit to rotate the bit. A position detecting means for detecting a position or a rotation angle in the rotation direction of the stepping motor;
The said control means controls the said PWM signal so that the rotational speed obtained from the information of the detected said position or rotational angle becomes a set rotational speed. Screw tightening device. The storage means further arranges an average torque obtained by averaging a predetermined number of torques arranged in the order calculated using the designated number of torques every time the latest torque is calculated, in order from the latest average torque. Remember,
The control means uses the torque or the average torque stored in the storage means, calculates a difference between the adjacent torques or the average torque, and compares the respective differences so that the screw is seated. And determining whether the position or the rotation angle detected by the position detection means has reached a set position or rotation angle, and determining whether the seated state has been reached. 5. The screw tightening device according to claim 4 , wherein when it is determined that tightening has been completed, it is determined that tightening has been completed, and the input of the PWM signal is interrupted. The storage means further arranges an average torque obtained by averaging a predetermined number of torques arranged in the order calculated using the designated number of torques every time the latest torque is calculated, in order from the latest average torque. Remember,
The control means uses the torque or the average torque stored in the storage means, calculates a difference between the adjacent torques or the average torque, and compares the respective differences so that the screw is seated. After determining that the seated state has been reached, again using the torque or the average torque stored in the storage means, calculating the difference between the torque or the average torque adjacent to each other, The difference is compared to determine whether or not the yield point of the screw has been reached, and when it is determined that the yield point has been reached, it is determined that tightening is complete and the PWM signal input is shut off. 4. The screw tightening device according to 4 . The storage means further stores the set torque, the set rotation speed, the rotation speed obtained by driving the stepping motor, all torques and the number of rotations required for screw tightening, The screw fastening apparatus of Claim 5 or 6 . A control method executed by control means provided in the screw tightening device,
Calculating the torque of the stepping motor from the current value detected by the driving means provided in the screw tightening device;
A storage step for storing a specified number of torques in order from the latest torque each time a new torque is calculated;
Determining a screw tightening state using the calculated torque;
Continuing or blocking the input of the PWM signal to the drive means according to the determined state;
Have
In the determining step, it is determined whether or not an average torque obtained by averaging the latest torque or a predetermined number of torques arranged in order from the latest torque is equal to or greater than a set torque. If it is determined that the tightening has been completed, the PWM signal input is shut off.
Control method. Detecting the position or rotation angle of the rotation direction before Symbol stepping motor,
Rotational speed obtained from the information of the test out the said position or rotation angle, further comprising controlling the PWM signal such that the rotational speed set,
The control method according to claim 8 . In the storing step, an average torque obtained by averaging a predetermined number of torques arranged in the order calculated using the designated number of torques each time the latest torque is calculated is arranged in order from the latest average torque. Remember ,
In the step of determining, before using the crisis憶by the torque or the average torque, to calculate the difference between the torque or the average torque adjacent, in a state where the screw is seated by comparing respective differences or determines whether the after it is determined that the state that the seat, before dangerous is the position or the rotational angle issued, to determine if it has reached the set position or the rotational angle, the continuation or In the step of blocking, it is determined that the tightening is completed when it is determined that the set position or rotation angle has been reached, and the PWM signal input is blocked.
The control method according to claim 9 . In the storing step, an average torque obtained by averaging a predetermined number of torques arranged in the order calculated using the designated number of torques each time the latest torque is calculated is arranged in order from the latest average torque. Remember ,
In the step of determining, before using the crisis憶by the torque or the average torque, to calculate the difference between the torque or the average torque adjacent, in a state where the screw is seated by comparing respective differences or determines whether the after it is determined that the state that the seat again, using the torque or the average torque that is pre-Kiki憶, calculates the difference between the torque or the average torque adjacent each To determine whether or not the yield point of the screw has been reached, and in the step of continuing or shutting off, if it is determined that the yield point has been reached, it is determined that tightening has been completed, and Shut off input,
The control method according to claim 9 .
that's all