Tightening device

A tightening device is able to check that a fastening member has been fastened to a desired set torque or greater after being tightened, without loosening the fastening member. The tightening device is provided with a mode switching switch for switching between a first tightening process of adjusting the output of a motor after measured torque that is measured by a torque detector has reached a preset first control start torque, such that the measured torque reaches a preset first set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the first set torque, and a second tightening process of driving the motor at an initial output that is less than in the first tightening process, adjusting the output of the motor after the measured torque that is measured by the torque detector has reached a preset second control start torque, such that the measured torque reaches a preset second set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the second set torque.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tightening device that is able to tighten a fastening member such as a bolt or a nut using a plurality of tightening processes.

2. Description of the Related Art

In order to increase the accuracy with which fastening members such as bolts or nuts are tightened, a known tightener measures the tightening torque that acts on the fastening member, and is numerically controlled to end the tightening when the measured torque reaches a set torque (e.g., see JP 2013-166211A).

Also, additional tightening that involves torque being further applied to tighten a fastening member that has already been tightened is performed in some cases (see JP 2013-166211A).

There is a need for a way of checking whether tightening has actually been performed to a desired set torque or greater, after a fastening member has been tightened or after additional tightening has been performed.

In tightening the wheel nuts of a vehicle, the wheel nuts are firstly tightened and run in, and then loosened and tightened again in order to check whether tightening has been performed to a prescribed set torque. Further running in thus needs to be performed when wheel nuts that have already been tightened once are loosened and retightened, making it difficult to determine whether the tightening torque has really reached the set torque.

An object of the present invention is to provide a tightening device that is able to check that a fastening member has been fastened to a desired set torque or greater after being tightened, without loosening the fastening member.

SUMMARY OF THE INVENTION

In order to solve the above problems, a tightening device of the present invention is a tightening device including a motor, a motor drive circuit that drives the motor, a drive shaft that is rotated by the motor, has a socket mounted on a tip thereof, and is configured to tighten a fastening member, a torque detector that detects a tightening torque that acts on the socket, and a control unit that controls the motor drive circuit based on a set torque set in advance and a measured torque measured by the torque detector. The control unit includes a motor switching switch that switches between a first tightening process of controlling the motor drive circuit, adjusting an output of the motor after the measured torque that is measured by the torque detector has reached a preset first control start torque, such that the measured torque reaches a preset first set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the first set torque, and a second tightening process of controlling the motor drive circuit to drive the motor at an initial output that is less than in the first tightening process, adjusting the output of the motor after the measured torque that is measured by the torque detector has reached a preset second control start torque, such that the measured torque reaches a preset second set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the second set torque.

The mode switching switch desirably has a display unit that enables the mode that has been switched to, out of the first tightening process and the second tightening process, to be visually checked.

Effects of the Invention

According to the tightening device of the present invention, the tightening mode can be changed to shift to a second tightening process by operating a mode switching switch, after a fastening member has been tightened in a first tightening process with a first setting torque as the target value. In the second tightening process, a motor is driven at an initial output that is less than the initial output in the first tightening process, and tightening is implemented with a second set torque as the target value. By performing this second tightening process, it can be confirmed that the fastening member is tightened to at least the second set torque.

The second tightening process is able to prevent over-tightening, or so-called overshooting, with respect to the second set torque, since the initial output of the motor is less than in the first tightening process, and tightening is performed by increasing the torque in a phased manner through repeated increases and decreases in torque.

Also, because it can be visually checked which tightening process is the residing tightening process when the mode switching switch is operated, erroneous operation can be prevented.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment in which a tightening device10of the present invention is applied to a numerically controlled tightening device constituted by a tightener20serving as a main body that performs the tightening, a control device30that controls the tightener20, and a torque detector50that measures torque, as shown inFIGS. 1 and 2, will be described. Note that a configuration can also be adopted in which some or all of the functions of the control device30are incorporated in the tightener20, or some of the functions of the control device30may be executed by an external PC or the like.

Also, in the following embodiment, the tightening process consists of a first tightening process and a second tightening process as shown inFIG. 3, with the first tightening process being a normal tightening mode, and the second tightening process serving as a checking tightening mode that can check whether the tightening torque is a set torque or greater.

FIG. 1is a diagram illustrating an outline of the tightening device10of the present invention, andFIG. 2is a schematic block diagram of the tightening device10. As shown in the diagrams, the tightening device10is constituted by the tightener20and the control device30, and the tightener20is provided with the torque detector50which detects torque acting on a socket.

In the embodiment shown inFIG. 1, a double-shaft power wrench in which a drive shaft21consists of an inner shaft and an outer shaft22is exemplified as the tightener20. However, the power wrench is not limited to a double-shaft power wrench and may be a single-shaft power wrench, and the tightener20may be an impact wrench, an impact driver, an impact/hammer drill, or the like.

In the double-shaft tightener20, the inner shaft and the outer shaft22forming the drive shaft21can be rotated in opposite directions to each other by a motor24built into a housing23. The inner shaft and the outer shaft22can be connected to the motor24by a deceleration mechanism28such as a planetary gear mechanism.

The tightener20is provided, at a tip of the inner shaft, with a socket that is capable of mounting a fastening member such as a bolt or a nut. Also, a reaction receiver25that is equipped with an arm whose tip projects in a substantially perpendicular direction relative to the axial center of the drive shaft21is attached to a tip of the outer shaft22.

The tightener20, on receiving an instruction from a control device30shown inFIG. 2as a result of a trigger switch26shown inFIG. 1being operated, drives the motor24and rotates the drive shaft21. Also, as shown inFIG. 1, the tightener20is equipped with a switch27for forward-reverse switching, and the rotation of the motor24can be reversed by operating the switch27for forward-reverse switching to enable tightening and loosening of a fastening member. The switch27for forward-reverse switching can be given as a switch that switches the rotation of the drive shaft21between forward and reverse mechanistically, through a gear change, clutch operation or the like of the deceleration mechanism28. Also, the switch27for forward-reverse switching may be a switch that reverses the voltage that is supplied to the motor24.

The tightener20is equipped with the torque detector50for detecting the torque acting on the socket. The torque detector50transmits a signal relating to torque to the control device30. As shown inFIG. 1, a torque detector in which a torque sensor51that detects tightening torque is directly mounted between the drive shaft21and the socket can be employed as the torque detector50. The torque acting on the socket may be torque detected from a change in the electrical system of the tightener20, such as the change in motor current, for example. Also, the torque acting on the socket may also be obtained through conversion from the rotation angle of the drive shaft21, the motor24, the deceleration mechanism28or the like.

Because the torque detector50rotates in tandem with the drive shaft21when mounted in the drive shaft21as shown inFIG. 1, cable connection with the control device30is not possible. Accordingly, it is desirable that the signal relating to tightening torque measured by the torque sensor51is amplified by an amplifier circuit52, input to the CPU54after undergoing A/D conversion in an A/D converter circuit53, and wirelessly transmitted via a RF (Radio Frequency) circuit55and an antenna56, as shown inFIG. 2. Power supply to the torque detector50can be performed by installing a small battery in the torque detector50.

As a specific embodiment, a distortion gauge adhered to the outer shaft22can be exemplified as the torque sensor51. The tightening torque acting on the outer shaft22is output as a voltage change caused by the resistance change of the distortion gauge.

The control device30is, as shown inFIG. 1, electrically connected to the tightener20by a connection cable60, and is capable of communicating with the tightener20and supplying power to the tightener20. Note that the control device30needs to perform setting and adjustment according to the performance and characteristics of the tightener20. Accordingly, erroneous measurement or the like may occur when a different tightener20is connected to the control device30. Thus, it is desirable for the connection cable60to directly couple the tightener20to the control device30in an undetachable manner. Note that a configuration may be adopted in which the tightener20and the control device30are connected by a connector64, with the length of the connector64being selectable according to the work environment.

The control device30can, furthermore, be connected to a commercial power source by a power cable62that has a plug61connected to a tip thereof.

As a specific embodiment, the control device30incorporates a control means32shown inFIG. 2in a box-type casing31, as shown inFIG. 1. The control means32is provided with a control unit33that is mainly constituted by electronic components including a CPU34, a memory35such as RAM or ROM, and a D/A converter, and can be realized by various programs or the like stored in the memory35. InFIG. 2, a functional block relating to typical functions that are realized by these connections is depicted. It should naturally be understood that these functional blocks can be realized using only hardware, only software, or a combination of hardware and software.

A set torque display unit40that displays a set torque that is desired by a user, and a measured torque display unit41that displays the tightening torque measured by the torque detector50are provided on one surface of the casing31, as shown inFIG. 1. Also, torque setting buttons47and48for the user to increase or decrease the set torque, and a mode switching switch44for switching between the tightening modes of a first tightening process and a second tightening process are provided. Furthermore, a torque setting range display unit46that indicates the range over which the set torque of the tightening device10can be set is provided on the casing31.

A digital display employing LEDs, for example, can be used for the set torque display unit40and the measured torque display unit41. One or both of these display units can, in the case where an anomaly of some kind occurs in the tightening device10, be used as an error display unit for displaying the anomaly. Note that, inFIG. 1, reference numeral42denotes a set torque sub display unit that displays the set torque when the torque setting buttons47and48are operated, and is smaller than the set torque display unit40.

The torque setting buttons47and48are a minus button47for reducing the set torque and a plus button48for increasing the set torque. These torque setting buttons47and48can also be used as error cancellation buttons by operating one of the buttons when an anomaly of some kind occurs in the tightening device10.

The mode switching switch44is a switch for switching between two different tightening modes, and a press button switch, a dial switch, a slide switch or the like can be employed therefor. A display unit that displays the residing tightening mode is disposed in a suitable place in the mode switching switch44or on the casing31, so as to enable the tightening mode to which the mode switching switch44is set to be visually checked. In the illustrated example, an LED45that is illuminated in correspondence with one of the tightening mode is disposed in the display unit. The integrated LED45is illuminated when the mode switching switch44that is illustrated is set to one of the tightening modes (the second tightening process in the present embodiment). It is conceivable, for example, to display the residing tightening mode on the abovementioned measured torque display unit41or the like, and to switch this display when tightening is started, although, in this case, the tightening mode cannot be checked while tightening is being performed. Also, the user is required to perform other operations in order to check the tightening mode. On the other hand, in the present invention, the residing tightening mode can be visually checked as a result of the mode switching switch44itself being illuminated, which has the advantage of preventing erroneous operation and the like.

The torque setting range display unit46indicates the minimum and maximum set torque of the tightening device10, as shown inFIG. 1. The setting range stamped into a plate as shown inFIG. 1or printed on a sticker and attached to the casing31can be exemplified as the torque setting range display unit46. A digital display can also be used therefor similarly to the above set torque display unit40and the like.

The control unit33constituting the control means32has, as shown inFIG. 2, the abovementioned display units40,41and42, buttons47and78, and mode switching switch44connected thereto, together with a motor drive circuit36for driving the motor24of the tightener20via the trigger switch26, and an RF circuit37and an antenna38for performing wireless communication with the torque detector50. For example, output adjustment of the motor24by the motor drive circuit36can be performed by phase control or PWM control.

All programs for controlling the tightener20are stored in the memory35. For example, stored in the memory35are set torques set by the user in correspondence with the respective tightening modes of the first tightening process and the second tightening process, tightening programs and various parameters corresponding to the respective tightening modes, the residing tightening mode, the control amount of the motor drive circuit36for adjusting the output of the motor24based on the measured torque that is received and the set torque, and the like.

Control of the tightening device10configured such as described above can be broadly divided, as shown inFIG. 3, into a mode switching flow (FIG. 4, step S001), a set torque changing flow (FIG. 5, step S002), and a tightening flow (FIG. 6) including the first tightening process (step S003) and the second tightening process (step S004).

Mode Switching Flow

The mode switching flow is a flow for switching between the first tightening process and the second tightening process.

More specifically, as shown inFIG. 4, this involves processing for switching, when the mode switching switch44is operated (step S101), the residing tightening mode between the first tightening process and the second tightening process (step S102), and storing the residing tightening mode in the memory35of the control unit33(step S103). The tightening mode switched to by the mode switching switch44can be discriminated by referring to the LED45. In the present embodiment, the LED45is turned off in the first tightening process and turned on in the second tightening process. Note that, in order to prevent erroneous operation, it is desirable to deactivate operation of the mode switching switch44during the set torque changing flow, the first tightening process and the second tightening process which will be discussed later.

Set Torque Changing Flow

The set torque changing flow (step S002) shown inFIG. 5is performed after the mode switching flow (step S001) as shown inFIG. 3. This set torque changing flow is executed following the mode switching flow at the time of the initial setting of the tightening device10or in the case of changing the set torque of the respective tightening modes. In the present embodiment, the set torque (first set torque) of the first tightening process and the set torque (second set torque) of the second tightening process are set. In the case of using the tightening device10in a state where the set torque has already been set or changed, execution of the set torque changing flow can be skipped.

The set torque changing flow is for setting and storing the set torque for the residing tightening mode, when the torque setting buttons47and78are operated.

As a specific embodiment, when the torque setting button47or48is operated (step S201), the control unit33increments or decrements the set torque that is stored in the memory35by the designated value, according to the operation of the torque setting button47or48(step S202), as shown inFIG. 5. Processing for storing the new set torque in the memory35as the set torque is then performed (step S203).

Note that it is desirable to deactivate operation of the torque setting buttons47and48during the mode switching flow, the first tightening process and the second tightening process in order to prevent erroneous operation, and a configuration may also be adopted in which the processing moves to step S203after waiting for the torque setting button47or48to subsequently be operated within a predetermined time period after the torque setting button47or48has been operated.

Tightening Process

After the set torque of each tightening mode has been set using the set torque changing flow (step S002), actual tightening process that depends on the selected tightening mode (step S003, step S004) follows, as shown inFIGS. 3 and 6.

Description of Tightening Modes

Here, an outline of the tightening modes of the first tightening process and the second tightening process according to one embodiment of the present invention will be described.

Although the values differ, in each tightening mode, as shown inFIGS. 7 and 8, the motor24is started at a predetermined initial output (V0) and maintains the initial output (V0). After the measured torque that is detected by the torque detector50has reached a predetermined control start torque (VF) (the first control start torque in the first tightening process, and the second control start torque in the second tightening process), the output of the motor24is feedback controlled based on the measured torque. In feedback control, the motor24is driven while adjusting the output within a predetermined range defined by a maximum output (VR) and a minimum output (VB) of the motor24. The measured torque thereby increases in a phased manner through repeated increases and decreases in torque.

Power supply to the motor is then blocked when the measured torque reaches the set torque set in advance.

First Tightening Process

The first tightening process is a tightening mode in which the motor24has a large initial output.

In this tightening mode, the initial output (V0) of the motor24, as shown inFIG. 7, is larger than in the tightening mode of the second tightening process which will be shown next (seeFIGS. 7 and 8). Accordingly, there if a risk of the tightening torque overshooting if the first tightening process is executed in order to check whether a tightened fastening member is tightened to a predetermined torque or greater. On the other hand, because the motor24has a large initial output, there is an advantage in that tightening can be performed in a short time.

Second Tightening Process

The second tightening process is a tightening mode for checking whether the fastening member tightened in the abovementioned first tightening process is tightened to a predetermined torque or greater.

The second tightening process is a tightening mode in which the initial output (V0) of the motor24, as shown inFIG. 8, is less than the first tightening process.

Thus, although the second tightening process takes longer to reach a predetermined set torque due to the low initial output (V0) of the motor24that is set, there is an advantage in that over-tightening (overshooting) can be prevented.

A more detailed control flow of the tightening modes is shown inFIG. 6. Note that although the first tightening process and the second tightening process are described together, when tightening a fastening member, first, the first tightening process of step S003is executed, and then the second tightening process of step S004is executed after tightening the fastening member to a predetermined set torque. Selection of these tightening modes is performed by operating the mode switching switch44.

The tightening flow is started by turning on the trigger switch26in a state where the socket of the tightener20is fitted to the fastening member (step S301). With the tightener20shown inFIG. 1, the trigger switch26is turned on by the user pulling the trigger switch26with a finger.

When the trigger switch26is turned on (step S301), the control unit33controls power supply from the motor drive circuit36to the motor24according to the residing tightening mode and the set torque thereof with reference to the memory35, and drives the motor24at the initial output (V0) (step S302). The reaction receiver25thereby rotates in the reverse direction to the tightening direction of the socket and contacts another fastening member or the like, and the fastening member starts being tightened by the socket.

The initial output (V0) is set to satisfy the following relationship, where VB is the minimum starting output of the motor24: initial output of first tightening process>initial output of second tightening process≧VB. More favorable checking tightening can be performed when the initial output of the second tightening process coincides with or most nearly approximates the minimum starting output (VB).

When the motor24starts driving, the torque detector50detects the torque acting on the socket, and transmits the detected torque to the control means32as the measured torque. The motor is driven at the initial output (V0) until the measured torque reaches the prescribed control start torque (VF) corresponding to each tightening mode (No at step S303; range indicated by circled number1inFIGS. 7 and 8). When the measured torque reaches the prescribed control start torque (VF) (YES at step S303; P inFIGS. 7 and 8), motor feedback control is started (step S304; range indicated by circled number2inFIGS. 7 and 8). Note that prescribed torque (VF) can be set in correspondence with the tightening mode. The control start torque (VF) can be set respectively in the first tightening process (first control start torque) and the second tightening process (second control start torque), in which case: first control start torque (VF)≧second control start torque (VF). Desirably, the following relationship is satisfied: first control start torque (VF)>second control start torque (VF). For example, inFIGS. 7 and 8, the first control start torque is 0.7 times the set torque T (VF=T×0.7), and the second control start torque is VF=50 N·m (<T×0.5).

In the motor feedback control (step S304), as shown inFIGS. 7 and 8, in the case where the rate of increase of measured torque is greater than a predetermined value, based on the measured torque from the torque detector50(Yes in step S305), the control unit33performs control to reduce the power supply from the motor drive circuit36to the motor24(step S306), and if the rate of increase of measured torque is less than or equal to the predetermined value (No in step S305), the processing proceeds to the following step S307.

As shown inFIGS. 7 and 8, conversely, in the case where the rate of increase of measured torque from the torque detector50is less than a predetermined value (Yes in step S307), the control unit33performs control to increase the power supply from the motor drive circuit36to the motor24(step S308), and if the rate of increase of measured torque is greater than or equal to the predetermined value (No in step S307), the processing proceeds to the following step S309.

The feedback control (steps S305to S308) is executed until the measured torque from the torque detector50reaches the set torque T set in correspondence with each of the tightening modes (No in step S309). When measured torque reaches the set torque T (Yes in step S309), the control unit33blocks the power supply from the motor drive circuit36to the motor24, and stop the output of the motor24(step S310; circled number3inFIGS. 7 and 8).

A graph showing the change in tightening torque in the tightening flow corresponding to each tightening mode, and a graph showing the change in output of the motor24are respectively shown as A and B inFIGS. 7 and 8.

Referring toFIGS. 7 and 8, it can be seen that the measured torque increases approximately linearly in each of the tightening modes due to the initial output (V0) being applied, and then when the first control start torque or the second control start torque (VF) corresponding to the tightening mode is reached, the measured torque increases in a phased manner through repeated increases and decreases in torque, and approaches the set torque T.

Because the motor24has a large initial output in the first tightening process compared with the second tightening process, tightening can be performed in a short time, although at the risk of the tightening torque overshooting. In this case, the fastening member would be tightened to an even greater tightening torque if the first tightening process were implemented in the second tightening process which is for checking the tightening torque.

In the present invention, overshooting is unlikely to occur, because the tightening torque is checked in the checking tightening mode of the second tightening process in which the initial output (V0) of the motor24is less than in the first tightening process. Accordingly, it can be accurately confirmed that the fastening member is tightened to the set tightening torque or greater.

That is, when the second tightening process is implemented on a fastening member that was tightened to less than the set torque in the first tightening process, the tightening torque can be increased to the set torque. On the other hand, when the second tightening process is implemented on a fastening member that was tightened to the set torque or greater in the first tightening process, it can be confirmed that the fastening member is tightened to the set torque or greater, without further increasing or loosening the tightening torque.

Being able to check that tightening has been performed to the set torque or greater in the second tightening process, without loosening the fastening member, is highly effective when applied to the tightening of wheel nuts, which was conventionally performed by loosening and retightening the wheel nuts.

The foregoing description is intended to illustrate the present invention, and should not be construed as limiting the invention defined in the claims or as restricting the scope of the invention. Also, the configuration of each element of the invention is not limited to the foregoing examples, and various modifications can be made within the technical scope of the claims.

For example, the first tightening process and the second tightening process can also be executed continuously on each fastening member, or the first tightening process may firstly be executed on a plurality of fastening members, and the second tightening process may then be executed collectively on these fastening members. Also, a configuration may be adopted in which only the second tightening process is executed on a fastening member tightened by another tightening device.