- 1 -
`
`Pro-Dex v. Intelligent Automation
`U.S. Patent 7,091,683
`Pro-Dex Ex. 1053
`
`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 1 of 9
`
`5,154,242
`
`G3aadS
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`401031340
`
`NOLLIGNOS-LV3S [eoHATIOHULNOD
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`{waataia]HOLVINIIWD
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`HOSNAS
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`HOSN3SLN3HHND
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`
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`HOSNS3SHOLOW3HNLVUSdN3L
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`
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`HOLYSANODIWLSIG-OL-SOTVN
`
`
`
`- 2 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 2 of 9
`
`5,154,242
`
`Fig.2
`
`/
`NT
`
`
`i
`|
`t
`|!
`D__CONTROL
`
`SPEED
`
`HIGH SPEED
`
`I
`|
`
`CONTROL.
`!
`|
`lcuRRENT
`|
`CONTROL.
`|
`mereer [ete8 |
`
`PRE-SEATED-“|
`
`SEATED
`
`CURRENT |.___NOPot)
`INSTRUCT
`t
`|
`I
`|
`—
`|
`
`MOTOR
`SPEED
`
`.
`
`t
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`I
`
`1
`
`CURRENT~\ ;
`;
`f\i
`
`|_
`MOTOR
`CURRENT |
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`|
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`|
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`STAPTING
`
`(CURRENT
`
`|
`So
`OUTPUT
`|
`TORQUE |
`
`|
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`C
`B
`A
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`;
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`1
`|
`|
`-
`i
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`TIME
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`- 3 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 3 of 9
`
`5,154,242
`
`Fig.3
`
`N(REVOLUTIONS)
`
`TORQUE
`
`- 4 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 4 of 9
`
`5,154,242
`
`Fig.4
`
`START
`
`MODE SET
`
`LEARN/WORK
`
`
`
`
`
`MODE
`
`
`
`
`
`DATA ENTRY
`MODE
`
`ROUTINE A
`
`ROUTINE B
`
`DISTANCE
`SENSING
`MODE
`
`ROUTINE C
`
`- 5 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 5 of 9
`
`5,154,242
`
`Fig.5
`ig.
`
`("_ROUTINEA_—*Y
`
`100
`
`READY OR NOT
`
`\02
`
`Te)
`
`
`LEARN OR
`WOR
`x
`
`120
`(21
`|
`
`105
`IOG
`
`SEAT-SIGNAL
`RECEIVED FROM 61
`
`WORK
`
`INPUT FINAL
`
`REVOLUTION NUMBER
`
`.
`
`
`
`DECREMENTED
`TO ZERO
`
`YES
`
`
`
` lo?
`
`\23—-—~ser commen——
`124
`
`
`[_——s76rmotor} 108
`los
`;
`
` COUNTER
`
`
`DETERMINE PRE-SEATING
`OLUTION NUMBER
`
`(=COUNTED VALUE - PRE-SET VALUE }
`
`| lO
`'
`
`le7
`
`126
`STORE PRE-SEATING
`Wt
`129
`REVOLUTION NUMBER
`“RESTART MOTOR
`INO—“ear-sianat
`
`RECEIVED FROM 6
`130
`I3 |
`
`YES
`GRADUALLY INCREASE
`MOTOR CURRENT UP TO
`CURRENTLIMIT
`
`I32
`
`|
`
`WAIT FORA
`SHORT TIME INTERVAL
`
`STOP MOTOR
`
`
`
`- 6 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 6 of 9
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`5,154,242
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`Fig.6
`
`-
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`FASTENER DATA INPUTit
`&83
`
`YES
`
`LCULATE & STORE
`OLUf5
`
`READY OR NOT
`
`YES
`FINAL
`INPUT
`TIGHTENING TORQUE
`
`OBTAIN CURRENT LIMIT
`
`READ PRE-SEATING
`REVOLUTION NUMBER
`
`©) O
`
`5
`
`8
`
`SET COUNTER :
`START MOTOR
`2 | 0
`DECREMENT COUNTER
`2 |
`|
`
`DECREMENTED1Nezaes
`
`TER
`
`2l2
`
`2 | 3
`2 14
`2 | 5
`
`216
`
`2 17
`
`218
`
`STOP MOTOR
`WAIT
`RE-START MOTOR
`
`EAT-SIG
`RECEIVED FROM 6
`
`GRADUALLY INCREASE
`MOTOR CURRENT UP TO
`CURRENT LIMIT
`
`x
`IT F
`SHORTTIME INTERVAL
`
`STOP MOTOR
`
`2l94ozz
`
`
`
`- 7 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 7 of 9
`
`5,154,242
`
`Fig?=<—yrenrines
`300
`
`*es
`
`.
`
`YES
`
`303
`
`304
`
`305
`
`306
`
`INPUT FINAL
`TIGHTENING TORQUE
`
`OBTAIN CURRENT LIMIT
`
`START MOTOR
`
`PRE-SEAT SIGNAI
`
`RECEIVED FROM 45
`
`
`
`
`YES
`
`STOP MOTOR
`
`WAIT
`
`RE-START MOTOR
`
`peRECEIVED FROM 61
`
`
`YES |
`
`GRADUALLY INCREASE
`MOTOR CURRENT UP TO
`CURRENTLIMIT
`
`,
`
`WAIT FOR A
`SHORT TIME INTERVAL
`
`STOP MOTOR
`
`SIl
`
`312
`
`313
`
`
`
`- 8 -
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`

`

`U.S. Patent
`
`Oct. 13, 1992
`
`Sheet 8 of 9
`
`5,154,242
`
`Fig.8
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`
`
`
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`- 9 -
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`

`

`U.S. Patent
`
`Oct, 13, 1992
`
`Sheet 9 of 9
`
`5,154,242
`
`
`Fig.l2
`
`- 10 -
`-10 -
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`

`

`1
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`5,154,242
`
`2
`
`POWER TOOLS WITH MULTI-STAGE
`TIGHTENING TORQUE CONTROL
`
`SUMMARYOF THE INVENTION
`
`The above problem has beeneliminated in the present
`invention which provides a power tool which includes
`a DC motor for tightening a fastener through three
`consecutive stages. In a first stage, the motoris rotated
`at a high speed to be tightened to a pre-seated condition
`which is acknowledged by the power tool. Then, the
`motor is temporarily stopped and restarted at a low
`speed for tightening the fastener to its seated condition
`to complete a second stage. At a third stage, a current
`control takes over the speed control to gradually in-
`crease a field current in a feedback manner by con-
`stantly monitoring thefield current flowing through the
`motor up to a predetermined current limits selected as
`directly related to a final tightening torque at which the
`fasteneris tightened past the tightened condition. After
`the field current reaches the currentlimit, the motoris
`stopped to complete the tightening operation. The DC
`motor, which has a characteristic of increasing an out-
`put torque in direct proportion to an increasein a field
`current fed through the motor, includes a motoroutput
`shaft operatively connectedto a drivebit for tightening
`the fastener such as a screw and a nut. A speed/revolu-
`tion detector is provided for detection of a speed and
`revolutions of the motor. The motoris connected to a
`driver circuit whichis responsible for driving the motor
`at varying speeds and torques. A speed controller is
`associated with the driver to rotate the motor output
`shaft selectively at high and low speedsby controlling a
`voltage applied to the motor fortightening the fastener
`during the first and second stages. A current sensoris
`included to monitor the field current flowing through
`the motor and provide a feedback signal. Associated
`with the current sensor-is a current controller which
`varies the field current based upon the feedback signal
`to correspondingly vary the motor output torque dur-
`ing the third stage of tightening the fastener up to a
`desired tightness. The power tool further includes a
`pre-seat judge section which determines the pre-seated
`condition where the fastener is just before seated and
`generates a pre-seat signal indicative of the pre-seated
`condition, A seat detector is also included to detect a
`seated condition where the fastener is actually seated
`and to generate a seat signal indicative of the seated
`condition. An input section is provided to set a final
`tightening torque at which the fasteneris tightened past
`the seated condition and store the final
`tightening
`torque as directly related to a corresponding current
`limit for the field-current. A central controller is pro-
`vided to activate the speed controller only during the
`first and second stages and in turn activate the current
`controller only during the third stage. Thatis, the cen-
`tral controller operates to firstly activate the speed
`controller in such a manneras to drive the motor at the
`high speed,stopit in responseto the pre-seat signal [first
`stage], and to restart the motorat the low speed [second
`stage]: Upon receiving the seat signal, the central con-
`troller responds to activate the current controller in-
`stead of the speed controller in such a manner as to
`drive the motor by controlling to increase the field
`current in the feedback mannerata suitable rate up to
`the currentlimit [third stage] in order to further tighten
`the fastener past the seated condition at the final tight-
`ening torque determined by the current limit. Upon
`reaching the currentlimit, the central controller causes
`the current controller to stop feeding the field current,
`thereby stop the motor and completing to tighten the
`
`3
`
`20
`
`BACKGROUNDOF THE INVENTION
`1. Field of the Invention
`The present invention is directed to a power tools
`with multi-stage tightening torque control, and more
`particularly to a clutch-less power tool including a DC 1
`motor for tightening fasteners to a desired tightness
`through a plurality of control stages.
`2. Description of the Prior Art
`Japanese patent examined publication [KOKOKU]
`No. 60-4707] published on Oct. 19, 1985 discloses a
`torquing powertool utilizes an electric motor for tight-
`ening a fastener through two tightening stages. A con-
`trolis firstly made to apply a high voltage to the motor
`for driving the fastener at a high speed until the fastener
`is detected to be seated. Upon detection of the seated
`condition which is made by monitoring a critical in-
`crease in a field current flowing through the motor, the
`motor is temporarily stopped. Then, the motoris re-
`started with an increasing voltage up to a predeter-
`mined limit and is again stopped after an elapse of a
`predetermined time period in order to further tighten
`the fastener at a starting torque of the motor. Unfortu-
`nately, however, such voltage control will not compen-
`sate for variation in resistance which is most likely in
`the electric circuit of the motor due to the temperature
`variation of the motor during a continued use and there-
`fore fail to accurately determine a desired final tighten-
`ing. Consequently, it may bestill necessary to incorpo-
`rate a mechanical clutch limiting the tightening torque
`in orderto tighten the fastener reliably to an accurately
`predetermined tightness.
`is disclosed in Japanese
`Another prior power tool
`patent non-examined early publication (KOKAI) No.
`2-100882 published on Apr. 12, 1990. The patent pro-
`poses a multi-stage torquing powertool utilizes an elec-
`tric motor for tightening a fastener through a plurality
`of tightening stages in which thefastener is tightened at
`differently controlled torques. The powertool includes
`a distance sensor to monitor a gap distance between the
`fastener’s head and a work surface into which the fas-
`tener is being tightened and detect a pre-seated condi-
`tion when the gap distance reduced to a predetermined
`value as indicative of that the fastener is just before
`seated. A controlis firstly made to apply a high voltage
`to the motor for driving the fastener at a high speed
`until the fastener is detected to advance to the pre-
`seated condition, after which a low voltage is applied to
`the motorso as to tighten the fastener at a low speed to
`its seated condition for reducing an impactat the seat-
`ing. Upon detection of the seated condition, a reverse
`voltage is applied to stop the motor. Then, the motoris
`restarted with a gradually increasing voltage from a
`relatively low voltage to a predetermined limit in order
`to further tighten the fastener at a correspondingly
`increasing torque. The predetermined voltage limit is
`selected to define a tightening torque at which the fas-
`teneris tightened into the work surface past the seated
`condition. Because the power tool also relies on the
`voltage control for determination of the tightening
`torque,
`it will suffer from resistance variation in the
`electric circuit of the motor and fail to tighten the fas-
`tener accurately and reliably at a desired torque.
`
`60
`
`- 11 -
`-11-
`
`

`

`3
`fastenerto a desired tightness accurately in exact corre-
`spondence to the final tightening torque. Because of
`that the field current is monitored to effect feedback
`control of increasing the field current up to the prede-
`termined current limit and also because of controlling
`the field current rather than the voltage applied to the
`motor.
`it
`is possible to obtain an accurate tightening
`torque which isdirectly related to the field current and
`is free from possible variation in electrical resistance of
`the motorcircuit, thereby successfully eliminating any
`mechanical clutch while assuring a reliable and accurate
`torquing to a desired tightness.
`Accordingly,
`it
`is a primary object of the present
`invention to provide a clutch-less power tool which is
`capable of tightening the fastener accurately and reli-
`ably to a desired tightness.
`The central controller is capable of increasing the
`field current at differing rates up to the currentlimits of
`different values within a constant period of time so as to
`complete the tightening of the fastener within substan-
`tially the same period of time irrespective of the differ-
`ing requirements for the final tightening torque. Thus,
`the power tool can give an improved convenience of
`tightening the fasteners of differing torquing require-
`ments equally within substantially the same time period,
`which is therefore another object of the present inven-
`tion.
`
`ray Q
`
`= 5
`
`20
`
`nN a
`
`The powertool is preferred to include a temperature
`sensor which senses the temperature of the motor and
`provides
`a
`sensed temperature output
`indicative
`thereof. The central controller has a compensator
`which, in response to the temperature output, adjusts a
`level of the field current in compensation for tempera-
`ture-dependent variation in magnetic flux density of a
`magnetic circuit of the motor to thereby give a consis-
`tent tightening torque substantially free from tempera-
`ture variation. Such variation is likely to occur during a
`continued use of the toal and would changethe tighten-
`ing torque T whichis the function of the magnetic flux
`density @ and thefield current I, as expressed below:
`T«odnTt
`
`wherein n is the numberof turns of wire forming a coil
`of the motor.
`It is therefore a further object of the present invention
`to provide a powertoo! which is capable of compensat-
`ing for temperature-dependent variation in magnetic
`flux density of a magnetic circuit of the motor to pro-
`vide a more consistent tightening torque free from the
`temperature variation.
`The temperature compensation maybealso utilized
`to adjust a voltage applied to the motor from the source
`voltage in order to drive the motor consistently at the
`high speed as determined during thefirst stage of tight-
`ening the fastener to the pre-seated condition.
`The power tool of the present
`invention provides
`three different modes of determining the pre-seated
`condition of the fastener. A first mode is a learn-and-
`work mode in which the motoris driven to rotate for
`tightening a sample fastener to its seated condition in
`order to give a seating revolution number of the motor
`required to tighten the sample fastener to the seated
`condition. Thus obtained seating revolution numberis
`processed to be decreased by a few revolutions or less
`to give a pre-seating revolution number whichis stored
`in a memory. Atthis time, the motoris stopped to com-
`plete the operation of determining the pre-seat condi-
`tion. Then, a control is made to actually tighten the
`
`45
`
`50
`
`55
`
`60
`
`5,154,242
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`4
`fastenerby starting the motor, during which a compara-
`tor compares the actual numberof revolutions of the
`motor with the pre-seating revolution numbersuch that
`the pre-seat signal is issued once the actual revolution
`number reaches the pre-seating revolution number. In
`response to 10 the pre-seat signal, the motor is con-
`trolled to be temporarily stopped and is restarted to
`tighten the fastener at the low speed to the seated condi-
`tion [second stage} followed by being rotated by the
`current contro] to tighten the fastener to the desired
`tightness [third stage].
`A second mode is a data entry one in which data
`entry section is responsible for entering data indicative
`of pitch and effective thread length with regard to the
`fastener intended to be tightened. The data is stored in
`a memoryandis processed to calculate a seating revolu-
`tion number required for tightening the fastener to its
`seated condition and to obtain a pre-seating revolution
`number which is thus calculated seating revolution
`number minus a few numberof revolutions or less. A
`comparatoris responsible to compare the actual number
`of revolutions of the motor with the pre-seating revolu-
`tion number suchthat the pre-seat signal is issued once
`the actual revolution number reaches the pre-seating
`revolution numberfor stopping the motor.
`A third modeis a real-time sensing mode in which a
`distance monitor constantly monitors a gap distance
`between a bit end of the motor and a work surfaceinto
`which the fastener is being tightened, determines the
`pre-seated condition when the distance decreases to a
`predetermined value, and issues the pre-seat signal
`in
`response to the pre-seated condition for stopping the
`motor.
`
`is therefore a still further object of the present
`It
`invention to provide a power tool which includes a
`unique configuration of successfully determining the
`pre-seated condition.
`Preferably, the power tool can be made to have the
`above three modessoasto selectively utilize one of the
`modes dependent upon the user's requirement,
`thus
`improving flexibility in using the power tool.
`These andstill other objects and advantages of the
`present invention will become more apparent from the
`following detailed description of the embodiment when
`taken in conjunction with the attached drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagramillustrating a control system
`of a powertool in accordance with a preferred embodi-
`ment of the present invention;
`FIG.2is a timing chart for controlling a DC motorin
`the powertool;
`FIG. 3 is a graph illustrating a torque-speed [number
`of revolutions] relation of the DC motor;
`FIG. 4 is a flow chart illustrating a basic operation of
`the powertool;
`FIG. 5 is a flow chart illustrating a learn-and-work
`operation mode of the powertool;
`FIG.6 is a flow chart illustrating a data entry opera-
`tion mode of the powertool;
`FIG.7 is a flow chart illustrating a real-time sensing
`mode of the powertool;
`FIG. 8 is a schematic view illustrating a manner in
`which the power toollearns a length or the number of
`revolutions required for tightening a sample fastener to
`its seated condition;
`
`- 12 -
`-12-
`
`

`

`5
`FIG. 9 is a schematic view of the power tool pro-
`vided witha data entry pad and display;
`FIG.10 is a view showinga typical fastener configu-
`ration;
`FIG. 11 is a schematic view illustrating the power
`tool provided with a pilot rod for sensing a pre-seated
`condition of the fastener; and
`FIG. 12is a schematic view illustrating a sensor con-
`figuration associated with the pilot rod.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`Referring now to FIG. 1, there is shown a control
`system for a power tool in accordance with a preferred
`embodiment of the present invention. The powertools
`comprises a DC motor 10 having an output shaft (not
`shown) connected through a set of reduction gears (not
`shown)to a drive spindle carryinga bit for tightening a
`fastener such as a screw or the like. A battery (not
`shown) is incorporated in the power tool to provide a
`constant source voltage to energize the motor 10
`through a driver 20 of a conventional configuration
`having a switching transistor. A pulse-width-modulator
`(PWM)21is connectedto the driver 20 in order to vary
`a field current, i.e., motor current flowing through the
`motor 10 for adjusting the speed and Output torque of
`the motor 10 under the control of a central controller
`30.
`The central controller 30 is provided to achieve a
`three-stage tightening cycle for lightening the fastener
`while monitoring the speed of the motor 10 and the
`motor Current, and also to determine, based uponsuit-
`able input data, a pre-seated condition at which the
`fastener is just before seated. The tightening cycleis
`shown in FIG.2 to comprise a first stage [I], a second
`stage [II], and a third stage [III]. In thefirst stage[I], the
`motor 10 is driven to rotate at a high speed until the
`fastener comesto the pre-seated condition at which the
`motor10 is caused to rapidly slow downto a zero speed
`at the end of the first stage [I]. The second stage [IT]
`follows immediately to restart motor 10 at a low speed
`until the fastener is seated. The low speedis selected to
`a minimum speed of the motor 10 so as to reduce the
`seating impact as much as possible. Then, the third stage
`[111] commences to gradually increase the motor cur-
`Tent up to a predetermined current limit and stop feed-
`ing the motor current after the motor current reaches
`the current limit, thereby tightening the fastener at a
`final tightening torque determined in coincidence with
`the current limit. The central controller 30 comprises a
`main processor 31 responsible for the above three-stage
`tightening control and for determination of the pre-
`seated condition, as will be discussed in detail hereinaf-
`ter, an analog-digital converter 32, a memory 33, and a
`digital input/output 34.
`A tightening torque entry section 40 is provided to
`enter an analog value determining the final torque at
`which the fastener is tightened to a desired tightness.
`The analog value ofthefinal tightening torqueis fed to
`the analog-digital converter 32 where it is converted
`into a corresponding digital value which is indicative of
`the above current limit and is stored in the memory 33
`to be processed at the main processor 31 for the above
`tightening control during the third stage of the tighten-
`ing cycle of FIG. 2. Also fed to the analog-digital con-
`verter 32 is a signal indicative of a motor temperature
`sensed by a motor temperature sensor 50 provided
`within or in the vicinity of the motor 10. Further, the
`
`355
`
`60
`
`5,154,242
`
`6
`motor 10 is associated with a position/speed sensor 51
`which, for example, comprises a frequency generator
`[FG] to monitor the position and the angular speed of
`the motor 10 and outputs a corresponding speedsignal
`to a speed controller 60, a seat-condition detector 61,
`and a bit revolution calculator 62. The speed controller
`60 comparesthe speed signal with a pre-set speed value
`fed from the central controller 30 and issues a feedback
`signal through a switch 64 to the PWM 21 in order to
`keep the motor speed at a constant level designated by
`the pre-set value. That is, the speed controller 60 re-
`ceives from the central controller 30 the pre-set speed
`value which designates a high speed during thefirst
`tightening stage [I] and a minimum. speed during the
`second tightening stage [II] to drive the motor 10 selec-
`tively at the high and low speeds, respectively. The
`seat-condition detector 61 acknowledges that the fas-
`tener is seated when the speed signal shows a remark-
`able slow down or decrease below a predetermined
`value and issues a seat-signal indicative of the seated
`condition back to the central controller 30. The speed
`signal
`is also fed to the bit revolution calculator 62
`which divides the number of sensed revolutions by a
`reduction ratio of the reduction gear to provide the
`corresponding number of revolutions that the bit has
`experienced, the resulting data being fed to the central
`controller 30. The calculator 62 may be included in the
`central processor 30. A current sensor 22 is coupled to
`the driver 20 so as to monitor the motor current gener-
`ated in the driver 20 and flowing through an armature
`of the motor 10 and outputs a currentsignal to a current
`controller 63. The current signal
`is compared at the
`current controller 63 with a reference current value
`given from the central controller 30 to output a current
`feedbacksignal to the PWM 21through the switch 64 in
`order to regulate the motor current in an exact corre-
`spondence to the reference current value during the
`third tightening stage [III]. The reference current value
`is controlled to vary at the central controller 30 so as to
`correspondingly vary the motor current as indicated by
`curves A, B, and C of FIG. 2 up to the predetermined
`current limit, thereby tightening the fastener to a de-
`sired tightness orat the final tightening torque deter-
`mined by the currentlimit. The pre-set speed value and
`reference current value are given respectively to the
`speed controller 60 and the current controller 63 in
`analog values through a digital-to-analog converter 65
`from thecentral controller 30. The switch 64 operates
`underthe control ofthe central controller 30 such that
`it transmits to the PWM 21 only the speed feedback
`signal from the speed controller 60 until the seat condi-
`tion detector 61 acknowledges the seated condition, ie,
`duringthefirst and second stages of FIG. 2 and turns to
`transmit only the current feedback signal from the cur-
`rent controller 63 after the detection of the seated-con-
`dition.
`The powertool includes a modeselection switch 41
`for selecting one of three modes in which the central
`controller 30 can determine the pre-seated condition of
`the fastener. Thefirst modeis a learn-and-work modein
`which a sample fastener 1 is driven into a work surface
`by the powertool, as shown in FIG.8, to determine a
`pre-seat length PL at which the sample fastener 1 is
`expected to come into the pre-seated condition. To this
`end, the bit revolution calculator 62 counts the number
`of revolutions required for the bit to tighten the sample
`fastener 1 into the seated condition which can be ac-
`knowledged by the seat-condition detector 61. Thus
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`7
`obtained seating revolution number of the bit is sub-
`tracted by several revolutions of the bits or less to de-
`fine a pre-seating revolution number whichis stored in
`the memory 33 as directly related to the above pre-seat
`length for judgement of the pre-seated condition at the
`later operation of tightening the identical fastener into
`the work surface.
`The second modeis a data entry mode in which data
`Or parameters known to the intended fastener are input
`at a data entry section 42 as indicative of pitch P and
`effective thread length L ofthe fastener 1, as shownin
`FIG. 10. The data are processed at the main processor
`31 to calculate the seating revolution numberfor the bit
`to tighten the fastener 1 into the seated condition based
`upon the known relation N=L/P, wherein N is the
`number of revolutions of the fastener or the bit. The
`pre-seating revolution numberis also defined as thus
`calculated seating revolution number minus several
`revolutions of the bit or less. The seating and pre-seat-
`ing revolution numbersare stored in the memory 33 for
`judgementof the pre-seated conditionin the later tight-
`ening operation in consideration of the actual numberof
`the revolutions of the bits detected at the detector 61.
`Alternately, the central controller 30 may be configured
`to have a table storing groups of individual data with
`respect to different kinds of fastener such that the data
`for the specific fastener can be designated simply by
`entering a designation numeral, symbol, or the like as-
`signed to the intended fastener. For entering the indi-
`vidual data or designation symbol, the power tool is
`providedat its rear end with a key pad 43 with display
`44, as shownin FIG. 9, which maybealso utilized to
`enter the tightening torque.
`The third modeis a real-time sensing mode in which
`a distance sensor 45 monitors a distance between a bit
`end of the tool and a work surface into which the fas-
`tener is being tightened so as to determine the pre-
`seated condition when the distance decreases to a pre-
`determined value corresponding to several revolutions
`of the fastener or less. When the pre-seated condition is
`determined, the sensor 45 issues a pre-seat signal to the
`central controller 30 which responds to provide a stop
`signal to driver 20 to stop the motor 10. FIGS. 11 and 12
`showa distance sensor 45 which comprises a pilot rod
`46 extending in parallel with the bit from a tool housing
`5 and a miniature switch 47 incorporated in the tool
`housing 5. The pilot rod 46 is held movable along its
`length with respect to the tool housing § so as to adjust
`a gap distance D between the front distal end of the
`pilot rod 46 and the corresponding end ofbit 2. The ga
`distance D is normaliy adjusted to be a length corre-
`sponding to the several times of the fastener’s pitch or
`less such that the pre-seated condition is detected when
`the front distal end of the pilot rod 46 comesinto abut-
`ment against the work surface into which the fasteneris
`being tightened. The pilot rod 46 is biased forwardly by
`a spring 48 to maintain the gap and is coupledat its rear
`end to a movable contact of the switch 47 through an
`actuator 49 so that the actuator 49 will close the switch
`47 when the pilot rod 46 is forced to move rearwardly
`in response to the abutmentofthe pilot rod 46 against
`the work surface, whereby the switch 47 issues the
`pre-seat signal to the central controller 30 to temporar-
`ily stop the motor 10. For detection of the gap distance,
`a linear encoder may be utilized in place of the above
`distance sensor.
`Now, the operation sequence of the power tool is
`discussed in detail with reference to FIGS. 4 to 7. Ref-
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`20
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`40
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`60
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`erenceis firstly made of FIG. 4 which shows a flow
`chart of an overall operation of the power tool. Upon
`energization of the power tool [START], the system
`asks to set one of the above three modes [MODE SET].
`After selecting the mode, the system proceeds to check
`which modeis selected from the three modes and com-
`plete one of the corresponding routines A, B, C of the
`selected modes. Any one of the three mode can be
`stored as a default modeso that the system will pass the
`MODESETstep to complete the routine ofthe default
`mode unless the modeis to be changed. After complet-
`ing the routine of the individual mode, the system goes
`back to the MODESETstep.
`When the learn-and-work mode is selected, the sys-
`tem goesto the routine A, as shownin a flow chart of
`FIG. §, in which aninitialization step 100 is firstly made
`to reset the control circuit of the power tool and the
`system waits until it receives a ready signal indicative of
`that the powertoolis ready to operate[step 101]. After
`the ready signal is received, the system acknowledges
`that the system is ready to operate [step 102] and calls
`for which one between a Jearn-mode and a work-mode
`is designated [step 103]. When the learn-modeis desig-
`nated [step 104], the central controller 30 sets an inter-
`nal counter to be ready for counting the number of
`revolutions ofthe bit [step 105]and causes the motor 10
`to start rotating for tightening the sample fastener1 into
`the worksurface [step 106]. Thetightening is madeuntil
`the seat-signalis received from the seat-condition detec-
`tor 61 as a result of that the motor speed is sensed to
`decrease below the predetermined value [step 107].
`Whentheseat-signal is received, the controller 30 rec-
`ognizes that the fastener is seated and stops the motor 10
`[step 108]. At this occurrence,
`the controller 30 re-
`spondsto read the numberofthe revolutions Ofthebit
`as accumulated in the counter[step 109] and determines
`the pre-seating revolution number which is the counted
`value indicative of the revolution number of the bit
`minus a pre-set value corresponding to several revolu-
`tions ofthe bit orless [step 110]. Thus obtained pre-seat-
`ing revolution numberor valueis stored in the memory
`33 [step 111] to complete the learn-mode, after which
`the system goes back to the step 101 to again wait the
`ready signal. Subsequently, when the step 104 is
`reached and the work-modeis selected instead,
`the
`routine goes to a work-modestarting at a step 120 call-
`ing for inputofa desired final tightening torque which
`is processed to obtain a corresponding current limit
`level stored in the memory 33 and givento the current
`controller 63 [step 121]. Then, the controller 30 reads
`the pre-seating revolution number from the memory 33
`{step 122], sets it into a counter [step 123], and start
`rotating the motor 10 [step 124} for tightening the fas-
`tener into the work surface. At the same time, the
`counter starts decrementing the pre-seating revolution
`number by the numberof revolutions of the bits being
`obtained by the calculator 62 [step 125]. Accordingly,
`the motor 10 is driven to rotate constantly at the high
`speed under the control of the speed controller 60 to
`tighten the fastener until the counter is decremented to
`zero which is indicative of that the fastener has been
`tightened to the pre-seated condition. Upon the counter
`decrementedto zero [step 126], the central controller 30
`issues the stop signal to stop the motor10 [step 127] and
`waits for a short time interval [step 128] before the
`motor 10 is restarted [step 129]. At this time, the motor
`10 is again driven by the speed controller 60 to rotate at
`the minimum speed until the seat-signal is received from
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`10
`controller 30 acts on the PWM 21 to temporarily stop
`the motor 10 through a transientperiod at the end ofthe
`first stage [I]where the motorsees a breaking current, as
`shown in FIG. 2. Immediately after the motor 10 is
`stopped, the control proceedsto the secondstage [II] in
`which the motor 10 is restarted and driven to rotate at
`the minimum speed until the seat-signal is received from
`the seat-condition detector 61 as a result of that fastener
`is actually seated. Also during the second stage[II], the
`speed controller 60 is responsible for controlling the
`motor 10 to rotate constantly at the minimum speed
`predetermined by the central controller 30. After the
`fasteneris seated, the control proceedsto the third stage
`[IIT] in which the current controller 63 is brought into
`Operation instead of the speed controller 60 so as to
`increase the motor current with an attendant turn-over
`_ of the switch 64 for connection of the PWM 21 to the
`current controller 63 from the speed controller 60. In
`this stage [IIT], the motor current is controlled tofirstly
`kept substantially at zero level for a short time period
`and to increase gradually at a constant rate up.to the
`current limit determined by the central controller 30 as
`corresponding to the final tightening torque, as shown
`in FIG. 2. Upon reaching the current limit, the motor
`currentis kept thereat for a certain short time interval to
`thereby tighten the fastener exactly at the desired final
`tightening torque to the corresponding tightness, after
`Which the central controller 30 responds to cea