US20070144753A1

Movatterモバイル変換

Info

Publication number: US20070144753A1
Application number: US11/708,826
Authority: US
Inventors: Jerry Miller
Original assignee: Microtorq LLC
Current assignee: Microtorq LLC
Priority date: 2005-12-22
Filing date: 2007-02-21
Publication date: 2007-06-28

Abstract

Disclosed herein is a variable speed tool useful for use with securing or removing industrial fasteners. The tool also includes a means to torque the fastener to a certain precise torque. The tool can be used with an associated controller that provides control commands to the tool.

Description

RELATED APPLICATIONS

This application claims priority from co-pending U.S. application having Ser. No. 11/315,952 filed Dec. 22, 2005, the full disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of automatic drivers for fasteners. More specifically, the present invention relates to an apparatus for driving fasteners that is automatic and controllable. Yet more specifically, the present invention relates to a device for driving fasteners, where the apparatus delivers a specified torque.

2. Description of Related Art

Many prior art devices exist that are capable of driving fasteners apertures, such as threaded bolt holes and the like. These tools typically require the user to activate a switch or a trigger to activate the device. Further, some prior art devices rely on power sources such as compressed air to drive the associated motor, which can limit the applicability of a device since producing compressed air requires space for a compressor and is generally impractical. Other devices that employ electrical motors produce an output whose speed and torque can vary and is not precisely controllable or not controllable at all. However many instances where it is required to employ a rotary tool, the ability to control the speed and torque is important. Some fasteners require that they be installed to a specified torque, and it is important that how much the fastener has been torqued be easily verified by the operator of the device.

Some of these devices include means to measure the rotational force, or torque, exerted by the particular device. These means range from monitoring the current consumed by the device, pressure sensors applied to working parts of the device, and included various sensors within the device. Examples of prior art devices useful for driving fasteners can be found in U.S. Pat. No. 4,487,270, U.S. Pat. No. 4,887,499, U.S. Pat. No. 6,424,799, U.S. Pat. No. 4,571,696, and U.S. Pat. No. 4,502,549.

Therefore, there exists a need for an apparatus and a method for securing fasteners that is reliable, accurate, and can precisely torque a fastener to a specified torque. An additional need exists for a tool to be durable, hand held, and provide an indication the preciseness of the directly torqued value.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein is a rotary tool comprising a motor connected to a chuck assembly. Included with the tool is a variable voltage device responsive to a magnetic field. The motor may be selectively controlled by operation of the variable voltage device—where the control includes on off switching as well as motor speed control. The tool includes a push to start function; that is by urging the tool against the object being rotated the tool's rotational force and velocity is based on the urging force. Optionally, the variable voltage device can be a Hall effect sensor, either linear or digital. Also included is a gearbox connectively disposed between the motor and the chuck assembly. Lubrication comprising two parts gear oil and one part motor grease is disposed within the gearbox.

A field device is included on the chuck assembly that is capable of emitting a magnetic field. Positioning the field device by selective movement of the chuck assembly controllably drives the motor. This is done since positioning the field device manipulates the magnitude of the magnetic field provided to the variable voltage device from the field device. The magnitude of the magnetic field proportionally relates to the proximity of the variable voltage device in relation to the field device.

The rotary tool can further include a lever assembly having a field device formed thereon. The field device within the lever is also capable of emitting a magnetic field. Positioning the field device within the lever by selective movement of the lever assembly can controllably drive the motor. Positioning the field device manipulates the magnitude of the magnetic field applied to the variable voltage device from the field device within the lever. The magnitude of the magnetic field within the lever field device proportionally relates to how close the variable voltage device is in relation to the field device. Optionally, a handheld pistol grip assembly can be employed in lieu of the lever assembly.

A torque transducer may be included capable of measuring the value of the torque generated by the chuck assembly. Optionally included with the transducer is at least one strain gauge in cooperative engagement with the torque transducer. The at least one strain gauge transmits data representing the torque generated by the chuck assembly. This data monitored by the strain gage is usable to terminate operation of the driver when the torque generated by the chuck assembly reaches a predetermined amount.

Also optionally included with the rotary tool is at least one selector switch programmably capable of selectively reversing the polarity of the electrical power supplied to the driver. Additional selector switches can be included that are also programmable. The additional selector switches can be capable of selectively operating the driver in a different control mode.

Optionally, a system may be included to drive fasteners comprising a rotary tool combinable with a controller assembly. Here the rotary tool includes a motor capable of providing a rotational force, a chuck assembly operatively connectable to the motor, and a variable voltage device responsive to a magnetic field. The motor is in operative communication with the variable voltage device. The controller assembly should be capable of providing control instructions to the rotary tool where the control instructions comprise maximum torque magnitude, speed, among other operational variables.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING.

FIG. 1A depicts one embodiment of the present invention.

FIG. 1B illustrates an exploded view of one embodiment of the present invention.

FIGS. 2A-2E provide a partial cut-away version of embodiments of the present invention.

FIG. 2F provides a cutaway view of an embodiment of the present invention.

FIG. 2G illustrates a frontal view of an embodiment of the present invention.

FIG. 2H illustrates a side view of a tranducerized element.

FIGS. 3A and 3B depict a cutaway view of an embodiment of the present invention.

FIGS. 4A and 4B depict a cutaway view of an embodiment of the present invention.

FIG. 5 presents an embodiment of the present invention combined with a controller.

FIG. 6 provides an exploded view of a gear box in combination with a motor.

FIGS. 7A and 7B provide side and perspective views of embodiments of a tool grip.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein is a rotary tool system comprising a rotary tool combined with a controller system. With reference to the drawings herein, one embodiment of therotary tool10 is shown in perspective view inFIG. 1A and an exploded view inFIG. 1B. Therotary tool10 is useful for driving fasteners, such as bolts, nuts, screws, self-threading screws, etc. Further, therotary tool10 is capable of repeatably applying fasteners to a precise specifiable torque. In the embodiment shown inFIG. 1B, amotor36 is included capable of initiating a force used to torque the fasteners.

In the embodiment ofFIGS. 1A and 1B agear box38 is shown disposed adjacent themotor36 is operative connected to themotor36. Thegear box38 contains a series ofgears39 configured into a gear train or system in mechanical cooperation with themotor36. Thegears39 are arranged to receive the output rotational force delivered by themotor36 and convert that force into a specified torque at theoutput shaft40 connected to thegear box38. In one embodiment the gear train is comprised of at least two gear stages, where each stage converts the rotational torque and speed produced by themotor36. Thegear box38 increases the torque delivered by themotor36 with a corresponding decrease in the rotational speed of themotor36. The range of torque output at thegear box38 ranges from about 1 in-lb to about 50 in-lb.

To maximize torque/velocity conversion while minimizing space, the gear system may be a planetary gear system comprising sun and planet gears.FIG. 6 provides an embodiment of amotor36 combined with agear box38, where thegear box38 is shown in an exploded view. As shown, the firststage sun gear86 is attached to themotor36 and engages a series of threeplanetary gears88. Theplanetary gears88 are all attached to aplanet carrier91, from which extends asecond sun gear93 into a secondplanetary gear stage95. The output shaft of the second gear stage is theoutput shaft40. Sealing thegearbox38 eliminates gear maintenance and protects the gears from foreign matter such as dirt. The lubricant used in the gearbox may be two parts gear oil with one part of motor grease. This combination of oil and grease provide an exceptional high-pressure lubricity, and low viscosity in order to minimize the amount of lubricant used, which in turn reduces viscous shear.Needle rollers89 can be included between the annulus between the inner diameter of each planet gear (of each stage) and the outer diameter of thespindle93 it rides on. The use ofneedle rollers89 in this location of thegearbox38 significantly reduces friction and wear. Theneedle rollers89 also hold lubrication very well. The quantity ofneedle rollers89 for use with each gear depends on the size of the individual gear and the gear box, it is believed that determining this quantity is within the scope of those skilled in the art.

To minimize contact between gear stages anaxle bearing90 is disposed into a conical cavity between the planets on the centerline of each planet carrier (91 and97). When the mating sun gear (86 and93) from the previous stage (or the motor36) is inserted between the planet gears (88 and94), its face comes to rest against theaxle bearing90. The axle bearing may be comprised of a hardened metal ball. Examples of metals include stainless steel and chrome steel, however this ball could be made from any number of hardenable materials. This configuration produces very little friction since theaxle bearing90 and the sun gears (86 and93) are in tangential contact. When these two stages are rotating with respect to each other, the material surface velocities at the point of contact are low, which minimizes moment arm.

In order to adequately handle axial and radial loads on theoutput shaft40 of thegearbox38 as well as limit axial and radial play, a combination of two bearings is used. The bearing on the outboard most end of the gearbox is a conventional radial bearing. This bearing is meant to carry any side loads placed on theoutput shaft40 as well as a small amount of axial load. The inboard bearing is an angular contact bearing. This bearings primary function is to carry the axial loads, which are transmitted down the output shaft as well as a small amount of radial load. The load coupling of these two bearings is accomplished by a small spacer of a precisely held thickness, which is sandwiched between the inner races of both bearings. These bearings, in combination, produce a very free spinning, durable and accurate mechanism.

Enhanced performance and efficiency has been realized by some of the design improvements to thegear box38, for example, thesplined output shaft40 was strengthened to carry more torsional load. The gearbox output shaft retainer ring (not shown) was improved to carry more axial load without breaking free. Heat treatment, such as by nitriding, was added to surfaces on the planet carriers that come into contact with rotating planet gears. High-carbon steel alloy axles were included with the planet carriers to improve fatigue properties also the thickness of rear gearbox end cap was adjusted to minimize axial gear clearances.

Table 1 provides a summary of sample configurations of gear systems providing varying output torque, included with the table are the corresponding speed and ratios of the possible stages in the particular gear system.

TABLE 1


		1^ststage	2^ndstage	3^rdstage	combined
Torque	Speed	ratio	ratio	ratio	ratio

10 in/lb	1800	4.285:1	4.285:1	none	18.36:1
20 in/lb	1100	6.75:1	4.285:1	none	28.92:1
35 in/lb	800	6.75:1	6.75:1	none	45.56:1
50 in/lb	500	4.285:1	4.285:1	4.285:1	78.68:1

Optionally therotary tool10 can be tranducerized to provide a real-time monitoring of the magnitude of the torque exerted onto a fastener by therotary tool10. Preferably the torque monitoring system include aflexure25 secured to thegear box38 on the end of thegear box38 opposite to where it is connected to themotor36. At least onestrain gauge85 can be included within theflexure25 that senses the torque supplied by themotor36 and transmits that sensed torque information to thetool controller80. Preferably fourstrain gages85 are included with theflexure25. Theflexure25 is connected on its other end to thenose cap26. As can be seen inFIG. 1, thenose cap26 includesslots27 on its outer surface that mate withtabs17 formed on the front end of thebody12 of therotary tool10. As themotor36 supplies torque to the fastener, themotor36 in turn transmits an identical torque value tonose cap26. Since the themotor36 is mounted to theflexure25, theflexure25 experiences the torque supplied by themotor36. Thus by positioning astrain gage85 on theflexure25, the torque output of themotor36 can be measured by thestrain gage85. As the tool communicates with atool controller80, the torque output of thestrain gage85 connects to thetool controller80 as well. When the output torque of themotor36 reaches a pre-selected torque, thetool controller80 is programmable to immediately deactivate power to therotary tool10, thus ensuring that the fastener being secured by therotary tool10 is not over tightened.

Thestrain gage85 may be calibrated as an assembly using what is known as a “dead weight” calibrator. Weights, which are certified and traceable to NIHST, are used to generate a static moment by placing them on an arm at a specific distance. The calibration does not occur until the at least onestrain gage85 is combined within therotary tool10. This is done in order to take into account frictional losses in the tool. Preferably, the at least onestrain gage85 can be a standard encapsulated strain gage that is modulus compensated for use on aluminum flexures. The signal produced by the detection of strain in the at least onestrain gage85 is carried to thecontroller80 analog via theflex circuit33 and thetool cable82. Theflex circuit33 attaches directly to the flex circuit therefore eliminating wiring in therotary tool10. When fourstrain gages85 are used they may be attached to each other in a wheatstone bridge configuration and optionally using fine polyester varnished wire. As shown, the four dualelement strain gages85 are located 90° from each other on theflexure36. Fourstrain gages85 can minimize bending cross talk and improve accuracy.

Achuck assembly28 is provided with the embodiment ofFIGS. 1A and 1B and is connectable to theoutput shaft40, preferably through corresponding spline grooves formed on the outer surface of theshaft40 and an aperture (not shown) formed axially within theshaft29 of thechuck assembly28. As will be explained in further detail below, the length of the aperture should be long enough to allow theshaft29 to slide back and forth along a portion of the length of theoutput shaft40. Asocket31 is provided on one end of thechuck assembly28, thesocket31 shown is suitable for receiving a fitting (not shown) specifically sized to fit the particular fastener being driven by therotary tool10. Further, asleeve33 is provided that when tugged axially retracts a retaining ball within thesocket31 thereby enabling adding or removing the particular fitting for use with therotary tool10. Also disposed on thechuck assembly28 is acollar35 slidable along theshaft29. Thecollar35 includesthreads32 on the outer surface adjacent thenut30 formed to fit threads (not shown) in thenose cap26. Aring magnet34 is disposed on the end of theshaft29 opposite thesocket31. A snap ring (not shown) is included on theshaft29 that retains thecollar35 on the shaft between thesleeve33 and the snap ring. Thus while thecollar35 remains on theshaft29, it must be free to slide along theshaft29 between thesleeve33 and the snap ring. Accordingly when thechuck assembly28 is screwed to thenose cap26, theshaft29 can be slideably disposed in and out of the collar35 a certain distance while still being retained within thechuck assembly28.

The rotary tool is useful not only for driving and securing fasteners, but can also be useful as a drill motor, a sander, a buffer, a saw, and any other application where a driving force is used. Moreover, the novel application of the push to start feature disclosed herein is applicable with all functions for which the present device can be used.

Referring now toFIGS. 3 and 4, other electrical circuitry that can be included with the present invention include variable voltage devices (VVD) such as a Hall effect sensor. As is well known, the output voltage of the VVD depends on the magnetic flux density applied to the VVD. Thus, subjecting the VVD to a magnetic field can increase the output voltage of a VVD. Likewise, removing the magnetic field can eliminate the VVD output voltage. Accordingly a switching mechanism can be produced by combining a field device that produces a magnetic field, such as a magnet, with a VVD. A simple application of this phenomenon involves creating a voltage source by positioning a magnet (either permanent or electro) close to a Hall effect sensor. One example of a field device is a permanent magnet, and one example of a VVD is a Hall effect sensor.

Alternatively, themotor36 can be variably driven by manipulation of thelever20. Referring now toFIGS. 4A and 4B, an alternative embodiment is disclosed. Here alever field device76, such as a permanent magnet, is disposed within the body of thelever20. Thelever20 is hingedly attached to therotary tool10 on one of its ends viapins54 inserted into ports of theend cap18. A correspondinglever VVD78 is preferably positioned within agroove47 formed on the outer surface of awiring shell46. Similar to thechuck assembly28, aspring21 is included to urge the free end of thelever20 outward away from the body of therotary tool10. Urging thelever21 toward the body of therotary tool10, thelever field device76 should begin to approach the proximity of thelever VVD78. Also similar to the operation of thechuck assembly VVD73, thelever VVD78 will begin to emit voltage to themotor36 as thelever field device76 approaches it. Thus themotor36 can be manipulated by depressing thelever21 in much the same manner as it is manipulated by retracting theshaft29.

Optionally, thelever21 can be replaced by apistol grip assembly61, where thepistol grip assembly61 comprises ahandle65, abase69, andtrigger72. Thehandle65 provides a grip for the users hand. Thebase69 is secured to thehandle65 and securable to thebody12 of therotary tool10. Thetrigger72 can be hingedly attached to thebase69 and include atrigger field device74 disposed thereon such that when thetrigger72 is depressed thetrigger field device74 is moved towards thebody12. Thepistol grip assembly61 should be secured to thebody12 such that thetrigger field device74 will be proximate to thelever VVD78 when thetrigger72 is depressed. Thus therotary tool10 can be actuated by depressing thetrigger72.

Two or more selector buttons (14 and16) can optionally be provided to enhance the flexibility of therotary tool10 functions. Each selector button (14 and16) can contain a field device, such as a permanent magnet within. When assembled, the selector buttons (14 and16) should be aligned with selector button VVDS (70 and71) disposed within thegroove47.Springs15 should be included with each selector button (14 and16) to urge the buttons outward from thebody12 of therotary tool10 absent a force pushing the buttons inward. By programming the associatedcontroller80, actuation of the selector buttons (14 and16) inward can vary the function of therotary tool10. For example, thecontroller80 can be programmed such that inwardly pressing thefirst selector button14 will toggle the polarity of the voltage delivered to themotor36 thereby reversing the rotational direction of thechuck assembly28. Additional options include the requirement that the buttons (14 and16) be depressed twice, similar to the operation of a mouse of a personal computer, before the requested function occur. The selector buttons (14 and16) can be programmed to initiate or control any number of external devices or process either directly or indirectly related to the operation of the tool. More commonly the selector buttons (14 and16) can be used to control the direction of rotation of the tool as well as changing preprogrammed tool set points or parameter sets. It is believed that the programming of the associatedcontroller80 can be accomplished by those skilled in the art without undue experimentation.

While standard wiring or circuit boards could be used, it is preferred that the circuitry of the rotary tool be included on aflex circuit33. Theflex circuit33 can provide a way to conduct power to drive themotor36 and provide wiring to conduct control commands as well. As is well known, theflex circuit33 can be comprised of a flexible resin like material, as such theflex circuit33 can be tailored to fit within the present invention while consuming a minimum amount of space within therotary tool10. Further, theillumination LEDS58, theindication LEDS62, and lever and selector button VVDS (70,71, and78) can be situated directly on theflex circuit33. Design of anappropriate flex circuit33 for use with the present invention is well within the capabilities of those skilled in the art.

A digitally programmable device, such as a memory chip, may be included with therotary tool10. During final assembly and calibration of the tool, the programmable device may be programmed at least with identification, calibration, and operating conditions desired by therotary tool10. The information can include the model number of thespecific rotary tool10, serial number, date of manufacture, date of calibration, maximum speed and maximum torque that therotary tool10 can attain, the calibration value, the motor angle counter per tool output revolution (this describes the gear ratio), and other useful operating parameters. Operation of the system requires constant real-time communication with atool controller80. Programmed within thetool controller80 are the operating parameters for thespecific rotary tool10 being used. During use thetool controller80 interrogates the memory chip within thespecific rotary tool10 to ensure that the specific tool is capable of performing the intended task. If the tool is capable of performing the task at hand, the controller will allow thespecific rotary tool10 to be operated; otherwise thecontroller80 will not activate the tool. This interrogation happens upon power up or when thespecific rotary tool10 is first connected to thecontroller80. The controller can be programmed with a lap top computer using a graphic user interface under the Windows operating system.

Activation by the push to start mode includes the step of first inserting the fastener where it is to be fastened. For example, if the fastener is a threaded screw, in the push to start mode the screw will be inserted into the hole (threaded or unthreaded) where it is to be secured. Then a force can be applied by the operator to the rear end of therotary tool10 that in turn pinches the screw between the fitting and the hole. As long as this force applied by the operator exceeds the spring constant of thespring42, theshaft29 will be retracted within thecollar35. As previously noted when the shaft is retracted within thecollar36, thefield device34 is located proximate to thechuck assembly VVD73—as is illustrated inFIG. 3B. As previously noted, when thefield device34 approaches thechuck assembly VVD73, voltage is emitted from thechuck assembly VVD73 that in turn begins to drive themotor36. Driving themotor36 produces rotation of thechuck assembly28 via thegear box38 andoutput shaft42. Rotation of thechuck assembly28 can be used to drive the fastener into securing engagement with the associated hole by the transfer of rotational force from thechuck assembly28 to the fastener.

Alternatively, therotary tool10 can be operated by depressing thelever20 up against thebody12 of therotary tool10. In the embodiment of the invention inFIGS. 4A and 4B alever field device76 is shown disposed within thelever20. As thelever20 is depressed towards the body, thelever field device76 approaches thelever VVD78. In the same manner as the push to start mode, thelever VVD78 begins to emit a voltage whose magnitude is in relation to the strength of the magnetic field applied to it by thelever field device76. The voltage emitted by thelever VVD78 can then be applied to driver themotor36 where the magnitude of the voltage emitted by thelever VVD78 directly corresponds to the rotational speed of themotor36.

The push to start and throttle lever can either be used individually or in combination with each other. There are however instances where they are useful in combination. One can be used as an interlock for the other. It can be configured so that the throttle lever has to be fully depressed before the push to start can be activated. This configuration prevents operation of the tool before the operator has a good grip on it. Conversely it can be configured so that the push to start has to be fully depressed before the throttle can be activated. This configuration prevents the rotation of the tool before sufficient axial load is applied to the fastener as in the case of a self tapping screw. In the case of automated operation in a fixture, the push to start can be used as a form of presence detection.

During the time therotary tool10 is driving the fastener (either by the push to start mode or by depressing the lever20), the magnitude of the torque delivered to the fastener by therotary tool10 is measured by the at least onestrain gage85 disposed within theflexure25. The strain gage bridge produces an analog output that is continuously monitored during tool operation. The strain gages should be arranged in such a fashion as to be only sensitive to torsion along the axis of theflexure25. Eachstrain gage85 has two elements that are oriented 90 degrees to each other and 45 degrees to the axis of theflexure25. There are four gages arrayed around the circumference of the flexure in 90° intervals. Under torsion the strain gages85 will unbalance the Wheatstone bridge therefore producing an output. Under bending, compression, or tension the loads will cancel therefore maintaining a balanced bridge and producing little or no output. The torque value measured by the at least onestrain gage85 is uploaded to thecontroller80 as thecontroller80 interrogates data from therotary tool10. Thus, a real time measurement of the torque applied to the fastener can be obtained by thecontroller80 through its constant monitoring of the at least onestrain gage85. Further, thecontroller80 can be programmed to instantaneously deactivate therotary tool10 when the torque measured by the at least onestrain gage85 matches the shut off torque stored in thecontroller80. More specifically, when the torque as measured by thestrain gate85

controller

80 combination reaches the preselected torque, thecontroller80 immediately and actively stops rotation of the tool, thus ensuring that the fastener being secured by the tool is not over tightened. The braking or stopping of the tool is accomplished through the use of plug reversing and dynamic braking. Plug reversing involves applying full reverse power to themotor36 until thestrain gage85 andcontroller80 senses zero torque. Dynamic braking takes advantage of the fact that amotor36 is also a generator. By shorting the power leads of themotor36 to each other, the effect is to force themotor36 to resist its own rotation in proportion to its rotational velocity. Therefore, one of the many advantages realized by the present invention is the ability to precisely tighten fasteners exactly to a desired torque without the danger of over or undertightening a fastener. This advantage is due in part to the real time monitoring of torque and the instantaneous response of thecontroller80 actively deactivating therotary tool10.

The controller can be programmed with a target torque and speed. Optionally the controller can be set to run therotary tool10 at two different speeds. The first speed would be relatively high and would run until a selected torque, which is not the target torque, is reached. The second, or downshift speed, would run slower and then stop at the target torque. For example if the target torque is 20 in-lbs the controller may be set as follows: Initial speed of 1000 rpm until a down shift torque of 12 in-lbs is reached. Then a down shift speed of 250 rpm until the target torque is reached. Additionally, angle measurement and control can be implemented. Angle control can either be substituted for torque or used in combination with torque. An AND relationship can be established with torque and angle. By setting a torque target of 20 in-lbs and an angle target of 60°, both targets have to be met or exceeded in order to count as a successfully fastened joint. The angle count is started at a threshold torque of perhaps 10 to 20 percent of the target torque. In this case that would be 2 to 4 in-lbs. Other parameters can be set to form upper and lower torque and angle limits around the targets. For example with a 20 in-lb target the limits may include a torque low limit of 18 in-lbs and a high limit of 22 in-lbs with an angle low limit of 50° with an angle high limit of 70°. These limits are used to form a window around the target for the purposes of establishing the criteria for a properly torqued fastener. If the angle is to low before achieving the target torque then the fastener has likely cross threaded. If the angle is to high then the fastener has likely stripped, broken or was not present.

EXAMPLE

In one embodiment of themotor36 is coupled to agear box38 comprised of two gear stages, where the two stages provide a conversion of speed to torque. In one example of operation the first stage has a speed to torque ratio of about 6.75:1 and the second stage has a speed to torque ratio of about 4.285:1. To maximize torque/velocity conversion while minimizing space, the preferred gear system is a planetary gear system. In this system the first stage sun gear is attached to the motor output shaft and engages a series of three planetary gears. The planetary gears are all attached to a planet carrier, from which extends a second sun gear into the next planetary gear stage. The output shaft of the second gear stage, which has a spline gear formed thereon, mates with the output drive.

In one embodiment the gearboxes are in a sealed oil gearbox. Sealing the gearbox eliminates gear maintenance, helps keep the gears clean, and protects the gears from foreign matter. The light oil in lieu of a more viscous lubricant, such as grease, greatly enhances the efficiency of torque transmission. One example of lubricating oil for use with the gears comprises a mix of two parts of synthetic gear oil with one part of motor assembly grease. The synthetic gear oil weight can range from 75W90 to 75W140 and weights in between. The motor assembly grease may comprise a calcium-based grease with an anti-wear rating. A lubricating oil formed with this composition provides a balance of good high-pressure lubricity, low viscosity as compared to conventional power tool greases, and enough tackiness to require only 1 milliliter of oil therefore greatly reducing viscous shear.

With regard to thefield device34 disposed on theshaft29, in one embodiment thefield device34 is a ring magnet that is plastic injection molded using permanent magnet particles (such as Neodymium Iron Boron) suspended in Nylon. This configuration provides relatively high field density combined with low cost. Further, the ring magnet should be radially magnetized, the outer diameter of the ring magnet is magnetized in a first polarity and the inner diameter is oppositely polarized. This is done so that the output of the Hall sensor within thechuck assembly VVD73 stays consistent regardless of the rotational orientation of theshaft29. It is preferred that the Hall output vary as a result of axial movement only. If the ring magnet were magnetized with alternating poles on the outside diameter, thechuck assembly28 would stop rotating as the poles reversed.

The gears may be made from medium-carbon steel selected because of its hardness and heat-treating properties. Optionally, the gear material may comprise low-alloy steel optimized for nitriding. Medium-carbon steel or low-alloy steel optimized for nitriding may also be used in the planet carriers. In one embodiment, the gear axles are made from high-carbon steel that is a high strength gear material with excellent bending fatigue properties.

Some of the advantages realized by the present invention include a high degree of reliability and durability. The operating limit of many fastening tools before failure is about 500,000 cycles, in fact tools that are capable of operating up to 1,000,000 cycles without failure are considered very durable. In contrast the present invention has been found to operate in excess of 5,000,000 cycles without failure, which greatly exceeds the durability expectations of such a tool. Further, the present invention is also capable of this high number of cycles when subjected to high duty cycle applications. That is when an operating process is being repeated very quickly with many cycles per hour. Additionally, the performance of agear box38 produced in accordance with the specifications of this application is superior to many other gear boxes used for similar applications. For example, similar type gear boxes generally have a maximum operation rotational speed at up to 7000-8000 revolutions per minute (rpm), whereas thegear box38 of the present invention is capable of rotational speeds up to 50,000 rpm.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the push to start feature can be physically disabled. Also, all four torque capacities can optionally be available in fixture mount configurations. A different front end cap is supplied with the tool to allow for easier and more reliable mounting of the tool in fixtured applications. Instead of a tapered end cap with headlights, a threaded end cap with a shoulder is provided including two different styles of mounting flanges. The fixture mounted configuration allows for the minimization of center to center mounting distances. In effect the tools can be mounted on 1.125″ centers 1.125″ is the diameter of the tool. This is important when fasteners are located very close to each other. This is of primary concern in automated applications where there is no human interaction or when multiple tools are mounted in combination with each other in a hand operated power head. Further, the variable voltage device can be any device that responds to some external stimulus, such as voltage, current, pressure, or magnetic, or that switches at a threshold of stimulus. The variable voltage device can be selected from items such as a linear response device, or a digital response device.

These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Claims

1. A rotary tool comprising:

a motor;

a chuck assembly operatively connectable to said motor;

a gearbox operatively disposed between said chuck assembly and said motor; and

a lubricant in the gearbox comprising about two parts gear oil and about one part of motor grease.

2. The rotary tool ofclaim 1, further comprising a variable voltage device responsive to a magnetic field, wherein said motor is in operative communication with said variable voltage device and wherein selectively moving the chuck assembly varies the magnitude of the magnetic field applied to the variable voltage device and proportionally varies the power supplied to said motor and thereby variably alters the corresponding rotational speed of the chuck assembly.

3. The rotary tool ofclaim 1, wherein the gearbox comprises components formed by heat treatment.

4. The rotary tool ofclaim 3, wherein the heat treatment comprises nitriding.

5. The rotary tool ofclaim 1, wherein the gearbox comprises a first stage and a second stage.

6. The rotary tool ofclaim 5, wherein the gear ratio of the first stage and the second stage is selected from the list consisting of 4.285:1, 6.75:1, and combinations thereof.

7. The rotary tool ofclaim 1, wherein the gear oil comprises oil having a weight of from 75W90 to about 75W140.

8. The rotary tool ofclaim 1, wherein the motor grease comprises a calcium-based grease with an anti-wear rating.

9. The rotary tool ofclaim 2 further comprising plastic injection molded permanent magnet particles for creating the magnetic field.

10. The rotary tool ofclaim 9 wherein the permanent magnet particles comprise neodymium iron boron.

11. The rotary tool ofclaim 1 further comprising a transducer having a strain gage.

12. The rotary tool ofclaim 11 further comprising a flexure combined with said strain gage.

13. The rotary tool ofclaim 1, wherein said tool is hand held.

14. The rotary tool ofclaim 11, wherein said transducer provides real time feed back information of the magnitude torque of the torque applied by the tool.

15. The rotary tool ofclaim 11 further comprising a controller that communicates with the rotary tool.

16. The rotary tool ofclaim 15 wherein said transducer provides said real time feed back information to the controller.

17. The rotary tool ofclaim 1, wherein said tool is capable of accurately applying a magnitude of torque to a fastener that ranges from about 1 in-pounds to about 50 in-pounds.

18. The rotary tool ofclaim 1, wherein said tool is capable of accurately applying a magnitude of torque to a fastener that ranges from about 1 in-pounds to about 20 in-pounds.