Abstract:
A power tool for operating on a workpiece, the power tool having a housing and a motor disposed within the housing. A controller is connected to the motor and receives user inputs for turning on the motor and a power tool battery pack is connected to the controller and the motor. At least one light is connected to the controller for illuminating the workpiece. The controller can turn on the light in a predetermined pattern to alert the user to a tool condition, such as the charge level being below a predetermined level.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/559,349 filed Apr. 2, 2004 entitled “Fastening Tool” and U.S. patent application Ser. No. 11/095,722 filed Mar. 31, 2005, entitled “Method For Operating A Power Driver”. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to driving tools, such as fastening tools, and more particularly to a method for operating a driving tool. 
     BACKGROUND OF THE INVENTION 
     Power nailers are relatively common place in the construction trades. Often times, however, the power nailers that are available may not provide the user with a desired degree of flexibility and freedom due to the presence of hoses and such that couple the power nailer to a source of pneumatic power. Accordingly, there remains a need in the art for an improved power nailer. 
     SUMMARY OF THE INVENTION 
     In one form, the teachings of the present invention provide a method that can include: providing a driving tool having a driver, a motor assembly and an electrical power source, the driver being movable along an axis, the motor assembly including a motor and an output member, that is driven by the motor and employed to transmit power to the driver to thereby cause the driver to translate along the axis; transmitting electrical power from the electrical power source to the motor over a first cycle portion to thereby rotate the output member; determining a parameter related to a rotational speed of the output member; and increasing a time interval of the first cycle portion if a magnitude of the parameter is less than a predetermined threshold. 
     In another form, form the teachings of the present invention provide a method that can include: providing a driving tool having a driver, a motor assembly and an electrical power source, the driver being movable along an axis, the motor assembly including a motor and an output member, that is driven by the motor and employed to transmit power to the driver to thereby cause the driver to translate along the axis; transmitting electrical power from the electrical power source to the motor over a first cycle portion to thereby rotate the output member; determining a parameter related to a rotational speed of the output member; and decreasing a time interval of the first cycle portion if a magnitude of the parameter is greater than a predetermined threshold. 
     In yet another form, the teachings of the present invention provide a method that can include: providing a driving tool having a driver, a motor assembly and an electrical power source, the driver being movable along an axis, the motor assembly including a motor and an output member, that is driven by the motor and employed to transmit power to the driver to thereby cause the driver to translate along the axis; and operating the driving tool over a complete cycle with a first cycle portion and at least one second cycle portion, the complete cycle including: transmitting electrical power from the electrical power source to the motor over the first cycle portion to thereby rotate the output member; determining a first parameter, the first parameter being related to the back electromotive force that is generated by the motor without providing electrical power to the motor; adjusting a time interval of the first cycle portion if a magnitude of the parameter is less than a predetermined first threshold or greater than a predetermined second threshold; transmitting electrical power from the electrical power source to the motor over a first one of the second cycle portions to thereby rotate the output member; re-determining the first parameter after completion of the first one of the second cycle portions; and determining an apparent voltage of a next one of the second cycle portions based on a magnitude of the first parameter. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a side view of a fastening tool constructed in accordance with the teachings of the present invention; 
         FIG. 2  is a schematic view of a portion of the fastening tool of  FIG. 1  illustrating various components including the motor assembly and the controller; 
         FIG. 3  is a schematic view of a portion of the fastening tool of  FIG. 1 , illustrating the controller in greater detail; 
         FIG. 4  is a sectional view of a portion of the fastening tool illustrating the mode selector switch; 
         FIG. 5  is a schematic illustration of a portion of the controller; 
         FIG. 6  is a plot illustrating exemplary duty cycles of a motor of the present invention; 
         FIG. 7  is a schematic illustration of a portion of the nailer of  FIG. 1  illustrating the controller and the mode selector switch in greater detail; and 
         FIG. 8  is a plot illustrating the relationship between actual motor speed and the temperature of the motor when the back-emf of the motor is held constant and when the back-emf based speed of motor is corrected for temperature. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference to  FIG. 1 , an electric fastener delivery device, which may be referred to herein as a nailer, is generally indicated by reference numeral  10 . While the electric fastener delivery device is generally described in terms of a fastening tool  10  that drives nails into a workpiece, the electric fastener delivery device may be configured to deliver different fasteners, such as a staple or screw, or combinations of one or more of the different fasteners. Further, while the fastening tool  10  is generally described as an electric nailer, many of the features of the fastening tool  10  described below may be implemented in a pneumatic nailer or other devices, including rotary hammers, hole forming tools, such as punches, and riveting tools, such as those that are employed to install deformation rivets. 
     With continuing reference to  FIG. 1  and additional reference to  FIGS. 2 and 3 , the fastening tool  10  may include a housing  12 , a motor assembly  14 , a nosepiece  16 , a trigger  18 , a contact trip  20 , a control unit  22 , a magazine  24 , and a battery  26 , which provides electrical power to the various sensors (which are discussed in detail, below) as well as the motor assembly  14  and the control unit  22 . Those skilled in the art will appreciate from this disclosure, however, that in place of, or in addition to the battery  26 , the fastening tool  10  may include an external power cord (not shown) for connection to an external power supply (not shown) and/or an external hose or other hardware (not shown) for connection to a source of fluid pressure. 
     The housing  12  may include a body portion  12   a,  which may be configured to house the motor assembly  14  and the control unit  22 , and a handle  12   b.  The handle  12   b  may provide the housing  12  with a conventional pistol-grip appearance and may be unitarily formed with the body portion  12   a  or may be a discrete fabrication that is coupled to the body portion  12   a,  as by threaded fasteners (not shown). The handle  12   b  may be contoured so as to ergonomically fit a user&#39;s hand and/or may be equipped with a resilient and/or non-slip covering, such as an overmolded thermoplastic elastomer. 
     The motor assembly  14  may include a driver  28  and a power source  30  that is configured to selectively transmit power to the driver  28  to cause the driver  28  to translate along an axis. In the particular example provided, the power source  30  includes an electric motor  32 , a flywheel  34 , which is coupled to an output shaft  32   a  of the electric motor  32 , and a pinch roller assembly  36 . The pinch roller assembly  36  may include an activation arm  38 , a cam  40 , a pivot pin  42 , an actuator  44 , a pinch roller  46  and a cam follower  48 . 
     A detailed discussion of the motor assembly  14  that is employed in this example is beyond the scope of this disclosure and is discussed in more detail in commonly assigned U.S. Provisional Patent Application Ser. No. 60/559,344 filed Apr. 2, 2004 entitled “Fastening Tool” and commonly assigned co-pending U.S. application Ser. No. 11/095,727 entitled “Structural Backbone/Motor Mount For A Power Tool”, which was filed on Mar.  31 ,  2005 , and both of which are hereby incorporated by reference as if fully set forth in their entirety herein. Briefly, the motor  32  may be operable for rotating the flywheel  34  (e.g., via a motor pulley  32   a,  a belt  32   b  and a flywheel pulley  34   a ). The actuator  44  may be operable for translating the cam  40  (e.g., in the direction of arrow A) so that the cam  40  and the cam follower  48  cooperate to rotate the activation arm  38  about the pivot pin  42  so that the pinch roller  46  may drive the driver  28  into engagement with the rotating flywheel  34 . Engagement of the driver  28  to the flywheel  34  permits the flywheel  34  to transfer energy to the driver  28  which propels the driver  28  toward the nosepiece  16  along the axis. 
     A detailed discussion of the nosepiece  16 , contact trip  20  and the magazine  24  that are employed in this example is beyond the scope of this disclosure and are discussed in more detail in U.S. Provisional Patent Application Ser. No. 60/559,343 filed Apr. 2, 2004 entitled “Contact Trip Mechanism For Nailer”, U.S. Provisional Patent Application Ser. No. 60/559,342 filed Apr. 2, 2004 entitled “Magazine Assembly For Nailer”, U.S. Pat. No. 7,213,732 entitled “Contact Trip Mechanism For Nailer” and U.S. patent application Ser. No. 11/050,280 entitled “Magazine Assembly For Nailer” filed on Feb. 3, 2005, all of which are being incorporated by reference as if fully set forth in their entirety herein. The nosepiece  16  may extend from the body portion  12   a  proximate the magazine  24  and may be conventionally configured to engage the magazine  24  so as to sequentially receive fasteners F therefrom. The nosepiece  16  may also serve in a conventional manner to guide the driver  28  and fastener F when the fastening tool  10  has been actuated to install the fastener F to a workpiece. 
     The trigger  18  may be coupled to the housing  12  and is configured to receive an input from the user, typically by way of the user&#39;s finger, which may be employed in conjunction with a trigger switch  18   a  to generate a trigger signal that may be employed in whole or in part to initiate the cycling of the fastening tool  10  to install a fastener F to a workpiece (not shown). 
     The contact trip  20  may be coupled to the nosepiece  16  for sliding movement thereon. The contact trip  20  is configured to slide rearwardly in response to contact with a workpiece and may interact either with the trigger  18  or a contact trip sensor  50 . In the former case, the contact trip  20  cooperates with the trigger  18  to permit the trigger  18  to actuate the trigger switch  18   a  to generate the trigger signal. More specifically, the trigger  18  may include a primary trigger, which is actuated by a finger of the user, and a secondary trigger, which is actuated by sufficient rearward movement of the contact trip  20 . Actuation of either one of the primary and secondary triggers will not, in and of itself, cause the trigger switch  18   a  to generate the trigger signal. Rather, both the primary and the secondary trigger must be placed in an actuated condition to cause the trigger  18  to generate the trigger signal. 
     In the latter case (i.e., where the contact trip  20  interacts with the contact trip sensor  50 ), which is employed in the example provided, rearward movement of the contact trip  20  by a sufficient amount causes the contact trip sensor  50  to generate a contact trip signal which may be employed in conjunction with the trigger signal to initiate the cycling of the fastening tool  10  to install a fastener F to a workpiece. 
     The control unit  22  may include a power source sensor  52 , a controller  54 , an indicator, such as a light  56  and/or a speaker  58 , and a mode selector switch  60 . The power source sensor  52  is configured to sense a condition in the power source  30  that is indicative of a level of kinetic energy of an element in the power source  30  and to generate a sensor signal in response thereto. For example, the power source sensor  52  may be operable for sensing a speed of the output shaft  32   a  of the motor  32  or of the flywheel  34 . As one of ordinary skill in the art would appreciate from this disclosure, the power source sensor  52  may sense the characteristic directly or indirectly. For example, the speed of the motor output shaft  32   a  or flywheel  34  may be sensed directly, as through encoders, eddy current sensors or Hall effect sensors, or indirectly, as through the back electromotive force of the motor  32 . In the particular example provided, we employed back electromotive force, which is produced when the motor  32  is not powered by the battery  26  but rather driven by the speed and inertia of the components of the motor assembly  14  (especially the flywheel  34  in the example provided). 
     The mode selector switch  60  may be a switch that produces a mode selector switch signal that is indicative of a desired mode of operation of the fastening tool  10 . One mode of operation may be, for example, a sequential fire mode wherein the contact trip  20  must first be abutted against a workpiece (so that the contact trip sensor  50  generates the contact trip sensor signal) and thereafter the trigger switch  18   a  is actuated to generate the trigger signal. Another mode of operation may be a mandatory bump feed mode wherein the trigger switch  18   a  is first actuated to generate the trigger signal and thereafter the contact trip  20  abutted against a workpiece so that the contact trip sensor  50  generates the contact trip sensor signal. Yet another mode of operation may be a combination mode that permits either sequential fire or bump feed wherein no particular sequence is required (i.e., the trigger sensor signal and the contact trip sensor signal may be made in either order or simultaneously). In the particular example provided, the mode selector switch  60  is a two-position switch that permits the user to select either the sequential fire mode or the combination mode that permits the user to operate the fastening tool  10  in either a sequential fire or bump feed manner. 
     The controller  54  may be configured such that the fastening tool  10  will be operated in a given mode, such as the bump feed mode, only in response to the receipt of a specific signal from the mode selector switch  60 . With brief additional reference to  FIG. 7 , the placement of the mode selector switch  60  in a first position causes a signal of a predetermined first voltage to be applied to the controller  54 , while the placement of the mode selector switch  60  in a second position causes a signal of a predetermined second voltage to be applied to the controller  54 . Limits may be placed on the voltage of one or both of the first and second voltages, such as ±0.2V, so that if the voltage of one or both of the signals is outside the limits the controller  54  may default to a given feed mode (e.g., to the sequential feed mode) or operational condition (e.g., inoperative). 
     For example, the mode selector switch  60  and the controller  54  may be configured such that a +5 volt supply is provided to mode selector switch  60 , placement of the mode selector switch  60  in a position that corresponds to mandatory sequential feed causes a +5 volt signal to be returned to the controller  54 , and placement of the mode selector switch  60  in a position that permits bump feed operation causes a +2.5 volt signal to be returned to the controller  54 . The different voltage may be obtained, for example, by routing the +5 volt signal through one or more resistors R when the mode selector switch  60  is positioned in a position that permits bump feed operation. Upon receipt of a signal from the mode selector switch  60 , the controller  54  may determine if the voltage of the signal is within a prescribed limit, such as ±0.2 volts. In this example, if the voltage of the signal is between +5.2 volts to +4.8 volts, the controller  54  will interpret the mode selector switch  60  as requiring sequential feed operation, whereas if the voltage of the signal is between +2.7 volts to +2.3 volts, the controller  54  will interpret the mode selector switch  60  as permitting bump feed operation. If the voltage of the signal is outside these windows (i.e., greater than +5.2 volts, between +4.8 volts and +2.7 volts, or lower than +2.3 volts in the example provided), the controller  54  may cause the fastening tool  10  to operate in a predetermined mode, such as one that requires sequential feed operation. The controller  54  may further provide the user with some indication (e.g., a light or audible alarm) of a fault in the operation of the fastening tool  10  that mandates the operation of the fastening tool  10  in the predetermined mode. 
     The lights  56  of the fastening tool may employ any type of lamp, including light emitting diodes (LEDs) may be employed to illuminate portions of the worksite, which may be limited to or extend beyond the workpiece, and/or communicate information to the user or a device (e.g., data terminal). Each light  56  may include one or more lamps, and the lamps may be of any color, such as white, amber or red, so as to illuminate the workpiece or provide a visual signal to the operator. Where the lights  56  are to be employed to illuminate the worksite, the one or more of the lights  56  may be actuated by a discrete switch (not shown) or by the controller  54  upon the occurrence of a predetermined condition, such the actuation of the trigger switch  18   a.  The lights  56  may be further deactivated by switching the state of a discrete switch or by the controller  54  upon the occurrence of a predetermined condition, such as the elapsing of a predetermined amount of time. 
     Where the lights  56  are to be employed to communicate information, the light(s)  56  may be actuated by the controller  54  in response to the occurrence of a predetermined condition. For example, the lights  56  may flash a predetermined number of times, e.g., four times, or in a predetermined pattern in response to the determination that a charge level of the battery  26  has fallen to a predetermined level or if the controller  54  determines that a fastener has jammed in the nosepiece  16 . This latter condition may be determined, for example, through back-emf sensing of the motor  32 . 
     Additionally or alternatively, the light(s)  56  may be employed to transmit information optically or electrically to a reader. In one embodiment, light generated by the light(s)  56  is received by an optical reader  500  to permit tool data, such as the total number of cycles operated, the type and frequency of any faults that may have occurred, the values presently assigned to various adjustable parameters, etc. to be downloaded from the fastening tool  10 . In another embodiment, a sensor  502  is coupled to a circuit  504  in the fastening tool  10  to which the light(s)  56  are coupled. The sensor  502  may be operable for sensing the current that passes through the light(s)  56  and/or the voltage on a leg of the circuit  504  that is coupled to the light(s)  56 . As the illumination of the light(s)  56  entails both a change in the amount of current passing there through and a change in the voltage on the leg of the circuit  504  that is coupled to the light(s)  56 , selective illumination of the light(s)  56  may be employed to cause a change in the current and/or voltage that may be sensed by the sensor  502 . A signal produced by the sensor  502  in response to the changes in the current and/or voltage may be received by a reader that receives the signal that is produced by the sensor  502 . Accordingly, those of ordinary skill in the art will appreciate from this disclosure that the operation light(s)  56  may be employed to affect an electric characteristic, such as current draw or voltage, that may be sensed by the sensor  502  and employed by a reader to transmit data from the tool  10 . 
     The controller  54  may be coupled to the mode selector switch  60 , the trigger switch  18   a,  the contact trip sensor  50 , the motor  32 , the power source sensor  52  and the actuator  44 . In response to receipt of the trigger sensor signal and the contact trip sensor signal, the controller  54  determines whether the two signals have been generated at an appropriate time relative to the other (based on the mode selector switch  60  and the mode selector switch signal). 
     If the order in which the trigger sensor signal and the contact trip sensor signal is not appropriate (i.e., not permitted based on the setting of the mode selector switch  60 ), the controller  54  does not enable electrical power to flow to the motor  32  but rather may activate an appropriate indicator, such as the lights  56  and/or the speaker  58 . The lights  56  may be illuminated in a predetermined manner (e.g., sequence and/or color) and/or the speaker  58  may be employed to generate an audio signal so as to indicate to the user that the trigger switch  18   a  and the contact trip sensor  50  have not been activated in the proper sequence. To reset the fastening tool  10 , the user may be required to deactivate one or both of the trigger switch  18   a  and the contact trip sensor  50 . 
     If the order in which the trigger sensor signal and the contact trip sensor signal is appropriate (i.e., permitted based on the setting of the mode selector switch  60 ), the controller  54  enables electrical power to flow to the motor  32 , which causes the motor  32  to rotate the flywheel  34 . The power source sensor  52  may be employed to permit the controller  54  to determine whether the fastening tool  10  has an energy level that exceeds a predetermined threshold. In the example provided, the power source sensor  52  is employed to sense a level of kinetic energy of an element in the motor assembly  14 . In the example provided, the kinetic energy of the motor assembly  14  is evaluated based on the back electromotive force generated by the motor  32 . Power to the motor  32  is interrupted, for example after the occurrence of a predetermined event, which may be the elapse of a predetermined amount of time, and the voltage of the electrical signal produced by the motor  32  is sensed. As the voltage of the electrical signal produced by the motor  32  is proportional to the speed of the motor output shaft  32   c  (and flywheel  34 ), the kinetic energy of the motor assembly  14  may be reliably determined by the controller  54 . 
     As those of ordinary skill in the art would appreciate from this disclosure, the kinetic energy of an element in the power source  30  may be determined (e.g., calculated or approximated) either directly through an appropriate relationship (e.g., e=½ l×ω 2 ; e=½ m×v 2 ) or indirectly, through an evaluation of one or more of the variables that are determinative of the kinetic energy of the motor assembly  14  since at least one of the linear mass and inertia of the relevant component is substantially constant. In this regard, the rotational speed of an element, such as the motor output shaft  32   a  or the flywheel  34 , or the characteristics of a signal, such as its frequency of a signal or voltage, may be employed by themselves as a means of approximating kinetic energy. For example, the kinetic energy of an element in the power source  30  may be “determined” in accordance with the teachings of the present invention and appended claims by solely determining the rotational speed of the element. As another example, the kinetic energy of an element in the power source  30  may be “determined” in accordance with the teachings of the present invention and appended claims by solely determining a voltage of the back electromotive force generated by the motor  32 . 
     If the controller  54  determines that the level of kinetic energy of the element in the motor assembly  14  exceeds a predetermined threshold, a signal may be generated, for example by the controller  54 , so that the actuator  44  may be actuated to drive the cam  40  in the direction of arrow A, which as described above, will initiate a sequence of events that cause the driver  28  to translate to install a fastener F into a workpiece. 
     If the controller  54  determines that the level of kinetic energy of the element in the motor assembly  14  does not exceed the predetermined threshold, the lights  56  may be illuminated in a predetermined manner (e.g., sequence and/or color) and/or the speaker  58  may be employed to generate an audio signal so as to indicate to the user that the fastening tool  10  may not have sufficient energy to fully install the fastener F to the workpiece. The controller  54  may be configured such that the actuator  44  will not be actuated to drive the cam  40  in the direction of arrow A if the kinetic energy of the element of the motor assembly  14  does not exceed the predetermined threshold, or the controller  54  may be configured to permit the actuation of the actuator  44  upon the occurrence of a predetermined event, such as releasing and re-actuating the trigger  18 , so that the user acknowledges and expressly overrides the controller  54 . 
     While the fastening tool  10  has been described thus far as employing a single kinetic energy threshold, the invention, in its broader aspects, may be practiced somewhat differently. For example, the controller  54  may further employ a secondary threshold that is representative of a different level of kinetic energy than that of the above-described threshold. In situations where the level of kinetic energy in the element of the motor assembly  14  is higher than the above-described threshold (i.e., so that operation of the actuator  44  is permitted by the controller  54 ) but below the secondary threshold, the controller  54  may activate an indicator, such as the lights  56  or speaker  58  to provide a visual and/or audio signal that indicates to the user that the battery  26  may need recharging or that the fastening tool  10  may need servicing. 
     Further, the above-described threshold and the secondary threshold, if employed, may be adjusted based on one or more predetermined conditions, such as a setting to which the fastener F is driven into the workpiece, the relative hardness of the workpiece, the length of the fastener F and/or a multi-position or variable switch that permits the user to manually adjust the threshold or thresholds. 
     With reference to  FIGS. 1 and 4 , the fastening tool  10  may optionally include a boot  62  that removably engages a portion of the fastening tool  10  surrounding the mode selector switch  60 . In the example provided, the boot  62  may be selectively coupled to the housing  12 . The boot  62  may be configured to inhibit the user from changing the state of the mode selector switch  60  by inhibiting a switch actuator  60   a  from being moved into a position that would place the mode selector switch  60  into an undesired state. Additionally or alternatively, the boot  62  may protect the mode selector switch  60  (e.g., from impacts, dirt, dust and/or water) when the boot  62  is in an installed condition. Further, the boot  62  may be shaped such that it only mates with the fastening tool  10  in a single orientation and is thus operable to secure the switch  60  in only a single predetermined position, such as either the first position or the second position, but not both. Optionally, the boot  62  may also conceal the presence of the mode selector switch  60 . 
     Returning to  FIGS. 2 and 3 , the fastening tool  10  may also include a fastener sensor  64  for sensing the presence of one or more fasteners F in the fastening tool  10  and generating a fastener sensor signal in response thereto. The fastener sensor  64  may be a limit switch or proximity switch that is configured to directly sense the presence of a fastener F or of a portion of the magazine  24 , such as a pusher  66  that conventionally urges the fasteners F contained in the magazine  24  upwardly toward the nosepiece  16 . In the particular example provided, the fastener sensor  64  is a limit switch that is coupled to the nosepiece  16  and positioned so as to be contacted by the pusher  66  when a predetermined quantity of fasteners F are disposed in the magazine  24  and/or nosepiece  16 . The predetermined quantity may be any integer that is greater than or equal to zero. The controller  54  may also activate an appropriate indicator, such as the lights  56  and/or speaker  58 , to generate an appropriate visual and/or audio signal in response to receipt of the fastener sensor signal that is generated by the fastener sensor  64 . Additionally or alternatively, the controller  54  may inhibit the cycling of the fastening tool  10  (e.g., by inhibiting the actuation of the actuator  44  so that the cam  40  is not driven in the direction of arrow A) in some situations. For example, the controller  54  may inhibit the cycling of the fastening tool  10  when the fastener sensor  64  generates the fastener sensor signal (i.e., when the quantity of fasteners F in the magazine  24  is less than the predetermined quantity). Alternatively, the controller  54  may be configured to inhibit the cycling of the fastening tool  10  only after the magazine  24  and nosepiece  16  have been emptied. In this regard, the controller  54  may “count down” by subtracting one (1) from the predetermined quantity each time the fastening tool  10  has been actuated to drive a fastener F into the workpiece. Consequently, the controller  54  may count down the number of fasteners F that remain in the magazine  24  and inhibit further cycling of the fastening tool  10  when the controller  54  determines that no fasteners F remain in the magazine  24  or nosepiece  16 . 
     The trigger switch  18   a  and the contact trip sensor  50  can be conventional power switches. Conventional power switches, however, tend to be relatively bulky and employ a relatively large air gap between the contacts of the power switch. Accordingly, packaging of the switches into the fastening tool  10 , the generation of heat by and rejection of heat from the power switches, and the durability of the power switches due to arcing are issues attendant with the use of power switches. Alternatively, the trigger switch  18   a  and the contact trip sensor  50  can be microswitches that are incorporated into a circuit that employs solid-state componentry to activate the motor assembly  14  to thereby reduce or eliminate concerns for packaging, generation and rejection of heat and durability due to arcing. 
     With reference to  FIG. 5 , the controller  54  may include a control circuit  100 . The control circuit  100  may include the trigger switch  18   a,  the contact trip sensor  50 , a logic gate  106 , an integrated circuit  108 , a motor switch  110 , a first actuator switch  112 , and a second actuator switch  114 . The switches  110 ,  112  and  114  may be any type of switch, including a MOSFET, a relay and/or a transistor. 
     The motor switch  110  may be a power controlled device that may be disposed between the motor  32  and a power source, such as the battery  26  ( FIG. 1 ) or a DC-DC power supply (not shown). The first and second actuator switches  112  and  114  may also be power controlled devised that are disposed between the actuator  44  and the power source. In the particular example provided, the first and second actuator switches  112  and  114  are illustrated as being disposed on opposite sides of the actuator  44  between the actuator  44  and the power source, but in the alternative could be situated in series between the actuator and the power source. The trigger switch  18   a  and the contact trip sensor  50  are coupled to both the logic gate  106  and the integrated circuit  108 . The integrated circuit  108  may be responsive to the steady state condition of the trigger switch  18   a  and/or the contact trip sensor  50 , or may be responsive to a change in one or both of their states (e.g., a transition from high-to-low or from low-to-high). 
     Actuation of the trigger switch  18   a  produces a trigger switch signal that is transmitted to both the logic gate  106  and the integrated circuit  108 . As the contact trip sensor  50  has not changed states (yet), the logic condition is not satisfied and as such, the logic gate  106  will not transmit a signal to the first actuator switch  112  that will cause the logic gate  106  to change the state of the first actuator switch  112 . Accordingly, the first actuator switch  112  is maintained in its normal state (i.e., open in the example provided). The integrated circuit  108 , however, transmits a signal to the motor switch  110  in response to receipt of the trigger switch signal which causes the motor switch  110  to change states (i.e., close in the example provided), which completes an electrical circuit that permits the motor  32  to operate. 
     Actuation of the contact trip sensor  50  produces a contact trip sensor signal that is transmitted to both the logic gate  106  and the integrated circuit  108 . If the trigger switch  18   a  had continued to transmit the trigger switch signal, the logic condition is satisfied and as such, the logic gate  106  will transmit a signal to the first actuator switch  112  that will cause it to change states. Accordingly, the first actuator switch  112  is changed to a closed state in the example provided. Upon receipt of the contact trip sensor signal, the integrated circuit  108  transmits a signal to the second actuator switch  114  which causes the second actuator switch  114  to change states (i.e., close in the example provided), which in conjunction with the changing of the state of the first actuator switch  112 , completes an electrical circuit to permit the actuator  44  to operate. 
     Various other switches, such as the mode selector switch  60  and/or the power source sensor  52 , may be coupled to the integrated circuit  108  to further control the operation of the various relays. For example, if the mode selector switch  60  were placed into a position associated with the operation of the fastening tool  10  in either a bump feed or a sequential feed manner, the integrated circuit  108  may be configured to change the state of the motor switch  110  upon receipt of either the trigger switch signal or the contact trip sensor signal and thereafter change the state of the second actuator switch  114  upon receipt of the other one of the trigger switch signal and the contact trip sensor signal. 
     As another example, if the power source sensor  52  generated a signal that was indicative of a situation where the level of kinetic energy in the motor assembly  14  is less than a predetermined threshold, the integrated circuit  108  may be configured so as to not generate a signal that would change the state of the second actuator switch  114  to thereby inhibit the operation of the fastening tool  10 . 
     From the foregoing, it will be appreciated that actuation of the motor assembly  14  cannot occur as a result of a single point failure (e.g., the failure of one of the trigger switch  18   a  or the contact trip sensor  50 ). 
     With reference to  FIGS. 3 and 6 , the controller  54  may be provided with additional functionality to permit the fastening tool  10  to operate using battery packs of various different voltages, such as  18 ,  14 ,  14  and/or 9.6 volt battery packs. For example, the controller  54  may employ. pulse width modulation (PWM), DC/DC converters, or precise on-time control to control the operation of the motor  32  and/or the actuator  44 , for example to ensure consistent speed of the flywheel  34 /kinetic energy of the motor assembly  14  regardless of the voltage of the battery. The controller  54  may be configured to sense or otherwise determine the actual or nominal voltage of the battery  26  at start-up (e.g., when the battery  26  is initially installed or electrically coupled to the controller  54 ). 
     Power may be supplied to the motor  32  over all or a portion of a cycle using a pulse-width modulation technique, an example of which is illustrated in  FIG. 6 . The cycle, which may be initiated by a predetermined event, such as the actuation of the trigger  18 , may include an initial power interval  120  and one or more supplemental power intervals (e.g.,  126   a,    126   b,    126   c ). The initial power interval  120  may be an interval over which the full voltage of the battery  26  may be employed to power the motor  32 . The length or duration (ti) of the initial power interval  120  may be determined through an algorithm or a look-up table in the memory of the controller  54  for example, based on the output of the battery  26  or on an operating characteristic, such as rotational speed, of a component in the motor assembly  14 . The length or duration (ts) of each supplemental power interval may equal that of the initial power interval  120 , or may be a predetermined constant, or may be varied based on the output of the battery  26  or on an operating characteristic of the motor assembly  14 . 
     A dwell interval  122  may be employed between the initial power interval  120  and a first supplemental power interval  126   a  and/or between successive supplemental power intervals. The dwell intervals  122  may be of a varying length or duration (td), but in the particular example provided, the dwell intervals  122  are of a constant duration (td). During a dwell interval  122 , power to the motor  32  may be interrupted so as to permit the motor  32  to “coast”. The output of the power source sensor  52  may be employed during this time to evaluate the level of kinetic energy in the motor assembly  14  (e.g., to permit the controller  54  to determine whether the motor assembly  14  has sufficient energy to drive a fastener) and/or to determine one or more parameters by which the motor  32  may be powered or operated in a subsequent power interval. 
     In the example provided, the controller  54  evaluates the back emf of the motor  32  to approximate the speed of the flywheel  34 . The approximate speed of the flywheel  34  (or an equivalent thereof, such as the value of the back emf of the motor  32 ) may be employed in an algorithm or look-up table to determine the duty cycle (e.g., apparent voltage) of the next supplemental power interval. Additionally, if the back emf of the motor  32  is taken in a dwell interval  122  immediately after an initial power interval  120 , an algorithm or look-up table may be employed to calculate changes to the duration (ti) of the initial power interval  120 . In this way, the value (ti) may be constantly updated as the battery  26  is discharged. The value (ti) may be reset (e.g., to a value that may be stored in a look-up table) when a battery  26  is initially coupled to the controller  54 . For example, the controller  54  may set (ti) equal to 180 ms if the battery  26  has a nominal voltage of about 18 volts, or to 200 ms if the battery  26  has a nominal voltage of about 14.4 volts, or to 240 ms if the battery  26  has a nominal voltage of about 12 volts. 
     With reference to  FIG. 8 , the back-emf of the motor  32  may change with the temperature of the motor as is indicated by the line that is designated by reference numeral  200 ; the line  200  represents the actual rotational speed as a function of temperature when the back-emf of the motor is held constant. With additional reference to  FIG. 3 , the control unit  22  may include a temperature sensor  202  for sensing a temperature of the motor  32  or another portion of the fastening tool, such as the controller  54 , to permit the controller  54  to compensate for differences in the back-emf of the motor  32  that occur with changes in temperature. In the particular example provided, the temperature sensor  202  is coupled to the controller  54  and generates a temperature signal in response to a sensed temperature of the controller  54 . As the controller  54  is in relatively close proximity to the motor  32 , the temperature of the controller  54  approximates the temperature of the motor  32 . 
     The controller  54  may employ any known technique, such as a look-up table, mathematical relationship or an algorithm, to determine the effect of the sensed temperature on the back-emf of the motor  32 . In the particular example provided, the relationship between the actual rotational speed of the motor  32  indicates linear regression, which permitted the use of an empirically-derived equation to determine a temperature-based speed differential (AST) that may be employed in conjunction with a back-emf-based calculated speed (S BEF ) to more closely approximate the rotational speed (S) of the motor  32  (i.e., S=S BEF −ΔS T ). The line designated by reference numeral  210  in  FIG. 8  illustrates the actual speed of the motor  32  as a function of temperature when the approximate rotational speed (S) is held constant. 
     Alternatively, the controller  54  may approximate the rotational speed (S) of the motor  32  through the equation S=|S BATV +ΔS BEF −ΔS T | where S BATV  can be an estimate of a base speed of the motor  32  based upon a voltage of the battery  26 , ΔS BEF  can be a term that is employed to modify the base speed of the motor  32  based upon the back-emf produced by the motor  32 , and ΔS T  can be the temperature-based speed differential described above. In the particular example provided, the voltage of the battery can be an actual battery voltage as opposed to a nominal battery voltage and the S BATV  term can be derived as a function of the slope of a plot of motor speed versus battery voltage. As determined in this alternative manner, the speed of the motor can be determined in a manner that is highly accurate over a wide temperature range. 
     It will be appreciated that while the fastening tool  10  has been described as providing electrical power to the electric motor  32  except for relatively short duration intervals (e.g., between pulses and/or to check the back-emf of the motor  32 ) throughout an operational cycle, the invention, in its broadest aspects, may be carried out somewhat differently. For example, the controller  54  may control the operation of the motor  32  through feedback control wherein electric power is occasionally interrupted so as to allow the motor  32  and flywheel  34  to “coast”. During the interruption of power, the controller  54  can occasionally monitor the kinetic energy of the motor assembly  14  and apply power to the motor if the kinetic energy of the motor assembly  14  falls below a predetermined threshold. Operation of the fastening tool in this manner can improve battery life. 
     While the invention has been described in the specification and illustrated in the drawings with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various embodiments is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.