Abstract:
The present invention is an articulating hand power tool with a main housing having a longitudinal axis, a head portion rotatably engaged with the main housing for placement at a plurality of angles with respect to the longitudinal axis of the main housing, an integrated circuit board located within the main housing and at least one controller accessible from outside of the main housing for controlling the integrated circuit board.

Description:
This application claims the benefit of provisional U.S. patent application Ser. No. 60/733,546, filed on Nov. 4, 2005. The disclosure of this provisional patent application is hereby totally incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an electric hand tool and more particularly to an articulating power hand tool. 
     BACKGROUND 
     Power tools including battery operated tools are well-known. These tools typically include an electric motor having an output shaft that is coupled to a spindle for holding a tool. The tool may be a drill bit, sanding disc, a de-burring implement, or the like. The power source may be a battery source such as a Ni-Cad or other rechargeable battery that may be de-coupled from the tool to charge the battery and coupled to the tool to provide power. 
     The power source is coupled to the electric motor through a power switch. The switch includes input electrical contacts for coupling the switch to the power source. Within the switch housing, a moveable member, sometimes called a switch, is coupled to the input electrical contacts and to a wiper of a potentiometer. As the moveable member is pressed against the biasing component of the switch, it causes the input electrical contacts to close and provide current to one terminal of the electric motor and to the wiper of the potentiometer. The moveable member is biased so that the biasing force returns the moveable member to the position where the input electrical contacts are open when the moveable member is released. The current is coupled to a timing signal generator, such as a “555” circuit, through the potentiometer. As the member or trigger continues to be pulled against the biasing force so that the wiper reduces the resistance of the potentiometer from an open circuit to a low resistance or short circuit condition, the level of the current supplied to the timing signal generator increases. 
     The output of the timing signal generator is coupled to the gate of a solid state device, such as a MOSFET. The source and drain of the solid state device are coupled between a second terminal of the electric motor and electrical ground. In response to the timing signal turning the solid state device on and off, the motor is selectively coupled to electrical ground through the solid state device. Thus, as the timing signal enables the solid state device to couple the motor to electrical ground for longer and longer intervals, the current flows through the motor for longer intervals. The longer the motor is coupled to power, the faster the electric motor rotates the output shaft of the motor. Consequently, the tool operator is able to vary the speed of the motor and, correspondingly, the rotational speed of the tool in the spindle by manipulating the trigger for the power switch. 
     The timing signal generated by the timing circuit selectively couples the motor to the power source because it alternates between a logically on-state and a logically off-state. During the logically off-state, the motor is no longer coupled to the power source. The windings in the motor, however, still have current in them. To provide a path for this current, a freewheeling diode is provided across the terminals of the motor. 
     The trigger of the power switch is also coupled to two sets of contacts. One of these contact sets is called the bypass contact set. When the trigger reaches the stop position of its travel against the biasing component, it causes the bypass contacts to close. The closing of the bypass contacts causes the current through the motor to bypass the solid state device and be shunted to electrical ground. This action enables the motor to remain continuously coupled to the power source and reach its maximum speed. 
     The other set of electrical contacts controlled by the switch trigger are the brake contacts. These contacts are closed when the trigger is at the fully biased off position. As the trigger is moved against the biasing force, the brake contacts open. The brake contacts couple one terminal of the electric motor to the other terminal of the motor. In response to the trigger being released from a position that enables power to be supplied to the motor, the brake contacts close to provide a current path through the motor for dynamic braking of the motor. This enables the motor to stop more quickly than if the motor simply coasted to a stop under the effects of friction. 
     While the power switch described above is effective for tool speed control, it suffers from some limitations. Known power switches are limited because of the effect of carrying the battery current through the switch. When the battery current is first applied to the contacts, the current level may be sufficient to cause arcing. Arcing may cause the contacts to become pitted or otherwise damaged. Additionally, large currents also tend to heat the components within the switch. Consequently, the switch may require a heat sink or a larger volume to dissipate heat within the switch. The larger size of the housing for the switch may also impact the design of the tool housing to accommodate the switch geometry. Another factor affecting the geometry or size of the switch housing is the potentiometer that generates the variable speed signal. Typically, the distance traveled by the wiper of the potentiometer is approximately the same as the distance traveled by the trigger. In many cases, this distance is approximately 7 mm and this distance must be accommodated by the potentiometer and the housing in which the potentiometer is mounted. 
     The direction of motor rotation depends upon whether the battery current flows through the motor from the first terminal to the second terminal or vice versa. Because bidirectional rotation of battery operated tools is desirable, most tools are provided with a two position switch that determines the direction of battery current through the electric motor. In some previously known switches for battery operated tools, this two position switch is incorporated in its own housing that is mounted to the switch housing. The additional two position switch housing may exacerbate the space issues already noted. In other known switches, the two position switch may be integrated within the switch housing. This arrangement, while perhaps smaller than the two housing construction, adds another set of contacts to the switch with the attendant heat or contact deterioration concerns that arise from the motor current flowing through these contacts. 
     Another limitation of known power switches relates to the torque control for power tools. In some battery operated tools, mechanical clutches are used to set a torque limit for the tool. When the resistance to the rotation of the tool causes the torque generated by the tool to increase to the torque limit, the clutch slips to reduce the torque. The torque may then build again until it reaches the limit and the clutch slips again. The iterating action of clutch slippage followed by renewed torque buildup is sensed by the operator as vibration. This vibration informs the operator that the tool is operating at the set torque limit. This slippage also causes wear of the mechanical components from friction and impact. 
     Electric drills suffer the foregoing limitations. Moreover, electric drills are usually constructed as straight-drilling machines in which the drill spindle extends parallel to the motor shaft and axis of the housing and, for specific purposes, as angular-drilling machines in which the drill spindle is aligned at a right angle to the motor shaft and housing axis. In certain applications in which both straight and angular drilling must be carried out, as is the case in installations in wooden house construction, the two machines must be at hand for continuous alternation. 
     What is needed is an articulating power hand tool which does not require a large housing for mechanical switches. What is further needed is an articulating power hand tool with a reduced forward section and a compact articulating system to allow for use of the tool in confined areas. 
     SUMMARY 
     The present invention is an articulating hand power tool. In one embodiment, the tool includes an articulating hand power tool with a main housing having a longitudinal axis, a head portion rotatably engaged with the main housing for placement at a plurality of angles with respect to the longitudinal axis of the main housing, an integrated circuit board located within the main housing and at least one controller accessible from outside of the main housing for controlling the integrated circuit board. 
     In another embodiment, a hand power tool includes a longitudinally extending main housing, a head portion configured to be engaged with the main housing at a plurality of angles with respect to the longitudinal axis of the main housing, each of the plurality of angles within a single plane, an articulation gear system for providing motive force to a bit holder in the head portion including a motor side pinion gear having an axis of rotation generally parallel to a longitudinal axis of the housing and an output pinion gear having an axis of rotation generally parallel to a longitudinal axis of the head portion, wherein the motor side pinion gear is operatively connected to the output side pinion gear through a bevel gear, a controller operable from outside of the main housing and located generally on the plane and an integrated circuit located within the main housing and responsive to the controller. 
     One method in accordance with the invention includes rotating a head portion of a power tool to one of a plurality of angles with respect to the longitudinal axis of a main housing of the power tool, moving a variable speed trigger switch located outside of the main hosing, generating a variable speed signal with an integrated circuit located within the main housing in response to the movement of the variable speed trigger, controlling the speed of a motor located within the main housing based upon the variable speed signal and transferring motive force from the motor to a component within the head portion. 
     These and other advantages and features of the present invention may be discerned from reviewing the accompanying drawings and the detailed description of the preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may take form in various system and method components and arrangement of system and method components. The drawings are only for purposes of illustrating exemplary embodiments and are not to be construed as limiting the invention. 
         FIG. 1  shows a perspective view of an articulating drill incorporating features of the present invention; 
         FIG. 2  shows a side elevational view of the articulating drill of  FIG. 1  with the rechargeable battery pack removed; 
         FIG. 3  shows a perspective view of the articulating drill of  FIG. 1  with the battery pack, a portion of the main housing cover, and a portion of the head housing removed and a bit in the bit holder; 
         FIG. 4  shows a cross-sectional view of the head portion, the articulating gear system and the planetary gear system of the articulating drill of  FIG. 1 ; 
         FIG. 5  shows an exploded perspective view of the head portion, including an automatic spindle lock system, of the articulating drill of  FIG. 1 ; 
         FIG. 6  shows a top plan view of the head portion of the drill of  FIG. 1  with some components located within bays in the head housing; 
         FIG. 7  shows a top plan view of a bracket used to support an output pinion shaft in the articulating drill of  FIG. 1 ; 
         FIG. 8  shows a side plan view of the bracket of  FIG. 7 ; 
         FIG. 9  shows a top elevational view of the planetary gear section, articulating section and head portion of the articulating drill of  FIG. 1  with the main housing and a portion of the head housing removed; 
         FIG. 10  shows a side elevational view of the articulating gear system of the articulating drill of  FIG. 1  including a bevel gear and two pinion gears; 
         FIG. 11  is a perspective view of a portion of the head housing of the drill of  FIG. 1  with a plurality of teeth in a well which are formed complimentary to teeth on the articulation button; 
         FIG. 12  shows a perspective view of the articulating button of the articulating drill of  FIG. 1 ; 
         FIG. 13  shows a perspective view of the bottom of the articulating button of  FIG. 12 ; 
         FIG. 14  shows a partial top elevational view of the inner surface of the outer housing of the articulating drill of  FIG. 1  with teeth formed complimentary to the teeth on the articulation button and a hole for receiving a raised portion of the articulating button; 
         FIG. 15  shows a top elevational view of the inner surface of the outer housing of the articulating drill of  FIG. 1 ; 
         FIG. 16  shows a partial plan view of the articulating drill of  FIG. 1  with the head portion aligned with the main housing portion and without a dust lid; 
         FIG. 17  shows a partial plan view of the articulating drill of  FIG. 1  with the head portion aligned with the main housing portion with a dust lid; 
         FIG. 18  shows a side elevational view of the articulating drill of  FIG. 18  with the head portion rotated to an angle of 90 degrees from the main housing portion of the drill and a portion of the main housing portion removed to show the position of the dust lid of  FIG. 17 ; 
         FIG. 19  shows a side elevational view of the articulating drill of  FIG. 18  with the head portion rotated to an angle of 180 degrees from the main housing portion of the drill and a portion of the main housing portion removed to show the position of the dust lid of  FIG. 17 ; 
         FIG. 20  shows a detail view of the dust lid of  FIG. 19 ; 
         FIG. 21  shows a perspective view of the articulating drill of  FIG. 1  with the variable speed trigger switch, clutch control and a portion of the main housing removed; 
         FIGS. 22   a ,  22   b  and  22   c  show various views of a printed circuit board of the articulating drill of  FIG. 1  in accordance with principles of the invention; 
         FIG. 23  shows a perspective view of the articulating drill of  FIG. 21  with a collapsible boot with an internal reflective surface installed over a light generator and a light sensor; 
         FIG. 24  shows a schematic/block diagram of the drill of  FIG. 1  incorporating an optical switch for motor speed control; 
         FIG. 25  shows a side elevational view of a drill bit in the form of a screw driver bit that may be used with the articulating drill of  FIG. 1 ; 
         FIG. 26  shows a cross-sectional view of the drill bit of  FIG. 25  being inserted into the articulating drill of  FIG. 1 ; 
         FIG. 27  shows a cross-sectional view of the drill bit of  FIG. 25  inserted into the articulating drill of  FIG. 1 ; 
         FIG. 28  shows a partial top elevational view of a bevel gear in accordance with principles of the invention with two pinion gears at a 90 degree spacing; 
         FIG. 29  shows a partial top elevational view of the bevel gear of  FIG. 28  with the two pinion gears at a 180 degree spacing; 
         FIG. 30  shows an electrical diagram/schematic of a powered tool that dynamically brakes the tool motor using a motor interface circuit having a half bridge to provide vibratory feedback to the operator that the torque limit has been reached; 
         FIG. 31  shows an electrical diagram/schematic of a circuit that may be used with the drill of  FIG. 1  which dynamically brakes the drill motor using a motor interface circuit having a full H-bridge circuit to provide vibratory feedback to the operator that the torque limit has been reached; and 
         FIGS. 32A and 32B  show an electrical diagram/schematic of a powered tool that provides solid state motor speed control in correspondence with a variable speed signal from an optical switch and that dynamically brakes the motor to indicate a torque limit has been reached. 
     
    
    
     DESCRIPTION 
     An articulating drill generally designated  100  is shown in  FIG. 1 . In the embodiment of  FIG. 1 , the drill  100  includes a main housing portion  102  and a head portion  104 . The main housing portion  102  houses a motor and associated electronics for control of the drill  100 . The main housing portion  102  includes a battery receptacle for receiving a rechargeable battery pack  106  as is known in the art. In one embodiment, the rechargeable battery pack  106  comprises a lithium-ion battery. The battery pack  106  is removed by depression of the battery release tabs  108 .  FIG. 2  shows the drill  100  with the battery pack  106  removed. The drill  100  may alternatively be powered by an external power source such as an external battery or a power cord. 
     A variable speed trigger switch  110  controls the speed at which the motor rotates. The direction of rotation of the motor is controlled by a reversing button  112  which slides within a finger platform  114 . Ventilation openings  116  allow for cooling air to be circulated around the motor inside of the main housing  102 . A clutch control  118  sets the maximum torque that may be generated when using the drill  100 . At the position shown in  FIG. 1 , the clutch control  118  is at the highest setting or drill mode. At the highest setting, the clutch is disabled to provide maximum torque. By sliding the clutch control  118  downwardly from the position shown in  FIG. 1 , a user may set a desired torque limit that is allowed to be generated by the drill  100  as discussed in more detail below. Accordingly, at settings other than the highest setting, a torque above the setting of the clutch control  118  causes the clutch to activate. 
     The main housing portion  102  also includes an articulation button  120  and a plurality of angle reference indicators  122  molded onto the outer surface  124  of the main housing  102 . In the embodiment of  FIG. 1 , there are five angle reference indicators  122  used to identify five angular positions in which the head portion  104  may be placed. 
     The head portion  104  includes a collet locking device  126  and an angle indicator  128 . The angle at which the head portion  104  is positioned is indicated by the angle reference indicator  122  with which the angle indicator  128  is aligned. As shown in  FIG. 1 , the head portion  104  is at a 90 degree angle with respect to the main housing portion  102 . In  FIG. 2 , the head portion  104  is axially aligned with the main housing portion  102 . Although the embodiment of  FIGS. 1 and 2  has five angle reference indicators  122 , there may be additional or fewer angle reference indicators  122  and corresponding angles at which the head portion  104  may be placed with respect to the main housing portion  102 . 
     Referring now to  FIGS. 3-6 , the collet locking device  126  is located around a bit holder  130  which is in turn supported by a ball bearing  132  that is fixed within a bearing pocket  134  of the head housing  136 . The collet locking device  126  includes a sleeve  138  with recesses  140 . A spring  142  is positioned about the bit holder  130 . The bit holder  130  includes a hole  144  which receives a cylinder pin  146  and recesses  148  which receive steel balls  150 . 
     The bearing  132  abuts the head housing  136  of the head portion  104  at the outer rear periphery of the bearing  132 . More specifically, the bearing  132  abuts a flange  152 . In this embodiment, the flange  152  is continuous about the housing  136 , although a flange may alternatively be in the form of a plurality of fins located about the inner portion of the housing  136 . 
     The bit holder  130  is operably coupled to a drive collet  154  which is in turn connected to an output pinion shaft  156  through a drive plate  158  which is fixedly attached to the output pinion shaft  156 . A lock ring  160  surrounds the drive collet  154  and three locking pins  162 . The lock ring  160 , the drive collet  154 , the drive plate  158 , and the locking pins  162  all comprise an automatic spindle lock system such that the output bit holder  130  can only be driven from the pinion side as known in the art. When driven from the bit side, i.e., when the tool  100  is used as a manual screwdriver, the spindle lock system keeps the output pinion shaft  156  from rotating thus facilitating use of the tool  100  as a manual screwdriver. In an alternative embodiment, a manually manipulated locking device may be used. 
     A pinion gear  164  is located at the opposite end of the output pinion shaft  156  from the drive plate  158 . One end of the output pinion shaft  156  is maintained in axial alignment by a bearing  166  which fits within bearing pocket  168 . The opposite end of the output pinion shaft  156  is supported by a sleeve  170 . The sleeve  170  is supported on one side by a flange  172  on the head housing  136 . On the opposite side, the sleeve  170  is supported by a bracket  174  also shown in  FIGS. 7 and 8 . 
     The bracket  174  includes a support area  176  configured complimentary to a portion of the sleeve  170 . Two connection arms  178  are configured to be attached to the head housing  136  as shown in  FIG. 9 . The bracket  174  eliminates the need to provide a matching flange for flange  172  molded into the opposite side of the head housing  136 . The elimination of the need for an opposing flange allows for a significant increase in design freedom as the space requirements for the support structure for the sleeve  170  are reduced. The bracket  174  may be stamped from W108 steel to provide the needed rigidity and strength. 
     Referring now to  FIG. 10 , the pinion gear  164  forms a portion of an articulating gear system  180 . The articulating gear system  180  further includes a bevel gear  182  which is engaged at the output portion of the articulating gear system  180  with the pinion gear  164  and further engaged on the motor portion by pinion gear  184 . The shaft  186  of the bevel gear  182  is supported at one end within a hole  188  (see  FIG. 4 ) of the frame  190 . The frame  190  is made from a zinc and aluminum alloy ZA-8. This material provides a sufficiently low coefficient of friction to ensure relatively small frictional forces exist between the shaft  186  and the frame  190 . 
     The shaft  186  is radially and axially supported at the opposite end by a ball bearing  192  supported by the frame  190 . At this end of the shaft  186 , however, comparatively larger forces are generated than at the end of the shaft  186  inserted within the hole  188 . More specifically, as shown in  FIG. 10 , both pinion gear  164  and pinion gear  184  are located on the same side of the bevel gear  182 . Accordingly, as the articulating gear system  180  rotates, a force is generated on the bevel gear  182  in the direction of the arrow  194  toward the base  196  of the bevel gear  182 . This force acts to disengage the bevel gear  182  from the pinion gear  164  and the pinion gear  184 . With this increased force acting upon the bevel gear  182 , an unacceptable amount of axial force would be transmitted to the bearing  192 . Accordingly, a thrust bearing  198  is provided to protect the ball bearing  192  and to provide a low friction support for the base  196  of the bevel gear  182 . The thrust bearing  198  is made of a material with an acceptably low coefficient of friction such as oil impregnated bronze commercially available from McMaster Carr of Chicago, Ill. Accordingly, the friction generated at the base  196  of the bevel gear  182  is maintained within acceptable levels. 
     Referring again to  FIG. 4 , the pinion gear  184  is fixedly attached to a planetary gearbox shaft  200  which receives torque from a planetary gear system generally indicated as reference numeral  202 . The planetary gear system  202  receives torque from a motor as is known in the art. The planetary gear system  202  is located within a planetary gear housing  204  which is inserted partially within the frame  190 . This arrangement allows for the planetary gear system  202  to be separately manufactured from the other components while simplifying assembly of the planetary gear system  202  with the other components. This modularity further allows for alternative gearings to be provided in the planetary gear system  202  while ensuring a proper fit with the other components. 
     Generally, it may be desired to provide a simple friction fit between the planetary gear housing  204  and the frame  190 . In the embodiment of  FIG. 4 , however, the articulating gear system  180  generates an axial force along the planetary gearbox shaft  200 . This axial force acts to disengage the planetary gear housing  204  from the frame  190 . Accordingly, pins  206  and  208  which extend through both the planetary gear housing  204  and the frame  190  are provided. The pins  206  and  208  ensure the planetary gear housing  204  does not become detached from the frame  190  during operation of the drill  100 . Alternatively, the planetary gear housing  204  and the frame  190  may be formed as an integral unit. 
     Continuing with  FIG. 4 , the frame  190  is configured to slidingly mate with the head housing  136 . To this end, the head housing  136  includes a shroud portion  210  which is complimentarily formed to the frame  190  about the ball bearing  192 . The head housing  136  further includes a recess  212  which is configured to receive the portion of the frame  190  which defines the hole  188 . Also shown in  FIG. 4  is a well  214  which includes a plurality of teeth  216  shown in  FIG. 11 . 
     With further reference to  FIGS. 12-14 , the well teeth  216  are formed complimentary to a plurality of teeth  218  which are formed in the articulation button  120 . The articulation button  120  includes a raised center portion  220  which is configured to fit within a hole  222  in the main housing portion  102 . The teeth  218  of the articulation button  120  are further configured to mesh with a plurality of teeth  224  formed on the inner side of the main housing portion  102  around the hole  222 . The articulation button  120  also includes a spring receiving well  226  on the side of the articulation button  120  facing the well  214 . When assembled, a spring (not shown) is located within the well  214  and extends into the spring receiving well  226  forcing the raised center portion  220  of the articulation button  120  toward a position wherein the articulation button  120  projects into the hole  222 . 
     Referring to  FIGS. 4 and 15 , the frame  190  is supported axially in the main housing portion  102 , which in this embodiment is made of plastic, by a rib  228 . The rib  228  lies beneath a fin  230  of the frame  190  when the frame  190  is installed in the main housing portion  102  as shown in  FIG. 3 . The planetary gear system  202  is mechanically secured to a motor  232  which is itself electrically connected to a printed circuit board  234  which in turn is electrically connected to a battery contact holder  236 . The contact holder  236  mates with battery pack receptacles on the battery pack  106  and transmits battery power to the electronic circuit board  234  through lead wires (not shown). Another pair of lead wires (not shown) extend from the circuit board  234  to the motor terminals  238  to deliver the required voltage level to the motor  232 . 
     Referring now to  FIG. 5 , a gap  240  is provided in the portion of the head housing  136  surrounding the bevel gear  182  which allows the head housing  136  to be rotated with respect to the main housing portion  102  while the pinion gear  164  remains engaged with the bevel gear  182 . When the head portion  104  is axially aligned with the main housing portion  102 , however, the gap  240  is exposed as shown in  FIG. 16 . The articulating gear system  180  is thus exposed allowing contaminants access to the articulating gear system  180  which could foul the articulating gear system as well as presenting a safety concern since clothing, fingers or hair could become enmeshed in the articulating gear system  180 . Accordingly, a floating dust lid  242  shown in  FIG. 17  is used to prevent contamination of the articulating gear system  180  and to avoid exposure of moving gears to an operator through the gap  240 , particularly when the head housing  136  is axially aligned with the main housing portion  102  as shown in  FIG. 17 . 
     The dust lid  242  is located in a channel  244  defined by the main housing portion  102  and the head housing  136  as shown in  FIGS. 18-20 . The position of the dust lid  242  at the lower portion (as depicted in  FIGS. 18 and 19 ) of the channel  244  is constrained either by a movable dust lid travel limiter  246  positioned on the head housing  136 , shown most clearly in  FIGS. 11 and 20 , or by a portion  248  of the frame  190 . The position of the dust lid  242  at the upper portion of the channel  244  is constrained either by a neck portion  250  of the head housing  136  or by a lip  252  in the main housing portion  102 . 
     Referring now to  FIGS. 3 , and  21 - 23 , the clutch control  118  is mechanically interfaced with a linear potentiometer  254  on the circuit board  234 . Also located on the circuit board  234  is a light sensor  256  which is covered by a collapsible rubber boot  258  which is in turn mechanically fastened to the variable speed trigger  110 . A reflective surface  260  (see  FIG. 24 ) is located on the inside of the rubber boot  258 . A plastic spring locating member  262  which is mechanically secured to the circuit board  234  serves to locate and support a spring  264  which is mechanically fastened to the variable speed trigger  110 . The spring  264  biases the variable speed trigger  110  in a direction away from the circuit board  234  about a pivot  266 . The circuit board  234  also contains a two position slide switch  268  which is mechanically interfaced to the reversing button  112 . 
     Manipulation of the variable speed trigger  110  about the pivot  266  changes the position of the reflective surface  260  relative to the light sensor  256  to produce a variable speed control signal. While the embodiment of tool  100  incorporates an optical signal generator and receiver for provision of a variable speed control signal, such a tool may alternatively use a pressure transducer, a capacitive proximity sensor, or an inductive proximity sensor. In these alternative embodiments, a pressure sensing switch for generating the variable motor speed control signal may include a pressure transducer for generating a variable speed control signal that corresponds to a pressure applied to the pressure transducer directly by the operator or through an intermediate member such as a moveable member that traverses the distance between the stop position and the full speed position. 
     An embodiment of the variable motor speed control signal implemented with a capacitive proximity sensor may include a capacitive sensor that generates a variable speed control signal that corresponds to an electrical capacitance generated by the proximity of an operator&#39;s finger or moveable member&#39;s surface to the capacitive sensor. An embodiment implemented with an inductive proximity sensor generates a variable speed control signal that corresponds to an electrical inductance generated by the proximity of an operator&#39;s finger or moveable member&#39;s surface to the inductive sensor. 
     Referring to  FIG. 24 , the variable speed control circuit  270  of the tool  100  is schematically shown. The variable speed control circuit  270  includes a power contact  272  which is operably connected to the variable speed trigger switch  110 . An optical signal generator  274  is coupled to the battery  106  and arranged on the circuit board  232  such that light emitted from the optical signal generator  274  is directed toward the reflective surface  260  of the variable speed trigger switch  110  and directed toward the light sensor  256 . 
     The light sensor  256  and the optical signal generator  274  may be located in the same housing or each may be within a separate housing. When the two components are located in the same housing, the light generator and sensor may emit and receive light through a single sight glass in the housing. Alternatively, each component may have a separate sight glass. An integrated component having the light generator and sensor in a single housing is a QRD1114 Reflective Object Sensor available from Fairchild Semiconductor of Sunnyvale, Calif. Such a housing is substantially smaller than a potentiometer that has a wiper, which traverses approximately the same distance as the trigger traverses from the stop to the full speed position. 
     The optical signal generator  274  and the light sensor  256  may be an infrared light emitter and an infrared light receiver. In an alternative embodiment, an IR transceiver may be contained within a flexible dust cover that is mechanically fastened to the back of the variable speed trigger switch. In such an embodiment, the inside of the cover in the vicinity of the moveable trigger reflects the optical signal to the receiver for generating the speed control signal. 
     Control of a tool incorporating the light sensor  256  may be adversely affected by external energy sources such as the sun. Accordingly, in one embodiment, the collapsible boot or dust cover  258  is made from an opaque material or coated with an opaque material such that energy from the sun which may leak past the housing and trigger arrangement does not affect the signal received by the light sensor  256 . Alternatively, a light sensor that is sensitive to a specific frequency band may be used with a device which shields the light sensor from only that specific frequency band. In further embodiments, other circuitry or coding which uniquely identifies the energy from the reflected signal from interfering energy may be used. 
     The light sensor  256  is an optical transistor having a collector  276  coupled to the battery pack  106  through the contact  272  and an emitter  278  coupled to electrical ground though a voltage divider  280  and a capacitor  282 . A timing signal generator  284  receives voltage from the voltage divider  280 . In the tool  100 , the timing signal generator  264  is a commonly known “555” timer, although other timing signal generators may be used. 
     The output of the timing signal generator  264  is coupled to a gate  286  of a MOSFET  288  that has a drain  290  coupled to one of the motor terminals  238  and a source  292  coupled to electrical ground. The other motor terminal  238  is coupled to the battery pack  106  through the contact  272 . A freewheeling diode  294  is coupled across the motor terminals  238 . A bypass contact  296 , which is operatively connected to the variable speed trigger switch  110 , is located in parallel to the MOSFET  288  between the motor terminal  238  and electrical ground and a brake contact  298  is in parallel with the freewheeling diode  294 . 
     Operation of the drill  100  is explained with initial reference to  FIGS. 24-26 . The collet locking device  126  is configured to operate with bits such as the screw driver bit  300  shown in  FIG. 24 . The screw driver bit  300  and the bit holder  130  are complimentarily shaped. In this example, both the screw driver bit  300  and the bit holder  130  are generally hexagonal in shape, although alternative shapes may be used. The screw driver bit  300  has a diameter slightly less than the bit holder  130  so that it may fit within the bit holder  130 . The screw driver bit  300  includes a notched area  302  and a tail portion  304 . 
     Initially, the sleeve  138  is moved to the right from the position shown in  FIG. 4  to the position shown in  FIG. 26  thereby compressing the spring  142 . As the sleeve  138  moves, recesses  140  in the sleeve  138  are positioned adjacent to the recesses  148  in the bit holder  130 . Then, as the screw driver bit  300  is moved into the bit holder  130 , the tail portion  304  forces the steel balls  150  toward the recesses  140  and out of the channel of the bit holder  130 , allowing the tail portion  304  to move completely past the steel balls  150 . 
     At this point, the notched area  302  is aligned with the recesses  148 . The sleeve  138  is then released, allowing the spring  142  to bias the sleeve  138  onto the bit holder  130  which is to the left from the position shown in  FIG. 27 . As the sleeve  138  moves, the recesses  140  are moved away from the recesses  148  thereby forcing the steel balls  150  partially into the channel of the bit holder  130  as shown in  FIG. 27 . Movement of the steel balls  150  into the channel of the bit holder  130  is allowed since the notched area  302  is aligned with the recesses  148 . At this point, the bit  300  is firmly held within the bit holder  130 . 
     The head housing  136  is then articulated to a desired angle with respect to the main housing portion  102 . Initially, the spring (not shown) in the spring receiving well  226  forces the articulation button  120  to extend into the hole  222 . Accordingly, the teeth  218  of the articulation button  120  are meshed with the teeth  224  in the main housing portion  102  as well as the teeth  216  in the well  214  of the head housing  136 , thereby angularly locking the articulation button  120  (and the head housing  136 ) with the main housing portion  102 . Additionally, the dust lid  242  is constrained at the upper portion of the channel  244  by the neck portion  250  of the head housing  136  and at the lower portion of the channel  244  by the portion  248  of the frame  190  as shown in  FIG. 18 . 
     The operator then applies force to the articulation button  120  causing the spring (not shown) to be depressed thereby disengaging the teeth  218  from the teeth  224 . Thus, even though the teeth  218  remain engaged with the teeth  216 , the head portion  104  is allowed to pivot with respect to the main housing portion  102 . As the head portion  104  is articulated, for example, from the position shown in  FIG. 1  to the position shown in  FIG. 2 , the pinion gear  164  articulates about the bevel gear  182 . By way of example,  FIG. 28  shows the positions of the pinion gears  164  and  184  with respect to the bevel gear  182  when the drill  100  is in the configuration shown in  FIG. 1 . In this configuration, the pinion gear  164  is approximately 90 degrees away from the pinion gear  184  about the perimeter of the bevel gear  182 . As the head portion  104  is articulated in the direction of the arrow  306 , the pinion gear  164  articulates about the bevel gear  182  in the same direction. Thus, when the head portion  104  is aligned with the main housing portion  102 , the pinion gear  164  is positioned on the bevel gear  182  at a location 180 degrees away from the pinion gear  184  as shown in  FIG. 29 . 
     Throughout this articulation, the pinion gears  164  and  184  remain engaged with the bevel gear  182 . Accordingly, the bit holder  130  may be rotated by the motor  232  as the head housing  136  is articulated. Additionally, the articulation of the head housing  136  causes the movable dust lid travel limiter  246  to contact the dust lid  242  and push the dust lid  242  along the channel  244 . Thus, the dust lid  242 , which is configured to be wider than the gap  240  as shown in  FIG. 17 , restricts access from outside of the drill  100  to the articulating gear system  180 . 
     When the articulating drill  100  is rotated to the desired location, the operator reduces the force applied to the articulating button  120 . The spring (not shown) in the spring receiving well  226  is then allowed to force the articulation button  120  away from the well  214  until the articulation button  120  extends through the hole  222 . Accordingly, the teeth  218  of the articulation button  120  are meshed with the teeth  224  in the main housing portion  102  as well as the teeth  216  in the well  214  of the head housing  136 , thereby angularly locking the articulation button  120  (and the head housing  136 ) with the main housing portion  102 . 
     The desired direction of rotation for the bit  300  is then established by placing the reversing button  112  in the position corresponding to the desired direction of rotation in a known manner. Rotation is accomplished by moving the variable speed trigger switch  110  about the pivot  266  to close the power contact  272 . The closing of the contact  272  completes a circuit allowing current to flow to the optical signal generator  274  causing light to be emitted. 
     The emitted light strikes the reflective surface  260  and a portion of the light is reflected toward the light sensor  256 . The amount of light reflected by the reflective surface  260  increases as the reflective surface  260  is moved closer to the light sensor  256 . The increased light sensed by the light sensor  256  causes increased current to be conducted by the light sensor  256  and the flow of current through the light sensor  256  causes current to flow from the collector  276  to the emitter  278 . Thus, as the intensity of the light impinging on the light sensor  256  increases, the current conducted by the light sensor  256  increases. This increase in current causes the voltage level presented by the voltage divider  280  to the timing signal generator  284  to increase. The increased signal is the variable speed signal and it causes the timing signal generator  284  to generate a timing signal in a known manner. In the depicted drill  100 , the timing signal generator  284  is a commonly known “555” timer, although other timing signal generators may be used. 
     The timing signal generator  284  generates a timing pulse having a logical on-state that corresponds to the level of the variable speed signal. This signal is presented to the gate  286  of the MOSFET  288 . When the signal present at the gate  286  is a logical on-state, the MOSFET  288  couples one of the motor terminals  238  to ground while the other motor terminal  238  is coupled to battery power through the main contact  272 . Thus, when the variable speed trigger switch  110  reaches a position where the light sensor  256  begins to detect reflected light and generate a variable speed signal, the timing signal generator  284  begins to generate a signal that causes the MOSFET  288  to couple one of the motor terminals  238  to ground. Once this occurs, current begins to flow through the MOSFET  288  and the motor  232  begins to rotate in the direction selected by the reversing button  112 . 
     The freewheeling diode  294  causes appropriate half-cycles of the current in the windings of the motor  232  to flow out of the motor  232 , through the diode  294 , and back into the motor  232  when the MOSFET  288  does not conduct in response to the timing signal being in the off-state. This action is known as freewheeling and is well known. 
     When the variable speed trigger  110  is in the full speed position, the timing signal is predominantly in the on-state and the bypass contact  296  closes. The closing of the bypass contact  296  enables the battery current to continuously flow through the motor  232  so that the motor  232  rotates at the highest speed. 
     When rotation is no longer desired, the operator releases the variable speed trigger switch  110  and the spring  264  causes the variable speed trigger switch  110  to rotate about the pivot  266  causing the bypass contact  296  to open. Additionally, the brake contact  298  closes thereby coupling the motor terminals  238 . The coupling of the two motor terminals  238  to one another through the brake contact  298  enables dynamic braking of the motor. 
     The electronic control of the tool  100  thus requires less space for the components that generate the variable speed signal than prior art control systems. Because the distance traveled by the variable speed trigger switch  110  does not have to be matched by the light signal generator  274  and the light sensor  256 , considerable space efficiency is gained. Additionally, the light signal generator  274  and the light sensor  256  do not require moving parts, so reliability is improved as well. Advantageously, the light signal generator  274  and the light sensor  256  may be mounted on the same printed circuit board  234  on which the timing signal generator  284  is mounted. 
     As the drill  100  is operated, the bit  300  is subjected to axial forces. The axial forces may result from, for example, pressure applied by the operator or by an impact on the bit. In either instance, the articulating gear system  180  is protected from damage without increasing the bulk of the components within the articulating gear system  180 . This is accomplished by directing axial forces from the bit  300  to the main housing portion  102  of the drill  100  while bypassing the articulating gear system. With initial reference to  FIG. 27 , an impact on the bit  300  tends to move the bit  300  further into the drill  100 , or to the left as depicted in  FIG. 27 . In prior art designs, not only could such a force damage the gear system, but the steel balls used to retain the bit within the bit holder would frequently jam necessitating replacement of the collet locking device. 
     As shown in  FIG. 27 , however, the cylinder pin  146  is positioned such that the tail portion  304  of the bit  300  will contact the cylinder pin  146  before the wall of the notched area  302  contacts the steel balls  150 . Thus, an axial impact will not cause the steel balls  150  to jam. Of course, the cylinder pin  146  must be made from a material sufficient to withstand the axial impact. In accordance with one embodiment, the cylinder pin  146  is made of AISI 4135 steel. 
     Referring now to  FIG. 4 , in the event of an axial impact, the force is transferred from the cylinder pin  146  to the to the bit holder  130 . The axial force is transmitted from the bit holder  130  to the bearing  132  which is located within the bearing pocket  134 . Accordingly, the axial force is transferred into the flange  152  (see also  FIG. 5 ) of the head housing  136 . The head housing  136  in this embodiment is made from aluminum alloy A380 so as to be capable of receiving the force transmitted by the bearing  132 . The force is subsequently transferred to the frame  190  and into the rib  228  of the main housing portion  102 . 
     More specifically, two paths for the transfer of axial forces are provided around the articulating gear system  180 . The first path predominantly transfers axial forces when the head housing  136  is axially aligned with the main housing portion  102 . In this configuration, axial forces pass from head housing  136  to the frame  190  primarily through the recess  212  where the head housing  136  engages the frame  190  about the hole  188  (see  FIG. 4 ) and at the shroud portion  210  where the head housing  136  engages the frame  190  outwardly of the base of the bevel gear  196 . 
     The second path predominantly passes axial forces when the head housing  136  is at a ninety degree angle with respect to the main housing portion  102 . In this configuration, axial forces are again transferred from the cylinder pin  146  to the to the bit holder  130 . The axial forces then pass primarily from the teeth  216  in the well  214  of the head housing  136  to the teeth  218  on the articulation button  120  and then to the teeth  224  in the main housing portion  102 . 
     When the head housing  136  is neither completely aligned with the main housing portion  102  or at a ninety degree angle with respect to the main housing portion  102 , axial forces generally pass through both of the foregoing pathways. Accordingly, the effect of axial forces on the articulating gear system  180  of the drill  100  are reduced. Because the articulating gear system  180  is thus protected, the articulating gear system  180  may be constructed to be lighter than other articulating gear systems. 
     In one embodiment, a printed circuit board which may be used in the drill  100  or another power tool includes a circuit that provides vibratory feedback to the operator as shown in  FIG. 30 . The vibratory feedback circuit  308  includes a microcontroller  310 , a driver circuit  312 , and motor interface circuit  314 . The driver circuit  312  in this embodiment is an integrated circuit that generates driving signals for a half-bridge circuit from a single pulse width modulated (PWM) signal, a torque limit indicating signal, which may be the same signal as the PWM signal, and a motor direction control signal. The driver circuit  312  may be a half bridge driver, such as an Allegro 3946, which is available from Allegro Microsystems, Inc. of Worcester, Mass. 
     The output of the driver circuit  312  is connected to a motor  316  through two transistors  318  and  320  which may be MOSFETs, although other types of transistors may be used. The transistor  318  may be connected to either terminal of the motor  316  through switches  322  and  324  while the transistor  320  may be connected to either terminal of the motor  316  through switches  326  and  328 . A shunt resistor  330  is coupled between the transistor  320  and electrical ground. The high potential side of the resistor  330  is coupled to the microcontroller  310  through an amplifier  332 . A power source  334  is also provided in the vibratory feedback circuit  308  and a maximum torque reference signal is provided from a torque reference source  336  which may be a linear potentiometer such as the linear potentiometer  254 . 
     The half-bridge control of the motor  316  eliminates the need for a freewheeling diode because the driver circuit  312  generates motor interface circuit signals for selectively operating the motor interface circuit  314  to control the rotational speed of the motor  316 . More specifically, a variable speed control signal  338 , which may be from a trigger potentiometer or the like, is provided to the microcontroller  310  for regulation of the rotation of the motor  316  by the microcontroller  310 . Based upon the variable speed control signal  338 , the microcontroller  310  generates a PWM signal that is provided to the driver circuit  312 . In response to the PWM signal, the driver circuit  312  turns transistors  318  and  320  on and off. 
     During typical operations, the transistor  318  is the complement of the transistor  320  such that when the transistor  320  is on, the transistor  318  is off. The rate at which the transistor  320  is turned on and off determines the speed of motor  316 . The direction of rotation of the motor  316  is determined by the position of the switches  322 ,  324 ,  326  and  328  under the control, for example, of a reversing switch. 
     The current through the motor  316  is provided through the transistor  320  and the resistor  330  to electrical ground when the transistor  320  is in the on-state. This current is related to the torque at which the motor  316  is operating. Thus, the voltage at the high potential side of the resistor  330  is related to the torque on the motor  316 . This motor torque signal is amplified by the amplifier  332  and provided to the microcontroller  310 . The microcontroller  310  compares the amplified motor torque signal to the torque limit signal established by the torque reference source  336 . The torque limit signal, which may alternatively be provided by a different type of torque limit signal generator, provides a reference signal to the microcontroller  310  that corresponds to a current through the motor  316  that represents a maximum torque setting for the motor  316 . 
     In response to the microcontroller  310  receiving a motor torque signal that exceeds the maximum torque setting for the motor  316 , the microcontroller  310  generates a braking signal that is provided to the driver circuit  312 . In response to the braking signal, the driver circuit  312  turns transistor  320  to the off-state and leaves transistor  318  in the on-state. This enables regenerative current to dynamically brake the rotation of the motor  316 . 
     As dynamic braking occurs, the torque experienced by the motor  316  decreases until the sensed torque is less than the maximum torque setting for the motor  316 . The microcontroller  310  then returns the transistor  320  to the on-state, thereby rotating the motor  316  and increasing the torque experienced by the motor  316 . In this manner, the motor  316  alternates between rotating and dynamically braking which causes the tool to vibrate and alert the operator that the torque limit has been reached. An effective frequency for providing this vibratory feedback is 30 Hz. The torque limit indicating signal that results in this operation continues as long as the trigger remains depressed. Alternatively, the microcontroller may be programmed to generate the torque limit indicating signal for a fixed duration and then to stop to reduce the likelihood that the motor will be overpulsed. 
     In one embodiment, vibratory feedback is provided for the drill  100  with the circuit shown in  FIG. 31 . The vibratory feedback circuit  340  includes a microprocessor  342 , an H-bridge driver circuit  344  and a motor interface circuit  346 . Four MOSFETs  348 ,  350 ,  352  and  354  control power to the motor  232  from the rechargeable battery pack  106  under the control of the H-bridge driver circuit  344 . A shunt resistor  356  is provided between the MOSFETs  352  and  354  and electrical ground. The signal at the high potential side of the resistor  356  corresponds to the torque being generated by the motor  232 . This motor torque signal is amplified by an amplifier circuit  358 , which may be implemented with an operational amplifier as shown in  FIG. 31 , and provided to the microcontroller  342 . The microcontroller  342  compares the motor torque signal to the torque limit signal and generates a torque limit indicating signal in response to the motor torque signal being equal to or greater than the torque limit signal. The torque limit indicating signal may have a rectangular waveform. 
     In one embodiment, the microcontroller  342  provides a torque limit indicating signal that is a rectangular signal having an off-state of at least 200 μseconds at a frequency of approximately 30 Hz. This torque limit indicating signal causes the driver circuit  344  to generate motor interface control signals that disconnect power from the motor  232  and couple the MOSFETs  348 ,  350 ,  352  and  354  together so the current within the windings of the motor  232  flows back through the motor  232  to dynamically brake the motor  232 . 
     The dynamic braking causes the motor  232  to stop. Before application of the next on-state pulse, the microcontroller inverts the signal to the direction control input of the H-bridge driver  344 . Thus, the subsequent on-state of the rectangular pulse causes the H-bridge driver circuit  344  to operate the H-bridge to couple the motor  232  to the rechargeable battery pack  106  with a polarity that is the reverse of the one used to couple the motor  232  and the rechargeable battery pack  106  prior to braking. This brake/reverse/start operation of the motor at the 30 Hz frequency causes the tool to vibrate in a manner that alerts the operator that the torque limit has been reached while preventing the bit from continuing to rotate during the clutching operation. The dynamic braking may also be used without inverting the signal. 
     In yet another embodiment, the rectangular waveform may be generated for a fixed duration, for example, 10 to 20 pulses, so the motor is not over-pulsed. Also, the microcontroller  342  may invert the direction control signal to the H-bridge driver  344  during the off-time of the rectangular waveform so that the motor  232  starts in the opposite direction each time. This action results in the net output rotation being zero during the clutching duration. Additionally, the microcontroller  342  may disable the clutching function in response to the motor direction control signal indicating reverse, rather than forward, operation of the motor  232 . 
       FIGS. 32A and 32B  show an embodiment of a circuit used in a tool that eliminates the need for mechanical contacts. The circuit  360  includes an optical speed control switch  362 , a two position forward/reverse switch  364 , a microcontroller  366 , a driver circuit  368 , an H-bridge circuit  370 , a motor  372 , a shunt resistor  374 , a motor torque signal amplifier  376 , and a torque limit signal generator  378 . In this embodiment, power is coupled to the motor  372  through the H-bridge circuit  370 , but the main contact, brake contact, and bypass contact are no longer required. Thus, this embodiment significantly reduces the number of components that are subject to mechanical wear and degradation. Because the optical control switch  362 , microcontroller  366 , driver circuit  368 , H-bridge circuit  370 , and torque signal amplifier  376  may all be implemented with integrated circuits, then ICs may be mounted on a common printed circuit and the space previously occupied by the mechanical contacts and variable signal potentiometer are gained. This construction further enables the tool components to be arranged in more efficient geometries. 
     In the circuit  360 , the optical speed control switch  362  operates as described above to generate a variable control signal from the reflection of an optical signal directed at the reflective surface of a pivoting trigger. The variable speed control signal is provided to the microcontroller  366  for processing. The microcontroller  366 , which may be a microcontroller available from Texas Instruments and designated by part number MSP430, is programmed with instructions to generate a PWM pulse with an on-state that corresponds to the level of the variable speed signal. The microcontroller  366  provides the PWM signal to the driver circuit  368  for generation of the four motor interface control signals used to couple battery power to the motor  372 . The direction in which the motor  372  is driven is determined by the contacts in the two position forward/reverse switch  364  through which a signal is provided to the microcontroller  366 . In the circuit  360 , the contacts of the two position forward/reverse switch  364  do not need to carry the current provided to the motor  372  so the contacts of the two position forward/reverse switch  364  may be smaller than contacts in other systems. The directional signal is also provided by the microcontroller  366  to the driver circuit  368  so the driver circuit  368  is capable of two directional control of current in the H-bridge circuit  370 . 
     The motor torque signal amplifier  376  provides the torque signal from the high potential side of the shunt resistor  374  to the microcontroller  366 . The torque limit signal generator  378  may be implemented with a potentiometer as described above to provide a reference signal for the microcontroller  366 . When the microcontroller  366  determines that the motor torque signal equals or exceeds the motor torque limit, the microcontroller  366  generates a torque limit indicating signal so the driver circuit  368  generates the motor interface control signals that operate the motor  372  in a manner that causes vibration. For the TD340 driver circuit, the torque limit indicating signal generated by the microcontroller  366  is a rectangular signal having an off-state of at least about 200 μseconds at a frequency of about 30 Hz. 
     While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, applicant does not intend to restrict or in any limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those skilled in the art. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.