Abstract:
A fastening tool is provided with a housing having a fastener outlet. A striker is mounted for translation in the housing to drive a fastener from the fastener outlet in an unloaded position. A biasing member cooperates with the striker to urge the striker towards the unloaded position. A motor is oriented in the housing. A cam is driven by the motor, and has a cam surface in cooperation with the striker such that rotation of the cam translates the striker to a loaded position and to a release position whereby the biasing member drives the striker to the unloaded position. The cam surface is profiled to require a constant torque from the rotary input during translation of the striker to the loaded position while loading the biasing member.

Description:
TECHNICAL FIELD 
     Various embodiments relate to motor-driven fastening tools. 
     BACKGROUND 
     Power fastening tools include various driving mechanisms. One fastening tool includes a solenoid actuator that drives a blade which drives a fastener. Another fastening tool includes a motor-driven gearbox with an eccentric drive which lifts a plunger against a spring, then releases the plunger, with the spring driving the plunger and attached blade which drives the fastener. Another fastening tool includes a motor-driven gearbox that drives a linkage to compress air in a cylinder. The compressed air is then released into a smaller cylinder, driving a blade which drives a fastener. Another fastening tool includes a battery to power a device which ignites an air-fuel mixture, from which a rapid expansion within a cylinder drives a plunger and attached blade which drives the fastener. 
     SUMMARY 
     According to at least one embodiment, a fastening tool is provided with a housing having a fastener outlet. A striker is mounted for translation in the housing to drive a fastener from the fastener outlet in an unloaded position. A biasing member cooperates with the striker to urge the striker towards the unloaded position. A motor is oriented in the housing. A transmission is coupled to the motor to receive a rotary input from the motor and to provide a rotary output. A cam is coupled to the transmission to receive the rotary output. The cam has a cam surface in cooperation with the striker such that rotation of the cam translates the striker to a loaded position and to a release position whereby the biasing member drives the striker to the unloaded position. The cam surface is profiled to require a constant torque from the rotary input during translation of the striker to the loaded position while loading the biasing member. 
     According to at least another embodiment, a fastening tool is provided with a housing having a fastener outlet. A striker is mounted for translation in the housing to drive a fastener from the fastener outlet in an unloaded position. A biasing member cooperates with the striker to urge the striker towards the unloaded position. A motor is oriented in the housing. A transmission is coupled to the motor to receive a rotary input from the motor and to provide a rotary output. A cam is coupled to the transmission to receive the rotary output. The cam has a cam surface in cooperation with the striker such that rotation of the cam translates the striker to a loaded position and to a release position whereby the biasing member drives the striker to the unloaded position. The cam surface is profiled to reduce an input torque from the rotary input at an intermediate position between the loaded position and the unloaded position. 
     According to at least another embodiment, a fastening tool is provided with a housing having a fastener outlet. A striker is mounted for translation along an axis in the housing to drive a fastener from the fastener outlet in an unloaded position. A biasing member cooperates with the striker to urge the striker towards the unloaded position. A motor is oriented in the housing parallel to the striker axis. A transmission is coupled to the motor in alignment with the motor, to receive a rotary input from the motor and to provide a rotary output. A cam is coupled to the transmission in alignment with the transmission to receive the rotary output. The cam has a cam surface in cooperation with the striker such that rotation of the cam translates the striker to a loaded position and to a release position whereby the biasing member drives the striker to the unloaded position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary perspective view of a fastening tool according to an embodiment; 
         FIG. 2  is a schematic view of a drive mechanism of the fastening tool of  FIG. 1 ; 
         FIG. 3  is a graph of torque over rotation of the drive mechanism of  FIG. 2 ; 
         FIG. 4  is a graph of displacement over rotation of the drive mechanism of  FIG. 2 ; 
         FIG. 5  is a fragmentary perspective view of a fastening tool according to another embodiment; 
         FIG. 6  is an axial end view of a drive mechanism of the fastening tool of  FIG. 9 ; 
         FIG. 7  is a graph of torque over rotation of the drive mechanism of  FIG. 10 ; and 
         FIG. 8  is a graph of displacement over rotation of the drive mechanism of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     With reference now to  FIG. 1 , a fastening tool  20  is illustrated according to an embodiment. The fastening tool  20  is depicted as a fastening tool for dispensing staples and brad nails, also known as a tacker. Of course various power fastening tools are contemplated. 
     The fastening tool  20  is depicted as a handheld power tool. The fastening tool  20  has a housing  22  that is formed from a pair of housing portions, of which housing portion  24  is depicted in  FIG. 1 . The housing  22  includes a mating housing portion (not shown) to the housing portion  24  which collectively retain and enclose functional components therein. The fastening tool  20  includes a magazine  26 , as known in the art, which retains a series or strip of fasteners therein. The fasteners may be adhered together, as is known in the art. A fastener outlet  28  is provided in the housing  22  for egress of a fastener from the magazine  26 . The magazine  26  is spring-loaded to move the fasteners forward after each fastener is driven from the magazine  26 . 
     A striker  30  is mounted in the housing  22  for linear translation in the housing  22  along an axis  32  through the fastener outlet  28 . The striker  30  is referred to as a blade due to its shape and, in some embodiments, the blade  30  shears one fastener from the strip of fasteners. The blade  30  is connected to a biasing member or power spring  34  provided by a plurality of stacked leaf springs as shown, or as a singular leaf spring that is thicker that the individual springs shown. Translation of the blade  30  to a loaded position deforms the power spring  34  thereby loading the power spring  34 , such as that depicted in  FIG. 1 . At the loaded position, the blade  30  provides clearance in the magazine  26  to translate the strip to present the next sequential fastener in alignment with the fastener outlet  28 . Release of the blade  30  causes the power spring  34  to drive the blade  30  to an unloaded position thereby impacting the fastener, and driving the fastener from the fastener outlet  28  and into a workpiece. 
     A power source is provided to the fastening tool  20 , by an electrical input, which is regulated by a power switch  36 . The power source may be supplied by a cord that is plugged into an external power supply. Alternatively, the power source may be connected to a battery for a cordless power tool. The power source is connected to an electrical motor  38 . The electrical motor  38  is depicted aligned parallel to, and offset from the striker axis  32 . The motor  38  provides a rotary input to a transmission or gearbox  40  which reduces an input rotational speed from the motor  38  while increasing an output torque, which is depicted in coaxial alignment. A cylindrical cam  42  is coupled to the gearbox  40  and driven by a rotary output of the gearbox  40 , which is also depicted in coaxial alignment to the gearbox  40  and the motor  38 . The cam  42  has a cam surface  44  that is in engagement with a follower  46  on a plunger or carriage  48 . The carriage  48  is mounted for translation in the housing  22  and supports the blade  30 . Rotation of the cam  42  raises the carriage  48 , and consequently the blade  30  to the loaded position, and subsequently releases the blade  30 . Further rotation of the cam  42  reengages the follower  46  of the carriage  48  and repeats this operation. 
     The housing  22  is formed with a handle grip portion  50  for manual gripping of the fastening tool  20 . An aperture  52  is formed in the housing  22  between the handle grip portion  50  and the magazine  26  for receipt of fingers of a user. A manual actuator, such as a trigger  54  extends from the housing  22  into the aperture  52  for manual control. The trigger  54  actuates a manual switch  56  that is in electrical communication with a controller or printed circuit board  58  that may be oriented within the handle grip portion  50  for controlling power to the motor  38 . 
     Referring now to  FIG. 2 , a drive mechanism  60  of the fastening tool  20  is illustrated schematically. The drive mechanism  60  includes the power spring  34 , which is retained in the housing  22  at a proximal end  62 . The housing  22  also provides a fulcrum  64  for engaging the power spring  34  during deformation of the power spring  34 . A distal end  66  of the power spring  34  is engaged with the carriage  48 , which is supported for translation in the housing  22  by bearings  68 . The cam  42  rotates in a direction that is clockwise when viewed in a downward direction in  FIG. 2 . The cam  42  includes a helical rib  70  extending from a cylindrical body  72  of the cam  42  to provide the cam surface  44  to engage the follower  46 , which may include a roller bearing or bushing for reducing friction. 
     Prior art eccentric drives provide a sinusoidal translation of the plunger. Due to increasing force caused by deformation of a power spring, an output torque required of a motor of a prior art eccentric drive is not linear with a peak torque midway through the cycle. The prior art motor is sized based on the peak torque. Conversely, very little torque is required at the beginning of the cycle. Eccentric drives often release the blade at the loaded position and reengage almost half a rotation from release, resulting in very little work for half the cycle. 
     The inefficiencies of the prior art are minimized by the cam surface  44 . The cam surface  44  includes a slope that decreases as the carriage  48  is raised against the power spring  34 . Therefore, as the force required to deform the power spring  34  increases, the slope decreases. The slope of the cam surface  44  is greatest after engagement with the follower  46  at ‘a’ and steadily decreases until release at position ‘d’.  FIG. 3  illustrates a graph of torque τ required by the cam  42  over rotary displacement indicated by θ. After engagement of the follower  46  to the cam surface  44  at point ‘a’, the torque increases, then remains generally constant due to the decreasing slope of the cam surface  44 . 
     By levelling off the torque, the work is distributed through the cycle, thereby lowering a peak torque in comparison to prior art eccentric drives. Additionally, by offsetting the release position ‘d’ and the reengagement position ‘a’ by less than a half rotation, the work is distributed across an almost full cycle, instead of a half cycle. By lowering the peak torque, a smaller motor  38  is employed in comparison to prior art tools. The smaller motor  38  results in a smaller, more compact tool  20 , thereby improving functionality and reducing weight. The smaller motor  38  consequently uses less energy. For battery-operated tools, a larger quantity of cycles may be performed before requiring recharging or replacement of the battery. Large fluctuations of motor load generally shorten motor life; and therefore, motor life may be lengthened with a more consistent torque load. 
       FIG. 4  illustrates the slope of the cam surface  44  depicted in a Cartesian graph of displacement y, or deflection of the power spring  34 , over rotary displacement θ. The slope can be mathematically derived to allow nearly constant motor torque during lifting operations. 
     Referring again to  FIG. 2 , the cam surface includes a detent  74  to allow the spring  34  to be held partially loaded. The detent  74  is illustrated at rotational locations ‘b’ and ‘c’ in the graphs of  FIGS. 3 and 4 . After a fastener is driven from the outlet  28 , the controller  58  may begin a subsequent cycle, and stop at the detent  74  until a subsequent manual trigger pull. By holding the spring  34  partially loaded, near the release point ‘d’, a faster response to user input is provided as compared to awaiting a full cycle. The detent  74  permits the follower  46  to rest thereby avoiding back-driving a resultant torque to the transmission  40  and motor  38 . The detent  74  may be oriented at an intermediate position wherein the blade  30  is not fully raised, thereby preventing advancement of the sequential fastener. In a failure condition of the fastening tool  20 , such as an impact, a fastener is not aligned with the blade  30  to prevent an inadvertent fastener discharge. 
       FIG. 5  depicts a fastening tool  124  according to another embodiment. The fastening tool has a housing  126  that is formed from a pair of housing portions, of which housing portion  128  is depicted. The fastening tool  124  includes a fastener magazine  130 . A fastener outlet  132  is provided in the housing  126 . A blade  134  is mounted in the housing  126  for linear translation along an axis  136 . The blade  134  is connected to a carriage  138 , which is also mounted to the housing  126  for translation. A power spring  140  is provided by a compression spring. Translation of the carriage  138  to a loaded position deforms the power spring  140  thereby loading the power spring  140 . 
     A power source, such as a battery  141  is provided in the housing. A power switch  142  controls a functional condition of the tool  124 . The battery  141  provides an electrical input that is connected to an electrical motor  144 . The electrical motor  144  is depicted aligned perpendicular to the blade axis  136 . The motor  144  provides a rotary input to a gearbox  146  which reduces an input rotation from the motor  144  while increasing an output torque, which is depicted in coaxial alignment. A spiral cam  148  is coupled to the gearbox  146  and driven by a rotary output of the gearbox  146 , which is also depicted in coaxial alignment to the gearbox  146  and the motor  144 . The cam  148  has a cam surface  150  that is in engagement with a follower  152  on the carriage  138 . Rotation of the cam  148  raises the carriage  138 , and consequently the blade  134  to the loaded position, and subsequently releases the blade  134 . Further rotation of the cam  148  repeats this operation. 
     The housing  126  is formed with a handle grip portion  154  for manual gripping of the fastening tool  124 . An aperture  156  is formed in the housing  126  between the handle grip portion  154  and the magazine  130  for receipt of fingers of a user. A trigger  158  extends from the housing  126  into the aperture  156  for manual control. The trigger  158  actuates a manual switch  160  that is in electrical communication with a controller or printed circuit board  162  that may be oriented within the handle grip portion  154  for controlling power to the motor  144 . 
       FIG. 6  illustrates the cam  148 , which is configured for torque and displacement similar to the first embodiment. Translation of the blade  134 , and loading of the spring  140  occurs between points ‘a’ and ‘d.’. The cam  148  includes a detent  164  at points ‘b’ and ‘c’ for a temporary reduction of torque.  FIGS. 7 and 8  illustrate similar torque C versus displacement D and deflection y versus displacement D characteristics to the first embodiment. Orientation of the motor  144  and gearbox  146  horizontally permits different packaging of the fastening tool  124 . 
     While various embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.