Abstract:
An improved interface for releasably connecting a power control module or battery pack to an electrical appliance or tool. The power control module includes a power control trigger and provides electrical power to a motor of the appliance. The power control switch is located on the appliance, and is actuated by a portion of the trigger extending through the interface. The interface includes a pair of dovetail connections with interlocking flanges, requiring a two-motion procedure for assembly and disassembly. A latch release assembly interacts with the trigger to avoid powering the motor during assembly, and to prevent disassembly with the trigger pulled.

Description:
TECHNICAL FIELD 
     This invention relates generally to portable electrical power tools, and specifically to interfaces for releasably connecting power control modules to electrical appliances, and to methods of connecting such interfaces. 
     BACKGROUND OF THE INVENTION 
     Electrical power tools are in widespread use, and with improving battery technology, cordless tools are becoming lighter, more efficient and more common. Any given user may have several such tools for performing different functions around the home, garden or job site. There have been many attempts at designing such tools to be modular, in order to avoid unnecessary duplication of hardware common to all of a user&#39;s power tools. 
     The design of the interface between common and specific modules is critical to the safety and reliability of such a modular system. When transferring electrical power or signals across such an interface, care should be taken to ensure reliable electrical contact. In addition, the modules should lock together in a manner which avoids inadvertent separation. 
     Modular cordless systems, in which a common module contains a storage battery and task-specific modules contain electric motors, require electrical power to be transferred across the module interface. It is important in many applications that motors of such tools not be inadvertently energized during assembly and disassembly of the common module, or battery pack, with any given task-specific module, or tool chassis. 
     SUMMARY OF THE INVENTION 
     The invention features an improved interface for releasably connecting an electrical appliance and a power control module having a power control trigger and being adapted to provide electrical power to a motor of the appliance. 
     According to one aspect of the invention, the interface (which defines an interface plane between the appliance and power control module) includes a flange extending from one of the module and appliance and arranged to be inserted through an aperture in the other of the module and appliance as the module and appliance are moved toward the interface plane in a disengaged position. The other of the module and appliance defines a corresponding slot to receive the flange as the module and appliance are subsequently slid across one another along the interface plane to an engaged position. The interface also includes a latch extending from one of the module and appliance to engage a detent of the other of the module and appliance, to releasably retain the module and appliance in their engaged position. A first electrical contact, attached to one of the module and appliance, is arranged to engage a second electrical contact attached to the other of the module and appliance with the module and appliance in their engaged position, to transfer electrical power from the module to the appliance. 
     In some embodiments, the interface also includes an actuator extending from the power control module and operable by the trigger. The actuator is arranged to engage an electrical switch mechanism of the appliance to control a flow of electrical current from the power control module to the appliance. 
     The actuator, in some instances, is a lever extending from the power control module and adapted to move in a direction along the interface plane to depress the electrical switch mechanism as the trigger is actuated. 
     In some cases, one of the module and appliance also includes a latch release mechanism exposed for manual operation to and adapted to release the latch to enable the module and appliance to be moved to their disengaged position. Preferably, the latch release mechanism is constructed and arranged to physically block operation of the actuator while the latch release mechanism is operated. It is also preferred that the actuator be constructed and arranged to physically block operation of the latch release mechanism while the trigger is actuated. 
     The latch release mechanism may include a pair of depressible buttons, which may be connected by a resilient member, disposed on opposite sides of one of the module and appliance, for example. 
     In some preferred configurations, the interface is constructed and arranged to allow moving the module and appliance to their engaged position without operating the latch release mechanism. 
     In some cases, the actuator is constructed to engage and retain the latch release mechanism in a non-latched position when the trigger is pulled while the latch release mechanism is in its non-latched position. For example, the actuator may define an undercut engageable by a hooked protrusions extending from opposing ears of the latch release mechanism. 
     In a presently preferred embodiment, the latch and latch release mechanism are components of the appliance. 
     In some embodiments, one of the module and appliance has two flanges extending in opposite directions generally parallel to the interface plane and perpendicular to the slot. The other of the module and appliance defines two slots, arranged in opposition, for receiving the flanges with the module and appliance in their engaged position. 
     The one of the module and appliance having the two flanges also has, in some configurations, an auxiliary flange spaced apart from, and parallel to, the two flanges. The other of the module and appliance further defines a third slot, of different dimensions than the other two slots, for receiving the auxiliary flange as the module and appliance are moved to their engaged position. 
     Preferably, the interface is constructed and arranged to permit the flange to be inserted through the aperture with the module and appliance in only one orientation. 
     In some preferred interfaces, the first and second electrical contacts extend along the interface plane such that the contacts slide across one another as the module and appliance are moved toward their engaged position. 
     According to a second aspect of the invention, the interface includes a wide dovetail portion extending from the appliance and arranged to be inserted, through an aperture in the power module, toward the interface plane with the module and appliance in a disengaged position. The power module defines a first slot to receive the wide dovetail portion of the appliance as the power module and appliance are subsequently slid across one another along the interface plane to an engaged position. The interface also includes an actuator extending from the power control module and operable by the trigger. The actuator is arranged to engage an electrical switch mechanism of the appliance to control a flow of electrical current from the power control module to the appliance. Furthermore, the interface includes a latch extending from the appliance to engage a detent of the power module, to releasably retain the module and appliance in their engaged position. The latch is operable by a latch release mechanism exposed for manual operation on the appliance. The interface also includes an electrical contact attached to the power module and arranged to engage an electrical contact of the appliance with the module and appliance in their engaged position, to transfer electrical power from the module to the appliance. 
     In some cases, the power module also defines a second slot, spaced apart from the first slot along the interface plane and adapted to receive a narrow dovetail portion extending from the appliance, as the module and appliance are slid along the interface plane toward their engaged position. Preferably, the wide dovetail portion is between about 75 and 85 millimeters in width, as measured across the interface plane, and the narrow dovetail portion is between about 55 and 65 millimeters in width, as measured across the interface plane. 
     According to a third aspect of the invention, the interface includes flanges on each of the power control module and appliance, a latch pawl, electrical contacts on each of the power control module and appliance, an actuator, and a latch release. The flanges are arranged to overlap as the power module is slid along the interface plane, to an engaged position on the appliance. The latch pawl extends from the appliance to engage a detent of the power control module, to releasably retain the module in its engaged position. The contacts are arranged for electrical engagement when the module is in the engaged position, to transfer electrical power from the module to the appliance, and the actuator extends from the power control module to activate an electrical switch of the appliance when a trigger of the power control module is actuated. The latch release mechanism is exposed for manual operation to retract the latch pawl and physically block activation of the electrical switch by the actuator during power control module installation and removal. 
     According to a fourth aspect of the invention, a power control module, for providing power to a portable electrical appliance, includes a housing having a mounting face configured for releasable attachment to a corresponding face of the electrical appliance. The mounting face defines an aperture for receiving a flange of the appliance face as the housing and appliance faces are moved toward one another in a disengaged position, and a slot contiguous with and extending from the aperture along the mounting face, for receiving the flange of the appliance face as the housing and appliance faces are slid across one another to an engaged position. An electrical contact of the power control module extends from the housing and is exposed to engage a mating contact of the appliance as the housing and appliance are moved to their engaged position. The contact is adapted to transfer electrical power from the power control module to the appliance. A trigger is movably attached to the housing and exposed to be manipulated by an operator to control the appliance. 
     In some embodiments the power control module also includes a battery contained within the housing (which may define a graspable handle, for instance) and electrically connected to the electrical contact. 
     In some cases, the power control module is adapted to receive electrical power from an external power source while attached to the appliance. The power control module may include, for instance, an electrical cord for plugging the module into an AC electrical outlet. 
     In some cases, the power control module has an external contact for connection to an external DC power source. 
     Various embodiments of the power control module have one or more of the features discussed above with respect to the interface of the invention. 
     According to a fifth aspect of the invention, a portable electrical appliance is configured to accept, in a releasable attachment, the above-described power control module. The portable electrical appliance, adapted to be powered by the removable power module, includes an electrical motor arranged to do useful work and has a power module mounting face with two sets of outwardly extending flanges and an electrical contact for receiving electrical power from the power module for driving the motor. The two sets of flanges are spaced apart, in a direction parallel to the slots, for receiving a mating set of flanges of the power module between them in a first assembly motion. The two sets of flanges overhang associated slots adapted to receive mating flanges of the power module during a second assembly motion, generally perpendicular to the first assembly motion, to retain the power module on the appliance. 
     In some cases, one set of the flanges extends over a greater width, measured in a direction perpendicular to the slots, than the other set of flanges. In a presently preferred embodiment, the wider set of flanges extends over a width of about 82 millimeters. 
     The appliance also includes, in some instances, a latch extending outwardly into one of the overhung slots and adapted to engage a detent of the power module to releasably retain the module and appliance in an engaged position. 
     According to a sixth aspect of the invention, an improved portable electrical power tool is provided. The tool includes an appliance and a removable power module. The appliance has an electrical motor arranged to do useful work, and a housing with a mounting face having an extending flange and an electrical contact for receiving electrical power. The removable power module has a housing with a mounting face configured for releasable attachment to the mounting face of the appliance housing. The mounting face of the power module housing defines an aperture for receiving the flange of the appliance mounting face as the mounting faces are moved toward one another in a disengaged position. The mounting face of the power module also defines a slot, contiguous with and extending from the aperture along the power module mounting face, for receiving the flange of the appliance mounting face as the mounting faces are slid across one another to an engaged position. The power module also includes an electrical contact and a trigger. The electrical contact extends from the power module housing and is exposed to engage the contact of the appliance as the power module is moved to its engaged position. The contact is adapted to transfer electrical power from the power control module to the appliance. The trigger is movably attached to the power module housing and is exposed to be manipulated by an operator to control the appliance. 
     In some embodiments, the removable power module is a battery pack containing at least one electrical storage battery. The battery may be adapted to be recharged through the electrical contact extending from the power module housing, and may be adapted to be recharged within the battery pack while the battery pack is installed on the appliance. 
     In some preferred embodiments, the power tool is an outdoor home gardening tool, such as a trimmer, blower, cultivator, pruning saw, hedge trimmer or the like. The power tool may also be a woodworking tool, such as a circular saw or sander, or other useful device, such as a light or a vacuum-cleaner, for example. 
     According to a seventh aspect of the invention, a method of releasably installing a removable power control module on an electrical appliance is provided. The method includes the steps of 
     (1) bringing the mounting faces of any of the above-described appliances and power modules together in face-to-face relation in a disengaged position, while inserting the flange of the appliance housing into the aperture of the power module housing mounting face; and 
     (2) while holding the latch release mechanism in an actuated state, sliding the power module and appliance mounting faces across one another in a predetermined direction to an engaged position, the flange of the power module mounting face being received within the slot of the appliance housing mounting face and the electrical contact of the power module engaging the contact of the appliance housing. 
     The invention can provide a safe, reliable interface between power-providing and power-consuming modules of a power tool system. Undesirable power transfer during assembly and disassembly can be avoided, and the two-motion procedure required to expose the contacts and separate the interface can help to protect from accidental release as well as requiring a desirably small amount of overall travel for engagement. By locating the trigger in a handle on the power pack, a comfortable weight distribution can be established. By locating the power switch within the power-consuming module, the switch may be efficiently matched to the power requirements of the associated motor and be selected to provide a mode of control appropriate for the given tool. Furthermore, inadvertent energization of the motor by voltage accidentally applied to the exposed contacts of the power-consumption module can be avoided. In addition, the number of electrical contact points at the interface can be kept to only two, through which the battery may be directly charged without the need for actuating any switches on the power module. 
     Other advantages and embodiments will be apparent from the following description, the drawings and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a power trimmer. 
     FIGS. 2A-2C sequentially illustrate the installation of the battery pack onto the trimmer of FIG.  1 . 
     FIGS. 3A-3D illustrate other power tools adapted to be powered by the power pack of FIG.  2 . 
     FIG. 4 is a perspective view of the power pack, showing its mounting face. 
     FIG. 5 is a cross-sectional view, taken along line  5 — 5  of FIG.  4 . 
     FIG. 6 is a perspective view of the battery pack mounting face of the trimmer chassis. 
     FIGS. 7A and 7B illustrate the latch release allowing and inhibiting, respectively, operation of the trigger switch. 
     FIG. 8 is a perspective view of a one-piece latch release. 
     FIG. 9 shows the battery pack being mounted to a recharging station. 
     FIG. 10 is a side view of a corded electrical power module. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to FIG. 1, power string trimmer  10  consists of a motorized chassis  12  and a removable battery pack  14 . Chassis  12  includes a head  16  with an internal electric motor (not shown) arranged to drive a partially shielded rotary string hub  18  with an extending string element  19  for cutting weeds and grasses. Head  16  is connected to an upper chassis housing  20  by a tube  22  through which wires conduct electrical power from battery pack  14  to the motor of head  16 . The trimmer is held by both hands in use, with a forward stirrup grip  24  and a rear handle  26  on the battery pack. A forefinger-operable trigger  28  in handle  26  controls the flow of power from the battery pack to the trimmer motor, and a trigger lock  30  automatically locks the trigger in its “off” position until actuated, preventing inadvertent trigger operation. 
     Referring to FIGS. 2A-2C, battery pack  14  is readily attached to the upper chassis housing  20  of the trimmer in a two-motion sequence. First, as shown in FIG. 2A, the mounting faces of the battery pack  14  and upper chassis housing  20  are brought together in a motion perpendicular to the faces (indicated by arrow “A”) with the alignment indicator  32  of the battery pack housing aligned with an “unlocked” indicator  34  of the upper chassis housing. At the end of this first motion, the battery pack  14  and upper chassis housing  20  are positioned as shown in FIG.  2 B. Next, the battery pack and upper chassis housing mounting faces are slid across one another along their interface plane  35 , as indicated by arrows “B” in FIG. 2B, until alignment indicator  32  is aligned with a “locked” indicator  36  of the upper chassis housing  20 , and the mounting latch (discussed below with respect to FIGS. 6-8) snaps into place to securely retain the battery pack in place upon the upper chassis housing. Indicators  32 ,  34  and  36  are integrally molded as features of the plastic housings of the battery pack and upper chassis, and feature appropriate icons. 
     To remove battery pack  14  from upper chassis housing  20 , the sequence of FIGS. 2A-2C is reversed. First, the user depresses a pair of latch release buttons  38  located on either side of the upper chassis housing (only one is shown in these views). Depressing the latch release buttons releases a battery pack mounting latch (not shown) and enables the user to slide the two mounting faces across each other to the position shown in FIG. 2B, where they may be separated perpendicularly as shown in FIG.  2 A. With the battery pack mounted as shown in FIG. 2C, the internal configuration of the trigger mechanism and the mounting latch, as discussed in more detail below, disallows depressing latch release buttons  38  while trigger  28  is pulled, and disallows pulling the trigger while the latch release buttons are depressed. Thus, the trigger and latch cooperate to prevent contact arcing and inadvertent energizing of the trimmer motor during battery pack mounting and detachment, as well as accidental unlatching of the battery pack  14  from the chassis  12  (FIG. 1) while the power consuming device is operating. 
     Cordless battery pack  14  may be employed to power a large variety of power tools and equipment. For example, FIGS. 3A-3D illustrate, in order, string trimmer chassis  12 , a leaf blower  40 , a long reach hedge trimmer  42 , and a pruning saw  44 . Each tool is provided with a similar battery pack mounting face  46  adapted to receive the battery pack. Other portable cordless electrical tools, such as hand-held vacuum cleaners, paint sprayers, cultivators, rotating brushes, high-power flashlights and the like, are also envisioned. Thus, one or two battery packs may be employed to sequentially operate an entire suite of tools and appliances. 
     The battery pack mounting configuration will now be more fully discussed. As shown in FIG. 4, battery pack  14  has left and right housing halves  48  and  50  of injection molded ABS plastic, joined along line  52  and held together by a series of threaded fasteners accessed through sockets  54 . Together, housing halves  48  and  50  form a generally flat mounting face (the near end of the battery pack, as shown in FIG. 4) for securing the battery pack to any one of the tools discussed above. At the mounting face, the housing halves form two sets of opposed, inwardly facing flanges  56   a  and  56   b,  and  58   a  and  58   b,  which define undercuts for receiving outwardly facing flanges of the mounting face of the mating tool. Adjacent flanges  56   a  and  56   b,  the extensions of the two housing halves are spaced apart to define a wide aperture  59  of width “W a ” of about 84 millimeters (mm), with the inner edges of flanges  56   a  and  56   b  separated by only about 72 mm. Slots  60  beneath flanges  56   a  and  56   b  receive cooperating flanges of the mating tool, which are first inserted through aperture  59  during the motion illustrated in FIG.  2 A. During battery pack disengagement, overhanging chamfers  61  at the lower edge of aperture  59  catch the mating tool flanges when the two mounting faces are slid apart beyond the aligned position shown in FIG.  2 B. To clear chamfers  61 , the tool housing must be first moved slightly back toward its locked position to align the tool flanges with aperture  59  and completely separate the battery pack from the tool. 
     Flanges  58   a  and  58   b  are separated by only about 50 mm, and overhang slots  62  which receive a corresponding set of outwardly facing flanges of the mating tool. The difference in separation widths between the two sets of opposing flanges helps to key the battery pack mounting to disallow mounting in all but the intended orientation. At the inner end of slots  62 , a molded wall  64  provides, together with the curvature of the upper end  66  of the mounting face, a firm stop for the motion illustrated in FIG.  2 B. 
     As shown, all of the mounting flanges are molded with double wall construction for rigidity and strength. The inner walls of flanges  56   a  and  56   b  are relieved to form covered pockets  68  for receiving the pawls of the mounting latch discussed below. With the battery pack mounted, the pawls of the mounting latch of the tool engage perpendicular edges  70  of pockets  68  to lock the battery pack in place. 
     Extending from the mounting face between flanges  58   a  and  58   b  are a pair of phosphor bronze electrical contacts  72  in electrical communication with a rechargeable storage battery (not shown) within the battery pack. Contacts are secured to a terminal board  74  secured to the battery pack housing and forming a central rib  76  extending between the contacts to help avoid shorting. 
     Also extending from the mounting face is a switch actuator  78  which, with the battery pack mounted, is arranged to operate a power switch of the tool (not shown) when moved parallel to the mounting face by depressing battery pack trigger  28  (FIG.  1 ). 
     A charging port  80  in the underside of the battery pack accepts a direct current (DC) power plug for recharging the battery when not in use, and blind pockets  81  molded into the underside of the housing are for locating the battery pack on an optional charging saddle or for hanging the battery pack against a vertical surface. 
     Referring to FIG. 5, switch actuator  78  and trigger  28  are portions of a single, unitarily molded acetal polymer lever  80  which is rotatably secured to the battery pack housing at a pivot  82 . Thus the trigger linkage “reaches through” the interface plane, into the tool, to operate a switch located within the tool. This enables the switch itself to be sized appropriately for the power requirements of the tool motor, which may vary between different tools. When trigger  28  is pulled in the direction of arrow “C” (as shown in solid outline), actuator  78  is moved downward, in the direction of arrow “D”, and an integrally molded finger  83  extending rearward from trigger  28  is deflected against a protrusion of the housing. When the trigger is released, the spring force of the deflected finger  83  biases the actuator upward and returns the trigger to the released position shown in dashed outline. A projection  84  extends from the upper surface of trigger  28  to interact with trigger lock  30 , which is biased rearward by a molded cantilever finger  85  of lock  30  which is deflected against a fixed housing projection with lock  30  in a forward, trigger-releasing position as shown. With the lock “off” (as shown), the trigger is readily depressed. When the trigger is subsequently released, the spring force of cantilever finger  85  moves the lock rearward (in the direction of arrow “E”), where the underside of the lock interferes with projection  84  and prevents pulling of the trigger until lock  30  is again released by holding the lock forward while pulling trigger  28 . 
     Enclosed within the battery pack housing is a storage battery  86  with sufficient capacity to operate any of the associated tools over an extended period of time. In one presently preferred embodiment, battery  86  is of the sealed lead acid (SLA) type, but nickel-cadmium (NiCAD), nickel-metal hydride (NiMH) or any other type of rechargeable battery may be employed. Preferably, battery  86  has an operative capacity of at least about 5 amp-hours. Battery  86 , in this embodiment, operates at a nominal DC voltage of about 12 volts and a normal operating current for powering the string trimmer is about 8 to 12 amps continuous. 
     Referring to FIG. 6, the mounting face of the upper tool housing  20  of the trimmer chassis has both wide and narrow dovetail portions  88  and  90  that mate with the flanges of the mounting face of the battery pack housing. Wide dovetail portion  88  has outwardly extending flanges  92   a  and  92   b  that extend over a width “W b ” of about 82 mm and defines a channel  94  for receiving the switch actuator of the battery pack. A switch (not shown) in the base of the channel opens and closes an electrical circuit through the tool motor (also not shown). Flanges  92   a  and  92   b  overhang slots  96  along the sides of the wide dovetail portion into each of which a moveable latch pawl  98  extends. Narrow dovetail portion  90  has outwardly extending flanges  100   a  and  100   b  that extend over an overall width of about 48 mm and overhang slots  102  along the sides of the narrow dovetail portion. 
     Enclosed within narrow dovetail portion  90  are a pair of electrical contacts  104  in electrical communication with the tool motor (not shown) through the tool power switch (also not shown). Contacts  104 , similar in construction to contacts  72  of the battery pack (FIG. 4) are mounted to a terminal board  74  with a central rib  76 . The outer surfaces of contacts  104  (and contacts  72  of FIG. 4) are all sloped with respect to the interface plane between the battery pack and tool housings. During engagement, the contacts are arranged to slide over one another, helping to wipe excess oxidation and other non-conductive material from their contact surfaces. The sloped design also helps to ensure that electrical contact is made only along a very narrow band (so-called “line contact”) at the outer portions of the contacts. 
     The wide and narrow dovetail portions of the mounting face of the trimmer housing are also provided with tapered ribs  106  on both inner and outer faces of flanges  92   a,    92   b,    100   a  and  100   b.  Ribs  106  help to minimize tolerance play between the battery pack and chassis housings, and also reduce sliding friction by ensuring sliding contact only along the narrow tops of the ribs. Thus, the dovetail joint provides a tight, secure fit with minimal engagement/disengagement effort. 
     FIGS. 7A and 7B illustrate the interaction of the latch release of the tool and the switch actuator of the battery pack. During battery pack mounting and dismounting (FIG.  7 B), the two ears  108  of the latch release come together between actuator  78  and power switch  110  (i.e., into channel  94  of FIG. 6) to prevent the actuator from depressing the plunger  112  at the top of the switch. During assembly of the battery pack to the tool, forward chamfers  111  on pawls  98  help to automatically retract ears  108  as the battery pack is slid to its engaged position, without the user having to depress the latch release buttons. When the battery pack is in its mounted position (as in FIG.  2 C), the latching pawls  98  at the outer ends of latch release ears  108  snap into the latch pockets  68  of the battery pack housing (FIG.  7 A), with ears  108  sufficiently separated to allow passage of actuator  78 . With the trigger pulled, and actuator  78  engaging switch  110 , the actuator blocks the inward movement of ears  108  and prevents the user from releasing the latch. If the trigger is inadvertently pulled while the latch is in the position shown in FIG. 7B, hooked protrusions  113  engage a corresponding undercut  115  of actuator  78  to prevent the latch ears from separating and exposing switch  110  until the trigger is released. Switch  110  in the string trimmer embodiment is a non-latching, push-on, release-off switch. For some other tool applications, variable-resistance switches are employed to control variable-speed motors, for example. By locating the switch on the interchangeable tool chassis instead of on the battery pack, various switch types may be employed for different tools, as desired. 
     As shown in FIG. 8, latch release  114  is a unitarily molded, plastic member with two pair of parallel beam flexure members  117  extending from a rear cross-member  116  to act as flexure springs to bias ears  108  and buttons  38  of the latch release apart toward an unstressed position. The parallel beam arrangement helps to provide a nearly linear motion of ears  108  and buttons  38  during latch release and engagement. The flexure of members  117  can be seen, for instance, by comparing FIGS. 7A (members straight) and  7 B (members flexed). 
     FIG. 9 shows a recharging cradle  118  with a mounting face  120  similar to that described above with respect to FIG. 6, but without a latch. When not in use, battery pack  14  is cradled within the charger, engaged against face  120 , to recharge its internal battery. Cradle  118  includes appropriate transforming and rectifying circuitry to provide a desired DC voltage for charging directly through the contacts  72  (FIG. 4) of the battery pack. Alternating current (AC) power is received through a standard grounded pigtail  122  from a wall outlet (not shown). Status lights  124  indicate battery pack charging and mounting status. Cradle  118  may be either rested on a table or hung on a vertical wall surface. 
     Referring to FIG. 10, a corded power pack  126  is adapted to power the tools illustrated in FIGS. 3A-3D, but has an electrical cord  128  for accepting AC voltage, instead of a DC storage battery. Its housing contains the necessary power conversion circuitry (not shown) for converting  110  volt AC power to DC power of the desired voltage. 
     Other embodiments are within the scope of the following claims.