Abstract:
A power hand drill has a subsurface object locator for detecting the presence of an object beneath a surface being probed with the locator. The drill has a housing with a flat accessory mounting surface having a pair of attachment tabs. The locator has a locator housing with a flat base and a pair of key hole slots engaged with the tabs for detachably mounting the locator housing to the accessory mounting surface of the drill housing. The locator includes sensing circuitry contained within the locator housing for detecting subsurface objects and has an object indicator mounted to the locator housing and connected to the sensing circuitry for indicating the presence of a subsurface object. A contoured surface on the locator housing provides a handrest for gripping when operating the drill.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 09/684,518, filed Oct. 19, 2001, which claims the benefit of U.S. provisional application Ser. No. 60/212,867 filed Jun. 20, 2000. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT  
       [0002]     Not applicable.  
       FIELD OF THE INVENTION  
       [0003]     This invention relates to attachments for hand drills, and in particular to a subsurface object locator attachment to a hand drill, sometimes known as a stud finder, for detecting a stud or other object behind an opaque surface, such as wall board.  
       BACKGROUND OF THE INVENTION  
       [0004]     Carpenters, electricians, do-it-yourselfers and others are often faced with the problem of locating the position of the wall studs behind the wall board material forming the wall surface. They are interested in hanging pictures, drilling holes and so on. However after the walls are finished and painted the location of the hidden substructure (i.e. the studs) is not visually detectable. The same is true of finding the location of hidden wooden frames in furniture and boats from the outside surface of the structure.  
         [0005]     Handheld electronic stud finders are well known. For example, U.S. Pat. No. 4,099,118 issued Jul. 4, 1978 discloses an electronic wall stud sensor which is suitable for detecting a wall stud behind a wall surface. This stud sensor uses electronic sensing circuitry to accurately determine the location of the stud behind the walls by activating the circuitry, holding the device near or against the wall and slowly moving the device until the stud is detected.  
         [0006]     When using a stud finder, it is often necessary to also use a power drill and screw driving device for making holes in the wall and mounting a fastener. Since the two devices are often used together it would be convenient and efficient to have a single device which would perform both functions. Unfortunately, the sensing electronics of the stud finder can be affected by other electronics making it less accurate, and thus, cannot be incorporated into the drill without suitable shielding. Moreover, the sensing circuitry needs to be held near or against the surface being probed, which would be difficult if made a part of the drill.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention provides a new device capable of efficiently finding the location of hidden objects or substrata such as studs, joists and other similar objects below the surface of walls, floors and similar type structures. The device may also be used to find the location of braces, wood frames or other substructures in wooden furniture such as tables and cabinets, wooden boats and similar type structures.  
         [0008]     Specifically, the invention provides a subsurface object locating accessory for a hand drill having a drill housing. The locator includes an accessory housing having a substantially flat surface and an attachment member for detachably mounting the accessory housing to the drill housing. The locator has sensing circuitry contained within the accessory housing for detecting subsurface objects and an object indicator mounted to the accessory housing and connected to the sensing circuitry for indicating the presence of a subsurface object.  
         [0009]     In a preferred form, the locator housing is shaped to provide a handrest for operating the drill. The substantially flat surface interfaces with the drill and an attachment member is located adjacent the substantially flat surface and forms part of a connection joining the accessory housing to the drill housing.  
         [0010]     The invention also provides a hand drill, which may be corded or cordless, that has a subsurface object locator detachably incorporated into its housing. The subsurface object locator is attached to the housing of the drill with a snap or other appropriate detachable fit, so that it may be carried to the work site as part of the drill, detached from the drill at the work site and used to probe a wall surface, and reattached to the drill housing when probing of the wall surface is finished.  
         [0011]     The locator can be moved across the wall to locate subsurface objects like wall studs. It senses any change in the dielectric constant of the wall material caused by the location of a subsurface object. It contains automatic circuitry for sensing the frequency change caused by the object and measuring the frequency shift. An LED (light emitting diode) display indicates the presence of the object.  
         [0012]     The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a cordless hand drill including a subsurface object locator of the invention;  
         [0014]      FIG. 2  is a view similar to  FIG. 1  from a different angle;  
         [0015]      FIG. 3  is a view similar to  FIG. 2  but with the subsurface object locator removed from the drill housing;  
         [0016]      FIG. 4  is a view similar to the preceding views but showing how the subsurface object locator is reattached to the drill housing;  
         [0017]      FIGS. 5   a - 5   e  are perspective ( FIGS. 5   a  and  5   b ), top ( FIG. 5   c ), side ( FIG. 5   d ), front ( FIG. 5   e ) and rear ( FIG. 5   f ) views of the main housing of the subsurface object locator;  
         [0018]      FIGS. 6   a - 6   d  are perspective ( FIG. 6   a ), top ( FIG. 6   b ), side ( FIG. 6   c ), and front ( FIG. 6   d ) views of a button for the subsurface object locator;  
         [0019]      FIGS. 7   a - 7   c  are perspective ( FIG. 7   a ), top ( FIG. 7   b ), and side ( FIG. 7   c ) views of a bottom cover for the subsurface object locator;  
         [0020]      FIGS. 8   a - 8   e  are perspective ( FIG. 8   a ), top plan ( FIG. 8   b ), side ( FIG. 8   c ), bottom ( FIG. 8   d ), and rear ( FIG. 8   e ), views of a mounting plate which forms a part of the housing of the drill and detachably mounts the subsurface object locator;  
         [0021]      FIG. 9  is a schematic diagram of a circuit for practicing the invention; and  
         [0022]      FIG. 10  is a schematic diagram illustrating the operation of the circuit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]     Referring to  FIGS. 1-4 , a drill  10  of the invention includes a subsurface object locator  12  detachably mounted to the drill housing  14 . The drill  10  as illustrated is a cordless drill, although it could be provided with a cord for power with the locator  12  in the same position. Referring particularly to  FIGS. 5   a - 5   e , the locator  12  has a main housing  16  which is contoured to fit to the shape of the housing  14  and provide a handrest  18  at the rear of the housing  16  which is contoured to fit a user&#39;s hand and provide a surface for thrusting against the rear of the drill with the users hand so as to operate the drill. The main housing  16  also has a buttonhole  20  into which the button  22  ( FIGS. 6   a - 6   d ) fits for turning on the locator. The housing  16  also has indicator light openings  24  which are covered with an appropriate lens so that an indication of when the locator  12  senses a subsurface object can be given to the user by illuminating LEDs through the windows  24  as more fully described below. In addition, the housing  16  has a tongue  26  extending from its front end which fits into a slot  27  of the housing  14  to help secure the locator  12  and align it to the contours of the housing  14 .  
         [0024]     As shown in  FIGS. 7   a - 7   c , a back plate  30  is attached to the bottom of the housing  16  by any suitable means, such as glue, ultrasonic welding or other means. A sensor plate  71  (see  FIG. 9 ) is made substantially as large as the bottom plate  30 , to maximize the sensitivity of the subsurface object locator. The circuitry of the locator is housed between the bottom plate  30  and the housing  16 , and is operated by the button  22 . Thus, to sense a subsurface object, the locator  12  is removed from the drill housing  14 , and its bottom is slid over the surface being sensed while holding down the button  22 . The indicator lights visible through openings  24  then indicate the edges of the subsurface object.  
         [0025]     Referring to  FIGS. 8   a - 8   e , and also  FIG. 3  and  FIG. 4 , a mounting plate  40  for mounting the locator  12  is fixed to the drill housing  14  by any suitable means. As illustrated, the plate  40  is fixed with a snap fit, having tabs  42  around its periphery which fit with corresponding slots or grooves in housing  14  to secure the plate  40 . Any other suitable attachment means such as screws, adhesive or other means may also be used.  
         [0026]     The plate  40  has two projections  44  with enlarged heads which fit into keyhole shaped openings  46  in the plate  30  to secure the locator  12  to the housing  14 . As mentioned above, the tongue  26  of the housing  16  fits into a correspondingly shaped opening in the housing  14  when the projections  44  are fit into the large ends of the openings  46  and the locator  12  is slid forward so as to secure it with a friction fit of the projections  44  entering the small ends of the openings  46 . Any other detachable connection of the locator  12  to the housing  14  could also be used.  
         [0027]     Shown in  FIG. 9  is a portion of a wall structure  60 , studs  61 ,  62  and wall board  63  to be illustrative of one way of operating the invention. In this case, it is desired to locate the positions of the hidden studs  61  and  62 . Although any suitable circuitry can be used, one possible circuit (shown in  FIG. 9 ) includes a metallic sensor plate  71  connected to a CMOS oscillator  70  which produces a square (or rectangular) wave output. The circuit consists of a timer IC  22 , the sensor plate and resistors. The frequency of the oscillator  70  is determined by IC  72 , the values of resistors R 1  and R 2  and the capacitance presented by the plate  71 .  
         [0028]     Referring to  FIGS. 9 and 10 , when the sensor plate  71  is above a section of the wall with no studs it will cause the oscillator  70  to run at a first frequency (f 1 ). When the sensor is above a section of the wall that has a stud below it the oscillator will have a different frequency (f 2 ). The capacitance of the plate  71  is determined by the surrounding medium including the wall material, the studs, the circuit and the person holding the device. It is desirable to reduce the stray capacitance as much as possible since this will improve the sensitivity of the plate  71 . The capacitance of plate  71  is influenced considerably by the operator and the housing of the device.  
         [0029]     Capacitance is related to its potential with respect to other objects. If an additional plate  75  is introduced in the vicinity of plate  71  with the same potential as plate  71 , it will reduce the “stray” effects. This improves the sensitivity of the plate  71  and allows it to sense further into the wall.  
         [0030]     The potential of plate  71  changes as the oscillator  70  operates. In a typical situation it may vary from 0 to 5 volts in amplitude. Hence the guard plate  75  must have its potential vary in the same way. This is accomplished by using a buffer amplifier  78 , with a gain of one, which has the voltage of the sensor plate  71  at its input and produces a near exact replica of it at its output, which is connected to plate  75  via line  77 . Hence plate  75  is driven at the same potential as plate  71 .  
         [0031]     As shown in  FIG. 10 , the sensor plate  71  is connected to the oscillator  70  and the guard plate  75  is driven from amplifier  78  so it has the same potential as the sensor plate  71 . The E-field  100  is now prevented from going in the direction of the guard plate  75 . This is because both plates are at the same potential and by electrical laws there can be no E-field between conductors of the same potential. With fewer E-field lines, there is less capacitance of sensor plate  71 . Hence it will be more responsive to dielectric changes in the direction opposite to the guard plate  75 . The guard plate  75  may be somewhat larger than the sensor plate  71  so as to extend beyond the edges of the sensor plate  71 , which redirects the E-field lines emanating from the edges of the sensor plate  71  in the direction toward the surface being probed.  
         [0032]     The microprocessor circuit  80  is programmed to measure the frequency difference f 1  minus f 2 , which can be done by any suitable means. For example, the microprocessor circuit  80  will typically include a counter. The counter can be programmed to count the number of times the oscillator output signal to the microprocessor goes high in a certain period, which yields a measure of the frequency of the oscillator output. If the frequency difference between the first measured frequency and the subsequently measured frequencies exceeds an amount deemed sufficient to indicate the presence of a stud, an LED is turned on.  
         [0033]     The circuit  80  actually has four LEDs D 2 , D 3 , D 4  and D 5  that can be activated at different amounts of frequency change. More or fewer LEDs could be used as indicators depending upon resolution and cost considerations. The circuit is powered by batteries  90  (e.g., four 1.5V pancake cells) through protective diode D 1  (e.g., a 1N270 diode) and line  92 . Resistor R 3  is used to limit the current in the LEDs. Resistor R 4  is used for a power on reset for circuit  80 . Button  22  operates switch  95  to enable power to circuit from the battery  90  to circuit  80 .  
         [0034]     Although visual LED indicators D 2 -D 5  are described here, it should be clear that audible indicators could be used as well. For example, different audible tones could be produced corresponding to various frequency differences encountered in scanning the wall, as the leading edge of a stud was approached, the frequency could go up, and as the trailing edge of the stud was passed the frequency could go down. In fact, there are occasions where audible indications may be better, such as in cases where the visible indicators may be hard to see.  
         [0035]     As the sensor is moved along the wall the frequency changes. As the frequency decreases, the circuit  80  senses this change and turns on one or more of the LEDs D 2 -D 5 . The LEDs could be turned on so as to overlap in on-times or not. In the preferred embodiment, the on-times do not overlap to preserve battery power.  
         [0036]     To use the device described, the sensor plate  71  is placed on or in close proximity to the wall where there are no studs and the button  22  is pressed which closes the switch  95 . This causes circuit  80  to be activated and it will measure the first frequency f 1  from the oscillator  70  and save it in memory. After this step is performed, which takes less than a second, the lowest LED D 3  (green) comes on and stays on as a power indicator, while the button  22  is pressed. This signals to the operator that the device can now be moved across the wall being probed. As the sensor is moved across the wall the circuit  80  is continuously measuring the second or subsequent frequency f 2  from oscillator  70  and comparing it to the first frequency f 1  by taking the frequency difference. When the difference exceeds a first threshold, the next LED up, LED D 4  (amber) will be lit and LED D 3  will go out. When the difference exceeds a second threshold, greater than the first threshold, the next LED D 5  (amber) will be turned on and LED D 4  will go out. When the difference exceeds a third threshold, greater than the second threshold and which indicates the presence of the leading edge of the stud, the highest LED D 2  (red) goes on and the LED D 5  goes out. LED D 2  stays on as the thickness of the stud is traversed by the device. When the trailing edge of the device is reached, the LEDs go off and on in the reverse sequence. Thus, a user trying to find a stud, will mark the leading edge of the stud when LED D 2  comes on, and will mark the trailing edge of the stud when the LED D 2  goes off.  
         [0037]     When a user first puts the device against a wall or other surface to be probed, there is no way of telling if it is initially placed over a stud or other subsurface object or not. The device assumes that it is not. However, if by chance it is, then the subsequently found frequency difference will be negative and unless special provision is made in the programming of the microprocessor, an error will result. It is an easy matter, however, to program the microprocessor so that if the f 1 -f 2  frequency difference is found to be negative, it means that the device was initially placed over a stud or other subsurface object. The device could be programmed to flash the LEDs or beep a buzzer in that event to alert the user to start over, placing the device in a different initial position.  
         [0038]     Referring again to  FIGS. 1-3  and  5   d , the drill housing houses a motor along an axis substantially parallel to the mounting surface  40 , and a handle portion along an axis substantially perpendicular to the mounting surface  40 .  
         [0039]     The housing  16  of the locator  12  slopes upward from the front end adjacent the tongue  26 . The sloped portion provides a grip allowing the operator to grasp the housing  16  of the locator  12  and to slide the housing  16  rearwardly for removal from the drill housing  14 .  
         [0040]     A preferred embodiment of a drill including an attachment of the invention has been described in particular detail. Many modifications and variations of the embodiment described will be apparent to those skilled in the art. Therefore, the invention is not limited to the embodiment described but should be defined by the claims which follow.