Power hand tool having a proximity detector

[0001] This invention relates to power hand tools, and more specifically, to power hand tools that have a proximity detector that detects when an operator is in position to operate the tool and automatically illuminates a light or provides a safety function.

[0002] Power tools including relatively small portable handheld power tools are commonly used in a wide variety of locations and lighting conditions, including those where the available light may be poor for a variety of reasons. It is common to use a work light or a flashlight in such situations. However, it is often inconvenient to hold the light in the correct position at the same time one is using the hand tool. If there is no place to clamp or hang a light, the operator of the tool must then hold the tool and the light steady while attempting to utilize the tool. This is particularly inconvenient if the operator is atop a ladder or in a situation where one of his/her hands is needed for another purpose.

[0003] The present invention is directed to a power hand tool with an automatic hand proximity detector that preferably senses the presence of the hand and turns on a light to illuminate the work piece. The proximity detector can also be used as a safety interlock for de-energizing a portable power tool of the type which uses an on-off switch to activate it, such as a router, for example.

[0004] FIG. 1 is a side plan view of a tool embodiment of the present invention;

[0005] FIG. 2 is a schematic diagram of a trigger circuit for the tool of FIG. 1;

[0006] FIG. 3 is a side plan view of a second embodiment of the invention having an IR emitter; and,

[0007] FIG. 4 is a schematic diagram of a preferred trigger circuit for the tool of FIG. 3.

[0008] The preferred embodiment of the present invention is a portable power hand tool with a proximity detector disposed in the housing to sense the hand of an operator and turn on a light, preferably a light emitting diode, that is also disposed in the housing. A trigger circuit is located within the housing and is connected to the detector, the light and a power source. The trigger circuit also includes a switch for connecting the power source to the light when the detector detects the presence of the user's hand.

[0009] Turning now to the drawings and referring to FIG. 1, a hand-operated power drill, designated generally 10, is illustrated, but many other power hand tools are suitable for use with this invention, such as circular saws, screwdrivers, routers, and the like. The drill includes a housing 12 having a detector 14 and a light 16 disposed therein. A trigger circuit, designated generally at 20 in FIG. 2, is located within the housing and is connected to the detector 14, the light 16 and an AC power source via lines 22. When the operator picks up the drill 10 to use it in a normal manner, the detector 14 senses the user's hand causing the circuit 20 to turn on the light 16 and illuminate the work area. After normal use, when the operator sets down the drill 10 and removes his hand, the electrical response of the detector 14 causes the circuit 20 to cut off power to the light 16.

[0010] Many types of detectors 14 capable of sensing the proximity of the operator's hand can be used with the present invention. Preferred detectors 14 include a photocell or an infrared sensor, although a capacitance detector of the type which detects a change in frequency of a base signal due to the proximity of one's hand can be used. Alternatively, any detector that senses an inherent property of one's hand, such as its heat, resistance, capacitance, ability to block light, reflectance, magnetic properties and the like are within the spirit and scope of the present invention. Most preferably, consistent operation of the detector 14 should not depend on the use of work gloves or other coverings to protect the hand.

[0011] The detector 14 is located in the housing 12 and positioned to sense the user's hand during the normal operation of the drill 10. Generally, when the user grips a drill, the hand is wrapped around a handle portion 26, with the palm positioned against a side of the handle 26 and one or two fingers on a trigger 28 that controls the drill speed. The remaining fingers generally wrap around the front 32 of the handle 26, while the thumb and thumb pad wrap around the back 34 of the handle for stability. The preferred location for the detector 14 is in an area of the handle 26 that is covered by the hand of either a right or a left-handed user. Most preferably, the detector 14 is located on the front 32 of the handle 26, below the trigger 28, where the ring finger and the small finger wrap around the front 32 of the handle 26, or at the back 34 of the handle opposite the trigger, where the palm or the hand or the thumb pad wrap around the back 34 of the handle 26.

[0012] The light 16 is also disposed in the housing 12. Any type of small lamp 16 of a size suitable for use on the housing 12, including flashlight bulbs may be used in this invention, but the lights 16 are preferably light emitting diodes (LEDs) due to their long life, small size and low power usage. In this regard, one or more high-intensity, white LEDs 16 are especially suitable for use with this invention as they produce large amounts of light. In the embodiment of FIG. 1, the light 16 is located in a lower portion 40 of the handle 26, but it may be located elsewhere on the housing 12 provided that it is capable of illuminating the workpiece. A lens 46 may be provided to concentrate the light in the vicinity of the work piece and/or to provide an esthetically pleasing appearance and also to provide protection for the LED.

[0013] Referring now to FIG. 2, the trigger circuit 20 controls the operation of the light 16 in response to the electrical signal from the detector 14 and is located within the housing 12, preferably in the handle 26 of the drill 10. The circuit is preferably powered from an AC power source via the cord 22, although it could be modified to be powered from a DC source such as an internal battery.

[0014] The characteristics of the electrical circuit change depending on the kind of the detector 14 that is employed. If the detector 14 is a photocell, resistance of the photocell 14 changes as it receives various amounts of light. Its resistance is high when the photocell 14 detects a dark condition (i.e., the presence of a hand over the detector), inhibiting flow of electricity through that portion of the circuit 20. However, when exposed to light, its resistance drops, which increases current flow.

[0015] The trigger circuit 20 electrically connects the detector 14, the light 16 and the power source to control power to the light 16 in response to the operation of the detector 14. The AC source is connected by line 22 to a capacitor 46 and a first resistor 48 which are in turn connected to an AC to DC converting rectifier bridge comprising four diodes 50 in circuit. The capacitor 46 acts a large AC resistance and the resistor 48 limits the initial current applied to the capacitor 46 and thereby protects the remaining circuitry from any power surges, including any initial power surge experienced when the drill 10 is first connected to the AC power source.

[0016] Since the circuit 20 operates in a constant current mode and preferably should not exceed a maximum voltage, the output of the bridge appears on line 52 and it is connected to a Zener diode 54 which reversibly breaks down when the voltage on line 52 exceeds a predetermined level. This occurs when the photocell 14 has a low resistance when it detects a bright light condition and the light 16 is turned off, thereby not using any current. When the photocell 14 detects a dark condition or hand being present, and results in the light 16 being illuminated by operation of the circuit 20, thereby drawing current, and the voltage applied to the Zener diode 54 drops below the breakdown value, and the Zener diode 54 stops current flow through it. The total constant current is in this manner shared between the light 16 and the Zener diode 54. The exact breakdown value of the Zener diode 54 is chosen depending on the type and voltage of the light 16 and other circuit considerations known to those of ordinary skill in the art. For a white LED 16, the Zener diode 54 is preferably of the common 5.1 volts breakdown type.

[0017] The trigger circuit 20 includes a resistor 56, which with the detector 14 creates a voltage divider to a gate 58 of a switching transistor 60. The transistor 60 is connected to line 62 that is connected to a resistors 64 and 66 and also to ground 68. The resistor 66 is connected to base 70 of a switching transistor 72 the emitter 74 of which is connected to the light and the collector of which is connected to ground 68. When the photocell 14 detects a bright light condition, its resistance is low and the transistor 60 is switched off which keeps the transistor 72 also in a non-conducting state. When the photocell detects a dark condition, the transistor 60 is switched on, which in turn causes the base of transistor 72 to go to a low voltage and place the transistor 72 into conduction which activates the light 16. Thus, the circuit 20 provides power from the power source to the light 16 when the detector 14 detects the presence of the operator's hand.

[0018] With regard to the circuit components, it has been found that a MOSFET transistor is suitable for transistor 60, with its drain 62 controlling the base 70 of a bipolar junction transistor 72. When the second conventional PNP transistor 72 is used, the light 16 tends to have a sharper transition between on and off. Although this may be desirable in some circumstances, the use of the second bipolar transistor 72 in the circuit may be considered optional. It should be understood that the MOSFET 60 may be replaced by another type of electronic triggering component, such as a comparator, and is considered to be within the scope of the present invention.

[0019] When the detector 14 is an infrared (IR) sensor, two types are optionally used. IR sensors 14 that detect the warmth of the hand are used in essentially the same manner as that shown in FIGS. 1 & 2. However, FIGS. 3 & 4 show a second embodiment 110 which require the presence of an IR emitter 182, as shown in a second embodiment of the tool 110 shown in FIG. 3. The presence of the operator's hand is detected by interruption of the IR beam 184 between the emitter and the detector 114. The IR emitter 182 and the detector 114 are suitably placed anywhere on the housing 112 that causes interruption of the IR beam 184 when the hand is placed in the normal position to operate the tool 110. If the detector 114 is placed on the back 134 of the handle 126, the IR emitter 182 can be located on the housing at the back of the tool 110 as shown in FIG. 3. When the detector 114 is located on the front of the trigger 126, a suitable location for the IR emitter 182 is on the front of the housing 112, near the chuck 144. The trigger circuit 120 is modified as shown in FIG. 4 to provide constant power to the IR emitter 182. A resistor 185 optionally adjusts the voltage to the IR emitter 182.

[0020] The trigger circuit 20 is also useful to terminate operation of the tool itself in conjunction with the light 16. This lockout functionality terminates power to the drill 10 if the operator' hand is not detected by the sensor 14, preventing uncontrolled operation of the tool if the drill 10 is dropped or the operator is incapacitated. Although the release of the trigger 26 should cease operation of the tool 14, the power lockout feature would serve as a backup safety feature if the trigger switch failed to cut power for any reason.

[0021] While many types of controlled switch component can be used, a relay is preferred. Referring to FIG. 2, a relay 76 that functions to interrupt power to the tool motor is preferably located in the housing and is controlled by a relay coil 78 that is in series with the light 16 so that it is activated and deactivated with the light 16 essentially simultaneously. While the coil 78 is in series as shown, it can be connected in parallel with the light 16, depending on the relative loads of each device. Normally, when the operator sets down the drill 10, there is no immediate need for either light or power until the tool is picked up again for the next use. Automatic deactivation of the light and power is not an inconvenience. However, in the case where the drill 10 is accidentally dropped, failure of the sensor 14 to detect the operator's hand automatically terminates power to the drill 10.

[0022] While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.

[0023] Various features of the invention are set forth in the following claims.