Robert Boschgmbh

Fritz Schadlich

Friedrich Hornung

Manfred Stabler

Werner Rieker

Steffen Wunsch

Kurt Paule

Gerhard Armbruster

Wolfgang Jundt

Gunter Schaal

Erich Borst

Martin Gerschner

Hans-Joachim Vogt

Klaus Gunther

Peter Stierle

Heribert Schramm

Werner Neubert

Thomas Muller

Heinz Walz

Klaus Klingenstein

Martin Kummer

Gunter Zilly

Eberhard Seidel

Klaus-Dieter Jaspert

Brigitte Hertell

Rainer Thaler

Uwe Krieg

To detect if a tool bit, such as a drill, a saw blade, or the like, upon being worked into a wall, meets a metallic obstruction, such as a conduit, reinforcement rod, hydraulic pipe or the like, an alternating voltage, preferably between 2 and 20 kHz, is coupled through a coupling capacitor (9) to the tool bit, and current flow to the tool bit is detected by a current measurement stage (10; 31, 32) to disconnect energy to the drive motor (5), for example by disabling firing of a thyristor (15), or closing a valve of a compressed-air tool. The coupling capacitor should have a capacity small enough to provide high impedance to network power frequency, and to insure a substantial change in current being supplied to the tool bit holder, typically a chuck, if the tool bit meets a metallic object in the wall. The a-c supply circuit can be formed as part of a trigger circuit for the thyristor, by pulse-energizing a trigger diode (28) upon repetitive charge of a capacitor (26) through a charging network (22, 23, 24, 25).

Safety circuit for hand tools, and method for safe operation thereof

A hand tool machine, in particular a drill machine, has a feeler device for determining the diameter of a tool element to be used with the hand tool machine. For measuring the tool elements prior to insertion into the clamping element of the hand tool machine, a feeler device is provided which is arranged separately from the clamping element and is connected with an indicator. The diameter determined by the feeler device is administered to a control unit which is controlling the driving motor. The control unit can also receive in addition further information concerning the material to be treated by means of an input device. In view of the measuring value with regard to the diameter of the tool element and the administered information concerning the material, the optimum rotary speed for the tool element and consequently for the driving motor is determined and adjusted.

Hand tool machine, in particular drilling machine

A signal representative of the mass moment of inertia of a grinding wheel and its drive motor is integrated for a fixed time interval during start-up of the motor beginning when the motor speed or the motor current has reached a predetermined small value, and the integration result is stored until the integrator and storage circuit are reset by a new start-up operation. The integrator result is used to modify a voltage which represents a desired operating speed so as to compensate for differences in value of the mass moment of inertia, making the desired speed smaller when the mass moment of inertia is greater, and vice versa. The result is to hit the desired speed in a manner compensating for the wearing down of the diameter of the grinding wheel, so that the peripheral speed of the grinding wheel is regulated at a substantially constant speed, even though in successive start-ups the grinding wheel diameter diminishes. The integrated signal may be the motor current which varies directly with the mass moment of inertia, or the rotary speed of the shaft which varies inversely with the mass moment of inertia. Sensitivity to changes in diameter is greater when the operating voltage is reduced during start-up and at least until the end of the measuring interval.

Method and apparatus for speed control of a grinder

In an electromagnetically operated driving tool, in which a cup-shaped plunger carrying a driver blade is axially slidable in a solenoid, an air damper, combined with a check valve, is provided to damp the plunger during its backward movement to an inoperative position. A hollow cylinder positioned in the plunger is vented through an opening in a housing of the tool and has an interior which is closed at its end with a liftable valve flap. A throttle gap is formed between the plunger and the cylinder, which is adjustable by a piston movable in the cylinder which is made of elastic plastics and is elastically expandable to vary the throttle gap.

Electromagnetically operated driving tool with air damper

To permit reliable turn-OFF of the motor when the torque of the motor is sufficient to provide for reliable seating of a screw or nut being driven thereby, start conditions of the motor are sensed, either in form of low-current condition or high power factor; high-torque conditions are sensed by low power factor, or high-current, in dependence on the desired torque level which results, respectively, in a comparatively steep phase angle-torque or current level-torque curve. A switch control is energized to turn-OFF the motor current if the phase angles, or the motor current, respectively, are beyond predetermined levels. To prevent in-rush current, or high power factors from affecting the operation of the turn-OFF system, timing circuits are provided to disable the turn-OFF system when the motor is first turned-ON or if the phase angle difference, as determined by time-comparator networks, between current and voltage, is below a predetermined value. Timing duration of at least one of the timing circuits can be controlled as a function of motor temperature to provide for linear response of the system, regardless of changes of motor operating parameter versus torque characteristics under varying motor temperature conditions.

Automatic screwdriver or torquing tool control system

A hand-held power tool with a circular-disk-shaped tool mounted on an output shaft which extends normal to a drive shaft has a guiding part which surrounds the tool in an immovable position at its cutting side. The guiding part has a wall arranged for abutting against a workpiece and having a through slot for the tool, and a guiding edge extending parallel to a cutting direction of the tool, and the guiding part being movably guided in direction normal to the wall.

Hand-held power tool with circular-disk-shaped tool

To provide for, selectively, control of the speed of a tool, such as a drill or boring tool coupled to an electric drill or boring machine motor, independently of the setting of a multi-speed transmission, speed of the tool is sensed by a contactless transducer (4, 7), one part of which is coupled to the chuck (1, 2) and the other to the housing (H) of the tool, to provide speed signals which incorporate the transmission ratio of the gear (G, 66). Speed control, for example under a command signal (40; 50), then will control the actual speed, regardless of the transmission setting, with the torque deliverable by the motor being controlled by the selected gear. The diameter of the drill or other tool bit is sensed also by the transducer, if coupled to the chuck jaws, to vary the output signal from the transducer as a function of chuck jaw diameter. The output signal can be selectively analyzed for frequency in a frequency evaluation stage (35), and for amplitude in an amplitude evaluation stage (34), the speed and chuck jaw spacing signals can be separated (FIG. 8) from a combined speed - chuck jaw spacing signal obtained, to provide for control of the motor as a function of material being worked on (40; A-D), of accessories (40) to associate output speed with materials and drill diameter in accordance with selected functions, or only of speed, for example for operating accessories such as screwdrivers, sanding disks, or the like.

Rotary electrical tool with speed control, especially drill

To prevent bounce of a hammer or plunger element coupled to an insertion blade of a stapling or nailing gun upon return of the plunger element to rest position by a spring (11), the plunger element (4) is in cup shape, sliding about a hollow cylinder (6) which is vented to ambient air (8) at one end, but closed at its other end by a flap-type check valve (9). Upon downward movement of the plunger element, for example under electromagnetic force of a solenoid (2), air can flow freely from the vent opening (8) into the hollow interior and through the then open check valve (9); upon return movement under force of a spring (11), the flap valve (9) will close, however, thus forming an air cushion or air damper and preventing rapid, uncontrolled return of the plunger element to rest position, due to an air throttling path (19) between the outside of the hollow cylinder and the inner surface of the plunger element (4), said air throttling path being defined by the operating clearance between the plunger (4) and the hollow cylinder (6). The hollow cylinder (6) may be constructed as a guide element, unitary with the valve, and made of plastic, the valve being secured by a living hinge to the remainder of the hollow cylinder.

Electric hammering apparatus with air-cushioned armature

An electric power machine, particularly an angle grinding tool is provided with a centrifugal overspeed protecting device including a fly weight in the form of a severing blade which interrupts a power supply conduit when the rotary speed of the machine is excessive. The protective device includes a cylindrical housing attached face to face to the shaft of the electric motor. The severing blade is in the form of a quadrangular frame defining a center opening. The cylindrical housing is provided with a diametric through bore of a rectangular cross-section matching the frame-like severing blade. A blind bore of a circular cross-section is coaxially superposed on the rectangular through bore and its upper part is formed with inner thread for receiving a setting screw. A helical tensioning spring is inserted in the center opening of the frame-like severing blade and rests on the bottom of the blind bore to urge the centrifugal severing blade against the setting screw. When the rotary speed of the shaft and thus of the housing exceeds a predetermined value the severing blade is displaced by centrifugal force out of the rectangular through bore and severs a conduit in the power supply circuit for the motor whereby the compressed biasing spring acts as a buffer. The setting screw adjusts the distance on the center of gravity of the severing blade from the axis of rotation of the motor shaft and thus determines the value of the limit rotary speed.

Electric power machine with protection against overspeed

To reduce operating noise, and particularly the impact of sound pressure waves on the internal structure of the planing machine, the edges defining separating walls against which sound waves may impinge are inclined with respect to the axis of rotation of the cutter (16) or a theoretical line (46) parallel thereto, thereby extending the time of impact of individual pressure waves emanating from the cutter of incremental surface areas of the respective edges (26, 48, 50; 42, 52, 54; 30) to simultaneously attenuate the impact of the pressure waves and the timing of the impact.

Low noise planing machine, particularly hand planer

To permit operation of the power tool only if both hands of an operator are engaged, the tool is formed with a handle portion which has a sensing surface thereon, electrically coupled to a current flow sensing circuit, preferably including an opto-coupler or a field-effect transistor (FET) circuit which permits firing of a triac, thyristor, or the like only if current flows over the sensing surface by area contact therewith. The sensing surface is energized, preferably, from a resistive or capacitative voltage divider; the capacitative voltage divider has the advantage that the triac firing circuit can cause the triac to fire during null or zero crossings of ac supplied power. If a locking-type switch is used, two handles or touch-areas are needed; if a spring-loaded switch is provided, it can function as one safety element, and a touch-area sensing surface as the other.

Electronic two-hand safety system for power tools

A power screwdriver that is equipped with a spring coupling between the motor drive and the tool spindle, a signal that indicates that a certain value of torque has been overstepped, at which the screwdriver must be sopped, first causes reversal of the motor, but before the motor appreciably turns in the reverse direction, powers shut-off, allowing the motor to coast. After another brief interval, power is reapplied to the motor in the original direction, again briefly. In this way it is possible for the final shut-off to occur when the motor is stopped and the spring is unstressed, avoiding oscillations of the motor-spring system. A triac bridge circuit makes possible quick reversals and brief applications of power. In such a bridge circuit, precautions must be taken to be sure one pair of triacs is extinguished before the other pair is ignited.

Method and apparatus for shutting off a power screwdriver

A torque limiting power screwdriver includes a housing in which there is supported for rotation and axial displacement a screwdriver spindle. A transmission transmits power from a motor to the screwdriver spindle. A torque overload coupling and a separating coupling are interposed in the transmission, being operative for interrupting the transmission of torque from the motor to the screwdriver spindle. The separating coupling is coupled and uncoupled in response to axial displacement of the screwdriver spindle between its coupling and uncoupling positions. The axial movement of the spindle is accomplished by a trigger movably mounted on the housing and connected by a Bowden cable or a lever transmission to the spindle. The spindle is connected by an axially movable coupling with an output member, especially with a bevel gear transmission accommodated in an angular head housing portion. A switching trigger is used to energize and de-energize the motor. The trigger and the switching trigger can be combined into a trigger unit, thus making possible one-hand operation. The trigger and switching trigger are so constructed and arranged that they force the succession of energization of the motor and coupling of the separating coupling during the commencement of operation, and the succession of uncoupling the separating coupling and de-energization of the motor during the termination of operation.

Torque limiting power screwdriver

A machine tool, especially a hand-held power tool, comprises a tool spindle and a clamping element turnably mounted on the spindle, in which the turnable clamping element is arrestable during rotation of the spindle for clamping or releasing a tool mounted thereon to thereby make a separate implement for preventing rotation of the clamping element during clamping or releasing the tool on the spindle unnecessary. In a special embodiment of the present invention the clamping or releasing forces during change of the tool are mechanically applied and the turning moment during clamping of the tool is limited to a predetermined value.

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Leinfelden-Echterdingen, Germany

Fritz Schadlich