Robert Boschgmbh

Friedrich Hornung

Fritz Schadlich

Martin Gerschner

Kurt Paule

Manfred Kirn

Wolfgang Jundt

Hans-Joachim Vogt

Klaus Gunther

Gunter Schaal

Steffen Wunsch

Arnim Fiebig

Julian Pfaundler

Klaus Guenther

Klaus Gu/ Nther

Bernd Upphoff

Fritz Sch/a/ Dlich

Steffen W/u/ Nsch

An electric motor has a switching device, a driving circuit connectable to a voltage supply through the switching device and having a drive shaft, a mechanically acting braking device for braking the drive shaft when disconnecting the electric motor from the voltage supply, a rotor serving to generate torque and acted upon by a mechanical braking force when switching off the voltage supply, at least one radially displaceable part which applies the braking force and is magnetizable and acted upon by an electromagnetic releasing force which is directed opposite to the braking force and is greater than the braking force, and a stator having an axial slit which is overlapped by the part, and at least one shorted turn arranged in an area of the slit.

Electric motor

Orbital disk grinder

To provide sufficient magnetization to the field of a series motor when the series motor is to be operated in dynamic braking mode, with a dissipating resistor or short circuit element (4) connected across the armature (5), a circuit connection is established between one of the main terminals of the motor through the series field to supply a minimum magnetization current, at least when the motor operates under dynamic braking conditions, typically a few to up to 15% of no-load current of the motor. This is sufficient magnetization so that, even in larger motors where remanent magnetism of the field structure is insufficient, reliable dynamic braking can be ensured. A switch (S; S.sub.1, S.sub.2) selectively connects the motor armature for motor drive or running operation and dynamic braking operation. The magnetization current supply can be through a capacitor, resistor, or resistor-capacitor combination, which can be permanently connected across the power supply (10, 11) of the motor, or connected in circuit only when the switch (S, S.sub.2) changes the motor into dynamic braking operation.

Electrical series motor with dynamic braking circuit

Thermal overload of a motor is avoided by measuring temperature and, when a limit temperature is exceeded, reducing the phase 'window' within each power cycle during which the motor is energized. The limit temperature is sensed by a temperature sensor which is warmed either by heat conduction through a cooling body or by an air stream from the motor. The overload protection apparatus requires no measuring resistance in the load circuit.

Phase control circuit for protection of a motor against thermal overload

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 device for independently regulating rotary speed and torque of an alternating current electric motor whose armature winding is connected as a branch of a bridge circuit balanced for a fixed rotary speed and a fixed operational voltage of the motor. The motor is controlled by a current phase adjuster having an input electrode. A polarity dependent resistive circuit including two anti-parallel diodes each connected in series with an adjustable resistor, forms a branch of the bridge circuit. A comparator in the form of an operational amplifier has its inputs connected to a diagonal of the bridge circuit and its output connected to the control input of the current adjuster. The rotary speed and torque are controlled independently by adjusting the resistors in the polarity dependent resistive means.

Device for regulating rotary speed of an alternating current electric

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

A helical spring couples a drive shaft geared to the motor with the work spindle. With this arrangement hard screwdriving operations can be extended in time so that time is added for the drive motor to come a stop after it is switched off. Transducers are provided for measuring the torque at which motor switch-off occurs, and also the cumulative angle of rotation, the latter for detecting defective screws. No switchdown of the drive speed is necessary before the screw is driven home.

Spring-coupled power screwdriver

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

Electronic control and regulating system

A mechanical switch is provided which, in a first position connects a current limiting circuit to a motor and, in a second position, disconnects the current limiting circuit from the motor. Mechanical activators are provided for the mechanical switch, to switch it from the first to the second position when the tool including the motor has a predetermined relationship to the workpiece. The mechanical activators provided for the mechanical switch operate the switch either when correct positioning of the tool relative to the workpiece results in a predetermined force being applied to the activator by the workpiece or when a shaft of the tool transmits a predetermined torque.

Mechanical apparatus for activating no load current limiting circuits in

A transformer having a secondary winding that delivers a regulating magnitude to a speed regulator circuit that approaches zero as the speed approaches the speed setting, is provided with two primary windings wound and connected so that they oppose each other in operation. The first is the conventional primary winding in series with the universal motor of which the speed is being controlled (as by a conduction phase angle control of the input voltage) while the second primary winding is in series with a resistance and, in some cases, also with a capacitor, with this series combination being connected in parallel with the armature winding of the motor for the best regulation, or in parallel with the motor as a whole if it is important to avoid additional internal connections to the motor. The capacitor is used to compensate for the inductive reactance of the second primary winding in cases in which that reactance is not negligible. A second capacitor across the secondary filters out commution 'hash.'

Speed control circuit for a universal electric motor

To reduce noise and idling speed of electric motors, particularly series motors, the speed-torque characteristic of the motor is dropped with respect to the loaded speed-torque characteristic, by sensing no-load operation of the motor and deriving a sensed signal, the sensed signal being applied to controlled switches to abruptly change the effective voltage applied to the motor between values corresponding to the no-load speed-torque characteristic, or the load speed-torque characteristic and resulting in the desired speed, in dependence on the value of the sensed signal. Preferably, the operating condition of the motor is sensed by an inductive transducer, and a speed change is obtained by phase control, or half-wave rectification.

Growing community of inventors

Stuttgart, Germany

Friedrich Hornung