Electric Power Tool With Code Receiver

The invention relates to a hand-held electric power tool which comprises a device for alternatively disabling and enabling operation of the tool.

Electric power tools, for example rechargeable battery powered or mains-connected screwdrivers, are frequently used in, for example industrial assembly. Since these types of power tools are portable, they are occasionally removed from the workplace without permission and are never returned. This represents a costly loss for the owner.

The object of the invention is to ensure, in the case of a portable power tool, that the tool can only be used in an authorised workplace.

According to the invention, the above object is achieved in that the power tool comprises a receiver and an electronic control means which is arranged to receive a code signal, wherein the electronic control means switches the tool on to an operable mode upon receiving the code signal, and wherein upon disconnection from the electrical supply voltage or after a certain time or operation interval, the tool returns to an inoperable mode and remains therein until the code signal is again received.

A code signal transmitter is permanently installed in the vicinity of the authorized workplace.

By virtue of this device, upon disconnection from the supply voltage, i.e. by removing the accumulator in a rechargeable battery powered tool or disconnecting the mains plug in a mains-operated tool, or after a certain time or operation interval, the tool is switched into the inoperable mode and remains therein. If the tool is removed from the authorized workplace, in the case of a rechargeable battery powered tool, it can only be used until the charge runs out; in the case of a mains-operated tool, it can no longer be operated at all; in the case of time-interval or operation-interval switching, the tool can no longer be operated after such interval has expired. This gives the owner great protection against theft, because relevant personnel will know that the tool is only usable at the workplace in connection with the code signal transmitter.

The tool according to the present invention will only be switched to the operable mode when the tool receives the code signal after reconnection of a battery unit in the case of a rechargeable tool, or reconnection to the mains or after expiry of the time or operation interval.

By means of different codings, groups of machines can be allocated to one of a number of working areas or code signal transmitters. Thus, the respective tools can only be used in the allotted working area. For example, in this manner it is possible to allocate screwdrivers having a specified torque setting to an assembly line (working area) at which such working operations only are to be carried out which require that particular torque setting. It is thereby ensured that in this working area, work is always carried out at the correct torque setting. Due to the specific coding in this working area, screwdrivers which are set to a different torque or in which the output torque is not determined cannot be used, because these tools do not switch into the operable mode in such working area.

It is also possible to allocate other technical criteria to the coding. Furthermore, the coding can also be carried out according to administrative conditions; for example, the coding may be designed in such a manner that tools belonging to one cost center are only switched into the operable mode by a code signal within the working area of such cost center.

Various advantages embodiments of the invention will be obvious in view of the following description of a preferred embodiment of the invention.

FIG. 1 shows a code signal transmitter having a transmission section and a hand-held power tool being in the vicinity thereof,

FIG. 2 shows a block circuit diagram of the power tool, and

FIG. 3 shows a flow chart of the electronic control means of the power tool

A code signal transmitter 1 is installed in a stationary manner in for instance a factory. The code signal transmitter 1 has a pulse generator 2 and an infrared transmitting diode 3. The code signal transmitter 1 periodically transits a digital code signal 4 via a transmission section 5. In the example, the code signal begins at t0:01100101 and ends at T. t1 is the duration of one of the ones or zeros. The code signal 4 can also be coded in another way.

At least one power tool 6 is allocated to the code signal transmitter 1. This tool has a receiver 7 comprising an infrared transistor 8, which receives the code signal 4 when the power tool 6 is brought into the vicinity of the code signal transmitter 1.

Instead of the infrared transmission section 5, a radio transmission section can also be provided. It Is also possible to provide a plug-in cable connection as a transmission section between the code signal transmitter 1 and the power tool 6.

In the embodiment illustrated in FIG. 2, the power tool 6 is equipped with an exchangeable battery unit 9. A charging device needed for the battery unit 9 may be advantageously integral with the code signal transmitter 1. This makes the association between the code signal transmitter 1, the charging device and the associated power tool 6 easy to monitor and simplifies the operational coupling thereof as described above.

The receiver 7 is connected to an electronic controller (control means) 11 incorporated in the tool 6. The electronic control means 11 operates with a microprocessor, which is allocated a power circuit 12, by which the exchangeable battery unit 9 is connectable to a D.C. motor 13 of the tool 6. A mechanical transmission 14 is connected between the D.C. motor 13 and a drive unit 15 for the screwdriver bit, drill or other tool (not shown) (cf. FIG.2).

To the electronic control means 11 there is connected a manual switch 16, by which the motor 13 can be switched on or off via the power circuit 12 by the operator. Furthermore, the tool comprises an actuator 17, which acts on the electronic control means 11 and with which a further operational parameter can be set. For example, in the case of a screwdriver, the torque can be adjusted.

The electronic control means 11 also controls two light diodes 18, 19, which indicate the operable mode or the inoperable mode of the tool 6. The light diodes 18, 19 can also indicate other operating States, for example the state of charge of the battery unit 9 and whether a screw joint has been tightened correctly or not. An acoustic signal transmitter 20 can be provided to signal faulty tightening processes.

As an additional feature of the code signal transmission system, data concerning desired operation characteristics like torque output, angle of rotation etc. may be transferred to the power tool together with the tool operation enabling code signal. Also, a code signal emitting means may be fitted to the power tool for sending back to a stationary signal receiver the actual operation data obtained during a certain interval of operation. These data may be stored, and an analysis of the performed operations may be carried out later on.

The modus operandi of the device will now be described with reference to FIG. 3.

A replacement of the battery unit 9 of the tool 6 by a recharged unit, represents a reset command and a start command (a) for the microprocessor of the electronic control means 1. Upon the start command (a), initialization of variable parameters takes place, which is indicated by the block (b). Thereafter, a probe cycle is started in which the infrared transistor is probed. If a signal is received, a bit is set to 1. If no signal is received, the bit is set to 0. This bit is then put into the first position in the receiving byte. After the time interval (t1), the cycle is repeated and the bit value is transferred to the next position in the receiving byte. After each cycle, the receiving byte is compared with the code word stored. If these correspond, the tool is switched to its operable mode. If, accordingly, the receiving byte corresponds to the code signal 01100101, then the block (g) switches to the operable mode, as shown by block (h). The tool 6 is then capable of being switched on and off by means of the manual switch 16. During the probe cycle, however, the tool cannot be switched on and off by means of the manual switch 16.

Having been switched to its operable mode via its electronic control means 11, the tool 6 may also be moved outside the range of the code signal transmitter 1. The probe cycle shown in FIG. 3 is then no longer carried out, but is initialized only when the battery unit 9 is exchanged or, in the case of a mains-operated tool connected to a mains power supply 21 via a cable connection 22 (as shown in FIG. 1), when the mains plug is pulled out and plugged in again.

If in the block (g) it is established that the receiving byte does not correspond to the code--01100101 in the example--then processing returns to block (c). The above-mentioned processes are repeated until the correct receiving byte is received.

After the operable mode (h) is obtained, the probe cycle of FIG. 3 is no longer carried out.

The alternative embodiments of the invention are not limited to the above described example but may be freely varied within the scope of the claims.

Accordingly, the infrared code signal transmission may be replaced by an inductive or a conductive electrical connection between the power tool itself and a code signal emitting device. This may be carried out by docking temporarily the power tool with the signal emitting device, thereby bringing an electric contact means on the power tool into a direct contact with a mating contact means on the signal emitting device.

Alternatively, the code signal receiver 7 and the control means 11 may be integrated with the replaceable battery unit 9, and the code signal emitting device may be integrated with the charging device for the battery unit 9.

A further security feature for preventing unauthorized use of the power tool is to have the code signal emitting device activated by a second code signal transferred via the mains power supply connected to the code signal emitting device

Still another way of limiting the use of the power tool is to give the code signal certain operator definable characteristics.