In power tool systems of the above type there is a necessity that the components of the system, i. e. the power tool, the control unit, and the cable, are compatible with each other to form an accurately and safely working system.

A key component is the cable, which apart from the risk that a cable of an incorrect type or size has been chosen in the first place, it is exposed to a mechanical wear during use of the power tool and, therefore, has a limited service life.

Accordingly, there is a need for a data informing means by which the identity as well as operational characteristics of the cable are obtainable. It is also very much needed a possibility to get an automatic check as to whether the components of the power tool system are of the correct type and size for the intended tool application. For instance, it is important that the cable is of the correct type and is able to cope with the actual power load intended for powering the actual tool. It is also important that the cable meets the safety requirements of various certifying bodies like U. L, Semko etc. The safety concerns not only the operational safety of the power tool system but also safety regarding distorsions from and to other equipment.

Personal safety of the operator has of course also high priority. Using a cable of an incorrect type may cause serious accidents.

As mentioned above, multi-core cables interconnecting portable power tools and stationary control units are exposed to a certain mechanical wear during use of the power tool, and since such cables are not only expensive to replace but they are crucial for guaranteeing a safe and proper power tool operation. A breakdown of such a cable may cause a dangerous situation for the operator. Also a cable break down often means a costly stop in production, especially at assembly line operations.

Typical use of power tool systems of the above described type is for screw joint tightening operations and for grinding. Screw joint tightening with power tool systems of this type is very common at assembly lines in the motor vehicle industry.

The main object of the invention is to create a power tool system of the above described type wherein a means is comprised for providing data relating to the identification characteristics of the cable.

A further object of the invention is to create a power tool system in which data are obtainable relating to the compatibility of the power tool, the control unit and the cable.

A still further object of the invention is to provide a method and a power tool system by which a power tool connected multi-core cable may be safely used to an extent where the service life of the cable could be made use of to a high degree without risking a cable breakdown.

According to the invention, the above objects are achieved by providing a multi-core cable of a power tool system as stated in the claims.

By a memory module carried by the cable there is obtained a registration and storing of the accumulated number of power tool operations performed via the cable to be compared with a predetermined acceptable number of tool operations for the actual power tool application.

In the accompanying drawing there is schematically illustrated a power tool system according to the invention where a portable electric power tool 10 is connected to a control unit 11 via a multi-core cable 12. The power tool 10 is hand held for manual support in different operation positions, whereas the control unit 11 is secured to a stationary non-illustrated structure in a vicinity of the power tool working site. The cable 12 is connected to the power tool 10 and to the control unit 11 by two connection pieces 13,14, and in one of these connection pieces 13 there is provided an electronic memory module in the form of a data chip (not shown). This data chip may contain several data relating to the identity and characteristics of the cable 12, including Model No. , Series No., manufacturing date as well as special data provided by the users such as date of purchase, specific work site, service history etc.

The chip is also intended to continuously register and accumulate the number of performed power tool operations as well as lapsed time etc. When reaching a predetermined number of tool operations or active period of time which is considered to be a safe limit from the mechanical wear point of view in the actual tool application, there is generated a warning signal. Then, the cable should be exchanged for a new one. The used cable could be used further in an another application where the mechanical wear is less intensive.

The cable 12 comprises a data bus by which the chip communicates with the power tool 10 and the control unit 11, and by this communication the chip is able to react on differences in the type of power tool connected to the cable and control unit.