GB2328630A

GB2328630A - Electric hand tool with pressure sensitive control

Info

Publication number: GB2328630A
Application number: GB9818742A
Authority: GB
Inventors: Thomas Leitenberger; Werner Huser; Wolfgang Hirschburger; Andreas Zimmermann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-09-01
Filing date: 1998-08-27
Publication date: 1999-03-03
Anticipated expiration: 2018-08-27
Also published as: FR2767737A1; DE19738092C1; JP4191288B2; FR2767737B1; JPH11123669A; GB9818742D0; GB2328630B

Abstract

An electric hand tool 10, such as a drill or jigsaw, has a housing 10 with a portion 14 accommodating an electric motor. A handle 18 is incorporated in the end of the housing. A switch 24 is located in the handle and is operated by trigger 22. A force sensor 30 is integrated into the housing and is connected to an electronic control device 26. A user holding the handle and operating trigger switch 22 can adjust the speed or torque of the tool by applying pressure F to a surface 32 of the force sensor. A memory element 38 may retain a desired speed without the need to maintain pressure on the sensor. The memory may be cleared by re-exerting a force on the sensor.

Description

2328630 i Electric tool The invention relates to an electric tool having

the features described in the preamble of claim 1.

Background art

Electric tools of the type described are known. For instance, a range of electric tools such as drills, hammer drills, jig saws etc. are known, in which it is desirable to vary operating parameters. Thus, for example, it is known to preselect a speed of the electric tool. To said end, there is associated with the drive motor an electronic control device, which comprises an externally operable setting means. The setting means in a known manner is a setting wheel, which is integrated in a handle of the electric tool and by means of which a speed is preselectable via the electronic control device.

The drawback here is, on the one hand, that operation of the setting wheel requires a change of grip on the electric tool, the other hand optionally having to be used to operate the setting wheel. On the other hand, the setting wheel penetrates an opening in the housing of the electric tool, with the result that either costly sealing measures are necessary or the interior of the housing is vulnerable to pollution, in particular by dust.

Advantages of the invention In contrast the electric tool according to the invention having the features described in claim 1 has the advantage that an influencing of the operating parameters is possible in a simple manner, in particular without a change of grip on the electric tool. By virtue of the fact that the setting means for setting or 2 adjusting the electronic control device is a force sensor, it is easily possible by exerting an operating force on the force sensor, preferably by means of a part of the operator's hand gripping the handle of the electric tool during operation of the electric tool, to set or lock in the electronic control device. A change of grip is not necessary for said purpose, with the result that safe operation of the electric tool is provided.

In a preferred refinement of the inventor, it is provided that the force sensor is integrated in a region of the handle which, when the handle is firmly enclosed by the operator's hand, is within reach of the thumb of said hand. Particularly when the force sensor is disposed immediately below a shell of the housing, the force sensor may be operated by exerting a point force upon the housing. In a preferred refinement of the invention, it is provided that in the region of the force sensor the housing is designed with a thinner wall so that operation of the force sensor is possible through the housing, in particular without providing an opening in the housmg.

It is in addition advantageous that, by designing the setting element as a force sensor, it is impossible for a mechanical load arising during the intended use of the electric tool, in particular vibrations, to lead to a variation of the position of the setting means.

Drawing There follows a detailed description of an embodiment of the invention with reference to the accompanying drawing, which shows a diagrammatic partial view of an electric tool.

3 Description of the embodiment

The drawing shows in a cutout manner the housing 10 of an electric tool 12. The electric tool 12 may be, for example, a hand drill, a hammer drill or the like. The housing 10 has a housing portion 14 for receiving a drive motor - as a rule, an electric motor - as well as a housing portion 16 for forming a handle 18. The housing parts 14 and 16. may be of a single- or multi-part construction. The handle 18 forms a through- opening 20, inside which an operating means 22 of an on/off switch 24 of the electric tool 12 is disposed. The on/off switch 24 is used to connect and disconnect a supply voltage of the electric motor.

The electric tool 12 further comprises an electronic control device 26 which is integrated, for example, in an installation area of the handle 18. Associated merely optionally with the electronic control device 26 is a setting wheel 28, which projects at least at one side from the handle 18 and is used to operate a potentiometer (not shown in detail) of the electronic control device 26.

A force sensor 30 is additionally integrated in the handle 18 and has its sensor surface 32 directed towards a shell 34 of the housing portion 16. In the region of the force sensor 30 the shell 34 may be designed with a thinner wall than the other regions of the housing portion 16. The force sensor 30 is connected by an, in the present case, indicated electrical connection 36 to the electronic control device 26. The force sensor 3 0 forms a setting means 3 6 of the electronic control device 26 for externally influencing operating parameters of the electric tool 12.

The position of the force sensor 30 inside the handle 18 is so selected that, when a hand of an operator is gripping the handle 18, the fingers of said hand may engage into the through-opening 20 and at the same time the force sensor 30 is 4 operable by means of the thumb without altering the position of the hand. To said end, the force sensor 30 is integrated substantially - as indicated - in an upper region of the handle 18. Naturally, other positions of the force sensor 30 are also possible where, for example, operation of the force sensor 30 is possible by means of the ball of the thumb when the handle 18 is gripped.

The electric tool 12 operates as follows:

After the electric tool 12 has been switched on at the on/off switch 22, the drive motor is connected by the electronic control device 26 to the supply voltage. However, the electronic control device 26 by means of suitable circuit components initially prevents the drive motor from starting up. Acceleration of the drive motor is controlled by exerting an operating force F upon the sensor surface 32 of the force sensor 30. Depending on the magnitude of the operating force F exerted by the thumb of the operator's hand - the speed of the drive motor may be varied between stationary and a maximum speed. It is preferably provided that a minimuni operating force F has to be overcome mi order to guarantee a slow initial rotation of the drive motor. Accidental acceleration of the drive motor is thereby prevented because the operating force F of a minimum value has to be exerted with relative pin-point accuracy upon the force sensor 30. By varying the operating force F during use of the electric tool 12 the speed of the drive motor may therefore be infinitely varied. Particularly as a result of the tactile feedback to the user, an extremely precise speed adjustment adapted to prevailing requirements and/or wishes is possible.

It is additionally possible by means of the setting wheel 28 to adjust differing maximum speed values. Thus, depending on the position of the setting wheel 28, given the same operating force F a different speed range is adjustable.

A memory element 38 of the electronic control device 26 may be used to maintain automatically a drive shaft speed which is proportional to an operating force F exerted upon the sensor surface 32 when the operating force F remains constant over a selectable period of time. Thus it is possible, for example, by continuously increasing the operating force F to select a specific speed which is automatically maintained by retaining the operating force F which corresponds to said speed, in which case it is possible at the same time to "let go of' the force sensor 30. Clearing of the memory element 38 may be effected either by re-exerting an operating force F upon the force sensor 30 and/or by operating the on/off switch 22.

Naturally, in a modification of the described embodiment it is possible to adjust, instead of a speed of an electric tool 12, a torque of the electric tool 12. The force sensor 30 flirther offers the possibility of scanning whether the electdc tool 12 is being held in the correct position. It is only after the force sensor 30 has been operated for the first time that a start-up of the electric tool 12 is enabled by the electronic control device 26. In particular, a lock-out preventing the electric tool 12 from being accidentally switched on is realized by said means.

6

Claims

1.

2.

3.

4.

5.

6.

Electric tool having a drive motor, the drive shaft of which drives a tool holder, as well as having an electronic control device for the drive motor for mfluencmg operatmg parameters of the electric tool, a setting means for externally influencing the operating parameters being associated with the electronic control device, characterized in that the setting means is a force sensor.

Electric tool according to claim 1, characterized in that the force sensor is integrated in a handle of the electric tool.

Electric tool according to one of the preceding claims, characterized in that the force sensor is disposed immediately under a shell of a housing portion of the electric tool, which housing portion forms the handle.

Electric tool according to one of the preceding claims, characterized in that a sensor surface of the force sensor is directed towards the shell.

Electric tool according to one of the preceding claims, characterized in that the shell in the region of the force sensor is designed with a thinner wall than the housing portion surrounding said region.

Electric tool according to one of the preceding claims, characterized in that the force sensor is disposed in such a way 7 that, when a hand of an operator is gripping the handle, an operating force may be exerted upon the force sensor without altering the position of the operating hand.

7.

8.

9.

Electric tool according to one of the preceding claims, characterized in that the electronic control device comprises a memory element, which acquires a signal of the force sensor corresponding to an operating force remaining constant and, given a constant operating force over a selectable period of time, automatically maintains the operating parameters corresponding to said constant operating force.

Electric tool according to one of the preceding claims, characterized in that associated with the electronic control device is a setting wheel, by means of which an efiective range of the force sensor for influencing the operating parameters is preselectable.

An electric tool substantially as herein described with reference to the accompanying drawing.