GB2420087A

GB2420087A - Hand machine tool

Info

Publication number: GB2420087A
Application number: GB0522588A
Authority: GB
Inventors: Steffen Wuensch; Wolfgang Hirschburger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-11-04
Filing date: 2005-11-04
Publication date: 2006-05-17
Anticipated expiration: 2025-11-04
Also published as: GB2420087B; DE102004053848A1; GB0522588D0; CN1799781A

Abstract

A hand machine tool with motor-drivable tool and with a lighting means for lighting its operating field can be better controlled and used with better efficiency. The lighting means is a stroboscopic light source with a blinking and/or flashing frequency. The flashing frequency of the lighting means may be set with electric or electronic switching means. The lighting means may be light-emitting diodes.

Description

Hand Machine Tool Because of the demand for high-quality operating

results, electric tools are equipped with devices which make it possible to set operating speeds and numbers of strokes, oscillations and impacts.

This is done with the aid of open loop or closed loop control electronics.

For example, the optimum drill speed for the material to be machined can be previously set on a setting wheel or a display depending on the diameter of the drill. The proposed setting values are technical standard values and are based not least on many years of practical experience.

They are communicated to users in the form of tables, diagrams or else by displays fitted directly on the device.

With this invention it is proposed to apply the known action of the stroboscope to the monitoring and setting of operating speeds and oscillating and lifting movements of electric tools, this being for the following reasons.

The values previously set on the electronics are in most cases exposed during practical use of the electric tool - influenced by the person operating it - to considerable fluctuations and can be kept to a certain extent constant only by relatively expensive control electronics.

During the machining process, e.g. while drilling in stone or wood, owing to the inhomogeneity of the materials a greatly varied contact pressure is used for operating, without achieving substantial drilling progress.

With decreasing progress of work the pressure on the drill is considerably increased, leading to unreliably high temperatures on the tool and in the device, ultimately resulting in its breakdown.

With the electric tool, at an appropriate place a light source is fitted is such a way that it adequately illuminates the operating area and the operating tool. An electronic circuit accommodated in the device controls this light source by making it blink with high frequency.

The individual light flashes ensure that a marking or the tool itself executes a circular or forwards and backwards movement and it then becomes sharply and clearly visible when this oscillating frequency coincides with the blinking frequency of the stroboscope.

In order to avoid damage to the tool and the device by impermissibly high temperatures, with this invention the user is given the option of monitoring numbers of rotations, strokes, oscillations and impacts by means of this optical aid and to maintain the physically "correct" operating point or at least to move within a narrow operating range. This is achieved by sensitive loading of the device and possibly by changing the Elo setting.

As preferred light source a white "super bright" light- emitting diode is used, which is excited by a relatively simple circuit, accommodated in a narrow space in the electric tool, for the required blinking frequency. The blinking frequency conforms to the preferred operating frequency in each case.

Using the example of a Delta grinder, the function of the stroboscope effect for monitoring the operating speed will be adequately explained below.

The focused light cone of a bright LED shines on to the front part of the grinding plate with a preset blinking frequency and on to the part of the operating surface immediately adjoining the edges and the tip of the grinding disc.

This lighting of the working surface improves the view of the surface to be ground and therefore the quality of the grinding result is considerably increased.

Markings in the form of dot(s) or line(s) can be applied to the top of the grinding disc, to make clear the effect.

During the grinding process the operator loads the device with a pressure resulting, based on his experience, from directions given by the device manufacturer or from trial and error.

With the invention the user is given a decisive aid in that when the optimum machining speed is reached the markings on the machining tool - in this case the grinding disc - or the grinding disc itself become clearly recognisable, as a distinct picture appears.

Below or above this oscillating frequency the picture becomes fuzzy again.

Therefore, by constantly checking the operating speed - the view is in any case directed at the front part of the grinding plate - the operator has the option of setting the optimum operating speed by pressing harder or less hard.

Extensive trials have of course been conducted to determine the most favourable blinking frequency for this type of device.

This simplest kind of operating speed monitoring can be extended as follows.

An analog blinking frequency in each case is allocated to the continuously adjustable setting and the setting divided into steps of the motor speed by means of electronic setters.

It is thus possible to obtain differentiated statements on optimum operating speeds for: - using various grinding disc grain sizes - grinding different materials - using different operating methods such as grinding, polishing and cleaning Example: Grinding with different grain sizes Elo setter Grinding Removal Opt. speed Blinking 1 disc grain output frequency size 1/mm 1/sec Coarse -1- 60 a great 6000 100 deal Average -2average 7000 116 Fine -3- 240 little sooo 133 This table can be extended by adding the option "material".

Differentiation of the operating speeds to 9 settings then becomes possible, for example on a display on the device.

Then the operating points Ml to K3 are set - see next table - the appropriate blinking frequency being allocated to the individual operating points.

Material Grinding Speed Flashing Operating grain 1/mm frequency point acc.

1/sec to display Metal fine 180...240 8000 133 Mi av. 100...150 6000 100 M2 coarse 40...80 4500 75 M3 Wood fine 7000 116 Hi average 5500 92 H2 coarse 4000 - 66 H3 Plastic fine 6000 100 Ri average 4500 75 K2 coarse ooo so 1(3 The next diagram shows the configuration of the electronics for the drive motor. Via phase control three starting speeds are established, for metal (n = 9000), for wood (n = 8000) and for plastic (n = 6500) In practical operation, i.e. under variable loading, the values established and preselected in each case for the flashing frequency are then reached.

The loading, i.e. the pressure on the device, is increased until the operating speed corresponds to the flashing frequency, i.e. a steady picture of the marking or the grinding disc becomes clearly visible.

H H2 fr3 4o

Instead of monochrome illumination, several monochromatic LEDs can also be used, representing various materials.

For executing this function the LEDs are used either in their basic colours individually or in the form of a "full- colour" LED, in which the basic colours are integrated in a common housing.

It is therefore conceivable that, e.g. "green" is used for wood, "blue" for metal and "red" for plastic to illuminate and monitor the operating speed.

Other machining criteria can also be varied in colour.

The use of coarse-grained grinding means with the object of removing, i.e. demanding a grinding output of, as much as possible in a short time, is then taken on by a "yellow" blinking LED, the use of a grinding paper grain size in the range of P80. . .150 by a blue and for the fine grinding process by a "green" LED.

All the above-mentioned proposals for monitoring the operating speed during practical use have been executed using the example of a Delta grinder. They can also, however, apply without restriction to eccentric, oscillating and linear grinders.

The proposals are also applicable to the following electric tools.

Drills and hammer drills - to recommended the most favourable drilling speed for drilling suitable for the material (steel, wood, stone) as a function of the diameter of the drill Circular saws - cutting speed optimised to various materials Compass saws - additionally to recommending the use of appropriate saw blades suitable for the material, the correct number of strokes, i.e. cutting speed, for this Routing machine - similar to in the case of drills: optimum allocation of speeds to the diameter of the milling cutter Belt grinder - choice of belt speed taking into account the materials to be machined and the various belt grain sizes Right angle grinder - establishing the optimum operating speed for cutting, rough machining, brushing, de-rusting and removing paint, taking into account the operating tools designed for the purpose

Claims

Claims 1. Hand machine tool with a motor-drivable tool and a

lighting means for lighting its operating field,

characterised in that the lighting means is a stroboscopic light source with a blinking and/or flashing frequency.
2. Hand machine tool according to claim 1, characterised in that it carries electric and/or electronic switching means with which the blinking and/or flashing frequency of the lighting means can be set.
3. Hand machine tool according to claim 2, characterjsed in that it has means with which the numbers of rotations, strokes, oscillations or impacts or such can be controlled as a function of the settable blinking and/or flashing frequency of the lighting means.
4. Hand machine tool according to claim 3, characterjsed in that it carries a light-emitting diode, in particular white, serving as lighting means.
5. Hand machine tool according to one of the preceding claims, characterised in that allocated to the lighting means are elements, in particular optical, for focusing the light beam on to the tool.
6. Hand machine tool according to one of the preceding claims, characterised in that it carries scale-related setting means for setting the blinking and/or flashing frequency.
7. Hand machine tool according to one of the preceding claims, characteriseci in that the lighting means has its own, independent current supply means, in particular a generator arranged on and/or in the hand machine tool.
8. Hand machine tool according to one of the preceding claims, characterjsed in that the numbers of rotations, strokes, oscillations or impacts are settable via the setting means of the blinking and/or flashing frequency continuously and/or in steps.
9. Hand machine tool according to one of the preceding claims, characterised in that several LEDs of different colours and activatable in succession and/or jointly, serve as lighting means.
10. Hand machine tool according to one of the preceding claims, characterised in that it carries a means which emits acoustic or tactile signals, in particular vibration signals, preferably if the blinking or flashing frequency coincides with the number of rotations, strokes, oscillations or impacts.
11. A hand machine tool substantially as herein described.