Optical depth measuring device to be mounted on drilling power t

Details Optical depth measuring device to be mounted on drilling power t Optical depth measuring device to be mounted on drilling power t

1988-11-10

1990-11-06

Evans, F. L.

Optics: measuring and testing

By polarized light examination

With light attenuation

356 1, 408 16, G01B 1122

Patent

active

049681460

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a hand-held machine tool preferably a drilling power tool. A drilling power tool is disclosed in DE-OS 31 26 245. In the known drilling power tool a profile rod is used for bore depth measurement and is made of a plastic material or metal. It extends parallel to the tool axis. The profile rod is displaceable along the tool axis in a holder which is fastened to the drilling tool. The profile rod can be locked by tightening a wing screw. It is tightened so as to project forward far enough so that the front tip of the rod abuts the workpiece when a predetermined bore depth is reached. A disadvantage of this measuring device is that the projecting distance of the rod and accordingly the predeterminable bore depth can only be roughly set as measured with the eye. It may happen that an unintentional longitudinal displacement of the rod occurs during tightening of the wing screw. Another disadvantage is that the reference point of the measurement is at a relatively far distance from the bore. The bore depth measurement range is defined by the length of the profile rod, which may not exceed a certain dimension for reasons of stability.


SUMMARY OF THE INVENTION

The object of the invention is a power tool having means which enables a high degree of accuracy in measuring the bore depth. According to the invention, measurement of the distance of the hand-held drilling tool from a workpiece to be machined is effected by the method of triangulation, known per se, which possesses a high degree of measuring accuracy. A radiation source, which projects an optical pattern onto a surface of the workpiece, and a radiation receiver, which is struck by the radiation reflected from the surface, are provided. There are no movable parts in the measuring device.
A semiconductor radiation source is preferably provided as a radiation source. A light diode, which emits a radiation in the visible spectral range, so that the reference point of the measurement is visible on the object to be processed, is particularly suitable for this purpose. Pulsed operation of the light diode enables a high pulse radiation output. The lower energy consumption in pulsed operation is noticeable in a particularly advantageous manner in battery-operated devices.
A high signal-to-noise ratio is achieved when the light diode is arranged in the focal point of a first collecting lens and the radiation receiver is arranged in the image plane of a second collecting lens located between the radiation receiver and the workpiece to be machined.
There are a number of possibilities of designing the radiation receiver, each of which has specific advantages.
In a first embodiment, the radiation receiver comprises radiation sensors first and second sensor, an optical beam splitter, and an additional optical structural component element arranged in front of the first radiation sensor. The optical structural component element can be a plane passband filter with a location-dependent transmission coefficient or a diaphragm with a location-dependent opening. The second radiation sensor provides a reference signal for the output signal of the first radiation sensor which is responsible for a position detection. The advantage of this arrangement consists in that the simplest radiation sensors, e.g. photodiodes, can be employed, and the measurement results are independent from the reflection coefficient of the surface to be machined.
In a second embodiment, a single plane radiation receiver is used, in front of which an optical structural component element is provided which comprises radiolucent and radiopaque regions. An optical grating is preferably used in this case. The quantity of counting pulses resulting from an interruption or transmission of the radiation, respectively, is a measure for a change in the distance. This construction can be modified in an advantageous manner by using a second radiation sensor and a second grating, wherein the radiolucent and radiopaque regions, respectively, of the two optical grati

REFERENCES:
patent: 4761072 (1988-08-01), Pryor

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