DE4212438A1 - Lateral beam offset generator for trigonometrical distance measurement of workpiece - has laser diode providing point illumination of workpiece, and planar parallel glass plate between workpiece and measuring head, with rotatable axis - Google Patents

Abstract

An imaging optic is also included, which images the diffuse reflection on the workpiece, across a prism on a linear CCD sensor, arranged in a configuration as in e.g. patent P 40 32 361.7. A planar parallel glass plate (7) is interposed between the measuring head and the workpiece (4), the plate being rotationally located about an axis (8) vertical to the illumination beam. The rotation of this plate (7) causes a parallel deflection of the beam (and also the reflected beam) at right angles to the distance measurement. A driving system is provided for the rotation. A pulse transmitter and a limit switch determine the angle of rotation. The point of impingement of the beam and the workpiece can be shifted along small yet very exactly defined paths perpendicular to the axis of the distance measurement. USE/ADVANTAGE - Scanning operation e.g. in axial direction of lathe using combination of optical deflection element and shutter unit. One unit only is used. Measuring head is very compact and is protected against contamination.

Description

1. Problem and state of the art

The invention relates to devices which, according to the principle of trigonometric triangulation, determine the distance to a workpiece in that they place a light spot on the surface of the Throw workpiece that reflects there and from an angle to the direction of incidence Receiving optics recorded and displayed on a location-sensitive linear sensor. The distance between the measuring head can be determined from the location on the sensor that is read out electrically and workpiece are closed. Arrangements of this type are in different versions known [G. Krattenmacher: Non-contact distance measurement electronics 5/1987, OS P 3615875.5, U.S. Pat. No. 4676869 dated June 23, 1987 and U.S. Pat. No. 4899041 from 6.2.90 and others], e.g. B. in the in the patent application P 4032361.7 configuration of the optical elements referred to here becomes.

If such a measuring head is used in a machine tool, there is a risk of contamination of the optical elements, in front of which through an optical window and through a mechanical one Shutter can be protected, as already described in P 4032361.7.

The previously known designs of measuring heads only determine the distance to the workpiece, measure so only in one axis. When used in a lathe, only the diameter of one can be used Cylinders can be determined. If the length of a cylinder section is also to be determined, this can be done out of the way, the turret between two abrupt changes in diameter, in the following referred to as "edges", covered. In order to be able to detect these edges with the measuring head, is in the previously known arrangement of the measuring head very slowly with high accuracy over the question Place to move. If accuracy in the micrometer range is required, intensive communication is required between the control of the lathe and the measuring head required or only an extreme slow feed possible.

2. Subject of the invention

It is the object of the invention to relocate this scanning process in the axial direction of the lathe into the sensor, the lathe now positioning the revolver with the measuring head at the desired position of the edge, the actual location of the edge thus being in the immediate vicinity. The scanning is now carried out by parallel displacement of the beam path of the sensor by a small amount (about +/- 0.5 mm), which is done by a plane-parallel glass plate inserted in the optical beam path ( Fig. 1 and Fig. 2), which is rotated by a drive motor . The lathe turret no longer has to be moved and communication about the location of the turret between the lathe control and the measuring head is not required. Furthermore, the measuring process is significantly accelerated and considerably more precise, since the triangulation system and offset optics form a mechanical / optical unit.

According to the invention, the glass plate also forms the optical window and is therefore an optical filter executed, which only allows radiation to pass, which is in the wavelength range of the laser diode. daylight and therefore different lighting conditions in the machine tool do not interfere.

The plane-parallel plate is installed in a drum-shaped closure body, which is designed so that the outlet window of the measuring head is completely and tightly closed when rotated by 90 degrees ( Fig. 3). This protects the optics from dirt and splash water. Only when activated, the shutter body is first rotated by 80 degrees at high speed until the optical window is free and the laser beam can fall on the workpiece. The measurement is now carried out at a reduced, precisely controlled speed until the position -10 degrees of the closure is reached.

This corresponds approximately to a parallel offset of the beam path from -0.5 mm to +0.5 mm in the axial direction the wave. Then the closure is turned back by -110 degrees and thus the measuring head secured against pollution.

An important advantage of this invention is the combination of an optical deflection element and a closure unit, only one drive is required for both functions. This allows the measuring head build very compact. Details are described below.

3. Description of the invention using an example

Figure 1 shows the basic structure of a measuring head for trigonometric distance measurement, the arrangement of the optical elements corresponding to application P 40 32 361.7. A laser diode with a collimator ( 1 ) sends an almost parallel, focused beam through the plane-parallel plate ( 7 ) onto the workpiece ( 4 ), typically a rotated shaft. The beam is reflected on the wave and the diffuse reflection is imaged through the plate ( 7 ) by a lens ( 5 ) via a radiation guiding prism ( 6 ) on a linear sensor ( 1 ). An arrangement of many individual diodes, which can be read out electronically via charge transfer structures, is typically used as the linear sensor (hereinafter referred to as CCD sensor). The CCD sensor is read out by electronics not shown here in such a way that the location of the image of the light spot can be determined. If the workpiece changes its diameter, the distance between the measuring head and the workpiece surface also changes, so that the angle at which the reflex is imaged. This results in a changed location on the CCD sensor, which is evaluated by the electronics.

The plane-parallel plate ( 7 ) is rotatably mounted about the axis ( 8 ). A rotation around this axis causes the beam path to be deflected, as shown in Figure 2. This picture shows the top view of the optical arrangement. The beam path outside the sensor head is offset by rotating the plate ( 7 ) by the angle ( 9 ) by a small amount ( 10 ). Both the illuminating beam and the beam path through the lens are hit in the same way.

Figure 3 above shows the version of the plane-parallel plate in the drum-shaped closure body. If the closure body ( 3 ) is aligned in the same way with respect to the housing ( 11 ), the light from the laser and the reflected light can enter and exit freely. This also applies to the angular range from here z. B. +/- 10 degrees. However, if the shutter body is turned 90 degrees, the shutter is completely closed, the optical elements cannot be contaminated by splashes coming from outside ( Figure 3, top right). A typical design of the closure body ( 13 ) with an inserted plane-parallel plate ( 7 ) is shown in the lower part of Figure 3. Only a small, oval opening ( 23 ) is provided for the exit area of the laser beam, underneath there is the relatively large window ( 23 ) corresponding to the entrance aperture of the receiving optics. This closure body is supported by two ball bearings ( 22 ) and ( 24 ). The exit of the laser beam ( 23 ) is also blackened inside the closure body in order to avoid reflections. The small diameter acts like a mechanical and optical diaphragm, so that the point at which the laser beam emerges from the window cannot be hit by side-pointed spikes and thus cannot be contaminated. If a coating has formed over time, the resulting diffuse reflections are suppressed by the optical effect of the diaphragm tube. This prevents optical interference from undesired workpiece reflections.

Fig. 4 shows the elements shown above in interaction, here also the gear ( 12 ) and the drive unit ( 19 , 20 , 21 ) are shown. The drive unit consists of the actual motor ( 19 ), a reduction gear ( 20 ) and a pulse generator ( 21 ). A stepper motor can also be used. Also not shown is a limit switch that detects the 90 degree position of the closure. The angular positions of the closure are determined by counting the pulses from the pulse generator, the limit switch defines the absolute start (counter reading = zero). Numerous other known solutions are possible for the drive of the closure and the determination of the angular position, which will not be discussed further here.

Claims (5)

1. Optical arrangement in a device for measuring distances and detecting workpiece edges according to the trigonometric method, consisting of a laser diode with collimator optics, which illuminates a workpiece in a point-like manner, an imaging optics that the diffuse reflection on the workpiece via a prism onto a linear CCD-Senso images, arranged in a configuration such as B. in the patent application file number P 40 32 361.7, characterized in that a plane-parallel glass plate is inserted into the beam path between the measuring head and workpiece, which is rotatably mounted in an axis perpendicular to the illuminating beam, so that with the rotation of this plate a parallel deflection of the beam and, at the same time, of the reflected beam is carried out transversely to the direction of the distance measurement, there being means for driving this rotation and means for determining the angle of rotation, whereby the location of the point of impact of the laser beam on the workpiece by small but very precisely defined paths perpendicular to the axis of the Distance measurement can be moved. 2. Arrangement according to claim 1, characterized in that the plane-parallel plate at the same time as serves optical window and is embedded in a drum-shaped closure body, which at one Rotation of about 90 degrees almost complete closure of the sensor head and thus protection Guaranteed against moisture and splashing water while in the position from about -10 degrees to about +10 degrees the beam path for the laser illumination of the workpiece and the recording of the reflected Completely releases light, with a practically linear relationship in this angular range between the angle of rotation and the beam deflection. 3. Arrangement according to claim 1 and 2, characterized in that the plane-parallel plate in the optical Meaning is designed as a filter and only wavelengths in a defined, limited wavelength range pass, which corresponds to the wavelength of the radiation emitted by the laser diode, so that the sensor head essentially only receives radiation originating from the laser diode. 4. Arrangement according to claim 1 to 3, characterized in that the plane-parallel plate through an electric motor is driven by a gear and the motor by an electrical pulse generator and counts the angular position of the Plate is determined and by measuring the pulse frequency the speed of rotation of the plate is determined. 5. The device according to claim 1 to 4, characterized in that the drum-shaped closure body is designed so that on the exit side of the laser beam a narrow, deep, blackened inside Bore is provided, which is effective as a mechanical and optical diaphragm and the optical Protects and ensures windows at the point of passage of the laser beam from splashes and dirt that the part of the laser radiation diffusely scattered at the window outlet due to soiling can reach the receiving optics reflected from no further location of the workpiece.