WO1988004416A1

WO1988004416A1 - Device for inspecting rotationally-symmetrical parts

Info

Publication number: WO1988004416A1
Application number: PCT/DE1987/000574
Authority: WO
Inventors: Günter HEGE; Michael Struck
Original assignee: Robert Bosch Gmbh
Priority date: 1986-12-08
Filing date: 1987-12-04
Publication date: 1988-06-16
Also published as: ES2005966A6; DE3641862A1

Abstract

The device is intended in particular for inspecting circular-cross-section sealing rings known as O-rings. Two radiation sources (10, 11) are provided emitting radiation (12, 15) of a given frequency. The common light beam (16) is directed on to the surface to be checked (29) of the O-ring (24) by means of a beam forming system (20) and a first rotary mirror (21) as well as by a concentrating lens (22). The radiation (30) reflected from the surface (29) arrives at an arrangement of sensors (33) after passing through another convex lens (31) and deflection by a second rotary mirror (32). The sensor arrangement (33) comprises a first radiation sensor (34) which sends to an evaluation unit (35) an output signal which depends on the point of impingement of the radiation on the active surface (36) of the first sensor (34). Two further radiation sensors (35, 44, 49) are provided which supply the evaluation unit (35) with an output signal that varies according to the radiation intensity of said sensors (44, 49). Upstream of the latter are arranged colour-permeable filters (42, 47), the pass-band of one filter (42) being modulated to the radiation frequency (15) of the first radiation source (10), and that of the other filter (47) being modulated to the other radiation frequency (12) of the second radiation source (11). The apparatus described automatically identifies faults characterized by different geometrical and colour markings on the O-ring surface (29).

Description

Device for testing rotationally symmetrical workpieces

State of the art

The invention relates to a device for testing rotationally symmetrical workpieces, in particular sealing rings with a circular cross section, so-called O-rings, according to the preamble of the main claim. Defects on O-rings can be geometrical defects on the parting line, e.g. shrinkage, notches along the parting line, protruding burr, excessive deburring, and geometrical defects without a preferred position, e.g. imperfections due to unfilled form, deposits in the form, inclusion of foreign material, flow marks , Cracks, as well as other defects, eg too rough surface, inclusion of foreign material without changing the geometry (color change). In order to achieve the desired quality of the O-rings with regard to freedom from defects, a single or repeated 100% manual visual inspection according to limit samples has been carried out so far. This test technique has the disadvantage that the 100% error-free nature cannot be achieved due to the human inadequacies and, in addition, the test costs for this part are very high. An O-ring test device that could perform an automatic O-ring test has not been disclosed to date. From DE-OS 32 32 885 a device for the automatic inspection of surfaces is known. A radiation source is provided, the focused radiation of which is guided over a workpiece surface, the radiation reflected by the surface being evaluated according to certain criteria for the surface quality. The reflected radiation strikes one. Radiation receivers in the bright field and, on the other hand, to a plurality of radiation detectors arranged in the same plane around the bright field detector, which detect the total angular distribution of the radiation backscattered from the workpiece surface in terms of amount and direction. Damage to the workpiece surface changes the radiation reflected in the dark field or bright field. However, the known device is not suitable for testing O-rings since, for example, the defect which only causes a color change due to the inclusion of foreign material in the O-ring surface without a change in geometry is not detected.

Advantages of the invention

The device according to the invention for testing rotationally symmetrical workpieces, in particular sealing rings with a circular cross section, so-called O-rings, has the advantage that all of the specified errors, in particular foreign inclusions without changing the geometry, can be detected. A radiation source is provided which emits radiation of a predetermined frequency lying in the optical frequency range. Part of the radiation reflected from the surface of the workpiece to be tested is directed onto a radiation detector which emits an output signal proportional to the irradiance to an evaluation device. The direction of the radiation reflected by the workpiece to be tested is detected by the same or by a further radiation detector, which emits a signal which is dependent on the point at which the radiation hits the detector the evaluation device delivers. A color deviation or a geometry error is recognized in the evaluation device by comparing the measured values recorded with stored comparison values.

Advantageous further developments and improvements of the device specified in the main claim are possible through the measures listed in the subclaims. It is advantageous if the workpiece is clamped on a rolling device which comprises a rotatable clamping mandrel and a slide for rolling the workpiece on the mandrel. Color detection is improved if two radiation sources are provided, which emit two radiations that can be predetermined and have a different frequency in the optical range. A detector is provided which emits a signal to an evaluation device which is proportional to the intensity of the radiation reflected by the workpiece to be tested at the one frequency, and a further detector is provided which emits a signal to the evaluation device which is proportional to the intensity of the radiation reflected from the workpiece to be tested at the other frequency. A color contrast measurement is possible with the output signals of the two color-selective detectors.

Semiconductor lasers whose output power can be controlled are particularly suitable as radiation sources. In cost-sensitive systems, however, halogen lamps can also be used, for example, from whose broadband emission spectrum the desired radiation components can optionally be selected using a color filter.

A power control of the radiation sources has the advantage that strong fluctuations in intensity at the radiation detectors caused by a strongly different reflecting workpiece surface can be reduced to easily manageable values. The device according to the invention uses the light section principle as the optical measuring method, which fulfills all the requirements for detection and measurement of the workpiece defects to be expected. In the light section method, a light beam or a light band is projected obliquely onto the workpiece to be tested, preferably at an angle of less than or equal to 45 ° to the surface normal. The profile curve of the surface is contained in the radiation reflected by the workpiece to be tested. The angle of inclination between the incident radiation and the surface normal increases the resolving power of the device by increasing the profile line. Within the limits of the depth of field of the lenses used, the light section process clearly reduces a three-dimensional geometry into a two-dimensional image, sequentially for the workpiece surface that is currently illuminated by the light beam. The entire surface of a workpiece can thus be checked in sections. So that the detectable surface area of the workpiece does not fall below a certain size without the workpiece having to be moved with the rolling device, at least one first movable mirror is provided, with which the incident radiation is cell-shaped or with another pattern via the O-ring to be tested to be led. If appropriate, a further rotatable mirror is arranged in the beam path of the reflected radiation, which enables the deflection of the reflected radiation to be adapted to the limited radiation detector surfaces.

Further details and advantageous developments of the device according to the invention result from further subclaims in connection with the following description. drawing

FIG. 1 shows a structure of a device according to the invention and FIG. 2 shows a light section arrangement in the region of an O-ring to be tested according to section line II-II 'from FIG. 1.

Description of the embodiment

1 shows a first and a second radiation source 10, 11. The radiation 12 emitted by the second radiation source 11 is combined with a deflection mirror 13 and a beam splitter 14 with the radiation 15 emitted by the first radiation source 10 to form a light beam 16. The term “light” is not intended to restrict the frequency range of the optical radiation 12, 15 emitted by the two radiation sources 10, 11 to the visible part of the optical frequency range. The term “optical frequency range” is understood to mean the frequency range of the ultraviolet, visible and infrared radiation. The two optical radiations 12, 15 each have a predetermined frequency. Lasers which emit radiation of the desired frequency are advantageously used for the two radiation sources 10, 11.

Semiconductor lasers are particularly suitable because their output power can be easily controlled via a control circuit 17. Thermal radiators, in particular halogen lamps, can also be used as an inexpensive alternative to lasers. The desired spectral component of the broadband radiation emitted by the thermal radiators is transmitted with the aid of first and second color transmission filters 18, 19. The light beam 16 arrives in a sharply focused manner as incident radiation 25 via a beam-shaping device 20 and via a rotatable deflecting mirror 21 and via an imaging optics embodied as a converging lens 22. Workpiece to be tested 24. The workpiece has a rotationally symmetrical shape. Such workpieces are, for example, sealing rings with a circular cross section, which are referred to as O-rings. In the further description, the device according to the invention is described on the basis of the testing of O-rings. The radiation 30 reflected by a surface segment 29 of the O-ring 24 passes through an imaging optics 31, which is preferably designed as a converging lens, and via a second rotatable mirror 32 to a sensor arrangement 33. The sensor arrangement 33 comprises a first radiation detector 34 which outputs an output signal outputs to an evaluation device 35, which depends on the impact point of the reflected radiation 30 on an active surface 36 of the first sensor 34. The reflected. Radiation 30 is imaged on the surface 36 of the first sensor 34 using a converging lens 37. Two beam controllers 38, 39 are arranged in the beam path between the second rotatable mirror 32 and the converging lens 37, which couple out part of the reflected radiation 30. The radiation 40 coupled out by the first beam controller 38 passes via a deflecting mirror 41 and a third color transmission filter 42 to a converging lens 43, which images the coupled out radiation 40 on a second radiation detector 44, which emits an output signal to the evaluation device 35 which is proportional to its radiation intensity is. The radiation 45 coupled out from the second beam splitter 39 passes via a further deflecting mirror 46 and a fourth color transmission filter 47 to a converging lens 48, which images the coupled radiation 45 onto a third radiation sensor 49, which emits an output signal to the evaluation device 35 which is proportional to it Irradiance is. The evaluation device supplies output signals to three actuating devices 50, 51, 52. The first actuating device 50 moves the first rotatable mirror 21 and the second actuating device 51 moves the second rotatable mirror 32. Both rotatable mirrors 21, 32 are rotated by one on the drawing plane in FIG. 1 perpendicular axis rotated in the two indicated arrow directions 53, 54. The third actuating device 52 moves a rolling device which comprises a clamping mandrel 25 which can be rotated about its axis 26 and a slide 27 which can be moved parallel to the axis 26 of the mandrel 25. The direction of parallel movement is designated by reference number 28.

Furthermore, the evaluation device 35 emits signals to the control circuit 17, which controls the radiation power of the two radiation sources 10, 11.

Furthermore, the evaluation device 35 is connected to an evaluation and input unit 56, which is provided on the one hand for the input of data and commands for the evaluation device 35 and on the other hand for the output of the measured values of the O-ring 24 to be tested, determined by the evaluation device 35.

FIG. 2 is a detailed image according to the section line II-II 'shown in FIG. 1, which shows the incident and reflected radiation 23, 30 between the two converging lenses 22, 31 in the region of the workpiece 24. The parts which correspond in FIGS. 1 and 2 are in each case entered with the same reference symbols. The incident radiation 23 forms an angle of incidence 57 with the surface normal 59 on the surface segment 29 of the workpiece 24. The radiation 30 reflected by the surface 23 forms an angle of reflection 58 with the surface normal 59. The device according to the invention works as follows:

The light beam 16 is guided with the first rotatable mirror 21 in a cell shape or with any other pattern over the surface segment 29 of the workpiece 24, for example an O-ring. The incident radiation 23 forms with the surface normal 59 of the segment 29 an angle of incidence 57, which is preferably less than or equal to 45 °. The radiation 30 reflected by the segment 29 has a change in position during the scanning, which reflects the profile line of the O-ring surface. If the angle of incidence 57 is chosen to be approximately 45 °, then the angle of incidence 58 is also approximately 45 ° and the profile curve that is created appears excessive in the ratio of root 2: 1. This measuring method has long been known as a light section method in optical surface inspection technology (K. Räntsch: Optics in precision measurement, Munich, Hanser, 1949).

The reflected radiation 30 reaches the active surface 36 of the first radiation sensor 34. Since the point of incidence of the incident radiation 23 on the O-ring 24 to be tested is known at all times, the point of incidence of the reflected radiation 30 on the first sensor 34 is also below that Prerequisite for an undisturbed surface 29, given at all times by optical imaging relationships. A deviation of the position is determined by the evaluation device 35 by comparison with a "good" pattern and processed further. Statistics and / or output via the input and output unit 56 then take place, for example.

The detectable surface segment 29 without moving the O-ring depends on the maximum possible deflections of the two rotatable mirrors 21, 32 and on the surface of the detectors 34, 44, 49. A change in location of the reflected radiation 30 on the first sensor 34, due to the movement of the first rotatable mirror 21, is automatically taken into account in the evaluation in the evaluation device 35. From a certain position of the first rotatable mirror 21, the reflected radiation no longer strikes the active surface 36 of the first sensor 34. The measurement range can then be expanded by the second rotatable mirror 32. At least with larger deflections by the first rotatable mirror 21, the reflected radiation 30 is tracked by the second rotatable mirror 32 in such a way that it always falls on the active surface 36 of the first sensor 34. Since the second rotatable mirror 32 is also controlled by the evaluation device 35 via the second actuating device 51, the position of the second rotatable mirror 32 is known at all times in the evaluation device 35 and can be taken into account when evaluating the measurement result.

The entire surface of the O-ring 24 cannot be scanned in one scan. Therefore, the O-ring 24 clamped on the mandrel 25 is rotated about its axis 26 by the adjusting device 52. In addition, the actuating device 52 actuates the slide 27, which can be moved parallel to the O-ring axis 26 and exerts a compressive force either on one or the other O-ring contact surface, which causes the O-ring 24 to roll on the mandrel 25.

Part of the reflected radiation 30 is coupled out by the beam splitter 38 and imaged on the second radiation sensor 44. However, only the radiation components which the third color transmission filter 42, which is matched to one of the two emitted radiations 12, 15, pass onto the second sensor. Part of the reflected radiation 30 is further masked out by the beam splitter 39, which is imaged on the third radiation sensor 49. Only those radiation components that match the fourth color transmission filter 47, which is matched to the other of the two emitted radiations 12, 15, can strike the third sensor 49 sieren. Since the second and third sensors 44, 49 each output an output signal to the evaluation device 35 that is proportional to the irradiance, these two sensors 44, 49 detect a change in the intensity of the two radiation components 12, 15 in the reflected radiation 30. A change in the location of the reflected radiation 30 on the surfaces of the two sensors 44, 49 has no effect on the measurement result, as long as the surface area is not left, in which the output signal is proportional to the irradiance. A change in the intensity of one or the other or both radiation components 12, 15 indicates a frequency-dependent reflection on the O-ring 24 to be tested if no change in position is detected by the first sensor 34 at the same time. From the determined relative change in the output signals of either the second sensor 44 or the third sensor 49 or a relative change in the ratio of the two signals to one another, a change in color of the surface segment 29 under test can be concluded. By storing the known color changes in the evaluation device 35 before the actual measurement begins, a quantitative indication of color changes, for example as changes in the color coordinates in the color triangle, can be displayed via the input and output device 56. Another evaluation method is a neighborhood analysis in which the position and color deviation of the reflected radiation 30 from one scanning point on the segment 29 to the next is detected and evaluated and compared with stored reference values.

A color change arises in particular due to inclusions of foreign material in the O-ring 24. With the device according to the invention, such errors can be detected and displayed. A simplified embodiment of the device according to FIG. 1 is given if only one radiation source is provided instead of the two radiation sources 10, 11. The sensor arrangement 33 contains the first radiation sensor 34, which detects the position of the reflected radiation 30 and a further radiation sensor, which measures the irradiance. In this arrangement, none of the color filters 18, 19, 42, 47 is required. A color change in the surface of the workpiece 24 leads to a change in the intensity of the reflected radiation 30. If the first sensor 34 detects no change in position and, at the same time, the intensity of the reflected radiation 30 changes, a color change in the workpiece surface can be concluded at least qualitatively.

A further possibility for simplifying the device with a radiation source is given by using only a single radiation sensor. This sensor simultaneously detects both the point at which the reflected radiation 30 strikes the sensor and the intensity. All types of one- or two-dimensional multi-sensor arrangements are suitable. Photodiode lines are preferably used.

In a further embodiment of the device according to the invention, more than two radiation sources can be provided, all radiation sources emitting radiation in the optical frequency range with frequencies different from one another. The sensor arrangement 33 then contains further decoupling paths 40, 45 for the reflected radiation 30, which lead to color-selective radiation sensors 42, 44 and 47, 49, respectively. With this arrangement, an even more precise color analysis can be carried out.

Claims

Expectations

1. Device for testing rotationally symmetrical workpieces, in particular sealing rings with a circular cross section, so-called O-rings, for surface defects, characterized in that at least one radiation source (10, 11) is provided, the radiation (12, 15) of which on the surface (29 ) of a workpiece (24) to be tested, imaging and beam shaping means (20, 22) being provided between the radiation source (10, 11) and workpiece (24), and in that a radiation sensor arrangement (33) is provided which has at least one sensor (34, 44, 49) which outputs an output signal to an evaluation device (35) which is proportional to the irradiance and which depends on the point at which the radiation strikes the sensor surface (36), the workpiece (24) and sensor (34, 44, 49) imaging means (31, 37, 43, 48) are provided.

2. Device according to claim 1, characterized in that the sensor arrangement (33) has at least one radiation sensor (34) which emits an output signal as a function of the impact of the incident radiation (30) on the surface (36) of the sensor (34) and that at least one further sensor (44, 49) is provided which emits an output signal which is proportional to the irradiance of the sensor (44, 49).

3. Apparatus according to claim 1 or 2, characterized in that at least two radiation sources (10, 11) are provided which emit predetermined different radiation lying in the optical spectral range.

4. The device according to claim 3, characterized in that the sensor arrangement (33) comprises at least a first radiation sensor (34) which has a signal as a function of the impact of the reflected radiation (30) on the surface (36) of the first sensor (34 ) and that at least two further sensors (44, 49) are provided which emit an output signal as a function of the irradiance, a color transmission filter (42, 47) being arranged in front of the second and third sensors (44, 49), respectively the transmission range of the first color transmission filter (42) is matched to the radiation (15) emitted by the first radiation source (10) and the second color transmission filter (47) is matched to the radiation emitted by the second radiation source (11).

5. Device according to one of the preceding claims, characterized in that a rolling device (25, 27, 52) is provided for complete detection of the workpiece surface.

6. The device according to claim 5, characterized in that the rolling device comprises at least one rotatable about the workpiece axis (26) mandrel (25) and a parallel to the axis (26) movable slide (27), wherein to rotate the mandrel (25) and A control device (52) controlled by the evaluation device (35) is provided for executing the movement (28) of the slide (27).

7. Device according to one of the preceding claims, characterized in that the radiation source (10, 11) is a laser.

8. Device according to one of the preceding claims, characterized in that the radiation source (10, 11) is a semiconductor laser.

9. Device according to one of claims 1 to 6, characterized in that the radiation source (10, 11) is a thermal radiator and that in front of the radiation source (10, 11) at least one color transmission filter (18, 19) is arranged, which a predetermined Frequency range of the radiation (12, 15) can pass.

10. The device according to claim 9, characterized in that the thermal radiation source (10, 11) is a halogen lamp.

11. Device according to one of the preceding claims, characterized in that a control circuit (17) for power control of the radiation source (10, 11) emitted radiation (12, 15) is provided.

12. Device according to one of the preceding claims, characterized in that at least one first rotatable mirror (21) between the radiation source (10, 11) and the workpiece (24) is provided.

13. Device according to one of the preceding claims, characterized in that at least one second rotatable mirror (32) between the workpiece (24) and the sensor arrangement (33) is provided.

14. Device according to one of the preceding claims, characterized in that a beam splitter (14) is provided for combining the radiation (15) of the first radiation source (10) and the radiation (12) of the second radiation source (11).

15. Device according to one of the preceding claims, characterized in that between the first rotatable mirror (31) and the workpiece (24), an imaging optics, preferably a converging lens (22) is arranged.

16. Device according to one of the preceding claims, characterized in that between the workpiece (24) and the second rotatable mirror (32) an imaging optics, preferably a converging lens (31) is arranged.

17. Device according to one of the preceding claims, characterized in that the incident on the surface to be tested (29) of the workpiece (24) radiation (23) with the surface normal (59) on the surface (29) of the workpiece (24) one Forms an angle of approximately 45 °.

18. Device according to one of the preceding claims, characterized in that for the rotation (53) of the first mirror (21) a first actuating device (50) and for rotation (54) of the second rotatable mirror (32) a second actuating device (51) is provided are connected to the evaluation device (35).