WO1989002574A1

WO1989002574A1 - Method and device for inspection of spherical metal balls

Info

Publication number: WO1989002574A1
Application number: PCT/SE1988/000449
Authority: WO
Inventors: Gustav Rennerfelt
Original assignee: Gustav Rennerfelt
Priority date: 1987-09-09
Filing date: 1988-09-01
Publication date: 1989-03-23
Also published as: SE8703500L; SE8703500D0

Abstract

A method and a device for inspecting the surface of spherical balls by using known optical and electrical sensors which are positioned on a quickly rotating sensor spindle. The novel feature resides in that the ball is rotated about one turn mechanically about a first axis of rotation (A-A) which suitably is at right angles to the axis of rotation of the sensor spindle and that thereafter the ball is rotated about one turn mechanically around another axis of rotation (B-B) at right angles to the other axes. During both rotations the sensor spindle is rotated and scans the ball surface.

Description

METHOD AND DEVICE FOR INSPECTION OF SPHERICAL METAL BALLS

The present invention refers to a method and a device for surface inspection of three-dimentional metal balls in respect to surface exactitude and material fissures.

The term surface inspection is intended to comprise registering of surfaces defects. The surface defects may comprise spots less perfect surface smoothness (not fully polishe ), small pits, scratches, scratch-patterened surfaces, fissures, burr and the like.

As far as bearing balls are concerned, optical inspection is often performed together with an electrcal eddy-current method (hereafter designated EC). EC is an eddy-current metod for detecting fissures on the surface and/or within the ball.

The method used at present for surface inspection is il¬ lustrated in Figure 1 and comprises quick rotation of the ball between two pairs of steel discs 2, 3. On the respective shaft one of the discs 3 is firmly attached to the shaft 4 whereas the other disc 2 is freely journalled. The shafts 4 extend at an angle in relation to each other. By rotating the two shafts 4 with different velocities a wobbling rotational movement of the ball 1 is obtained. This wobbling permits the two stationary detector probes, the optical probe 8 and the EC-probe 9 within a short time to perform a scan of the total surface of the ball.

In order to perform scanning of the ball during the necessary- short time, about 0.5 sec. total time, the ball must be accelerated very quickly to a rotational .speed of about 3000 rpm. In order to avoid slipping due to the moment of inertia of the ball the contact pressure of the discs must be high and the ball must be dry. The present method has the following drawbacks: a) The point contact of the discs with the ball easily produces surface defects.

b) It is difficult to control the wobbling movement so that the entire surface is inspected completely.

c) The useful live of the discs is limited. Worn discs increase the extent of surface defects beyond the defects caused by "new" discs.

d) Prior to inspection the balls are subjects to washing. It the balls are wet, the discs slip. The contact force must be increased whereby the risk of a surface defect is increased. Accordingly, a drying step is required causing an additional risk of corrosion defects.

Attempts are made to avoid these troublesome discs by air- supporting the balls. Figure 2 illustrates a ball 1 within a bearing cap 5 having a sintered, air-permeable bearing surface 6. Nozzles 7 tangentially face the ball surface and thereby accelerate this ball 1 to about 3000 rpm. Above the ball detectors 8, 9 are stationarly mounted.

Rather than detecting the surface with the aid of stationary probes, the surface may be scanned by means of rotary probes. Figure 3 shows the same type of air-bearing as shown in Figure 2. The two probes 8, 9 in this case are attached to a rotaty spindle head 10 rotating at about 6000 rpm. The symmetry axes of the probes are directed towards the centre of the ball. In this arrangement it is only necessary to accelerate the ball 1 to about 500 rpm. and to bring about a wobbling movement thereof with the aid of air jets.

A disadvantage of air bearings resides in the high requirements concerning cleanness of the aid supplied and of the surrounding atmosphere. In addition, it is difficult to control the wobbling movement with the air of air jets in such a way that the entire surface of the ball is inspected. It is a purpose of the present invention to eliminate the above-mentioned problems. The method and device for performing this purpose are indicated in the attached claims 1 and 10 respectively. Figure 4 illustrates the working principle. Rather than using the surface of the ball, which in fact is the surface the quality of which is to be determined and which must not be damages during the test, to serve as the bearing surface for the rotation, the ball 1 is picked-up by a rotary, precision-journalled spindle 2. The ball 1 is held by a slight pressure between the sphere-cap-shaped end surface of the spindle 2 and the plane surface of the holder-on 3. The contact between the sphere-cap-surface of the spindle 2 and the ball 1 is extended and the mutual relative speed is zero. Due to the small surface pressure and the low wear the sphere- cap surface of the spindle 2 and the holder-on 3 may be manufactured of e.g. brass or Delrin which very tenderly acts on the ball. The rotary spindle head 4 with the sensors 5, 6 rotates at a high velocity, about 6000 rpm. The spindle 2 rotates the ball about the axis A-A (Y-axis) about 1 turn. The sensors have then inspected about 65% of the surface of the ball. The two probes of the constantly rotating spindle head 4 comprise an EC-probe and an optical probe the detector of which may be a CCD-array or photo-diod with an optical system, a light-emitting diod and an electronic drive. The working distance of the EC-probe from the surface of the ball could be 0.1 +/- 0.03 mm. The focusing depth of the optics is of about the same order of magnitude.

In may cases it is sufficient to inspect 65% of the total surface of the ball. However, the invention permits inspection of 100% of the surface of the ball.

When the spindle 2 has finished its rotation and come to a standstil and a 100% inspection is desired, another spindle 7 is forwarded to hold the ball against its holder-on 8 and rotate the ball about 1 turn about the axis B-B (X-axis) prior to stop. The spindles 2.and 7 are disposed at right angle in relation to each other.

Hereafter, the invention will be described in detail by reference to the attached drawings in which

Figure 1 schematically shows a known device for surface inspection of three-dimentional surfaces,

Figure 2 illustrates another known device for surface inspec¬ tion of balls, the balls being supported by air bearings,

Figure 3 shows a known embodiment of the device according to Figure 2,

Figure 4 sequentially shows the method according to the present invention and a device for performing the method,

Figure 5 shows an embodiment of the invention in a first side view (left part) and a second side view (right part) shifted 90° in relation to the first side view.

Figure 6 illustrates another embodiment of the device according to the invention, on the one hand, in side view (left part), and on the other hand in partial plane view from above (right part), and

Figure 7 shows another embodiment of the invention.

Figures 1 to 4 have been described initially. Figure 5 shows an embodment of the invention.

The balls are fed forward in a conduit 7. A feeding mechanism, 9 comprising a slide 10, a servo motor 12, an angle gauge 13, a reduction gear 11, feeds by means of a spindle 8 having a sphere-cap-shaped end surface (heareafter designated as sphere cap tool) the ball 1 into position. The sphere cap tool 16 is moved towards the ball 1 by means of the servo motor 22, the angle gauge 21, the reduction gear 23 and the slide 24. The sphere cap tool 16 and thereby the ball 1 are rotated about one turn with the aid of the motor 19, the angle gauge 20 (which also may be a tacho ^•generator), the reductor gear 18 and the presision bearing 17.

During this operation the spindle pobe is continiously working. This spindle probe comprises a motor 2, a tacho 14, a motor clutch 3, a bearing unit having slip rings 4, a spindle head provided with probes 5.

If this first measurement registeres non-permissible surface defects the sphere cap tool is retracted and thereby the holder-on 33 which is coupled to this slide movement causing the ball to fall obliquely downward (compare the right-hand section of the Figure). The sorting-out may now be performed. in a conventional way and is not a part of the invention.

If during this first inspection the ball is approved and if a 100% inspection is desired, the ball is supported in a similar way by the sphere cap tool 32 and the holder-on 33. The operation of this attachment is performed by means of the motor 26, the angle gauge 25, the reduction gear 27 and the slide 28. The sphere cap tool 16 now releases the ball 1 and moves backward about 0.05 mm. The rotation which now is performed at right angles in relation to the prior inspection is performed by means of the motor provided with the angle gauge 29 (which may also by a tacho generator) the reduction gear 30 and the bearing 31. After a rotation of about one turn the rotation is stopped and both sphere cap tools 16, 32 are moved backward about 4 mm permitting the ball to fall obliquely down for additional quality sorting. The process is started anew with the next ball. The .treating time for this process amounts to about 0.5 sec.

Figure 6 illustrates another embodiment of the invention.

The ball 1 is fed down into bins in the indexing table 4. This table is fed forward one bin pitch by means of the motor 9 the angle gauge 10, the reduction gear 8, the bearing unit 7 and the table centre 5. In the inspection position the ball 1 is held in a similar way as previously described. View A-A shows two identical manipulating units positioned at an angle of 90° in relation to each other. The sphere cap tool 30 is axially controlled by means of the motor 27, the angle gauge 28, the reduction gear 26 and the slide 25. The axial holder- on is here represented by the plane surfaces 23, 24 in the bin receiving the balls. As for the rest, the control is performed in a similar way as described before. The continious- ly working probe head, the rotation of which is performed by means of the motor 12, the tacho 11, the clutch 13 and the bearing unit with slip rings 14 and cable 15 is axially guided by the slide 16, the motor 18, and angle gauge 17 and the reduction gear 19. After the inspection, sorting may be performed at various stations following after the inspection station. At these sorting stations ejectors are provided which push out the ball in question through holes 3.

Figure 7 illustrate another embodiment of the invention.

Rather than using a rotary optical probe, a curved line having the curve angle of 90° is scanned by a number of stationary CCD-arrays 2 (charged-coupled-devices) provided with fibre optics 3 guiding the light from the surface to the arrays. The ball is operated in the same way as described before by the sphere cap tool 12, the slide 11, the motor servo (not shown) the motor 14, the tacho 15, the reduction gear 13 pressing the ball 1 against the holder-on 4 which is attached to the support 5. The EC-probe is quickly rotated by the motor 9, the tacho 8, the bearing unit with slip rings 10 and the cable 7. As an alternative to fibre optics small optical systems may be used in front of every CCD-array or photo diod. In another alternative embodiment a number of photo diods may be used provided on several places around the surface of the ball.

Rather than causing the shpere cap tool to press the ball against a stationary holder-on it is possible in accordance with an alternative embodiment to hold the ball by means of a a magnet in the shpere cap tool, thereby eliminating the need of a holder-on. The ball may also be attached to the sphere cap tool by means of vacuum.

Thus the equipment described above may be combined in many different ways.

The invention is defined by:

The ball is held by a spindle and rotated relative slowly about an axis while at the same time a quickly rotating sensor scans the surface and yields an EC-inspection and an optical inspection.

A fully secure inspection of exactly the desired surface is obtained (no uncontrollable wobbling).

There is no point contact or sliding against the ball surface that might cause surface defects.

The method permits computer-controlled sorting (classification) of the balls.

Claims

1. A method of inspecting the surface of spherical balls with the use of known optical and/or electrical sensors positioned on a quickly rotating sensor spindle, characterized in that: a) the ball rotates around a first axis of rotation (A-A) forming an angle, preferably 90°, with the axis of rotation of said sensor spindle, b) after a suitable number of turns, preferably about 1 turn, about said first axis of rotation (A-A) the ball is rotated about a second axis of rotation (B-B) forming an angle preferably 90°, with the said two other axes.

2. The method as claimed in claim 1 in which the ball is fixed in a position and rotated in relation to said sensor spindle with spindles having axes of rotations (A-A) and (B- B) respectively, characterized in that they have sphere-cap- shaped end surfaces which, in turn urge the ball against a plane holder-on surface facing the spindle in question.

3. The method as claimed in claim 2, characterized in that the ball is attached to the sphere cap surface by means of vacuum within the sphere cap.

4. The method as claimed in claim 2, characterized in that the ball is attached to the sphere cap surface in question by means of magnetic force acting within the sphere cap.

5. The method as claimed in any of claims 2 to 4, charac¬ terized in that the said spindles are fed forward into the working position and back during the insertion of balls by means of servo-guided slides.

6. The method as claimed in claim 5, characterized in that one of the spindles having a sphere cap surface is stationary, moves toward the ball and fixes it, turns the ball abut 360°, stops the rotation and releases the ball first when the other spindle with its sphere cap surface has fixed the ball and repeated the procedure about this new axis of rotation.

7. The method as claimed in claims 5 or 6, characterized in that the ball feed is performed by a sphere cap tool which is axially guided by a servo slide.

8. The method as claimed in any of claims 5 to 7, charac¬ terized in that the ball feed is performed by a servo-guided table having ball bins so equiped that the surfaces thereof act as stationary holder-on surfaces according to claim 2.

9. The method as claimed in any of the preceding claims, characterized in that the optical sensor is stationary, forming one or several optical systems which together cover a curved line on the ball having a curve angle of about 90° and that only the electrical sensor, preferably a eddy-current sensor, is positioned on the quickly rotating sensor spindle.

10. A device for performing the method according to claim 1 comprising known optical and/or electrical .sensors provided on a spindle for quick rotation, characterized by a first spindle (2) having a sphere-cap-shaped end surface provided to abut against the surface of the ball and to rotate the ball around a first axis of rotation (A-A) forming an angle, preferably 90°, with the axis of rotation (Z) of the sensor spindle, a second spindle (7) having a sphere-cap-shaped end surface provided to abut against the surface of the ball and to rotate the ball about a second axis of rotation (B-B) forming an angle, preferably 90°, with the said two other axes.

11. The device as claimed in claim 10, characterized by a plane holder-on (6, 32, Figure 5, 23, 24, Figure 6) cooperating with one of the spindles (16, 32) against which the spindle in question urges the ball during its rotation around respec¬ tively the first and the second axis of rotation.

12. The device as claimed in claim 11 in which the said optical and electrical sensors are mounted on the mantle surface of a round, conically truncated disc, characterized in that the opening angle is about 90° causing about 65% of the surface of the ball to be inspected when the ball rotates about the first axis of rotation, that the sensor spindle is rotated at about 6000 rpm. and that the other two ball rotating spindles rotate at about 500 rpm.