APPARATUS FOR DETECTING THE POSITION OF AN OBJECT

Abstract: The invention relates to an apparatus for determining the position of a moving object. A transmitter generates a coherent beam of radiation (13) which is reflected by a first mirror (12) to an operating area. The radiation reflected by the detected object is reflected onto a second mirror (29) which is rotatable synchronously with the first mirror (12), and the reflected radiation is detected by a receiver. According to the invention, the transmitter, the receiver, the first mirror (12) and the second mirror (29) are located in a common plane.

Description: Apparatus for detecting the position of an object The invention relates to an apparatus according to the preamble of claim 1. An apparatus of this type is disclosed by EP-A-455305. The drawback of the known apparatus is that the sensor described there is relatively tall and takes up much room underneath the plane of observation. The invention eliminates the abovementioned drawback and to this end is designed as claimed in claim 1. This makes a simple sensor of limited overall height possible. According to a refinement, the apparatus is designed as claimed in claim 2. Synchronous rotation of the first mirror and the second mirror is thus implemented in a simple manner. According to another embodiment the apparatus is designed as claimed in claim 3. This enables synchronous rotation of the first mirror and the second mirror in a compact and simple design. According to a refinement, the apparatus is designed as claimed in claim 4. This enables accurate location of the object. According to a refinement, the apparatus is designed as claimed in claim 5. The accuracy of the location is thus further improved. According to a refinement, the apparatus is designed as claimed in claim 6. By carrying out an additional observation if required it is possible to obtain additional information in a simple manner for the purpose of determining the position of the object. According to a refinement, the apparatus is designed as claimed in claim 7. This allows position information to be generated in a simple manner, independently of the measurement of the rotational position of the mirrors. According to a refinement, the apparatus is designed as claimed in claim 8. This allows the position of the object to be determined by simple means . According to a refinement, the apparatus is designed as claimed in claim 9. This allows the positional data to be relayed, at more or less constant intervals, to a controller allowing these to be processed in a simple manner. The invention is explained below with reference to a few embodiments with the aid of a drawing in which: figure 1 shows a schematic side view of an application of the apparatus, figure 2 shows a schematic plan view from above of a first specific embodiment of the apparatus, figure 3 shows a schematic plan view from above of a second specific embodiment of the apparatus, figure 4 shows a schematic plan view from above of a third specific embodiment of the apparatus, figure 5 shows a schematic plan view from above of a fourth specific embodiment of the apparatus, figure 6 shows a plot of the observations by the apparatus in the case of a moving object, figure 7 shows a plot of the observations of the moving object of figure 6 at a higher scanning frequency, figure 8 shows a plot for reproducing the observation according to figure 7, wherein a limited number of observations is reproduced, and figure 9 shows a schematic plan view from above of a fifth specific embodiment of the apparatus. Figure 1 schematically shows an udder 2 of a mammal such as a cow with teats 1 where, for the purpose of milking the mammal, milking cups 5 must be applied automatically. The animal to be milked is standing in a milking stall. In an apparatus in which application takes place fully automatically, the milking cups 5 are moved underneath the teats 1 by means of a manipulator 6. In the example shown, the manipulator 6 moves a plurality of milking cups 5 simultaneously, although it is also possible for the manipulator 6 to move the milking cups 5 one by one to below the respective teats 1. When the milking cups 5 are applied it is necessary for the manipulator 6 to follow the movements of the animal and particularly the movements of the udder 2, for which purpose, preferably, the movements of one of the teats 1 are tracked, as it is known that during application of the milking cups 5 the relative positions of the teats 1 are more or less constant. To track one of the teats, the manipulator 6 is linked to a sensor 4. If required, the sensor 4 can also determine the positions of the other teats, for example by looking at the udder 2 from near different positions underneath the cow. The sensor 4 generates a sensor beam 3 in a horizontal plane above the milking cups 5. In the example shown here the sensor 4 is linked to the manipulator 6, a possible option involving, for example, the sensor being located next to the milking stall, provisions being made for traversing the sensor beam 3 in a vertical direction, so that the position of the teats 1 can be determined in animals whose teats 1 are at different heights. Regarding proper functioning of the sensor 4 it is necessary for the sensor beam 3 to be as flat as possible so that the tops of the milking cups 5 and the bottom of the udder 2 will not interfere with the measurements. Likewise it will be of advantage if the distance between the teats 1 and the sensor 4 can be relatively large, as the teats can then more readily be found during the initial stage of applying the milking cups 5, so that the animal to be milked will retain more freedom of movement. Figure 2 shows a first specific embodiment of sensor 4 in a schematic plan view from above. A housing 15 is provided with a window 11 and a base plate 14. Fastened to the base plate 14 is a rotatable disk 23 which can be rotated in a direction of rotation 20 about an axis of rotation M by a drive 19. The lateral surface of the rotatable disk 23 takes the form of a polygon, in the case shown that of an octagon, the planes of the polygon being designed as specular surfaces parallel to the axis of rotation M. In figure 2, the rotatable disk 23 is shown by full lines in a first rotational position 21, and by broken lines in a second rotational position 22. Disposed on the base plate 14 is a laser radiation source 16 which emits a coherent beam of radiation 13 toward one of the specular surfaces on the lateral surface of the rotatable disk 23 which forms a first mirror 12, the coherent beam 13 in the first rotational position 21 being reflected as a first scanning beam 8 and in the second rotational position 22 being reflected as a second scanning beam 10. The coherent beam 13 and the scanning beams 8 and 10 lie in a common plane which is perpendicular to the axis of rotation M, and the scanning beams generated by the first mirror 12 pass through the window 11 and sweep an operating area 7. Also disposed on the base plate 14 is a detector 26, the axis of rotation M being located between the detector 26 and the laser radiation source 16. The detector 26 is an instrument which is provided, in a known manner, with means to allow the direction of an incident beam of radiation to be determined. The detector 26 is provided, for example, with a lens by means of which incident radiation is focused onto a photosensitive sensor, by means of which the position of the focused image is determined. The position determined by the photosensitive sensor depends on the direction in which the light source is observed. The lens for incident radiation of the detector 26 is positioned such that it lies in a common plane with the coherent beam 13, the scanning beams 8 and 10 and the observed reflections. An object present in the operating area 7 at a first position A, an example of such an object being the teat 1 of a mammal, will reflect the first scanning beam 8 as a first reflection 25 which is detected, via a second mirror 29, by the detector 26. The second mirror 29 is one of the specular surfaces on the lateral surface of the rotatable disk 23. In the drawing, the line 25 shown there represents the center line of the detected beam. An object which is present at a second position B will reflect the first scanning beam 8 as a second reflection 27. This second reflection 27 is detected by the detector 26 at a different angle. On the basis of the first rotational position 21 of the mirrors 12 and 29, which are determined in a manner to be specified below, and the angles observed by the detector 26 it is possible to determine, in a controller 18, the position of the objects in the operating area 7. The calculated positions are relayed via a signal link 17, for example to the controller of the manipulator 6. An object at a third rotational position C is illuminated by a second scanning beam 10, after the rotatable disk 23 has rotated to the second rotational position 22. Part of the radiation reflected by the object passes to the detector 26 via a third reflection on the second mirror 29, after which the position of the object is determined in the above-described manner. To determine the rotational position of the rotatable disk 23, the base plate 14 has a sensor 24 mounted thereon, by means of which, during rotation of the rotatable disk, the event of passing through the junction between two plane mirrors on the lateral surface is detected. This signal is used to calculate, in the controller 18, the rotational positions of the first mirror 12 and the second mirror 29. In another embodiment, the drive 19 is provided with means such as, for example, an encoder, for determining the rotational position of the rotatable disk 23. As the first mirror 12 is rotated, the first scanning beam 8 will exit through the window 11 and scan the operating area 7 during part of the rotation only. During the remaining part of the rotation there is a risk that the scanning beam 8 will be reflected via the inside of the housing 14 and produce a signal in the detector 26. To prevent this undesirable situation, the laser radiation source 16, in one embodiment, is switched on, depending on the rotational position of the first mirror 12, only when the scanning beam 8 sweeps the operating area 7. In another embodiment, a detector 9 is positioned on the base plate 14 and the laser radiation source 16 is permanently switched on. The detector 9 detects the scanning beam 8 just before the scanning beam 8 is about to sweep the operating area. In the controller, the number of degrees by which the mirror must rotate before the operating area 7 is swept is known, as is the number of degrees covered by the operating area. The detector 26 is then switched on only while the operating area 7 is swept, so that reflections within the housing 14 are not observed. An additional advantage of this embodiment is that it is precisely known in the controller at what rotational position of the rotatable disk 23 the scanning beam 8 will reflect into the detector 9, so that any irregular distribution of the mirrors on the lateral surface of the rotatable disk is compensated for. In the specific embodiment shown in figure 2, the distance between the first mirror 12 and the second mirror 29 is indicated as distance a, a being a function of the diameter of the rotatable disk 23. The distance a is of significance in establishing the size and location of the operating area 7 where the positions of the objects can be determined accurately. In the embodiment shown, the distance a is about 80 mm, and the operating area 7 is about 300 by 300 mm, being located at a distance of from about 260 mm to 560 mm from the axis of rotation M. Given that the objects to be detected can be observed sufficiently accurately at a distance of about 560 mm, it is possible in a simple manner to determine the position of the teats 1 and to guide the milking cups 5 toward the teats. Figure 3 shows a second specific embodiment in which the rotatable disk 23 is in the form of a dodecagon, the scanning frequency thereby being increased while the speed of rotation of the rotatable disk 23 stays the same. Figures 4 and 5 show a third and . a fourth specific embodiment in which the first mirror 12 and the second mirror 29 are disposed on different rotatable disks 23. These disks rotate about axes of rotation Ml and M2 , respectively. The rotation of the two rotatable disks 23 is coupled by means of a toothed belt 30, the disks being driven by a drive which is not shown. The sensor 4 operates according to the above- described procedure, the advantage of these embodiments being that the sensor 4 can be designed to be narrower while dimension a stays the same. As an alternative to the drawn embodiment comprising one toothed belt it is also possible, in the case of a larger distance a, to employ a plurality of toothed belts using one or more intermediate shafts. Figure 6 shows a plot of a detection signal S of an object which is detected by the scanning sensor 4, the object moving relative to the sensor 4. The scanning period is indicated by T, and as the object is moving, the signal S is found to be generated at a different time each time, during the scanning period T. For the control of the manipulator 6 it is undesirable to thus receive the positional data at irregular intervals, since the signals cannot then be processed correctly. Figures 7 and 8 show how this situation can be improved. As a result of the scanning frequency being increased, thereby shortening the scanning period T, and a number of observations then always being ignored during a reporting period R which is considerably longer than the scanning period T, the interval between observations as reported to the controller of the manipulator 6 becomes more regular, said controller consequently being able to operate more accurately. In a preferred embodiment, the scanning period T is 13 msec and the reporting period R is about 40 msec as a result every second and third measurement being ignored each time. For a scanning period of 13 msec, the rotating disk 23 of the embodiment described in figure 2 must perform about 580 revolutions per minute. Figure 9 shows a fifth specific embodiment of the sensor 4. Here, transceivers 31 are positioned on opposite sides of the rotatable disk 23. Each transceiver 31 is able to emit a coherent beam of radiation 13 and also to receive reflected light. The transceiver 31 is designed, for example, to include a laser source which, via a small prism, projects a coherent beam of radiation into the center line of the transceiver 31. The transceiver 31 is likewise provided with a receiver comprising a lens and detection means for determining the unsharpness of the image formed by the lens. This unsharpness is a yardstick for the distance between the observed image and the lens. By making use of two transceivers P and Q, which optionally can operate shortly after one another, the distance to the object A or B to be detected is measured from two positions, so that its position can be determined. In the first shown position of the rotatable disk 23, indicated by full lines, the transceiver P emits a ray of light 13 which, after reflection by the first mirror 12, illuminates the object A. The reflection off the object A, having been reflected by the second mirror 29, is intercepted by the transceiver Q, and the distance of the reflection is determined as R QA . This distance is encircled by a first circle from the notional position Q' . Q' is the notional reflection of the transceiver Q with respect to the average position of the mirror 29. A very short time later, when the rotatable disk 23 still has more or less the same rotational position, the transceiver Q emits a ray of light which illuminates the object A, the distance R PA being determined in a comparable manner and being encircled by a second circle from the notional position (not shown) of P. The intersection of the first and second circle, which can be calculated in a simple manner, defines the position of A. Figure 9 shows how the position of a second point B can be determined in a comparable manner, the rotatable disk 23 having a second position which is shown by broken lines. In other embodiments, the method involving determination of the position via measurements of the incident angle and/or of the rotational position is combined with the position measurement by means of determining the distance to the two receivers. Thus the position of the objects in the operating area is determined in two ways, thereby allowing the position to be used more reliably in order to control the manipulator. Other combinations of the above-described sensors are likewise possible. In the above-described specific embodiments, the use of laser light is described. This involves generation of the laser radiation in a known manner in such a way that a pulsed light source is produced which does not emit radiation continuously. The object to be detected is illuminated sufficiently intensely during ignition, and the energy emitted is kept within limits, so that the radiation is not harmful.

Claims: CLAIMS 1. An apparatus for determining the position of an object (1,A,B,C) in an operating area (7) comprising a transmitter (16;31) for generating a coherent beam of radiation (13), a receiver (26;31) for intercepting radiation (25,27,28) reflected by the object, a first rotatable mirror (12) for reflecting the coherent beam of radiation, a mirror (29) rotatable synchronously with the first mirror for reflecting the reflected radiation, a first sensor and a second sensor for determining in two dimensions the position of the object, wherein the transmitter, the receiver, the first mirror and the second mirror are situated in a common plane. 2. The apparatus as claimed in claim 1, wherein the first mirror and the second mirror form part of a body (23) which has an axis of rotation (M) which is perpendicular to the common plane. 3. The apparatus as claimed in claim 1, wherein the first mirror and the second mirror each form part of separate bodies whose rotations are coupled and whose axes of rotation (1X11,1X12) are perpendicular to the common plane. 4. The apparatus as claimed in any one of the preceding claims, wherein the mirrors during observation rotate continuously and the first mirror comprises means (9; 24) for determining the rotation position of the mirrors when a reflection is detected. 5. The apparatus as claimed in claim 4, wherein the second sensor comprises means for determining the angle of incidence of the reflected radiation upon the receiver . 6. The apparatus as claimed in claim 4 or 5, wherein the second sensor comprises means for determining the distance at which the object is detected by the receiver. 7. The apparatus as claimed in any one of the preceding claims, wherein the first mirror cooperates with the first transceiver (P) and the second mirror cooperates with a second transceiver (Q) , the transceivers (31) alternately acting as transmitters and as receivers. 8. The apparatus as claimed in claim 7, wherein the first sensor comprises means for determining the distance at which the object is detected by the first transceiver and the second sensor comprises means for determining the distance at which the object is detected by the second transceiver. 9. The apparatus as claimed in any one of the preceding claims, wherein means are present for ignoring a number of observations which is always constant .

Inventors: DESSING JACOBUS PETRUS MARIA, OOSTERLING PIETER ADRIAAN, DESSING, JACOBUS, PETRUS, MARIA, OOSTERLING, PIETER, ADRIAAN
Applicants: DESSING JACOBUS PETRUS MARIA, OOSTERLING PIETER ADRIAAN, PROLION BV, DESSING, JACOBUS, PETRUS, MARIA, OOSTERLING, PIETER, ADRIAAN, PROLION B.V.
Application year: 2000
Main classification: A01J5
IPC codes: A01J5, G01S7