Feeler for producing measured value by touching a work piece

p0001The invention relates to a probe for measurement value formation when probing a workpiece according to the preamble of claim 1. Such probes are used in particular in multi-coordinate measuring machines in which the workpiece can be displaced relative to the button in several axes, the displacement is measured and when probing the workpiece measurement pulses are delivered.

p0002The measuring machine can be provided with a touch trigger probe, in which the workpiece with an extremely low measuring force is touched and the distance covered in the coordinate system at the time of probing is held. However, the measuring machine can also be equipped with a measuring probe for continuous scanning of surfaces, wherein the changing deflection of the probe is continuously measured and recorded. Many well-known button can be used for both modes.

p0003One problem with known devices is especially for the storage of the deflectable portion in the switch housing. At this storage extreme demands in terms of precision and operating characteristics. Especially when three coordinate measuring machine, the stylus with high precision in the three axes should be deflected or displaced without play or excessive friction occurs at the bearing point. Finally, should also be possible directly transmitted to the measuring element the Taststiftbewegung but without consuming transmission elements, etc. are required. Proposals for arrangements to coordinate more buttons are for example already known from DE-B-22 42 355 or in DE-B-27 12 181st However, these systems are relatively expensive and are not necessarily for a miniaturization of the components.

p0004Through the US-A-3,250,012 a push button has become known, in which the deflectable portion is mounted with a spherical cap in the housing, which is pressed by spring force against a joint socket. The stylus can be deflected in all directions, or move at exactly axial probing against the housing interior. A pressed against the flat surface of the spherical cap carriage transfers every movement of the spherical cap from its neutral resting position to a measuring element. This bearing is very advantageous in itself, since it can be produced easily and accurately and as each movement of the stylus is converted into a linear movement which is easily transmitted to the measuring element. A disadvantage of this known bearing, however, is that the stylus deflection in the X- and Y-axis is uncontrolled and therefore may run out of control. The stylus can rotate in the bearing itself also, which is undesirable in stellate styli and would lead to incorrect results. (See also DE-A-3603269)

p0005It is therefore an object of the invention to provide a switch of the aforementioned type in which precise measurement results can be achieved by exploiting the advantages of a spherical bearing. In particular, the deflection of the stylus is out running and twisting of the stylus is to prevent both trigger probes as well as measuring probes in continuous scanning operation. This object according to the invention is achieved with a button which has the features in claim. 1

p0006With the help of the fuse element in the ball element can be achieved at least in the neutral starting position in a deflection plane precise guidance. When trigger probes while it does not matter if this operation is removed with incipient deflection and the securing element not more is in operative connection with the guide member. Fractions of a second after the beginning of the excursion is the measurement result that is already stored, so that subsequent rotation of the stylus is inconsequential. The inventive arrangement ensures, however, that the stylus is in its neutral starting position rotationally mounted in the housing.

p0007A particularly advantageous arrangement is obtained if the safety element is a cylindrical pin whose axis is perpendicular to the central axis of the deflectable member or the feeler through the ball center. In this geometric arrangement can be seen, the stylus in one plane are deflected so that the cylindrical pin rotates about its own axis. He remains in engagement with the guide member. This arrangement allows a guide of the stylus in the X- and Y-axis, without complicated line guidance systems such as required in the aforementioned DE-B-22 42 355th

p0008The guide element is particularly simple from two parallel profiles, engages between the cylindrical pin of the fuse element at least in the neutral starting position. Of course, the cylindrical pin but could also, for example, engage in a groove on the housing inner wall. The parallel profiles can be but a particularly simple and precise form of cylindrical pins. The engagement of the cylindrical pin of the securing element is made easier still in that the end is conical.

p0009If the cylindrical pin is mounted to move axially in the ball element and means preload is pressed against the guide member, the highly precise guidance can be maintained not only in the neutral starting position, but also during a deflection movement. The conical end of the cylindrical pin is thereby pressed without play between the two pins of the guide member. The friction caused thereby is negligible and can be reduced through appropriate training of the cone angle. Further advantages can be there when the cylindrical pin with a screw is determined. With a switched operation of the stylus can be first dissolved the screw so that the cylindrical pin is pressed into the neutral position of the stylus against the guide member. In this position, the screw is tightened, so that the cylindrical pin is held in the neutral starting position always play between the two profiles of the guide element. If a permanent leadership wanted the scanning operation, the locking screw must be resolved of course, so that the cylindrical pin is permanently pressed against the guide member.

p0010The profiles of the guide element are advantageously mounted in a ring serving as a bearing for the ball element. The ball element can lie directly in the ring. A particularly high precision, however, achieved by a three-point bearing, wherein three bearing balls arranged on the ring, on which rests the ball element. The ring may be pressed on taster end of the housing in the housing, whereby a particularly high precision can be achieved.

p0011Further individual features and advantages of the invention will become apparent from the following description and from the drawings, in which exemplary embodiments are shown. Show it:<dl id="dl0001"><dt>figure 1</dt><dd>a cross-section through an inventive switch in an enlarged scale, </dd><dt>figure 2</dt><dd>a cross section through the bearing point of a modified embodiment,</dd><dt>figure 3</dt><dd>a horizontal section through the plane II according to Figure 2, but with slightly abgewandeltem Dowel,</dd><dt>figure 4</dt><dd>a plan view of the bearing point of the probe according to FIG 2, and</dd><dt>figure 5</dt><dd>a perspective view of the ball element in a simplified representation of the three axes of motion.</dd></dl>

p0012As shown in Figure 1, a key 1 comprises a housing 4, which is preferably cylindrical. At one end of the housing of the probe is clamped into a holder 3, which in turn can be attached to a coordinate measuring machine not shown here. In Figure 1, the probe 1 is shown in about 2.5-fold magnification, so that can be seen, the components in a small space with high precision must be accommodated.

p0013At the lower end of the probe housing 4, a deflectable part 7 is mounted, which carries a stylus 6 for probing a workpiece, the second The styli are interchangeably attached to the deflectable portion, for example by a screw connection, so that different configuration tactile pins can be clamped. In the embodiment, a probe star is shown with four single pins in the horizontal plane and with a pin in the axial direction. The ends of the individual pins are provided with buttons 21 balls as ruby.

p0014The mounting of the deflectable member 7 is effected by means of a ball member 9 which is constructed as a spherical cap. The ball element is pressed in axial direction against a bearing location, as will be described below with reference to Figures 2 to 4 in more detail. A fuse element 10 engages a housing-fixed guide member 11 so that the stylus 6 Evidently can not be twisted. By dashed lines the maximum deflection of the deflectable part 7 at an angle alpha is shown. With a switched measuring mode but this deflection only serves as collision protection with rapid probing of the workpiece, as the measurement result already registered with minimal deflection of the feeler 6 and the feed is switched off for the button.

p0015Inside the housing 4, a linearly movable carriage 12 is mounted. The carriage is formed as a circular ring and is pressed by spring force against the flat surface of the spherical cap, so that it always assumes a neutral starting position in unpolluted stylus. A pressure on the stylus from the bottom in the direction of arrow A or any permissible deflection of the stylus takes Evidently a linear displacement of the carriage 12 in the direction of arrow A.

p0016The linear motion is converted into a measuring pulse by means of a measuring element fifth The measuring element 5 can vary depending on the application, have a desired configuration. One example for inductive or capacitive systems, piezoelectric elements, magnetic or optical measuring and counting devices and the like would be. In the present embodiment, an incremental length-measuring system is shown, as it is described for example in EP-A-237 470 of the Applicant. Here, a beam of light is thrown through a provided with regular graduations, transparent scale 14 by means of a stationary light source arranged 20, which is fixed on a scale carrier 16th The scale carrier 16 is the continuation of the carriage 12 and is acted upon at its upper end by a bolt 15 which is biased under the force of the spring thirteenth The desired spring force of the bolt can be adjusted by means of an adjusting screw 19th The light pulses are registered behind the scale 14 by means of a receiving device 17 and supplied to an amplifier and computer not shown in detail here. The electrical connection to components outside of the probe 1 via a cable exit 18. Evidently, you can drag each deflection of the stylus 6 to an analog linear motion is converted, which can be determined with high precision and measured.

p0017In the figures 2 to 4 the mounting of the ball element or its guide 9 is shown in more detail, the motion geometry can be seen from FIG. 5 Figure 2 again shows the deflectable part 7 at the lower end of the housing 4. This part is non-positively connected with the spherical element 9 which is formed as a spherical cap. It also has a threaded bore 35 into which various tactile pins can be screwed. In order to prevent the penetration of dirt and dust into the bearing point, the deflectable part 7 is sealed against the housing 4 with an elastic bellows 31st An elastic buffer ring 32 provides also for a soft stop of the deflectable member 7 ringside 30th

p0018The spherical cap 9 is pressed by the slide 12 which engages the flat surface 36 against the pressed-in into the housing 4 ring 30th Unlike the embodiment according to Figure 1, however, the spherical surface is to not directly on the ring. Instead, the ring 30 is provided for example 33 from Rubin at a uniform angular distance with ball bearings. These bearing balls are up in wells and are as firmly glued to the ring. Alternatively, the beads may also be held in a bearing cage on the ring 30 and be rotatably mounted on the ring 30th The arrangement of the bearing balls can be seen in particular in FIG. 4

p0019The ring 30 has two parallel cylindrical profiles 26 are fixed, whose axes are parallel to the central axis 23 of the deflectable portion in the neutral starting position. These profiles can be, for example, high-precision machined hard metal pins or hardened metal pins. Transverse to the central axis 23 is a bore 28 disposed in the spherical cap 9 whose central axis precisely through the center 25 of the sphere (Figure 5). In this hole a cylindrical pin 22 is axially movable and tightly held. The movable cylinder pin 22 has at its end projecting from the ball end of a cone 27 and is pressed by a spring 29 in the bore 28 against the two cylindrical sections 26th

p0020Evidently puts the cone 27 relative to the profiles 26 upon deflection of the stylus arcuate movement back. If the stylus 22 in the spherical cap is fixed, so the cone is 27 only in the neutral starting position between the two profiles centered 26 while it moves away with increasing arc movement of the profiles. As already mentioned this centering enough in the neutral starting position when switching operation of the measuring machine. To 26 define the neutral starting position between the cone 27 and profiles accurately, a set screw 34 is released into the threaded hole 35 in the neutral starting position. Subsequently, the set screw is tightened, so that the cylindrical pin 22 remains fixed in the hole 28th In this way, the play-free centering of the pin 22 through the profiles 26 ensures always exactly in the original neutral starting position.

p0021For permanent measuring mode, the grub screw 34 remains permanently dissolved, so that the pin 22 is not only in the neutral starting position, but in every pivot position by the profile 26 is centered.

p00225 shows the coordinate system XYZ, in which a movement of the ball element 9 is possible. In an exactly axial loading of the probe in the Z direction of the cylindrical pin 22 is shifted between the two guide profiles 26, without the right angle between the cylinder pin 22 and the profiles changed 26th Since the axis of the cylindrical pin 22 passes exactly through the center of the sphere 25, the pin can rotate in a deflection of the ball element 9 in the Y direction in the direction of arrow B around its own axis 22nd It can be seen, is likewise no change in angle between the pin 22 and the profiles 26 If the ball element against it deflected in the X direction, so there is a rotation about the center of the sphere 25 in the direction of arrow C, wherein the angle between the cylinder pin 22 and the guide profiles 26 changed.