DE4030185A1 - Calibrating machine tools to generate complex shapes - optically scanning to provide data for comparison with reference e.g. for dental crown - Google Patents

Abstract

The blank material (8) is supported on a spindle and can be moved axially. Located on either side machining tools (11, 12) can be moved in a precision control mode to form the required profile. The form of the object can be obtained by creating a shadow on a group of CCD cells (72) when an i.r. source (71) is used. USE/ADVANTAGE - Precise calibration for dental mechanic.

Description

The invention relates to a method for calibrating a motor-driven and with the help of a feed device towards and away from a workpiece to be machined movable tool with respect to the workpiece or one Workpiece-holding holder, and device for performing procedure.

A particularly advantageous application of such a method and a device operating according to this method is disclosed in seen in dentistry, to the ready-to-use, form giving elaboration of a tooth restoration fitting body.

Such a method is described, for example, in EP-A-01 82 098 described. The tooth restoration fitting body is there in one Operation from a blank made of a suitable material, e.g. B. made of dental ceramics, individual and ready to use worked. A processing machine is provided for this purpose, which is a separator rotatably mounted in a tool carrier disc sheet contains. In addition, the processing machine contain a second, finger-shaped removal tool, with the more complicated one, with the cutting disc blade not work out editable shapes from the workpiece as well as the Have the surfaces of the fitting machined better.

The workpiece is placed on a holder that is tight is on the one hand and one or more stop surfaces, that have an exact positioning in relation to him Ensure the clamping device and on the other hand one or  several reference surfaces that allow adjustment of the position of the cutting blade with respect to the workpiece axis possible, contains.

To produce the desired shape of the fitting body are work Tool carrier and workpiece holder adjustable, where individually controllable adjustment motors for the tool thrust and the tool holder are present.

The fitting body is based on predetermined design data from the previously prepared tooth using a measurement Camera and a computer created with appropriate software are worked out from the workpiece blank.

To pre-orientate yourself about the position of the tool with respect to the workpiece and thus the feed To give the system a starting and reference point contains the known device in the field of the feed system for Tool a fork light barrier, with which the output position of the tool can be roughly defined.

To especially wear the work surfaces of the grinding being able to take tools into account can be done before a Machining a calibration of the tools regarding the Axes of the workpiece holder are made. This includes the known device a non-contact rotation number measuring device with a permanent magnet and an in ductive transducer. The frequency signals from the transducer go via a pulse shaper into a counter. In a logical Unit which, like the counter, belongs to a computer discrimination against certain, set frequency values, according to the speed of the tool. Under If the frequency rises above a certain value, tax becomes signals triggered.  

The calibration takes place in that the tool first with the normal idle speed to the narrowly tolerated Re reference surface of the workpiece holder opens. Because of this The drive of the tool will touch to a low level decelerated speed value. Based on the braking curve, the after the frequency value analysis described above can be determined calculated back to the point of contact or this arithmetically be determined.

In a second attempt, the reference point of the in the meantime, the workpiece has been rotated again by 90 ° discriminating against a higher speed value. This before gear corresponds to a smaller braking than the first Attempt.

Based on the positions determined using the braking curves and the starting position detected via the fork light barrier becomes the starting point for the start of editing or a into the machine control of the feed device Correction value determined. After calibration, the Be work of the blank in the not to be explained here Start wise.

Although with the known method and the one after that tendency device a calibration of the tool itself is possible, this method is possible with some spe specific disadvantages. So the braking curve is on who orientates the measurement by several parameters flows:

• - Speed or speed of the cutting disc
• - Shape of the cutting disc
• - Condition of the coolant and lubricant
• - Type of material that is "touched" on
• - Efficiency of the entire drive system

By these parameters which influence the measuring accuracy with regard to the achievable accuracy in determining the Starting position of the tool set certain limits.

The invention specified in claim 1 has the object reasons, in contrast an improved method and one after specify working device, in particular with the aim a calibration of tool and workpiece even more precisely to be able to make, and thus the starting position of the plant or a correction quantity for the tool feed to be able to specify more precisely.

Advantageous refinements and developments of the invention result from the subclaims. Based on the drawing an embodiment of the invention described in more detail. Show it:

Fig. 1 is a dental apparatus with the inventive device in a diagrammatic representation,

Fig. 2 shows part of the apparatus of Fig. 1 seen from above, in section,

Fig. 3 seen a part of the device according to Fig. 1 from the front,

Fig. 4, the workpiece position with holder in perspective Dar,

Fig. 5 is a block diagram for the control of the drives.

Fig. 1 shows a diagrammatic representation of the overall arrangement of a device according to the invention working in one embodiment for the manufacture of a tooth restoration fitting body, for. B. a tooth crown. The fitting body to be created can be constructed using an optical impression method with the help of a computer on a screen and then constructed in a processing machine from a suitable workpiece, e.g. B. made of dental ceramics. The individual components of this device are an optical camera 1 , a screen 2 , a keyboard 3 , a drawing ball 4 (trackball), a processing machine, generally designated 5 , and further mechanical, electrical and electronic components, not shown, contained in the housing 6 work together with the above components to create the fitting body. The basic structure and the mode of operation of such a device are described in the aforementioned European patent.

The housing 6 forms a processing chamber 7 into which some components of the processing machine, which will be explained in more detail later, protrude. These are essentially a holding and holding device for a workpiece 8 , from which the fitting body to be produced is manufactured, and two mutually opposite spindle arrangements 9 and 10 , which each have two tools (in FIG. 2 with 11 , 11 ' and 12 , 12 ' designated) wear for machining the workpiece 8 . The processing chamber 7 can be closed by means of a preferably transparent cover 13 during the processing. The housing 6 contains below the processing machine 5 a water tank 14 designed as a drawer and a chamber 15 in which a container for receiving a care product is held.

The processing machine 5 will he explained in more detail with reference to FIG. 2. Fig. 2 shows the machine in the region of the spindle assemblies 9, 10, sectioned in a plan view. First, the holder and storage of the work piece 8 , from which the fitting body is to be created, will be described in more detail. The workpiece 8 consists of a ceramic block 8 a, which is attached to a metallic pin-shaped holder 8 b by gluing or the like. The workpiece is inserted at the end of a spindle 16 designed as a hollow shaft and is held in a rotationally and tensile manner by means of a clamping device designated 17 .

The spindle 16 designed as a hollow shaft has at its end facing away from the workpiece 8 a spindle nut 25 which interacts with a threaded spindle 26 which is directly coupled to a drive motor 27 fastened to the housing 6 .

With the spindle 16 rotatably connected, a gear 28 , which is in engagement with a toothed shaft 29 , which is between two walls 6 a, 6 b of the housing 6 and just if directly coupled to a second drive motor 30 . The axes of the toothed shaft 29 and spindle 16 run parallel. The drive motor 30 with the toothed shaft 29 serves to set the spin del 16 in a rotational movement, while the drive motor 27 with the threaded spindle 26 ensures a longitudinal feed of the spindle 16 . For this purpose, the bearing 31 facing the workpiece is designed as a longitudinal and rotary bearing. The toothed wheel 28 is designed as a backlash-free double gear; it consists of two coaxially arranged toothed wheel halves 28 a, 28 b, which are supported against each other by a (not shown) spring element, so that regardless of the direction of rotation of the drive, one tooth flank of one or the other gear half with the toothed shaft 29 in A handle stands. Such a backlash-free double gear forms egg on the one hand a low-noise precision gear, on the other hand it serves the safe and exact transmission of motion with egg nem longitudinal feed of the spindle. The engagement connection spindle nut 25 , threaded spindle 26 and hollow shaft 16 requires only little space in the axial direction. The drive motor 27 also forms a fixed bearing for the unit and is connected directly, that is to say without a coupling, to the threaded spindle 26 . Threaded nut 25 and threaded spindle 26 can be built as a play-free ball screw drive or as a play-free slide screw drive. With a slide screw drive, a backlash-free nut can be combined with the hollow shaft.

The structure of the spindle arrangements 9 and 10 is explained in more detail below.

The spindle assembly 9 contains a ausgebil Dete spindle 32 as a hollow shaft, one end of which projects into the machining chamber 7 and carries a tool carrier head 33 there . An electric motor 35 is arranged in the center of a housing which is fixedly connected to the spindle 32 , the rotary movement of which is deflected by 90 ° via a bevel gear 36 onto the tool drive shafts provided on both sides. The axes of these drive shafts therefore run parallel to the spindle axis of the Spin del 32 . At the free end of the drive shafts, the machining tools 11 , 11 'are held by means of suitable clamping devices.

The oppositely arranged tool carrier head 43 for the spindle arrangement 10 has a similar structure; however, it contains no bevel gear teeth. A motor 40 arranged in the tool carrier head 43 drives the tool drive shafts directly here. The tool axes 45 therefore run parallel to the axis 47 of the workpiece feed spindle 26 . The tool carrier head 43 is, in contrast to the tool carrier head 33 , which carries finger-shaped tools, with disk-shaped or pot-shaped tools 12 , 12 'occupied. One side is preferably provided with a disk-shaped grinding or milling disk ( 12 ) and the other with a cup-shaped polishing disk ( 12 '), which can consist of diamond-coated soft material or can also be designed as an exchangeable brush. Because the tool carrier head 43 can be rotated through 180 ° about the spindle axis 46 , grinding and subsequent polishing of the fitting body can be carried out practically without interrupting work.

The two spindle assemblies 9 and 10 have the same drive and drive transmission elements with respect to their pivoting and advancing movement, which are explained below for the Spindelan arrangement 10 .

On the spindle 46 designed as a hollow shaft, a spindle nut 48 is fastened which engages with the threaded spindle 44 driven by a motor 49 . With these output elements, the spindle 46 can be adjusted in the axial direction.

With the spindle 46 rotatably connected, in turn, a double gear 51 , which is constructed similarly to that marked with 28 be. This double gear 51 meshes with a toothed shaft 53 driven by a further drive motor 52 . With this drive element, the entire tool carrier head 43 can be pivoted about the spindle axis by at least 90 °, but preferably by 180 °. A pivoting through 90 ° is indicated in order to pivot the tool carrier head from the working position shown in FIG. 2 into a basic or rest position in which access to the workpiece 8 is facilitated.

After the feed of the individual spindles he very precisely must follow, it is necessary to use the drive provided for this purpose precisely control motors. Therefore they become stepper motors used, which is in itself in very small incremental units be controlled. To compensate for step losses anyway can, it is suggested the stepper motors with a back message. This can be that close the feed spindle, or coupled to it, on contr stand, capacitance, inductance, ultrasonic, magnetic and / or sensor means based on an optical basis are provided are with a via a computer, not shown associated stepper motor are electrically connected. Through a such measuring system, which is both analog and incorrect can work mentally, it is possible to increase the accuracy of the Increase grinding machine.  

On a housing wall 6 c is a fork light barrier 54 is angeord net, which interacts with a ring 55 interrupted by a slot of the double gear 51 so that the rest or starting position of the spindle can be detected precisely, both with respect to their rotary ( Angular) position and in relation to their position in the direction of the feed axis. While the latter is detected by immersing the ring 55 in the fork light barrier, the angular position is detected by a signal when the slot 55 interrupting the slot is passed through the light barrier. With the help of the fork light barrier, the distance a between the tool axis 45 and the workpiece axis or workpiece holder axis 47 can thus be determined.

To fit the fitting body, in the present application case a tooth crown drawn in dashed lines in the workpiece 8 in FIG. 2, on the basis of predetermined construction data, which are created from the prepared tooth stump with the aid of the camera mentioned above, a computer with software, from the workpiece 8 To be able to, it is necessary to calibrate the tool and workpiece or workpiece holder or to determine a precisely defined starting position for the machining tools 11 , 12 , from which the workpiece machining can begin according to the specified design data. It is important to compensate for wear and / or manufacturing tolerances of the tools and any deviations of the workpieces from specified target values, as well as other deviations that occur due to aging of the components.

To calibrate or determine the starting position, construction-related fixed variables are taken into account, e.g. B. the above-mentioned distance (a) of the axes 45 , 47 from tool to workpiece or clamping device in the starting position detected by the fork light 54/55 , the distance (b) between the axis 47 of the workpiece or the holder and the touch surface (reference surface R), and the grinding wheel diameter as the specified target size. These known fixed quantities are stored in a memory of a computer which will be explained in more detail below.

Taking these fixed quantities into account, the Above-mentioned deviations from the target sizes determined by the machining tool by the the fork light barrier fixed starting position up to Contact with the reference surface on the workpiece or its Holder is driven and the corresponding to this actual value Size introduced into the computer and with the specified target sizes is processed. The deviations determined from this can be used as a correction variable in the machine control system, i.e. in the control program for the tool feed, who introduced the, where it is possible to either the starting position as Leaving the starting position and the correction in the given Incorporate design data to create the fitting body, So to change the design data, or this unchanged to leave and the starting position of the tool, so their starting position to change the correction size.

According to the invention, the actual values can be determined optically or optoelectronically in two ways. In one variant of the process chamber 7 is at a suitable position, an optical sensor 70 in the form of z. B. a reflex light barrier or a laser button is provided, which represents a measuring point in a defined point (M). When using a laser scanner, this is the focal point at which the laser beams are reflected. This measuring point M lies at the intersection of the plane of the two tools with the center line 47 of the workpiece 8 and the workpiece holder 16 , 17th

To determine the actual value, one moves with the feed device of the tool in question so far towards the workpiece until the machining surface of the tool (designated P in FIG. 2 for the tool 12 ) comes into the focal point or measuring point. The laser button then emits a signal which is processed according to the block diagram of FIG. 5.

The other version proposed according to the invention is explained in more detail with reference to FIGS. 3 and 4, with FIG. 3 not the plan view of the processing chamber, as in FIG. 2, but from the front, and FIG. 4 the workpiece in perspective view demonstrate. According to this arrangement, light is directed from an infrared light-emitting diode 71 onto a precisely defined point on the workpiece 8 a. The intended paragraph 8 c is previously created with the help of the tool 12 . The shadow cast by this illuminated paragraph 8 c is measured by means of a sensor element 72 , preferably a CCD line. The diameter determined from this and the difference to the nominal diameter result in a correction factor for the machine control.

With the same measurement system, the resulting shape can body during machining if necessary for dimensional accuracy examined and, if necessary, so that the machines control can be corrected.

A major advantage of the two proposed versions is that in itself no special reference areas at work tool holder need to be provided.

Before the calibration or the setting of the exact starting position is explained further, the principle circuit in FIG. 5 drive and control of the drive and adjusting motors for the tools 12 , 12 'and the workpiece 8 are described. Analogously, the control for the drive motor 35 of the tool 11 and for the unspecified adjusting motor of the feed device for the tool 11 , 11 '.

A computing unit denoted by 60 contains a speed setting element 61 with which the drive motor 40 can be set to a starting speed which can be freely selected per se. The computing unit 60 also contains two pulse generators 62 , 63 , with which the stepper motor 49 for feeding the tools 12 , 12 'and on the other hand the stepper motor 27 for feeding the workpiece 8 are controlled. A memory in the form of a counter 64 serves to be able to store the signals received from the fork light barrier 54 , 55 at the start of the feed movement until the workpiece 8 is touched by the grinding wheel 12 . A comparator 65 is supplied with a setpoint (+ input) on the one hand and an actual value (-input) on the other hand. The actual value is represented by signals either from the sensor provided, which can be the laser sensor 70 indicated in FIG. 2, or by signals from the CCD element 72 , which are prepared accordingly in a module 73 . It is expedient to give preference to a digital signal evaluation. If the two incoming signals at the comparator are different, the downstream pulse generator 62 supplies a pulse to the counter 64 and to the stepper motor 49 . On the one hand, the tool is moved a defined distance in the direction of the workpiece 8 , on the other hand, the distance covered is temporarily stored in the counter 64 . This process is repeated until the signals on the comparator match.

If a laser scanner 70 is used, this is the case when the focal point or measuring point M is reached. The Kompa rator 65 then turns off the pulse generator 62 . The counter 64 transfers the current counter reading to an arithmetic unit 66 , where it is stored. The stored value is a measure of the path actually traveled by the tool tip or working surface (denoted by P in FIG. 2), from the starting position to the center line (denoted by 47 in FIG. 2). A comparison with the already mentioned fixed values, which are stored in the arithmetic unit 66 , allows a correction variable to be determined and from this the starting position for processing correspondingly predetermined construction data stored in a memory 68 of a control unit 67 can be calculated, with deviations then either the Default data for the feed device or the starting position of the feed device can be changed accordingly. With these control data, the servomotors 49 , 27 and 30 and the drive motors 40 and 35 are then controlled from the control unit 67 , the control unit 67 also being an integral part of the computing unit 60 .

For the second version shown, the first step is to use the tool 12 on the workpiece 8 a to grind a cylindrical shoulder 8 c which can be chosen as desired in diameter. After moving the tool back to its starting position, this paragraph 8 c is optically measured by capturing its shadow on the CCD line 72 and from this its diameter is calculated. The actual value, ie the actual distance of the tool tip (P) from the center line 47, can be determined from the diameter and the grinding wheel diameter and, if there is a deviation from the specified target value, can be entered into the machine control as a correction variable.

The diameter or the starting position of the end mill 11 in the grinding unit opposite can also be determined according to the same principle.

Claims (8)

1. Method for calibrating a motor-driven tool that can be moved to and from a tool to be machined with the aid of a feed device with respect to the workpiece or a workpiece-receiving holder, in which the tool ( 11 , 12 ) is first of all Starting position is moved so far in the direction of the workpiece ( 8 a) or workpiece holder ( 8 b) until the machining surface (P) of the tool ( 11 , 12 ) has a switching point lying in the extension of the workpiece axis ( 47 ) or parallel to it ( M) reached a light barrier arrangement ( 70 ), the distance of the tool feed from the starting position to the switching point being detected by the signals that are generated to determine the exact starting position of the tool in, starting with the advance movement until the switching point is reached in relation to the workpiece or the workpiece holder or to determine a correction quantity for the workpiece rk tool feed can be entered into a computing unit ( 60 ) taking into account the detected starting position. 2.Method for calibrating a motor-driven tool that can be moved from an initial position to a workpiece to be machined and moved away from it with respect to the workpiece or a holder receiving the workpiece, in which the workpiece ( 8 a) by machining through the tool ( 11 , 12 ) a reference surface ( 8 c) is generated, in which the reference surface is measured optically and the measured values determined therefrom together with one of the path of the tool feed from the starting position to reaching the reference Area corresponding measured variable for determining the exact starting position of the tool in relation to the workpiece or the workpiece holder or for determining a correction quantity for the tool feed in a computing unit ( 60 ) and further processed there. 3. The method according to claim 1 or 2, which to create a medical, especially dental, tooth prosthetic fitting body is applied. 4. The method according to any one of claims 1 to 3, wherein the values determined by the computing unit ( 60 ) via the position of the tool ( 11 , 12 ) or the correction factor of a control unit ( 67 ) integrated or separate in the computing unit ( 60 ). are supplied, which are based on predetermined machining design data, the feed device ( 32 , 33 ; 43 , 46 , 49 ) for the tool ( 11 , 12 ) and an actuator ( 27 , 30 ) for the workpiece ( 8 a) in the sense of machining the workpiece control according to the given design data. 5. An apparatus for performing the method according to claim 1, in which a clamping device ( 17 ) for receiving the workpiece ( 8 a) and at least one feed device ( 32 , 46 ) for at least one rotatable processing tool ( 11 , 12 ) are present is, the feed device is designed and arranged so that the tool in the sense of material removal from the workpiece is movable towards and away from this, in which a light barrier arrangement in the form of z. B. a laser button ( 70 ) is present, the focal point (M) at the intersection of the workpiece axis ( 47 ) with the tool axis, in which means ( 54 , 55 ) for detecting egg ner starting position of the tool and the distance that the Tool from the starting position to reaching the focal point (M), are present, with a switching signal being generated in the focal point of the laser sensor ( 70 ), which the computing unit ( 60 ) for determining the exact starting position of the tool in relation to the workpiece or Determination of the correction quantity for the tool feed is fed and processed. 6. Device for performing the method according to claim 2, in which a clamping device ( 17 ) for receiving the workpiece ( 8 a) and at least one feed device ( 32 , 46 ) for at least one rotatable tool ( 11 , 12 ) is present wherein the feed device is so constructed and arranged that the tool in terms of a Materialab transmission on the workpiece to this to and is movable away from this, wherein the measurement of the reference surface (8 c) a light-emitting radiator, preferably a light emitting diode (71 ) is seen before, which illuminates the reference surface ( 8 c) and in which a shadow detection of the reference surface continues to be detected by the light-sensitive sensor, preferably a CCD line ( 72 ), the signals of an evaluation electronics corresponding to the shadow casting of the reference surface Computing unit ( 60 ) are supplied. 7. Device according to one of claims 1 to 6, in which a by a stepper motor ( 49 ) controllable in small steps feed device ( 43 , 46 , 49 ) is provided with which the tool ( 12 ) in at least one plane and in this plane can be moved towards and away from the workpiece ( 8 a) in at least one direction, in the drive motor ( 40 ) for the tool a speed-controllable DC motor is provided, which delivers speed-proportional signals via integrated sensors, in the case of which the computing unit ( 60 ) has a memory ( 64 ) in which the feed movements of the tool ( 12 ) corresponding sizes are stored, such as an actuator ( 61 ) containing the number of times the drive motor ( 40 ) for the tool ( 12 ) sets a starting speed, and in which the computing unit contains a comparator ( 65 ), in which correspondingly processed signals corresponding to an actual variable from the The light barrier ( 70 ) or the sensor ( 72 ) can be compared with a specified target size. 8. The device according to claim 7, wherein the computing unit ( 60 ) has a pulse generator ( 62 , 63 ) for controlling on the one hand the servomotor ( 49 ) for feeding the tool ( 12 ) and on the other hand the servomotor ( 27 , 30 ) for the workpiece ( 8 a) comprises, in which a counter ( 64 ) is present as the memory, which detects the path of the tool, starting from the starting position, and in which the computing unit contains an arithmetic unit ( 66 ) which, from the counter sizes, covers the distance traveled Tool and from this the starting position or the correction quantity is determined.