WO2005109166A1

WO2005109166A1 - Computer-compatible length touch probe

Info

Publication number: WO2005109166A1
Application number: PCT/EP2005/004224
Authority: WO
Inventors: Rainer Ziegenbein; Kai Kammers
Original assignee: Carl Mahr Holding Gmbh
Priority date: 2004-05-08
Filing date: 2005-04-20
Publication date: 2005-11-17
Also published as: DE102004023645A1; DE102004023645B4

Abstract

A length touch probe comprises a touching element for mechanically sensing a workpiece surface and comprises an inductive measuring device, which is connected to the touching element and whose deflection is converted into a corresponding analog measurement signal. In addition, the length touch probe comprises a communications device for communicating with a computer and a controlling and processing device inserted between the measuring device and the communications device. The control device serves to generate an analog control signal for the measuring device by using digital means and analog-to-digital conversion. The processing device obtains the analog measurement signal produced by the measuring device, digitizes this signal, and determines, by means of digital signal processing, a digital measured value characterizing the respective deflection of the touching element. The length touch probe can be designed together with the computer to form a linear path-measuring system via a suitable network connection, e.g. via a UBS interface or an LR-WPAN radio network. A synchronizing device is integrated in the length touch probe, and this synchronizing device, in the event of static and dynamic measurements effected by a number of length touch probes, enables a sequential readout of almost synchronously recorded measured values of all length touch probes.

Description

COMPUTER COMPATIBLE LENGTH GAUGE

The invention relates to a length probe and a probe system, which can be used in particular in connection with a computer.

From the patents DE 199 31 226 Bl, DE 199 37 204 Bl and DE 199 37 205 Bl and the German patent application with the file number 10 2004 017 992.1, which are assigned to the applicant of the present application, inductive length measuring probes with a in a housing can be moved stored probe element known, with which the surface of a workpiece is mechanically scanned. A measuring device arranged in the housing converts the deflection of the probe element into electrical signals. For this purpose, the probe element is rigidly connected to a core made of a ferromagnetic material, which is immersed in a coil arrangement comprising a primary coil and at least one secondary coil. The primary coil is -with analog AC signals are fed, amplitude-modulated AC voltages being continuously induced in the secondary coil depending on the current position of the core. These AC voltages can then be demodulated in order to obtain a DC voltage signal which characterizes the deflection of the pushbutton element.

In the known touch probes, an external measuring device is provided, which receives both an oscillator for feeding the primary coil, all the necessary amplifiers, and electronics with rectifiers and filters, which are required for evaluating the measurement signals. The measurement signals received are visualized or stored in order to be evaluated at a later point in time. There are also known external measuring devices, known as button boxes, which contain a suitable interface for connection to a computer, by means of which the stored measured values can be read out as required. In addition, special measuring computers are known from practice which contain hardware with the required electronic components.

It is perceived as a disadvantage that separate measuring devices or specially configured computers have to be used, which make many applications of length measurement complex and costly. With the advent of inexpensive PCs and other, for example also portable computers, the desire arises to be able to operate the length measuring probes with these computers simply without the interposition of measuring devices and without additional hardware.

Furthermore, in many applications, several length measuring probes are used at the same time in order to record the characteristics of a test object or workpiece by linking individual measured values. These characteristics include the thickness of a test object, perpendicularity, excentric Tricity etc. Especially with dynamic measurements, in which, for example, the coaxiality, the concentricity or runout deviation and the like of a moving test object with several measuring probes is recorded simultaneously, the measuring values of all probes must be recorded largely synchronously to one another Assign measurement time and link and evaluate it appropriately. Even if modern PCs are equipped with several connections to which different devices can be connected, synchronous use of several measuring probes is not possible insofar as the communication between the computer and the peripheral devices takes place sequentially. With the standard Universal Serial Bus (USB) interface, which is used to connect a keyboard, mouse, scanner and the like, a command from the computer to transmit data only reaches one ÜSB device at a time. External measuring devices or push button boxes with several connections and electronics are therefore used, which generate the control signal for all push buttons and process all measuring signals of the connected push buttons.

Proceeding from this, it is an object of the present invention to remedy the disadvantages of the length measuring probes and touch probes mentioned above and to provide a length measuring probe which can be operated in connection with a conventional computer, for example a PC.

Another object of the present invention is to provide a probe system with a computer and at least one compatible length probe.

A still further object of the invention is to provide a length measuring probe and a measuring probe system which enable a synchronous measurement value acquisition with a plurality of measuring probes which is initiated by a computer. To achieve the aforementioned tasks, a length measuring probe with the features of claim 1 and a measuring system according to claim 21 are created.

The length measuring probe according to the invention thus has a probe element that can be moved in a probe housing, for example longitudinally displaceably along a measuring axis, with which the workpiece surface can be mechanically (touching) scanned, and a measuring device that is also arranged in the probe housing, connected to the probe element and for this purpose is set up to convert the deflection of the probe element into a corresponding analog measurement signal. According to the invention, the length measuring probe also has a control and processing device connected to the measuring device and a communication device which is set up for communication with a computer. The control device is used to continuously feed the measuring device with an analog control signal, in particular a sinusoidal voltage signal or another suitable feed signal, such as a square-wave signal. The amplitude, phase and / or frequency of the excitation signal is modulated by the measuring device in proportion to the width and as a function of the direction of the deflection of the probe element. The processing device is set up to receive, process, in particular demodulate and digitize this amplitude, phase or frequency modulated measurement signal in order to obtain a digital measurement value which characterizes the momentary deflection of the probe element. If necessary, this measured value can be transmitted to the computer for further evaluation via the communication device.

By providing a communication device that is compatible with an interface of a computer and by integrating it and the control and processing device in the probe is a length probe that can be operated easily on a conventional computer. No additional repeaters, external measuring devices or button boxes or other adapters are required between the probe and the computer. As a result of the digitization, a measurement signal in the appropriate value-discrete form is available at the output in order to be transmitted to the computer via the interface.

In the sense of the application, a computer is generally understood to be a computer regardless of its system architecture. This can be a personal computer (PC) or a Macintosh computer. Furthermore, this includes in particular portable computers, such as laptops or notebooks, and also small and very small computers, as they are nowadays referred to as mini computers, handhelds, palmtops, PDAs or in some other way. The portable computers, small and microcomputers advantageously enable mobile operation of the length probe for service, assembly, commissioning and the like. The measuring systems constructed from a conventional computer and a length probe according to the invention are inexpensive and easy to use.

The length measuring probe is preferably an inductive measuring probe. The probe element can be rigidly connected to a displaceable core made of ferromagnetic material which interacts inductively with a coil arrangement of the measuring device by changing the inductances of the coils of the measuring device depending on the displacement. The measuring device can be designed in the form of a half bridge with a primary coil to be fed with the analog excitation signal and a secondary coil, in the form of a full bridge or in the form of a differential transformer. In the latter case, the measuring device can have a primary coil, which is arranged between two secondary coils, or it can also be a reverse one Configuration. The ferromagnetic core can, but does not have to, dip into the coil arrangement. The inductive coupling between the primary coil and the at least one secondary coil via the core induces an amplitude-modulated measurement signal on the secondary coil, the amplitude of which signals the deflection of the probe element. The phase or frequency of the control signals can also be modulated depending on the displacement.

Furthermore, a capacitive measuring device can also be used, in which the capacitive coupling between at least one transmitting electrode and at least one receiving electrode is changed and can be evaluated when the probe element is displaced. Known from the prior art are both measuring devices with transmitting and receiving electrodes which can be displaced relative to one another, as well as those measuring devices in which these electrodes stand still, while a material measure in the form of a series of counter electrodes is moved together with the probe element. Depending on the degree of coverage, the control signals supplied to the transmitter electrodes are influenced or coded differently by the counter electrodes. Advantageous embodiments of current-saving capacitive measuring devices and control and evaluation circuits therefor, which can be used in connection with the invention, are described in DE 100 351 92 Cl or in EP 0 785 415 B1, to which reference is expressly made here.

The control and processing device and at least the part of the communication device controlling the communication can be accommodated in the push button housing in order to obtain an integrated solution. Then only a cable leads out of the push button housing, at the end of which a suitable connection means is provided for connection to the computer. Instead, use the probe a transmission / reception unit can also be provided, which exchanges data with a corresponding transmission / reception unit of the computer via radio waves.

In an advantageous embodiment, the control and processing device and the communication device in the form of an electronic unit are accommodated in a small housing separate from the push button housing and are connected to the measuring device via a connection or cable. Existing probes can be retrofitted with little effort by merely replacing the line cable with a line cable according to the invention with the electronics unit. If the electronics unit is arranged at the end of the cable which is remote from the length measuring probe, its housing can also carry the appropriate connection means for connection to the computer. However, the devices mentioned can be distributed or arranged as desired along the line cable. Some of them could also be housed in the computer.

Line cables of different lengths depending on the application can be provided. It is also possible to provide a plug connection between the line cable and the measuring device in order to enable flexible replacement of the line cable.

If the communication device is set up for wired communication with the computer, the connection means is, for example, a plug which is designed to be suitable and complementary in shape to an interface connection, for example the socket, of the computer.

In principle, the interface between the length probe and the computer can be selected as desired. It can be a parallel or a serial interface, if it is possible to read out the digital measuring values of the probe received with the computer. In a particularly preferred embodiment, the interface also forms an energy source for supplying the length measuring probe. It has a line via which a direct voltage or a direct current provided by the computer can be supplied via the communication device to the electronic unit in order to operate it. No external energy source or internal battery is required for the length probe. This is particularly advantageous for mobile length probe units.

In a particularly preferred embodiment the universal serial bus (USB) interface standardized by the industry is provided as the interface between the length measuring probe and the computer. The communication device thus has a USB plug which leads outwards from the housing and can be plugged into a USB socket on the computer, and a USB interface with the necessary control means which monitor the data exchange with the computer in accordance with the USB protocol and Taxes. The USB interface advantageously provides a high data rate of 1.5 megabits per second, 12 megabits per second or even 480 megabits per second in order to ensure a sufficient transmission speed, even if additional USB devices are connected to the USB ports of the computer. The USB interface has a cable core that provides a DC voltage of +5 V. Another advantage of using the USB interface is that the length measuring probe can be connected and removed while the computer is running, without causing the computer to crash, data loss or even hardware damage. The connection of the USB length probe is noticed by the operating system of the computer, which automatically activates the corresponding drivers for the data transfer. The length measuring probe can be used at the same time. Another comparable interface can also be used instead of the USB interface.

In another advantageous embodiment of the invention, the communication device is set up for wireless communication with the computer. It preferably has an RF radio module, that is to say a transmitter / receiver unit, which can exchange data with a corresponding transmitter / receiver unit of the computer via high-frequency radio waves. According to the invention, a radio network is preferably used for devices with low power consumption and low data rate, as is known under the name Low Rate Wireless Personal Area Network (LR-WPAN). This radio network is based on the IEEE standard 802.15.4 and provides the sufficient radio range of usually up to 10 m as well as the option of integrating several devices, including length probes. The length measuring probe according to the invention is set up to passively transmit the data obtained upon a command from the computer or actively at defined times. The length measuring probe can be easily adapted for use in an LR-WPAN. A suitable energy source, in particular a battery or an accumulator, is to be integrated in the button.

In principle, it is possible to implement the control and processing device in the form of analog circuits. The measurement signal obtained then only has to be digitized in order to be made available to the communication device in the appropriate digital form. In an advantageous embodiment, however, the control device and the processing device work largely digitally. For this purpose, a microprocessor or microcontroller with a program running on it is advantageously used. The microprocessor contains a generator unit or logic which generates the, for example, sinusoidal excitation signal of a suitable frequency generated. This is then converted into an analog signal by a digital / analog converter and fed to the primary coil of the measuring device. The required oscillator voltage can also be generated by pulse width modulation. The digital / analog converter, together with an analog / digital converter, which converts the analog measurement signal originating from the measuring device into a digital intermediate signal, preferably forms a converter unit which is inserted between the microprocessor and the measuring device. The processing device contains a detector unit or logic which implements digital filters in the form of multiplier and summing elements in order to demodulate the digital intermediate signal by linking it to the digital excitation signal to determine the digital measured values.

Memory means, for example volatile and rewritable RAM memories, are preferably also assigned to the microprocessor in order to be able to temporarily store the measured values. Further information, e.g. Button-specific information, such as button type, button characteristic or sensitivity and correction curves (offsets) can be saved, which can be used by the microprocessor to correct measured values. As a result of the digital processing, an adjustment or calibration of the probe can be carried out fully automatically.

According to a further aspect of the present invention, a probe system is provided which has a computer and at least one length probe described above. The computer has an executable program for measured value acquisition and processing, in particular a firmware program which makes it possible to read out measured values recorded with the probe, to process them further and to visualize them if necessary. The communication interface used is preferably a USB interface or an LR-WPAN interface, as explained above, or a comparable interface. If several buttons are used, the interface protocol should provide that the computer periodically sends a synchronization signal to all connected devices in the network, which serves to synchronize the device's internal clock generators, but does not trigger any data exchange itself. For example. The specification of the USB protocol provides for the transmission of a special data packet, the so-called start-of-frame (SOF) token, with a maximum time error of ± 500 ns every 1.0 ms. The SOF token initiates a frame that defines the available transmission capacity. In a LR-WPAN, a specified network coordinator, e.g. the computer, can define a so-called superframe to divide the available transmission capacity, which contains 16 time slots or so-called slots and is initiated by a special signal, the so-called beacon, in the first slot of the superframe.

The length measuring probes according to the invention have a special logic or logic elements that detect a special synchronization signal, such as the SOF or beacon, and then cause the current digital measured value to be buffered. This enables largely synchronous acquisition of the measured values with all probes. The logic elements furthermore contain logic which recognizes a request from the computer to transmit the current measured value or measured values and initiates this via the communication device.

In a particularly preferred embodiment, the logic elements are also set up to assign a time stamp to the currently recorded measured value, which stamps the time of the measured value acquisition. As a result, they need Measured values are not to be read out by the computer in the period between two successive synchronization signals, but can be collected together with the respective time stamps in the memory device and later transmitted together. A temporal assignment of the measured values is always possible.

In preferred probe systems according to the invention, the time stamp is a date that is updated regularly by the computer and transmitted together with the synchronization signal. For example, the frame number contained in the start-of-frame token or, in an LR-WPAN, the sequence number contained in the beacon and constantly updated can be recorded and assigned as a time stamp.

With the concept according to the invention, several synchronous length measuring probes can be connected to the computer wirelessly or wired, directly or via distribution means. With a USB network, for example, up to 127 length measuring probes can be provided for the simultaneous detection of a workpiece surface. A sufficient number of length measuring probes according to the invention can also be integrated into a radio network. Very complex measurement tasks can thus be solved. With a maximum permissible number of distribution means and maximum cable length or with the longest possible radio link, a synchronization accuracy of the measured value acquisition of less than 1.0 μs, preferably less than 0.5 μs, is achieved. Advantageously, according to the invention, very compact mobile probe systems can also be implemented that do not require an external energy supply.

Further advantageous details of embodiments of the invention result from subclaims, the drawing and the associated description. In the drawing is one Embodiment of the subject of the invention shown. Show it:

1 shows a measuring system according to the invention with a length measuring probe and a computer in a partially cut open and partially highly schematic representation;

2 shows the length measuring probe according to the invention according to FIG. 1, in a schematic basic illustration in the form of a circuit diagram;

3 shows an application of the measuring system according to the invention using several length measuring probes in a wired network, in a schematic representation;

FIG. 4 shows a time diagram which illustrates the synchronization of the measured value recording and the data exchange between the length measuring probe and the computer according to FIGS. 1 to 4;

5 shows a highly schematic embodiment of a measuring system according to the invention which uses a radio network; and

FIG. 6 shows a time diagram which illustrates the synchronization of the measured value recording in the probe system according to FIG. 5.

FIG. 1 illustrates a linear displacement measuring system 1, which includes a length measuring probe 2, with which the surface 3 of a workpiece can be mechanically scanned, and a computer 4. The computer 4 shown here only in a highly schematic manner can be in the form of a conventional PC, a Macintosh computer or another, in particular portable cash computer or small or microcomputer. The computer 4 preferably has a processor means 5 with an operating system program which makes it possible to load and run various user programs. These programs include a firmware program 7, which is usually stored in a memory 8 assigned to the processor, for example a hard disk, and can be loaded into its working memory by the processor in order to further process the measurement values obtained from the probe 2 and visualize it on a screen, for example. The screen and other components of the computer that are not relevant here are omitted in FIG. 1 for the sake of simplicity.

As can be seen, the computer has an interface 9, which makes it possible to connect the length measuring probe 2 to the computer 4 in order to be able to establish a communication connection. A controller 11 is provided on the computer side to control this communication. As indicated by the block 9b shown in broken lines, the computer 4 can contain a number of interface connections which the controller 11 operates.

The length measuring probe 2 has a probe unit 12, a connection cable 13 and a connection unit 14 which is arranged at the outer end of the connection cable 13 and is used for connection to the computer 4. In the present case, an inductive button unit 12 is provided with an elongate, tubular housing 16, which has a preferably cylindrical outer surface suitable for clamping. Arranged in the cylindrical interior of the housing 16 is a pin-shaped sensing element 17, which is displaceably mounted in its longitudinal direction, the guide direction 18, by a guide device 18, in particular a precise ball guide. An inductive measuring device 21 is provided to detect the displacement of the probe element 17. The probe element 17 carries at its front end a measuring insert 22 which projects outwards from the probe housing 16. A suitably designed, for example spherical probe body is gripped on the measuring insert 22, with which the workpiece surface 3 is scanned. A bellows 23 clamped between the housing and the measuring insert seals the front end of the push button unit 12 from the outside. On the rear end of the probe element 17, which projects into the interior of the probe housing 16, a conical compression spring 21 is supported, which prestresses the probe element in the direction of the workpiece surface 3.

Furthermore, the rear end of the probe element 17 is rigidly connected to a core 26 of the inductive measuring device 21, which can be displaced together with the probe element 17. The core 26 is rod-shaped and made of a ferromagnetic material. It plunges into a coil arrangement with a primary coil 27 and two secondary coils 29a, 28b, which are arranged coaxially to the core 26 and the probe element 17. In operation, the primary coil 27 generates a magnetic field which, depending on the position of the core 26, induces different voltages in the secondary coils 28a, 28b which are characteristic of the deflection of the probe element 2.

The coils 27, 28a and 28b are connected via lines of the cable 13 to a control device 29, which supplies analog control signals for the measuring device 21 during operation, and a processing device 30, which digitizes, evaluates and evaluates the voltages or measuring signals generated by the push-button unit 12 Communication device 32 passes. The communication device 32 provided for controlling the communication with the computer 4 forms, together with the devices 29 and 30, the connection or electronics unit 14. This is housed in the interior of a housing 33, from which only a connection means 34 protrudes that matches the interface connection 9 of the computer 4 is trained.

The electronics unit 14 is illustrated in detail in FIG. 2 in the form of a simplified block diagram. It has a microprocessor 36, for example a digital signal processor, as well as a converter unit 37 and a clock generator 38 which specifies the system clock for the electronics 14. ^'The transducer unit 37 is connected via a data link 39 to the microprocessor 36 and includes a digital / analog (D / A) andler 41 which converts into an analog drive signal generated by the microprocessor 43, a digital control signal 42, and a Analog / digital (A / D) converter 44, which converts an analog measurement signal 46 generated and filtered by the network device 21 into a digital measurement signal 47. The analog drive signal 43 is filtered by a bandpass filter 48 and suitably amplified by means of an amplifier 49 in order to be fed to the primary coil 27 via the connecting cable 13. The measurement signal 52 tapped at the secondary coil 28 or the secondary coils 28a, 28b passes through an amplifier 53 and a low-pass filter 54 before it is fed to the A / D converter 44.

The microprocessor 36 forms the central control unit of the electronics 14 and the length probe 2. It has logic elements 45, to which a program code and hardware components of the microprocessor 36 belong and of which the most relevant functional units are shown schematically in FIG. This includes a control logic 56, which generates the digital control signal 42, for example a digitized sine signal of a suitable frequency, and can be implemented, for example, in the form of a counter or a table stored in a memory. Furthermore, the microprocessor 36 has a detector logic 57 with a rectifier 58 and an integrator 59. The rectifier 58 is used to rectify the digital measurement signal 48 in the correct phase by ses linked with the digital control signal 42 in a suitable manner. In the simplest version, the rectifier 58 is essentially formed by a multiplier. The integrator 59 is essentially formed by a summation logic which, for example, forms the arithmetic mean of the previously rectified signal in order to obtain a digital measured value 61 which characterizes the momentary deflection of the probe element 17. The microprocessor 36 exchanges data with the communication device 32 via a data connection 62.

The electronics 14 preferably also contain storage means 63 which can be integrated in the microprocessor 36 or formed by external memories and which make it possible to store the measured values 61 and preferably also further data. For example, button-specific information, such as characteristic curves, sensitivities and correction values, can be stored in order to automatically calibrate button 2 at the start of operation and to make the necessary corrections when generating the control signal and evaluating the measurement signal.

In operation, the control device 29 formed by the control logic 56 and the downstream components 41, 48 and 49 continuously generates the required feed signal 51 for the primary coil 27 of the inductive measuring device 21. Its secondary coils 28 continuously supply an amplitude-modulated analog signal 52, the amplitude of which The width of the deflection of the sensing element 17 and its sign indicate the direction of the deflection. The signal 52 is amplified, filtered and digitized by the components 53, 54 and 44 of the processing device 30 in order to obtain the corresponding measured values 61 solely by means of digital signal processing by the detector logic 57. If necessary, the measured values 61 are transmitted to the computer via the data connection 62 and the communication device 32. According to the invention, the communication device 32 is struck in the form of a. Form A interface. A conventional USB plug, which fits into a USB socket of the USB interface 9 of a computer 4 containing a USB controller 11, then serves as the connection means 33. The use of the standardized USB interface, as is widely used today on a computer for connecting peripheral devices such as a keyboard, mouse, scanner and the like, offers numerous advantages here: The USB connection has a supply voltage line with a DC voltage of + 5 V, which is made available by the computer and can thus be used via the communication device 32 and a power supply line 64 to supply power to the microprocessor 36 and the converter unit 37. No other external energy source is required. Furthermore, the USB standard enables sequential communication of the USB controller with several connected USB devices. Several length measuring probes 2 can therefore be used simultaneously for corresponding applications, as is illustrated, for example, in FIG. 3.

FIG. 3 illustrates in a simplified manner a measurement application in which a test object 66 is accommodated in a holding device 67, which is only shown schematically here. The essentially circular-cylindrical test object 66 has outer sections with a reduced diameter and a central section with an enlarged diameter. With several length measuring probes 2a, 2b, ... 2z, which are arranged along the longitudinal axis 65 of the test object 66, its surface is detected. The test object 66 is successively rotated about the axis 65 at a defined speed, while the length measuring probes 2a-2z scan the outer surface of the test object 66. The length measuring probes 2a-2z are held by a holding device (not shown in more detail here) and connected to the USB ports 9a, 9b, 9c of the computer 4. closed. Since the computer 4 generally has only a few USB connections 9a, 9b, 9c, depending on the equipment, star distributors (so-called hubs) 68a, 68b with one output and several inputs 9 'are used here. According to the standard, up to 5 hubs can be coupled with each other, so that six levels can be formed in the star-shaped topology of the USB, which enable up to 127 length sensors to be connected.

In the illustrated application and in particular in complex measurement applications, in which features such as runout or runout, coaxiality, centricity, conicity or the like are determined, it is necessary to record the measured values as synchronously as possible and to be able to assign them to a measurement point in order to be able to to be able to link them appropriately in the computer. Because of the sequential communication of the USB, however, a command from the computer to record and transmit a value only reaches one length measuring probe 2. The invention advantageously uses a special property of the USB protocol to ensure synchronization of the measurement value recording. According to the USB protocol, the available transmission capacity is divided into so-called frames 69 for devices with a low data rate or microframes for devices with a high data rate. As shown in FIG. 4, each frame 69 is initiated by the transmission of a special data packet, the so-called start-of-frame token 71 (SOF), which is transmitted to all connected devices. The specification of the USB protocol provides for the transmission of a SOF with a maximum error of ± 500 ns every 1.0 ms. Devices with a high data rate receive the packet every 125 μs + 62.5 ns.

The SOF signal 71 is typically used by peripheral devices to synchronize their internal clocks. The measuring probes 2 according to the invention, however, have a synchronization logic 70 which uses the SOF signal 71 for the synchronous recording of the measured values. One stroke delays the SOF signal according to standard measured a maximum of 40 ns, a cable of maximum length by a maximum of 30 ns. A SOF signal 71 emitted by the USB controller thus reaches all length measuring probes 2 with almost no time delay, at worst after 5x40 ns + 6x30 ns = 380 ns. This can ensure that all measured values assigned to a point in time are recorded with a time offset less than 0.5 microseconds. The absolute error is less than a microsecond.

The start-of-frame token 71 also contains a frame number 72 which the synchronization logic 70 uses to assign a time stamp to the respective measured value 61. Although devices with high data rate eight times more likely ^'framelets obtained as devices with low data rate is contained in the token 71 frame number 72 is raised only after eight transmitted packets. The frame number 72 is therefore always unique. In the inventive use of an operating range with the lower data rate, enables the 1000 measurements per second, ^'off. As soon as the communication device 32 receives an SOF signal, it generates an interrupt and transmits the received data packet to the processor 36, whose synchronization logic 70 instantaneously freezes the current measured value 61, for example by temporarily storing it in the memory means 63. In addition, the microprocessor 36 also stores the associated frame number 72. In the remaining time of the respective frame 69, the USB controller can sequentially address the individual length measuring probes 2a to 2z individually in order to receive the respective measured values 61 together with the frame number 72 in a suitably packaged form. This is shown as an example in FIG. 4.

Instead of a USB interface, another comparable interface can also be used if this makes it possible to reliably exchange data between the probe 2 according to the invention and the computer 4. In particular the interface should also provide a synchronization signal, similar to the SOF signal, which is transmitted to all devices integrated in the network and can be used according to the invention. An example of another suitable network is the radio network known as the Low-Rate Wireless Personal Area Network (LR-WPAN), which is based on the IEEE-802.15.4 standard and is intended for devices with low power consumption and low data rate. 4 shows a modified embodiment of a measuring system 1 according to the invention which is suitable for this purpose. As can be seen, the electronics unit 14 is advantageously integrated into the housing of the length measuring probe 2, although a separate housing 33 as in the embodiment according to FIGS. 1 to 3 is also shown could be used. The length measuring probe 2 has a communication device 32, which is set up for communication with the computer 4 via high-frequency radio waves. For this purpose, the length measuring probe 2 has an antenna 73 serving as a transmitting / receiving unit, while an antenna 74 also serving for transmitting and receiving is provided on the radio interface 9 of the computer 4. The antennas or radio modules 73, 74 are only illustrated symbolically here. They are preferably integrated in the push button housing 16 or the computer 4.

With regard to details on the LR-WPAN and the IEEE standard 802.15.4, reference is made to the respective specification. To understand the present problem and the problem of the invention, it suffices to mention that within the radio range of usually up to 10 m, all devices of an LR-WPAN can communicate with one another. The data transmission takes place in packets that can be sent on different frequencies. At any given time, only one device can transmit undisturbed. A command to record and transmit a measured value therefore only reaches one length measuring probe 2a, 2b, ... 2z. The time to respond All probes cannot be estimated because other devices can communicate at any time and can therefore delay the transmission.

A property of the physical layer of the LR-WPAN network is used for the synchronization of the measured value recording. In this, a device, for example the computer 4, takes over the task of the network coordinator, who can define a superframe 76, as illustrated in FIG. 6, in order to divide the available transmission capacity. This superframe 76 contains 16 time slots of defined duration, so-called slots 77, and is initiated by a special synchronization signal 79, the so-called network beacon, in the first slot of the superframe 76. The length of a superframe can be determined by the network coordinator. In addition, the first slot as a beacon extension also contains a sequence number 79, which is updated by the network coordinator and transmitted with each superframe 76.

The length measuring probes according to the invention receive the superframe beacon 78 with a time delay depending on their distance from the computer 4. However, the maximum time offset results from the maximum distance to the computer (10 m) and the speed of the propagation of the radio waves (approx. 3 x 10 ⁸ m / s) and is therefore less than 33 ns. The repetition precision when transmitting the Beacon 78 depends solely on the network coordinator.

The synchronization logic 70 of the length measuring probe 2 uses the superframe beacon 78 to record the measured value 61 in a corresponding manner, as described in connection with the SOF signal 71 in the USB network. The synchronization device 71 has the effect that the current measured value 61 is frozen and the sequence number 79 is added to it as a time stamp for the time assignment. The data 78, 79 are stored in the Cache means 63 buffered. The computer 4 can then directly address the respective measuring probes 2a-2z as a network coordinator and request them to transmit the data. Like the USB length probe, the LR-WPAN length probe can therefore be purely passive. Advantageously, the LR-WPAN network also enables devices to actively transmit data to the network coordinator by themselves. The individual length measuring probes 2a-2z can therefore transmit their measured values, time stamps and other data to the computer by themselves at defined times assigned to them during the remaining slots 2 to 16.

Numerous modifications are possible within the scope of the invention. For example, regardless of the embodiment, the electronics unit 14 can always be integrated in the push button unit 12 or be arranged at any point on the connecting cable 16. In addition, the phase can also be influenced by the measuring device instead of the amplitude, or a capacitive measuring device can be used, in particular for energy-saving applications. Furthermore, while the control device 29 and processing device 30 operate largely digitally here, they could also be set up to generate or process analog signals, so that they would only have to be digitized for storing and for transmitting the measured values. However, the embodiment illustrated in FIG. 2 is preferred because of the cost-effective implementation which enables flexible adaptation. In addition, commercially available audio codecs can be used for the converter unit 37, which already contain an A / D converter and a D / A converter in a single module.

A length measuring probe 2 has a probe element 17 for mechanically scanning a workpiece surface 3 and an inductive measuring device 21 which is connected to the probe element 17 is connected and its deflection is converted into a corresponding analog measurement signal. Furthermore, the length measuring probe 2 has a communication device 32 for communication with a computer 4 and a control and processing device 29, 30 inserted between the measuring device 21 and the communication device 32. The control device 29 is used to generate an analog control signal for the measuring device 21 by means of digital means 36 and analog / digital conversion. The processing device 30 receives the analog measurement signal originating from the measurement device 21, digitizes it and determines a digital measurement value characterizing the respective deflection of the probe element solely by means of digital signal processing.

The length probe 2 can be set up together with the computer 4 to form a linear position measuring system 1 via a suitable network connection, for example via a USB interface or an LR-WPAN radio network. A synchronizing device 70 is integrated in the length measuring probe 2, which, in the case of static and dynamic measurements with a plurality of length measuring probes 2, enables sequential readout of measured values of all length measuring probes 2 recorded approximately synchronously.

Claims

Claims:

1. Length measuring probe (2) with a probe element (17) movably mounted in a probe housing (16) for mechanical scanning of a workpiece surface (3), with a measuring device (21) in the probe housing

(16) and is connected to the probe element (17) in order to convert its deflection into a corresponding analog measurement signal (52), with a communication device (32) which is set up for communication with a computer, and with one between the measuring device ( 21) and the communication device (32) inserted control and processing device (29, 30), which serves to generate an analog control signal (43) and to process the analog measurement signal originating from the measuring device (21) in order to process the respective one To obtain deflection of the probe element (17) characterizing digital measured value (61).

2. Length probe according to claim 1, characterized in that the measuring device (21) is an inductive measuring device which has at least one primary coil (27) to be fed with the control signal (63) and at least one secondary coil (28, 28a, 28b), which is inductively coupled to the primary coil (27).

3. Length probe according to claim 2, characterized in that the measuring device (21) is set up to influence the amplitude or phase of the control signal (63) depending on the deflection of the probe element (17).

4. Length probe according to claim 1, characterized in that the measuring device (21) is a capacitive measuring device which has at least one transmitting electrode to be fed with a control signal and at least one receiving electrode which, depending on the deflection of the sensing element (17), is capacitively coupled to one another are.

5. Length measuring probe according to claim 1, characterized in that the 'control and processing device (29, 30) and the communication device (32) arranged in a common housing (33) outside the probe housing (16) and with a cable (13) the measuring device (21) are connected.

6. Length probe according to claim 1, characterized in that the communication device (32) is set up for wired communication with the computer (4).

7. Length probe according to one of claims 1 to 6, characterized in that the communication device (32) has a connection means (33) which is designed to match an interface connection (9) of the computer (4).

8. Length measuring probe according to claim 7, characterized in that the communication device (32) is set up to supply the length measuring probe (2) with energy made available by the computer (4).

9. Length probe according to claim 8, characterized in that the communication device (32) has a USB interface and a USB connector.

10. Length probe according to one of claims 1 to 5, characterized in that the communication device for wireless communication with the computer (4) is set up and has a radio module (73).

11. Length probe according to claim 10, characterized in that the communication device (32) is set up for integration into a radio network which is based on the IEEE 802.15.4 standard or a comparable standard.

12. Length probe according to claim 1, characterized in that the control and processing device (29, 30) is in the form of electronics (14) which has a microprocessor, preferably a digital signal processor.

13. Length measuring probe according to one of claims 1 to 12, characterized in that the control device (29) contains a generator (56), which generates a digital control signal, and a digital / analog converter (41) to the digital control signal (42 ) to convert into an analog signal.

14. Length probe according to claim 13, characterized in that the processing device has an analog / digital converter (44), which converts the analog measurement signal of the measuring device (21) into a digital intermediate signal, and a detector device (57), which consists of the intermediate signal determines the digital measured values (61).

15. Length probe according to one of the preceding claims, characterized in that the processing device (30) has storage means (63) in order to temporarily store at least the current measured value (61).

16. Length probe according to claim 15, characterized in that the storage means (63) are further provided to record probe-specific data, in particular linearity, sensitivity and / or correction values, in order to compensate for this when necessary for the evaluation and measurement of the length probe use.

17. Length measuring probe according to one of the preceding claims, characterized in that the control and processing device (29, 30) has logic elements (70) which serve to detect a synchronization signal (71, 78) originating from the computer (4) then cause a storage of the current measured value (61).

18. Length probe according to claim 17, characterized in that the logic elements (70) are further configured to assign a time stamp (72, 79) to the measured value (61) which is characteristic of the time of the measured value acquisition.

19. Length probe according to claim 18, characterized in that the time stamp (72, 79) is a continuously updated date, which is transmitted by the computer (4) together with the synchronization signal (71, 78) at substantially regular time intervals.

20. Length measuring probe according to one of the preceding claims, characterized in that the logic elements (70) are further configured to acquire and then receive a request from the computer (4) to send data, including the measured value (61), to the computer arrange for a data transfer.

21. Probe system (1) with a length probe (2) according to at least one of the The preceding claims and with a computer (4) which has an executable program for measured value acquisition and processing, and a communication interface (9, 11) for connecting different peripheral devices, including the length measuring probe (2), to the computer (4) for communication to enable with this.

22. Probe system according to claim 21, characterized in that it can be operated as a mobile unit which manages without an external energy supply.

23. Probe system according to claim 21 or 22, characterized in that it has a plurality of length sensors (2) in communication with the computer (4).

24. Probe system according to claim 23, characterized in that the measured values (61) of the length probe (2) integrated in the system are recorded synchronously.

25. Probe system according to claim 23, characterized in that it forms a wired system.

26. Probe system according to claim 22, characterized in that it forms a wireless radio system.

27. Probe system according to claim 25 or 26, wherein the communication interface (9, 11) corresponds to a standard protocol, preferably the USB standard, the IEEE 801.15.4 standard or a comparable protocol that periodically transmits a synchronization signal (71, 78) and preferably provides a signal (72, 79) characterizing the time course.