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Publication numberUS20090028286 A1
Publication typeApplication
Application numberUS 12/219,513
Publication dateJan 29, 2009
Filing dateJul 23, 2008
Priority dateJul 26, 2007
Also published asCN101352815A, CN101352815B, CN101354266A, CN101354266B, EP2019282A1, EP2019284A2, EP2019284A3, EP2019285A2, EP2019285A3, EP2028439A1, US7676945, US8437978, US8700351, US20090025243, US20090034677, US20130152418
Publication number12219513, 219513, US 2009/0028286 A1, US 2009/028286 A1, US 20090028286 A1, US 20090028286A1, US 2009028286 A1, US 2009028286A1, US-A1-20090028286, US-A1-2009028286, US2009/0028286A1, US2009/028286A1, US20090028286 A1, US20090028286A1, US2009028286 A1, US2009028286A1
InventorsTim Prestidge, Jonathan P. Fuge, Stephen E. Lummes, Stuart K. Campbell
Original AssigneeRenishaw Plc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Measurement apparatus and a method of using measurement apparatus
US 20090028286 A1
Abstract
A method of measurement using a measurement probe system includes the steps of (i) providing a measurement probe system having a measurement probe to a user, the measurement probe system being suitable for use with co-ordinate positioning apparatus and (ii) monitoring usage of the measurement probe system.
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Claims(17)
1. A method of using a measurement probe system, comprising the steps of:
(i) providing a measurement probe system comprising a measurement probe to a user, the measurement probe system being suitable for use with co-ordinate positioning apparatus; and
(ii) electronically monitoring usage of the measurement probe system.
2. A method according to claim 1 comprising the step of prohibiting further usage of the measurement probe system based on the monitored usage of step (ii), the prohibiting including disabling the measurement probe.
3. A method according to claim 2 comprising the step of prohibiting usage of the measurement probe system when the monitored usage exceeds a first predetermined usage threshold.
4. A method according to claim 3 comprising the step of allowing, on payment of a refresh fee, further usage of the measurement probe system after the first predetermined usage threshold has been exceeded.
5. A method according to claim 4 wherein, after payment of the refresh fee, the method comprises the further step of prohibiting usage of the measurement probe system when the monitored usage exceeds a second predetermined usage threshold, the further step of prohibiting including further disabling the measurement probe.
6. A method according to claim 2 wherein the disabling comprises the step of preventing the output of measurement data from the measurement probe system.
7. A method according to claim 1 comprising calculating a usage charge based on the monitored usage of step (ii).
8. A method according to claim 1 wherein the electronic monitoring comprises at least one of counting the number of measurements acquired by the measurement probe system and measuring the length of time that the measurement probe system is in use.
9. A method according to claim 1 wherein the measurement probe system comprises a probe usage counter for performing step (ii).
10. A method according to claim 1 wherein the measurement probe comprises a touch trigger probe comprising a probe body and a stylus, the touch trigger probe being arranged to produce a trigger signal when the stylus is deflected relative to the probe body, wherein the electronic monitoring comprises counting the number of trigger signals produced by the measurement probe.
11. A method according to claim 1 wherein the measurement probe system comprises a probe interface, the measurement probe and the probe interface being in communication via a wireless communications link.
12. A method according to claim 1 wherein step (i) comprises fitting the measurement probe system to a machine tool.
13. A method of using a measurement probe system, comprising the steps of:
(i) providing a measurement probe system comprising a measurement probe to a user, the measurement probe being suitable for use with co-ordinate positioning apparatus;
(ii) enabling the measurement probe so that the user can acquire measurements using the measurement probe system; and
disabling the measurement probe system after a predetermined amount of measurement probe system usage.
14. A method according to claim 13 wherein the disabling includes building a failure mode into the measurement probe such that the acquisition of measurements is prevented after a predetermined amount of measurement probe system usage due to failure of the measurement probe.
15. A method according to claim 14 wherein the measurement probe is formed from a first part and a second part, the first part being releasably attached to the second part to form the measurement probe, wherein the failure mode is built into the first part of the measurement probe.
16. A method according to claim 13 wherein the measurement probe includes a non-replaceable power source and the measurement probe is disabled once the power source is exhausted.
17. A method according to claim 13 comprising the step of electronically measuring usage of the measurement probe system.
Description
  • [0001]
    This nonprovisional application claims the benefit of U.S. Provisional Application No. 60/996,984, filed Dec. 13, 2007. This application also claims priority from European patent application 07252959.7 filed Jul. 26, 2007 and from European patent application 07252965.4 filed Jul. 26, 2007. The disclosure of each of the provisional application and of the two listed priority European applications is incorporated herein by reference in its entirety.
  • INTRODUCTION
  • [0002]
    The present invention relates to measurement apparatus and to methods of using such measurement apparatus. In particular, the invention relates to measurement probes and methods of use thereof.
  • BACKGROUND OF THE INVENTION
  • [0003]
    In the field of industrial metrology, it is known to use co-ordinate positioning apparatus to accurately measure or inspect the dimensions of an object such as a workpiece. To perform such a measurement function, co-ordinate positioning apparatus moves a measurement probe around within the working space of the machine so that the positions of various points on the surface of the object to be measured can be determined.
  • [0004]
    Co-ordinate positioning apparatus includes dedicated co-ordinate measuring machines (CMMs) that perform only a workpiece inspection function. Numerically controlled machine tools (e.g. metal cutting machines, lathes, machining centres etc) are also one type of co-ordinate positioning apparatus. For example, a measurement probe may be loaded into the spindle of a machine tool and used to inspect a workpiece that has been, or is about to be, machined by that machine tool. Providing a measurement probe system for use with such a machine tool thus offers users the opportunity to automate workpiece set-up and/or perform in-process measurements.
  • [0005]
    A wide variety of measurement probes are known, including both contact and non-contact devices. Touch trigger probes are one example of a measurement probe. A touch trigger probe, such as the device described in U.S. Pat. No. 4,153,998, typically comprises a kinematic mechanism in which a stylus holder becomes unseated from an associated seat in the probe body when the stylus contacts an object. Unseating of the kinematic mechanism also breaks an electrical circuit allowing a “contact” or trigger signal to be generated. As an alternative to such touch trigger probes, it is also known to measure stylus deflection using strain gauges or the like and to either provide a measure of stylus deflection or to issue a trigger signal when a certain amount of stylus deflection has occurred.
  • [0006]
    It is presently common practice for original equipment manufacturers (OEMs) to offer certain metrology options, such as various measurement probe systems, when selling machine tool equipment. There are also various companies that produce measurement probe systems that can simply be added to existing machine tool installations. However, a large amount of research and development activity is required to produce accurate and reliable measurement probe systems and a high level of precision is also required during manufacture to ensure the required measurement accuracy is reliably provided by each device. This leads to the cost of measurement probe systems being, by necessity, not insignificant.
  • [0007]
    For higher end machine tool apparatus, the cost of fitting a measurement probe system is small compared to the overall cost of the machine tool. In addition, the financial benefits of increased machine productivity that are gained by including such a measurement probe system are proportionally high. This is, however, not always the case for lower end machine tool systems. Typically, for such machine tools, the cost of a measurement probe option can be a substantial percentage of the cost of the machine tool. The high relative cost, possibly combined with a machine tool user that has no awareness of the process improvements that typically occur when machine tools are fitted with measurement probe systems, has thus lead to lower take-up of metrology options at the lower end of the machine tool market.
  • SUMMARY OF THE INVENTION
  • [0008]
    According to a first aspect of the invention, a method of measurement using a measurement probe system is provided, the method comprising the steps of; (i) providing a measurement probe system comprising a measurement probe to a user, the measurement probe system being suitable for use with co-ordinate positioning apparatus; and (ii) monitoring usage of the measurement probe system.
  • [0009]
    The present invention has arisen from the recognition that the relatively high upfront cost of providing measurement probe systems, such as measurement probes and associated probe interfaces, is often a substantial disincentive to potential users who are unaware of the benefits of incorporating such apparatus into their production processes. Although it is known to provide hire purchase or loan arrangements that allow the purchase cost to be spread over a longer period, such arrangements do not reduce the total financial commitment that is associated with such purchases but merely reduces the upfront cost. The method according to the first aspect of the invention thus permits a manufacturer to sell a measurement probe system at a lower cost than traditionally possible and to recoup the reduction in upfront income by charging those users that make ongoing use of the measurement system. This recouping of income is achieved through the step of monitoring usage of the measurement probe system. The invention thus extends the market for measurement systems to lower end machine tool users, without the need to reduce the metrology performance of such systems. Furthermore, end users also benefit as they are able to assess the productivity improvements that can be obtained with measurement probe based systems without having to risk substantial sums of upfront capital.
  • [0010]
    Advantageously, the method also comprises the step of prohibiting further usage of the measurement probe system based on the monitored usage of step (ii). Preferably, the method also comprises the step of prohibiting usage of the measurement probe system when the monitored usage exceeds a first predetermined usage threshold. The usage threshold may be set at an appropriate level that provides enough usage to set-up, test and/or evaluate the measurement probe system. Alternatively, enough usage may be provide to allow measurement operations to be performed for a longer period. The amount of usage provided may vary depending on the upfront fee paid by the user.
  • [0011]
    Conveniently, the method also comprises the step of allowing, on payment of a refresh fee, further usage of the measurement probe system after the first predetermined usage threshold has been exceeded. Advantageously, after payment of the refresh fee, the method comprises the further step of prohibiting usage of the measurement probe system when the monitored usage exceeds a second predetermined usage threshold. In other words, a refresh fee may be paid to allow use of the measurement probe system to be resumed. Resumption may be subject to a second predetermined usage threshold not being exceeded or may be indefinite. The amount of the refresh fee may be related to the amount of further usage that will be provided. For example, a lower refresh fee could be charged for a small amount of additional usage, whilst a much higher fee could be charged to provide continuing, indefinite, usage of the system.
  • [0012]
    The prohibition on further usage of the measurement probe system may be implemented in various ways. For example, a contractual or other suitable obligation may be placed on the user not to exceed the agreed limit. Advantageously, the step of prohibiting further usage of the measurement probe system comprises the step of preventing the collection and/or output of measurement data from the measurement probe system. For example, the measurement probe system may become inoperable to the user after the usage limit has been reached.
  • [0013]
    Instead of pre-paying for certain blocks of measurement probe system usage, the amount of usage over a period of time could be measured and the user billed accordingly for such usage. The method may thus conveniently comprise the step of requiring the user to pay a usage charge based on the monitored usage of step (ii). The charge may be directly proportional to the usage, or a banded scale of charges that vary with usage may be applied.
  • [0014]
    A variety of measures of measurement probe system usage are possible. Advantageously, step (ii) comprises at least one of counting the number of measurements acquired by the measurement probe system and measuring the length of time that the measurement probe system is in use. The length of time of use may also be measured in a variety of ways; for example, the amount of operational time or power-up time may be measured.
  • [0015]
    Preferably, the measurement probe system comprises a probe usage counter (e.g. an electronic counter) for performing step (ii). The measurement probe system may also include a visual indicator to communicate usage information to the user. Alternatively, the co-ordinate positioning apparatus may perform the usage monitoring step (ii).
  • [0016]
    The method may be implemented using any type of contact or non-contact measurement probe. Conveniently, the measurement probe is a touch trigger probe. The touch trigger probe may be arranged to produce a trigger signal when the stylus is deflected relative to the probe body. When using such a touch trigger probe, step (ii) advantageously comprises counting the number of trigger signals produced by the measurement probe. In such an example, the number of trigger signals typically relates to the number of points measured using the measurement probe (ignoring any false triggers etc).
  • [0017]
    The measurement probe system may include a measurement probe that is linked to a control computer. This control computer may also control, or be interfaced to, the co-ordinate positioning apparatus. A probe interface may also be provided as part of the measurement probe system for receiving data from the measurement probe and passing that data to a control computer. The measurement probe may be hardwired to the probe interface. Preferably, the measurement probe and the probe interface are in communication via a wireless (e.g. RF or optical) communications link. The measurement system may also comprise additional measurement probes. For example, the measurement system may comprise a spindle mountable measurement probe and a table top (tool setting) measurement probe. These may pass data to the control computer via a common probe interface or separate probe interfaces. The overall usage of such a measurement system may be monitored, or the usage of each measurement probe may be monitored separately.
  • [0018]
    The method of the present invention may also comprise the step of mounting the measurement probe system to any type of co-ordinate positioning apparatus. A step of using the co-ordinate positioning apparatus to acquire measurements using the measurement probe system may also be implemented. Advantageously, step (i) comprises fitting the measurement probe system to a machine tool. For example, such a step may comprise loading the measurement probe into the machine tool spindle or placing the measurement probe in an automated tool changer mechanism so that it can be automatically loaded into the machine tool spindle as and when required. The probe interface may also be physically attached to the machine tool in a suitable location and electrically interfaced to the appropriate control computer. The method may also comprise the step of determining co-ordinate position data using the output of the measurement probe and the positional (X,Y,Z) information of the machine tool.
  • [0019]
    According to a second aspect of the invention, a method of measurement using a measurement probe system comprises the steps of; (i) providing a measurement probe system comprising a measurement probe to a user, the measurement probe being suitable for use with co-ordinate positioning apparatus; and (ii) allowing the user to acquire measurements using the measurement probe system, wherein the acquisition of measurements using the measurement probe system is prohibited after a predetermined amount of measurement probe system usage.
  • [0020]
    The invention, in the second aspect, thus comprises a method of providing a measurement probe system to a user and prohibiting use of that system after a certain amount of measurement probe usage. The prohibition may arise from an agreement with the user to cap or restrict usage or, as described in more detail below, the measurement probe system may be arranged to prevent further usage once the system has been used for the predetermined amount of measurement probe system usage. This permits lower upfront cost measurement probe systems to be provided to users, with the manufacturer recouping the lost upfront income by requiring further user payments to extend the usage limit or to replace components of the system.
  • [0021]
    Advantageously, the acquisition of measurements using the measurement probe system is prohibited by building a failure mode into the measurement probe such that the acquisition of measurements is prevented after a predetermined amount of measurement probe system usage due to failure of the measurement probe. The failure mode may be a mechanical failure mode; e.g. a weakened component that catastrophically fails after a certain amount of usage. The failure may require all, or some, of the measurement probe system to be replaced. Advantageously, the measurement probe is formed from a first part and a second part, the first part being releasably attachable to the second part to form the measurement probe, wherein the failure mode is built into the first part of the measurement probe. The first, e.g. disposable, part may thus fail after a certain amount of use thereby preventing further usage of the measurement probe system. A user may then purchase a replacement first part that, when combined with the second part, allows resumption of the measuring process.
  • [0022]
    The above described failure mode may also be provided by exhaustion of a power source, such as a battery. For example, the measurement probe may be supplied with batteries having a certain power storage capacity. The power stored in the batteries will be depleted by use of the measurement probe and, once depleted, the user may be prohibited from further use of the measurement probe. For example, the measurement probe may include a battery compartment cover over which a security (e.g. holographic) sticker, seal or tag is placed by the manufacturer. Once the batteries are expended (i.e. after a certain, predetermined, amount of measurement probe usage) a refresh fee becomes payable to permit battery replacement.
  • [0023]
    Conveniently, the acquisition of measurements using the measurement probe system is prevented by powering the measurement probe using a non-replaceable power source (e.g. a battery) such that the acquisition of measurements is prevented once the power source is exhausted. The measurement probe may be provided in first and second parts as described above, with the non-replaceable power source being included in the first part.
  • [0024]
    Advantageously, the method comprises the step of measuring usage of the measurement probe system. In this manner, the prohibition on acquiring further measurements using the measurement probe system can be based on a measured usage value. Conveniently, the user is contractually inhibited (e.g. by a suitable agreement or contract) from acquiring measurements using the measurement probe system after reaching an agreed amount of measurement probe system usage.
  • [0025]
    The above method is described in terms of users and manufacturers of measurement probe systems. It should, however, be remembered that it is also common to sell measurement equipment through original equipment manufacturers (OEMs) as optional “add-ons” to other equipment. For example, measurement probe devices and associated control interfaces are often offered by machine tool manufacturers as optional items. The method is thus in no way limited to the method of sale and also encompasses the provision of measuring services through OEMs, distributors, agents etc.
  • [0026]
    Although the method of the present invention is described in terms of measurement probe systems, it should be noted that the method may be applied to other types of measuring equipment. Measuring equipment can be broadly categorised into dimensional and non-dimensional apparatus. Dimensional measurement apparatus allows a physical dimension of an object to be measured and may include, for example, measurement probes (such as touch trigger or scanning probes), optical position encoders etc. Non-dimensional measurement apparatus is also known for measuring a property or characteristic of an object other than a dimension; examples of such apparatus may include Raman spectrometers and Fourier transform infrared spectrometers. The method may thus be applied to dimensional and/or non-dimensional apparatus as required.
  • [0027]
    Further aspects of the invention relating to apparatus comprising a deactivation portion for inhibiting the use of measurement apparatus are described in Applicant's co-pending European patent application 07252959 (agents' ref: 738EP), the disclosure of which is incorporated herein by reference in its entirety. In particular, see pages 1 to 9 thereof.
  • [0028]
    Further aspects of the invention relating to modular measurement probe apparatus having a stylus module with an in-built failure mode are described in Applicant's co-pending European patent application 07253647 (agents' ref: 755EP), the disclosure of which is incorporated herein by reference in its entirety. In particular, see pages 1 to 11 thereof.
  • [0029]
    In summary, the present invention offers the potential to increase the market for measurement probe systems without having to compromise on the accuracy or quality of such systems. From a user's perspective, the lower upfront cost provided by the method reduces the financial risk associated with the acquisition of measurement probe systems thereby making such systems a more attractive option.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0030]
    The invention will now be described, by way of example only, with reference to the accompanying drawings in which;
  • [0031]
    FIG. 1 illustrates a measurement probe moved by a machine tool under computer control, and
  • [0032]
    FIG. 2 illustrates a measurement probe having an in-built trigger counter.
  • DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
  • [0033]
    Referring to FIG. 1, a measurement probe 500 is shown mounted to the spindle 502 of a machine tool. The spindle 502 is moveable in three dimensions (X, Y, Z) under the control of a computer controller 504. The machine tool also comprises, in a known manner, various position encoders that accurately measure the position (in X,Y,Z) of the spindle 502 and pass such position information back to the controller 504. Various alternative types of machine tool are also known.
  • [0034]
    The measurement probe 500 is a touch trigger probe in which the stylus holder is attached to the probe body by a spring-loaded kinematic arrangement of the type originally described in U.S. Pat. No. 4,153,998, the contents of which are hereby incorporated by reference. In use, a workpiece contacting stylus 506 is brought into contact with an object 510 to be measured. Deflection of the stylus 506 unseats the stylus holder from the probe body thereby breaking an electrical circuit. A processor is provided as part of the measurement probe to analyse the resistance of the circuit and to generate a trigger signal whenever the stylus is deflected by contact with an object; this is described in more detail in WO03/021182, the contents of which are hereby incorporated by reference.
  • [0035]
    The measurement probe 500 communicates with a probe interface 508 over a RF wireless link. The wireless link may use a spread spectrum (e.g. frequency hopping) protocol such as, or similar to, that described in more detail in WO2004/057552, the contents of which are hereby incorporated by reference. Other types of wireless link, for example an optical link, may alternatively be used. The trigger signal is relayed from the probe 500 to the interface 508 via the wireless link and then passed to the controller 504. The position of the spindle 502 when the trigger signal is issued is then stored. This allows, assuming the apparatus has been suitably calibrated, the position of a point on the surface of the object 510 to be established. Measuring multiple points in this manner allows various properties or dimensions of the object to be determined.
  • [0036]
    The above described operation of a machine tool based measurement probe system is known. However, as explained in more detail in the background section above, end users typically purchase measurement probe systems (e.g. the probe interface 508 and measurement probe 500) with a single upfront payment. However, the relatively high upfront cost of acquiring such a measurement probe system is often a substantial disincentive to machine tool users who are unaware of the potential benefits of incorporating such apparatus into their production processes. In particular, users of lower end machine tools are often unwilling to take the risk of investing in a measurement system when they are uncertain of the scale of the benefits that will be provided. Although it is known to provide hire purchase or loan arrangements that allow the purchase cost to be spread over a longer period, such arrangements do not reduce the total financial commitment that is associated with the purchase (in fact interest charges are likely to increase the total cost) but merely reduce the amount of upfront expenditure.
  • [0037]
    In order to increase the uptake of measurement systems, especially for low end machine tool users, the present inventors have devised a method for overcoming the requirement for a large, upfront, financial commitment. Importantly, this lower cost option does not require any reduction in the accuracy or reliability of the measurement system. In accordance with the present invention, usage of the measurement probe system is recorded. In the embodiment described with reference to FIG. 1, the computer control 504 is arranged to record the number of trigger signals that are received from the measurement system (i.e. from the measurement probe 500 via the interface 508). This is achieved by running an appropriate monitoring program on the computer control 504 that stores a count value and causes that count value to increment (or decrement) each time a trigger signal is received. It should be noted that the computer control 504 may comprise a numerical controller (NC) interfaced to a separate personal computer or it may comprise a front end computer that provides numerical control of the machine tool and also has sufficient processing power to run additional applications.
  • [0038]
    The measurement apparatus of FIG. 1, and in particular the computer controller 504, keeps a running total of the number of trigger signals that have been issued by the measurement probe. The user may, on purchasing the equipment, be prohibited from using the measurement system after a certain number of trigger signals have been issued. For example, purchase of the measurement system may be (e.g. contractually) conditional on it being used to provide no more than a certain number, say ten thousand, trigger signals. This may be considered a first usage threshold that limits the number of points that can be measured with the measurement system.
  • [0039]
    The first usage threshold may be increased before it is exceeded, for example by purchasing additional “triggers” from the manufacturer or their authorised agent etc. If the updated first usage threshold is reached or exceeded, further use of the measurement probe system is prohibited. After use has been prohibited, it may be possible to purchase additional “triggers” or counts that allow use of the measurement system to be resumed; for example, until a second usage threshold is reached or exceeded. Third and subsequent usage thresholds may subsequently be set in a similar manner. A complete removal of usage restrictions may also be permitted, for example on payment of a full release or upgrade fee, thereby converting the measurement system into a standard measurement system.
  • [0040]
    It is important to note that there is no obligation on the user to purchase additional triggers or pay any upgrade fee. This is entirely at the discretion of the user and can be based on an assessment of the value added to the relevant manufacturing process by the measurement system. Provision of such a system thus alters the cost/risk balance and makes the purchase of a measurement system a more attractive option to end users and especially to users of lower end machine tool equipment. The manufacturer also benefits from being able to increase market penetration due to the lower upfront cost whilst being able to recoup the necessary costs from those users who continue to use the measurement system once the benefits of the system in the particular application have become apparent.
  • [0041]
    In the embodiment described with reference to FIG. 1, the computer 504 is used to monitor measurement probe usage. However, different methods of monitoring usage may be implemented. Preferably, such monitoring is performed in an automated, e.g. electronic, manner but it would be possible for an operator to manually monitor usage (e.g. by counting or estimating how many times the probe is triggered). In preferred embodiments, the measurement probe system (e.g. the measurement probe or the probe interface) performs the usage monitoring function.
  • [0042]
    Referring to FIG. 2, a measurement probe 550 is illustrated that includes a trigger counter display 552. The measurement probe 550 is a touch trigger probe of the type describe above but also includes a suitable trigger counter. The trigger counter (not shown) may be provided as a dedicated trigger counter unit or may be implemented by a processor that also performs other probe functions (e.g. deflection signal analysis or data communications). The count measured by the trigger counter is, in this example, made available to the user via a trigger counter display 552, such as a liquid crystal display or the like, that is provided on the body of the measurement probe.
  • [0043]
    As shown in FIG. 2, the measurement probe 550 stores a trigger count of “1798” as it is moved towards an object 554. The stylus of the measurement probe 550 then contacts a point on the surface of the object thereby deflecting the stylus and generating a trigger signal that is passed to an associated interface over a wireless link. Generation of a trigger signal in this manner also causes the trigger counter to increment to “1799” which is displayed to the user. Each time a measurement point is acquired, the count thus increases by one.
  • [0044]
    Although a trigger counter display of the type illustrated in FIG. 2 provides a convenient way to communicate the trigger count to a user, numerous alternatives are possible. For example, the measurement probe may include an LED that illuminates when a measurement usage threshold is approached and/or reached. Alternatively, multiple LEDs may be provided that indicate the number of trigger counts that have been expended or are remaining. For example, consider a touch trigger probe having a usage limit of 10,000 counts. A green LED may be illuminated until 8,000 counts have been expended whereupon an amber LED is illuminated. The amber LED is extinguished and a red LED illuminated when the limit is reached. In this manner, some warning that the usage limit is being approached may be communicated to a user. The trigger count information from the measurement probe may also, or alternatively, be displayed by the probe interface and/or passed to the control computer for display.
  • [0045]
    It should be noted that although measuring trigger counts provides a convenient measure of measurement probe usage, other measures could also or alternatively be used. For example, the number of parts that have been measured by the measurement system could be counted (e.g. by the computer controller of the machine tool). As a variant of this, the number of parts that have been measured and have been found to be within acceptable measurement tolerances could be counted, thereby ignoring any measurements made on workpieces that have to be scrapped. A time based usage system may also be implemented. For example, the amount of time that the measurement system is in use could be measured. This may be a measure of the duration of machine tool, measurement probe and/or probe interface activation. Alternatively, it may be possible to measure for how long the measurement probe has been loaded into spindle and/or moved about by the machine. The usage of the measurement probe may also be derived from the combination of two or more measures; for example, the usage may be defined by the number of triggers issued and the amount of time the measurement probe has been active.
  • [0046]
    The above mentioned prohibition on further use after the usage limit has been reached may rely on the honesty of the user and/or a suitable contractual requirement can be placed on the user. Alternatively, the measurement system or the machine tool may include a mechanism (e.g. hardware or software based) that prevents the acquisition or use of further measurement data after the threshold is reached. A variety of suitable embodiments that prevent normal probe operation after a usage limit has been exceeded are described in more detail below and such devices offer the manufacturer the assurance that unauthorised use of the measurement system can not occur. Such hardware/software prevention mechanisms may be used in conjunction with contractual requirements.
  • [0047]
    Instead of setting a usage limit that is not to be exceeded, it is also possible to monitor usage of the measurement probe system and periodically charge the user a usage based fee. This still permits the upfront cost of the measurement probe system to be reduced and allows usage to be monitored and charged for accordingly. The fee is preferably set upfront and may include a graduate scale of costs in which each measurement becomes cheaper as more measurements are taken. Once a certain amount of usage has occurred and been paid for, further use of the measurement system may not incur any further cost. Again, such a usage based charging system does not require a significant upfront financial commitment from a user and still allows the manufacturer to profit if the measurement system is found to be advantageous in the user's particular machining process. This solution therefore also makes measurement systems more attractive propositions, especially to users of lower end machine tools.
  • [0048]
    The above examples that are described with reference to FIGS. 1 and 2 relate to touch trigger probes. It should, however, be noted that the invention is equally applicable to other types of contact and/or non-contact (e.g. optical, capacitive etc) measurement probes. For example, the measurement probe may comprise an analogue or scanning probe in which data relating to stylus deflection is generated. Similarly, the above examples describe machine tool based systems. The invention can also be applied to dedicated co-ordinate measurement machine (CMMs) or any other type of co-ordinate positioning apparatus.
  • [0049]
    Embodiments of apparatus comprising a deactivation portion for inhibiting the use of measurement apparatus are described with reference to FIGS. 1 to 11 in Applicant's co-pending European patent application 07252959 (agents' ref: 738EP).
  • [0050]
    Embodiments of modular measurement probe apparatus having a stylus module with an in-built failure mode are described with reference to FIGS. 1 to 3 in Applicant's co-pending European patent application 07253647 (agents' ref: 755EP).
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Classifications
U.S. Classification377/15, 33/559
International ClassificationG01B5/00, G07C3/00
Cooperative ClassificationG01B21/047, G01B5/012, G01B2210/58, G01B5/008, G01B5/02
European ClassificationG01B21/04D, G01B5/012
Legal Events
DateCodeEventDescription
Aug 27, 2008ASAssignment
Owner name: RENISHAW PLC, UNITED KINGDOM
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:PRESTIDGE, TIM;LUMMES, STEPHEN EDWARD;CAMPBELL, STUART KERSTEN;AND OTHERS;REEL/FRAME:021454/0287;SIGNING DATES FROM 20080819 TO 20080821