Patent Document

BACKGROUND 
   This invention relates to the identification of tools, e.g. measurement tools used for inspection of work pieces on a co-ordinate positioning machine. Such co-ordinate positioning machines include co-ordinate measurement machines (CMM&#39;s), machine tools and robots. 
   Measurement tools, e.g. probes that respond to surface contact, surface finish probes, proximity probes, crack detection probes, laser and other optical measuring probes, video cameras etc, all have individual requirements for the conditioning of their respective signals. Where a machine uses more than one tool, e.g. each tool being connectable to a universal mounting then it is desirable to have a means for identification of the tool that is mounted to the machine so that its signal can be conditioned correctly. Contact probes sometimes use extension bars and these too require identification. 
   SUMMARY 
   One approach to tool identification is described in EP236414. In that patent there is disclosed a tool identification system including a tool having contacts connected to an electrical resistance of a value corresponding to that particular tool type. When the tool is mounted to the machine the connections on the tool make with complementary connections on a universal mounting and the tool is interrogated. The resistance of the tool is measured and the type of tool can thus be recognised by the machine. The appropriate interface circuit for that type of tool can then be selected. 
   With increasing numbers of types of tool the limitations of this system have become apparent. Use of a standard resistor value series results in a limit to the number of resistance values that can be used and thereby a limit to the number of types of tool that can use such an identification system. Furthermore, errors in resistance values, e.g. due to poor manufacturing tolerance, age of the resistor, or unwanted resistance at the tool connections, can all lead to an incorrect recognition of the type of tool mounted to the machine. 
   According to one aspect of the invention there is provided a tool identification apparatus comprising: 
   a first part of a tool joint including a first electrical connection and a releasable mounting, said first part being for releasable coupling to a tool head having a second part of the joint which has a complementary mounting and a second electrical connection;
 
a tool identification data storage device for storing digitally tool identification data; and
 
a data communication link between the said electrical connection and the said tool identification data storage device for carrying said identification data.
 
   Preferably the data storage device is non-volatile memory. 
   Preferably the tool identification data storage device comprises a PIC device and wherein the data communication link comprises two conductive paths only. 
   Preferably the identification data storage device is located at the releasable joint. 
   Preferably the first part further includes a connector for interconnecting the part to a tool. 
   Preferably the two conductive paths provide a path for tool power as well as the data communication link. 
   According to another aspect the invention provides a tool identification system comprising: 
   tool identification apparatus according to the said one aspect and further comprising: 
   a tool holding head, the head having a second part of the tool joint having a further mounting for releasably coupling to the first part to the second part, the second part of the joint including a second electrical connection complementary to the first electrical connection for carrying the identification data. 
   Preferably the tool identification system further comprises: 
   at least one interface circuit having interface circuit identification data storage for storing interface circuit identification data, the or each interface circuit in use conditioning signals provided by a tool; and 
   an intermediate circuit in further data communication with both the second electrical connection and the or each interface circuit, in use the intermediate circuit being operable to provide an electrical link between the tool and the said at least one interface circuit if the said tool identification data corresponds with the said interface circuit identification data. 
   Preferably the intermediate circuit is further operable to provide a further link between the tool and a further interface circuit if no identification data is obtained. 
   According to yet another aspect the invention provides a tool identification system comprising: 
   a tool holding head, having a second part of a releasable joint; and 
   at least one tool, each tool having a tool identification module connected to the or each tool, the or each tool identification module having a first part of a releasable joint for coupling to the second part of the joint on the head, a connector for interconnecting the tool to the module, and a digital data store for identifying the tool to which the module is connected. 
   The invention extends to a module for interconnecting both electrically and mechanically a tool to a tool head, wherein the module has a digital data store for identifying the tool to which it is connected. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will now be described with reference to the drawings, wherein: 
       FIG. 1  shows a CMM with interchangeable measuring probes, incorporating the invention, and; 
       FIG. 2  shows a schematic illustration of the electrical arrangement of the invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  shows a known CMM  5  having a head  10  with a releasable kinematic joint  17 / 18 . The lower part  18  of the joint will be common to a number of measurement tools  12 , in this case measurement probes  12   a ,  12   b  and  12   c , and has a kinematic mounting attachable to the upper part of the joint  17 . Both parts  17  and  18  will have complementary kinematic mounting features. 
   Kinematic features are shown in a publication by H. J. J. Braddick called “Mechanical Design of Laboratory Apparatus”, Chapman &amp; Hall Limited, 1960 and may additionally include quasi or semi-kinematic designs. As an example of a kinematic mounting there is shown on each of the lower parts  18  three equispaced balls  26 , each of which sit in a complementary vee slot  27  on the upper mounting of the joint part  17 . The balls and slots are arranged in a triangular formation so six points of contact are made between the mountings at the upper and lower joint parts  17 / 18 . Other kinematic and semi/quasi-kinematic configurations are possible within the ambit of the invention, e.g. three balls contacting a triangular hole, a vee slot and a flat plate respectively. 
   The CMM has a head  10  which can be moved under the instruction of controller  51  in any of the X, Y or Z directions illustrated and thereby inspect the dimensions of a workpiece  7 , sat on base  11 , by means of contact of the workpiece by stylus  14  attached to probe  12   a . The CMM is also capable of exchanging automatically the probe  12   a  for another probe  12   b , 12   c  housed in a rack  40 . The kinematic joint provides repeatable repositioning of probes removed and replaced onto the head  10 . 
   One mechanism for automatic exchange and locking/unlocking of the probe to and from kinematic mounting of joint part  17  is described in detail in WO85/02138. The disclosure in that patent document is incorporated herein. Other joints and mountings can be used. Manual exchange of probes may also be employed. When a rack is used an operator is required initially to place the probes  12  into the rack  40  and this may be done in the incorrect order. Manual exchange of probes may also lead to the wrong probe being fitted to the machine. 
   Referring also to  FIG. 2  an intermediate circuit, in this case a microprocessor  20 , is used in this invention to interrogate probe  12  mounted to the head  10  via communication line  9  in order that it can be recognised. Additionally the microprocessor  20  also interrogates probe interface circuits  23 A,B and C via communication lines  33  to recognise each circuit  23  in order that the signals from the probe along line  30  can be routed to the correct interface circuit by relay switches at circuit  22 . From the appropriate interface circuit the signal is fed to the CMM controller  51  via lines  25  and optionally to a computer for processing of data. 
   The identification of the probes  12  and interface circuits  23  is possible because a data store  19  and  32  is held in each probe and interface circuit respectively. The data store is digital information in code form held in a non-volatile memory which can identify the probe/interface. This data store is read by the microprocessor  20 , and the microprocessor operates ranks of switches (relays)  22  so that information to and/or from the probe is communicated to/from the correct interface. 
   Since it is likely that the data store will be incorporated into different types of tools, it is convenient to locate the data store in the releasable joint part  18  so that the joint part can be standardised and used in all types of tool and no modifications to other parts of the tool will be required. Thus the joint part  18  may have a modular form, i.e. a discrete component which can be sold separately. This tool identification module will have a digital data store (e.g. a programmable integrated circuit (PIC)) which is programmed or is programmable so that it can identify the tool to which it is attached. 
   Each joint part  18  will have, as well as its kinematic features, a tool connector  21  for interconnecting the various tools e.g.  12   a,b  and  c  to the joint part  18 . The connector could be a simple screw type fixing. 
     FIG. 2  shows in more detail the electrical arrangement illustrated in  FIG. 1 . In this Fig the tools  12   a,b  and  c  can be seen housed in rack  40 . The tools (including probe  12   a ) have electrical contacts  16  at the releasable joint part  18  that co-operate with complimentary contacts  15  on the universal mounting of the joint part  17 . Two of the contacts  16  are connected to probe data store  19 , in this instance a programmable integrated circuit (PIC). The PIC has a digital code embedded in memory therein which can be recognised by the processor  20 . A similar PIC  32  is used as a data store in each interface circuit  23  and likewise, the processor  20  can recognise a code embedded in the PIC  32 . 
   An advantage of using a PIC is that just two wires  28  or other conductive paths can be employed to carry the stored data and interrogate the PIC, via a serial interface and these wires, at the tool at least, can be used for probe power also. Additionally the use of two wires means that backward compatibility is possible i.e. the probe etc, previously fitted with a resistor identification (as detailed in the discussion of the prior art) can be recognised also by the processor  20 . In such circumstances the processor  20  can be adapted to measure the resistance of the two wires. If the resistance varies from a known value used to denote a digital identification (i.e. the tool is an “old” resistance identified probe) then the processor can route a tool communication to a pre-defined port of the intermediate circuit  20 . This port may be in communication with an appropriate interface  23 , or may be in communication with a further intermediate circuit for selecting one of a number of interfaces depending on the resistance of the tool in the head  10 . Thus a digital system of tool identification can be made backwardly compatible with the known resistance type identification system. 
   Additionally, it may be desirable to make a group of tools compatible with a single (or a few) interface circuit(s), or vice versa. This can be achieved by adding identification codes, but not necessarily an additional PIC to the interface so that effectively it has more than one identity, each of which will be pairable with a code from a member of the compatible group of tools, or vice versa.

Technology Category: g