Abstract:
A probe  10  has internal circuitry capable of operating in a plurality of different modes, for example a variety of filter modes and turn off modes. A switch on the probe sends an input to a controller which is arranged to preset the mode in response to operation of the switch. The switch may be a push button  32  which is operated externally of the probe  10  by means of an actuator in the form of a plunger  34.  The probe has a workpiece-contacting stylus  11  mounted on a seat from which it is deflectable. The stylus and the seat may comprise the switch. An indicator, eg an LED  44,  indicates the mode in response to an output from the controller. The controller outputs a plurality of indications of different modes in a sequence and a mode is selected by operating the switch once the desired mode is indicated.

Description:
RELATED APPLICATION AND INTERFERENCES 
   This application is a national stage entry of PCT/GB02/00465, internation filing date Feb. 01, 2001. 
   BACKGROUIND 
   This invention relates to probes for use on position determining apparatus such as coordinate measuring machines, measuring robots and in particular machine tools. 
   An example of such a probe is shown in U.S. Pat. No. 4,153,998. Probes intended for use on machine tools, in which there is a wireless signal transmission system between the probe and the controller of the machine tool, are shown in European Patent Numbers 337669 and 337670. 
   As such probes have become more complex over the years, there has been a need for them to operate in different modes. 
   For example, it can be desirable for the signal produced by the probe to be filtered prior to transmitting it to the controller, in order to prevent the generation of spurious signals as a result of vibration. Therefore, the probe may be preset to use different types of filtering, or no filtering, depending on the machine tool and the environment into which it has been installed. 
   Furthermore, on machine tools such probes are commonly battery operated. The wireless signal transmission system also includes a receiver for receiving a switch-on or start signal. This switches the probe on from a sleeping state in which it consumes very low current, ready for normal use. It is then desirable to switch the probe circuitry off (back to the sleeping state) after use. The probe may have different preset modes, giving different manners in which the circuitry is turned off. 
   In known probes, such modes are preset by the use of DIP switches on a circuit board internally within the probe. This has a number of disadvantages. In order to change the preset mode, the operator has to dismantle the probe to access the DIP switches. There is a risk that the operator will damage the printed circuit board, and the probe has to be designed to permit such dismantling. Where the DIP switches act on a micro controller to preset the mode, there is a restriction on the number of input lines to the micro controller. With, say, three such input lines from a three-gang DIP switch, a maximum of eight modes can be preset. Any more modes would require a larger number of input lines to the micro controller. Finally, it would be desirable to provide a pre-setting device which is smaller, less expensive and more reliable than DIP switches. 
   SUMMARY 
   The present invention provides a probe for position determining apparatus, having internal circuitry capable of operating in a plurality of different modes, a switch, a controller connected to receive an input from the switch and arranged to preset the mode in response to operation of the switch, an indicator for indicating the mode in response to an output from the controller, the controller being arranged to output a plurality of indications of different modes in a sequence, and to select the mode just indicated upon an operation of the switch. 
   Preferably, the switch is mounted inside the probe but is operable by an actuator accessible from outside the probe. 
   In a first embodiment the switch comprises a push button. 
   In a second embodiment of the invention the probe has a workpiece-contacting stylus mounted on a seat from which it is deflectable, wherein the stylus and the seat comprise said switch. The seat may be kinematic. The controller receives an input from the switch when the stylus is deflected. 
   Each mode may also include a plurality of different sub-modes. The controller may be arranged to output a plurality of indications of different sub-modes in a sequence and select the sub-mode just indicated upon an operation of the switch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein: 
       FIG. 1  is a diagrammatic view of a probe on a machine tool; 
       FIG. 2  is a partly sectional view of part of a first embodiment of the probe of  FIG. 1 ; 
       FIG. 3  is a block circuit diagram showing a micro controller within the probe; 
       FIG. 4  is a flow chart of a program of the first embodiment which runs in the micro controller; 
       FIG. 5  is a side view of the second embodiment of the probe; 
       FIG. 6  is a sectional view of the probe of  FIG. 5  through A—A; 
       FIG. 7  is a sectional view of the probe of  FIG. 5  through B—B; and 
       FIG. 8  is a flow chart of a program of the second embodiment which runs in the micro-controller. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Referring to  FIG. 1 , a probe  10  is mounted in the spindle  12  of a machine tool, exchangeably with the normal cutting tools. The spindle  12  can move the probe in three dimensions X,Y,Z, relative to a workpiece  14  clamped on the table or bed  22  of the machine tool. Measurements are made by contact between a stylus  11  of the probe and the workpiece. Measurement signals from the probe are transmitted optically, as indicated by arrow  16 , to a receiver module  19  mounted on fixed structure  20  of the machine tool. The module  19  can also transmit an optical (e.g. infrared) switch-on or start signal, indicated by arrow  18 , to the probe  10 . The probe  10  is battery operated, and remains in a sleeping state until receipt of the switch-on signal  18 , whereupon it starts transmitting measurement signals  16 . 
     FIG. 2  shows a first embodiment of the probe  10  in more detail. Internally, it has two circuit boards  24 , on which are fitted light emitting diodes  26  for transmitting the optical measurement signals  16 . The boards  24  also have a plurality of photodiodes  28  (only one of which can be seen in  FIG. 2 ), for receiving the switch-on signal  18 . Furthermore, they have indicators in the form of red and green light emitting diodes (LEDs)  44 , 45 . The light emitting diodes  26 , the photodiodes  28  and the indicator LEDs  44 , 45  are distributed around the circumference of the probe, behind a glass window  30 . 
   One of the circuit boards  24  is provided with a push button switch  32 . This can be operated from externally of the probe, by means of an actuator  34  in the form of a plunger. The external end  36  of this plunger lies within a recess  38 , and can be actuated by means of a suitable pointed implement. 
   The following table illustrates various possible modes which can be preset by the use of the push button switch  32 . 
   
     
       
             
             
             
           
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               TURN OFF SELECT 
               FILTER SELECT 
             
           
        
         
             
               MODE 
               OPTICAL 
               TIME 10 sec 
               TIME 30 sec 
               TIME 134 sec 
               NO FILTER 
               ANALOGUE 
               DIGITAL 
             
             
                 
             
           
        
         
             
               1 
               ✓ 
                 
                 
                 
               ✓ 
                 
                 
             
             
               2 
               ✓ 
                 
                 
                 
                 
               ✓ 
                 
             
             
               3 
               ✓ 
                 
                 
                 
                 
                 
               ✓ 
             
             
               4 
                 
               ✓ 
                 
                 
               ✓ 
                 
                 
             
             
               5 
                 
               ✓ 
                 
                 
                 
               ✓ 
                 
             
             
               6 
                 
               ✓ 
                 
                 
                 
                 
               ✓ 
             
             
               7 
                 
                 
               ✓ 
                 
               ✓ 
                 
                 
             
             
               8 
                 
                 
               ✓ 
                 
                 
               ✓ 
                 
             
             
               9 
                 
                 
               ✓ 
                 
                 
                 
               ✓ 
             
             
               10 
                 
                 
                 
               ✓ 
               ✓ 
                 
                 
             
             
               11 
                 
                 
                 
               ✓ 
                 
               ✓ 
                 
             
             
               12 
                 
                 
                 
               ✓ 
                 
                 
               ✓ 
             
             
                 
             
           
        
       
     
   
   It will be seen that the items which can be selected fall into two groups. Under the heading “turn off select” there are various presettable possibilities for the manner in which probe circuitry is turned off (i.e. returned to its sleeping state in which it no longer transmits measurement signals  16 ). The first column under this heading indicates modes in which the probe circuitry is turned off by the receipt of another optical signal from the machine-mounted module  19 , as indicated by the arrow  18 . The remaining columns under this heading indicate that the probe is turned off after a preset period of non-use (i.e. during which the stylus  11  of the probe  10  has not contacted the workpiece  14 ). In various different modes, the probe may be turned off after periods of 10 seconds, 30 seconds or 134 seconds of non-use. 
   The final three columns of the above table, labelled “filter select”, indicate possible filtering which may be applied to the probe measurement signal before it is transmitted as the optical signal  16 . The filtering selected will depend upon the machine to which the probe is installed and the environment. If the installation is not susceptible to vibration, then modes in which no filtering is performed may be preset. Alternatively, in different installations, modes with analogue filtering or digital filtering may be preset. 
   It will be seen that the table shows 12 possible modes, which between them give all possible combinations of “turn off select” and “filter select”. 
   The push button  32  provides an input to a micro controller  40 , seen in  FIG. 3 . This has outputs  42  to the remaining circuitry on the circuit boards  24 , which provide the various possibilities for turn off and filtering indicated in the above table. It also controls the light emitting diode indicators  44 . 
   Referring to  FIG. 4 , the micro controller  40  acts as follows. In step  46 , in the sleeping state, the micro controller&#39;s program detects that the button  32  has been pushed. In steps  47 , 48  and  49 , it determines whether the button remains pushed for a period greater than 3 seconds. If the button is released within this 3 second period, then in program step  50  the micro controller outputs signals to the indicator  44  to indicate the current mode which has been preset previously. It does this by flashing the indicator  44  a number of times, corresponding to the mode number indicated in the above table (e.g. 3 flashes for mode 3). 
   Thus, the operator can obtain an indication of the current mode simply by depressing the button briefly (for less than 3 seconds). If desired, an alternative period such as 5 seconds may be used. 
   If the button is held depressed for more than 3 seconds, the program enters a loop comprising steps  51  to  59 . Firstly, step  51  sets the mode number to 1, and step  52  provides an output to the indicator  44  to indicate this mode. Alternatively, step  51  may be omitted and the loop can start with the mode currently set. As in step  50 , the mode is indicated by a corresponding number of flashes of the indicator  44 . 
   Next, in steps  53 ,  54  and  56 , the program pauses, for example for 2 seconds, while checking the state of the button. If the button is released during this pause, (step  54 ) the program exits the loop, and in step  60  the micro controller provides outputs on the lines  42  to preset the filters and the turn off circuits of the probe. It does so in accordance with the mode last set in step  51 . 
   If, in step  56 , the button has not been released at the end of the 2 second pause, then the loop continues, via program step  58  which increments the mode number. Should the maximum number of modes have been exceeded, then step  59  returns to the loop via step  51 , which resets the mode number to 1. The new mode is now indicated in step  52 , and steps  53 ,  54  and  56  pause to see if the operator releases the button. 
   Mode selection is therefore a very easy process for the operator. He simply presses the button, and holds it depressed while the program cycles through all the possible modes. He releases the button immediately after the mode required has been indicated. Thus, if he requires mode 5, he releases the button after the part of the cycle in which the indicator  44  flashes five times. 
   Of course, modifications are possible. In the above description, each time the program passes through step  52  it flashes for a number of times corresponding to the mode number (once for mode 1, five times for mode 5, etc). It may instead simply flash once on each pass through this program step. The operator then effectively counts the number of times that the program passes around the loop  52 ,  53 ,  54 ,  56 ,  58 , releasing the button  32  at the appropriate time. 
   It is also possible to provide a more sophisticated indicator  44 , giving a numerical indication, instead of a number of flashes. 
   It will also be appreciated that the modes indicated in the table above are intended merely as examples. Other aspects of the operation of the probe may be preset in the various modes, in addition or instead of the filtering and the turn off method. 
   The push button  32  in this preferred embodiment overcomes the problems of DIP switches discussed in the introduction. 
   A second embodiment of the probe  10  is shown in  FIGS. 5–7 .  FIGS. 6 and 7  are sections along the lines A—A and B—B respectively shown in  FIG. 5 . The probe  10  comprises a housing  24  and a stylus  11 . 
   The electronics are mounted on a flexible material  70  which is positioned in a compact spiral arrangement along the inside circumference of the probe housing. The electronics include light emitting diodes  26  for transmitting the optical measurement signals  16 , a plurality of photodiodes  28  for receiving the switch-on signal  18  and indicators  44  in the form of red and green light emitting diodes for indicating the mode. The light emitting diodes  26 , photodiodes  28  and indicators  44  are distributed around the circumference of the probe behind a glass window  30 . 
   The stylus  11  is mounted on a kinematic seat inside the housing. The kinematic seat comprises three vee-shaped grooves each formed between a pair of ball bearings  72 . The stylus has three cylindrical members  74  extending radially from its upper end which are urged into contact with the vee-shaped grooves by a spring  76 . This defines the rest position of the stylus  11 . Such an arrangement is well known and described in U.S. Pat. No. 4,153,998. 
   When the stylus is in this rest position an electric circuit which passes in series from one vee-shaped groove to the next adjacent one is completed. Each member is insulated from the stylus and other members and completes the circuit between the two sides of each respective vee-shaped groove. Deflection of the stylus results in at least one of the members breaking contact with the ball bearings and thus breaking the circuit. As described in U.S. Pat. No. 4,153,998 the breaking of the circuit is used to provide an input pulse to an automatic switching arrangement and thereby indicate that deflection of the stylus has occurred. In the present invention, this arrangement may also be used as a switch for changing between different preset modes, for example for selecting turn-off modes or selecting different filters. 
   The following table illustrates various possible modes which can be preset by using the probe stylus. 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               MODE 
               OPTION 
             
             
                 
                 
             
           
           
             
                 
               Turn-off mode select 
               Optical off 
             
             
                 
                 
               Short timeout 
             
             
                 
                 
               Medium timeout 
             
             
                 
                 
               Long timeout 
             
             
                 
               Probe filter select 
               Probe filter on 
             
             
                 
                 
               Probe filter off 
             
             
                 
               Start filter select 
               Start Rejection filter on 
             
             
                 
                 
               Start Rejection filter off 
             
             
                 
                 
             
           
        
       
     
   
   In this example there are three modes each mode having several options. The first mode in the table selects the turn-off method and has four options for pre-setting the manner in which the probe circuitry is turned off, as described in the previous embodiment. In the first option the probe circuitry is turned off following an optical signal from the machine mounted module as indicated by arrow  18  in  FIG. 1 . The remaining options indicate that the probe is turned off after a preset period of non-use, i.e. during which the probe stylus has not contacted the workpiece. For example, for a short time-out the probe turns off after about 10 seconds of non-use. A medium time-out may be about 30 seconds, and a long time-out may be about 134 seconds of non-use. 
   The second mode in the table is probe filter select as described in the previous embodiment. In this mode the options are the probe filter may be on or off. 
   The third mode in the table is the start signal filter select. This filter enables the probe to distinguish between the start signal ( 18  in  FIG. 1 ) and other external influences, such as light from fluorescent light bulbs, which may be confused with the start signal. However this filter introduces a time delay and thus may not be required when external influences are insignificant. In this mode, the options are the start signal filter may be on or off. Such a filter is disclosed in our European Patent Application No. 1130557. 
   As shown in  FIG. 3  the stylus is used as a switch  32  to provide an input to a micro-controller  40 . This micro-controller sends outputs  42  to the circuitry in the probe which allows different modes to be selected and different options within each mode to be selected. The micro-controller also controls the light emitting diode indicators  44  which flash different signals to indicate the different modes and options. 
   Referring to  FIG. 8 , the micro-controller  40  acts as follows. The micro-controller is in a sleep mode  88  until it detects a battery being inserted  80  in the probe which starts a first timer  82 . If the kinematic remains seated  84  (i.e. the stylus remains undeflected) for longer than 8 seconds  86 , the probe will return to the sleep mode  88 . However if the kinematic is unseated  84  for longer than 8 seconds  90 , then once the kinematic has reseated  92  the mode and option will both be set to the first mode and option respectively  94  and the micro-controller will enter the mode and option setting loop  96 – 114 . Alternatively this step can be omitted and the loop can start with the mode and option currently set. 
   Thus the micro-controller is activated by inserting the battery and the mode and option setting loop of the controller is entered by deflecting the stylus for a time period of eight seconds and then returning the stylus to its rest position. 
   When the mode and option setting loop  96 – 114  is entered a second timer is started  96  and the mode and option are displayed  98  by the indicator. As in the previous embodiment the indicator comprises LEDs. If more than 10 seconds has elapsed  100  without the kinematic unseating, then the micro-controller will return to its sleep mode  88 . 
   If the kinematic unseats  102  within 10 seconds  100  then a third timer is started  104 . If the kinematic reseats within 0.3 seconds  108 , the micro-controller will return to the beginning of the loop at  96 . If the kinematic has been unseated for greater than 0.3 seconds but less than 2 seconds  110  then the option is advanced  112 . If the kinematic has been unseated for greater than 2 seconds then the mode is advanced. 
   Thus once the micro-controller is in the mode and option setting loop, the option and mode may be advanced by deflecting the stylus for a short time period (i.e. for advancing the option) or a longer time period (i.e. for advancing the option). 
   Once either the mode or option are advanced, the micro-controller returns to the beginning of the loop  96 – 114 . The second timer is started  96  and the new mode and option are displayed  98 . The loop is exited if the kinematic remains seated for 10 seconds  100 . Otherwise the micro-controller continues around the loop until the desired mode and option have been selected. 
   The function of the first, second and third timers 82, 96, 104 may all be carried out by a single timer. 
   Use of the stylus on its kinematic mount as a switch has several advantages. This arrangement is compact and so the size of the probe is able to be reduced. In addition, the kinematics for the stylus are part of the existing probe and thus no additional parts are needed. 
   In the above description the indicator flashes a number of times corresponding to the mode number and option number each time it cycles through the different modes and options. It is also possible to provide a more sophisticated indicator giving a numerical indication instead of a number of flashes. 
   The above example has three modes, each mode having several options. Therefore the micro-controller can cycle between the three modes until the desired mode is selected and then cycle between the options of that mode until the desired option is selected. This is much quicker than cycling through every option of every mode in turn. The modes and options in the table are intended merely as examples. Other aspects of the operation of the probe may be preset in the various modes in addition or instead of the filtering and turn-off method.