WO2008056137A1

WO2008056137A1 - Connection interface for a measurement probe

Info

Publication number: WO2008056137A1
Application number: PCT/GB2007/004242
Authority: WO
Inventors: Nicholas John Weston; James Fergus Robertson
Original assignee: Renishaw Plc
Priority date: 2006-11-07
Filing date: 2007-11-07
Publication date: 2008-05-15
Also published as: GB0622170D0

Abstract

A connection interface between a coordinate positioning apparatus, such as a manual measurement arm, and a surface sensing device, such as a contact sensing rigid probe. The coordinate positioning apparatus is provided with at least one selection device, such as a set-up button, capable of being operated by a user. The connection interface has interface circuitry, a connection between said interface circuitry and circuitry of the coordinate positioning apparatus, a connection between said interface circuitry and circuitry of the surface sensing device. The interface circuitry has at least two modes of operation, a first mode in which operation of the at least one selection device creates an output signal, and a second mode, in which the selection device is isolated and wherein inputs received by the interface circuitry from the circuitry of the surface sensing device are output into the circuitry of the coordinate positioning apparatus as output signals which emulate the output signals from the selection device.

Description

CONNECTION INTERFACE FOR A MEASUREMENT PROBE

The present invention relates to a connection between a measurement probe and a coordinate positioning apparatus to which it is attached. More particularly, it relates to the connection of a measurement probe on a coordinate positioning apparatus which allows the controls of the coordinate positioning apparatus to maintain their normal function and additionally to control some functions of the measurement probe.

Coordinate positioning apparatus comprise apparatus such as coordinate measuring machines (CMMs) , machine tools, articulating arms etc which are able to position a part (eg, quill, spindle or arm) in a defined position in space and/or to measure the coordinates of that position in space. Such coordinate positioning apparatus may be automated or manual.

A probe may be mounted on a coordinate positioning apparatus for sensing a surface to be measured. Such a probe may be either a contact or non contact probe. Contact probes typically comprise a housing and a surface contacting stylus. Contact probes may have a deflectable stylus. In a touch trigger probe, deflection of the stylus is used to indicate that a reading of the coordinate positioning apparatus should be taken. In a scanning probe, the amount of deflection is combined with the readings of the coordinate positioning apparatus to determine the surface position. Rigid probes comprise a non deflectable stylus and for these probes, the user must manually press a button or other device to indicate that a reading should be taken by the coordinate positioning apparatus. Non contact probes do not physically touch the probe, for example optical, capacitive and inductive probes .

Touch sensitive rigid probes also exist. For example in a piezoelectric probe the stylus is vibrated by one or more piezoelectric element. When the stylus contacts a surface, a change in the characteristic vibration results and can be used to determine that contact has occurred. The MSP3 probe is a piezoelectric probe produced by Renishaw.

British Patent Application No. GB 2006435 discloses a surface measurement probe with a workpiece contacting stylus. The probe is provided with a driving transducer and generating transducer which both comprise piezoelectric crystals. An alternating current is applied to the driving transducer to produce vibrations which are in turn transmitted to the stylus. Vibrations of the stylus excite the generating transducer. If the stylus makes contact with the surface, the vibrations are reduced. This reduction in vibration is sensed from a change in parameters of the generating transducer. Thus it may be determined when the stylus comes into contact with the surface.

EP 0730210 discloses a portable coordinate measuring machine comprising a multi-jointed manually positionable measuring arm. This comprises a plurality of extension members attached to each other by joints defining one degree of freedom and including measurement transducers, which forms a measurement arm having five, six or seven degrees of freedom. The movable arm is attached to a base and a probe may be mounted onto the arm.

Such a portable coordinate measuring machine is manufactured by Faro Technologies.

A first aspect of the present invention provides a connection interface between a coordinate positioning apparatus and a surface sensing device connectable to the coordinate positioning apparatus, the coordinate positioning apparatus being provided with at least one selection device capable of being operated by a user, the connection interface comprising: interface circuitry, a connection between said interface circuitry and circuitry of the coordinate positioning apparatus; a connection between said interface circuitry and circuitry of the surface sensing device; wherein the interface circuitry has at least two modes of operation, a first mode in which operation of the at least one selection device creates an output signal; and a second mode, in which the selection device is isolated and wherein inputs received by the interface circuitry from the circuitry of the surface sensing device are output into the circuitry of the coordinate positioning apparatus as output signals which emulate the output signals from the selection device;

Preferably the interface circuitry comprises: a first switch which is connected to a voltage supply and acts to isolate said at least one selection device when power is supplied from the voltage supply; a second switch which when activated by an output from the surface sensing device, sends a signal to the coordinate positioning apparatus which emulates a signal generated by the at least one selection device.

Operation of the at least one selection device may be used to change modes in the surface sensing device.

In a preferred embodiment, the connection between said interface circuitry and circuitry of the surface sensing device comprises a plurality of concentric conductive rings. One or more of the plurality of concentric conductive rings may comprise two separate sectors .

The interface circuit may provide power to the surface sensing device via the connection between said interface circuitry and circuitry of the surface sensing device. The interface circuit may receive power from the coordinate positioning apparatus via the connection between said interface circuitry and circuitry of the coordinate positioning apparatus.

A second aspect of the present invention provides a coordinate measuring system comprising: a coordinate positioning apparatus onto which a surface sensing device is connectable, the coordinate positioning apparatus being provided with at least one selection device capable of producing an output signal on operation by a user; a processor which receives said output signal; a connection interface described above.

A third aspect of the present invention provides a coordinate positioning system comprising: a coordinate positioning apparatus onto which a surface sensing device is connectable, the coordinate positioning apparatus being provided with at least one selection device capable producing an output signal on operation by a user; a processor which receives said output signal; wherein the coordinate positioning system has at least two modes of operation, a first mode in which operation of the selection device causes an output signal to be sent to the processor, and a second mode in which the selection device is isolated and wherein signals produced by the surface sensing device emulate output signals from the selection device to the processor.

The at least one selection device on the coordinate positioning apparatus may thus be used to control the functions of the measurement probe in addition to its existing functions.

The processor may have at least two modes, a measurement mode in which input signals are used to take measurement points and a set-up mode in which input signals are used in a set-up process. The modes of the coordinate positioning system may be selectable by operation of the selection device. The processor modes may be selectable by operation of the at least one selection device.

In a preferred embodiment, the surface sensing device is a contact sensing rigid probe. The contact sensing rigid probe may have a vibrating surface contacting stylus and wherein change in the vibration characteristics is used to determine that the stylus has contacted a surface. The at least one selection device may be used to cause the contact sensing rigid probe to perform a frequency sweep.

The invention will now be more particularly described, by way of example only, and with reference to the accompanying drawings in which:

Fig 1 illustrates a set-up button connection circuit used in a manual articulating arm;

Fig 2 is a schematic illustration of the set-up button connection used in a manual articulating arm;

Fig 3 is a schematic illustration of a modified probe and button connection circuit;

Fig 4 is a perspective view of one end of the articulating arm, showing the physical probe interface; Fig 5 is a schematic illustration of a modified probe and button connection in the 'unconnected' state;

Fig 6 shows a modified probe and button connection schematic;

Fig 7 is a diagrammatic view of a manual positionable arm with a probe mounted thereon; and

Fig.8 is a flow diagram that shows the operation of the mode selection and the automatic detection of a stylus change.

Manually positionable arms are typically used with a rigid probe which can be positioned in multiple degrees of freedom, with its position being determined by transducers in the arm. A rigid probe is typically mounted on the arm and a button or other selection device is operated by the user when it is desired to take a measurement, so that the transducer values are recorded.

Fig 7 illustrates a manual positionable arm 1 comprising a manually operated multi-jointed arm 2 mounted on a support base 3. A probe 4 is mounted on the distil end of the arm 1. The arm is connected to a host computer 5 or other controller. Transducers in the joints of the arm are used to determine the rotational positions of the joints. This positional data is relayed to the host computer and used by software to determine the position of the probe tip.

A manually positionable arm may be provided with a selection device, such as a pair of set-up buttons which have dual user function. Firstly, they are used to take measurement points when the system is in measuring mode. This is necessary when a rigid probe is mounted on the manual coordinate positioning machine. Secondly, the set-up buttons act in a similar fashion to a mouse button. It is important that this functionality is maintained when a contact sensing rigid probe, such as a piezoelectric probe (eg Renishaw's MSP3 probe) is connected to the manual coordinate positioning machine.

The following description describes the integration of a contact sensing rigid probe (such as Renishaw's MSP3 probe) with a manually positionable arm. However, the invention is also suitable for integrating other probes on other coordinate positioning apparatus.

Figs 1 and 2 illustrate the circuit within the arm and corresponding schematic respectively of the unmodified arm.

Figure 1 illustrates the standard connection arrangement for the set-up buttons in the arm. An articulating arm/probe interface board 22 provides an interface for connection with the probe. Two circuit boards 10,12 contain the set-up buttons 14,16 , and are connected in a parallel circuit via connectors 18,20 to the articulating arm probe interface circuit board 22. These buttons 14,16 can be used interchangeably. An electrical schematic corresponding to Fig 1 is shown in Figure 2.

The parallel set=up buttons 14,16 illustrated in Fig 1 operate parallel switches 24,26; these are normally open and pulled up to +3.3V. When activated by the user closing either switch by pressing on the corresponding button, the input line 28 to the arm/probe interface board 22, Fig 1 is connected to ground causing either a measurement point to be taken, or a mouse click to be executed, depending on the software set up.

The connection circuit of Fig 1 can be modified so that the switches 24,26 operated by the set-up buttons 14,16 on the arm can be used to control functions of the probe mounted on the arm in addition to their existing functions, as described below.

Fig 3 illustrates the modified probe and button connection circuit, in which two circuit boards have been added to the system. A 1^st circuit board 30 taps off the +5V supply and ground for the probe, a 2^nd circuit board 32 electrically connects the probe to the arm.

The 2^nd circuit board 32, which electrically connects the arm to the probe, has four concentric copper rings, one of which is split in two individual sectors; this is shown in more detail in Fig 4.

Fig 4 illustrates the end of the articulating arm 1 on which the probe will be mounted. The arm 1 has a housing 36 with a first pair of buttons 38 (only one shown) and a second pair of set-up buttons 14, 16 (only one shown) . The buttons 38 are used by the measurement software and are shown for illustrative purposes only. They not the subject of any further aspect of this invention. At the end of the housing 36, there is provided a probe mount 42 onto which the probe is mounted. This has a threaded surface to receive a corresponding thread on the probe body. The first circuit board (30, Fig 3) is located witin the housing, behind the buttons 38,14,16. The second circuit board (32, Fig 3) has electrical contacts which connect with the probe when it is mounted on the probe mount 42.

The electrical contacts are made of three inner contacts 44, 46, 48 comprising three concentric rings and a split outer ring 50, 51.

When the probe is mounted on the arm, spring pins inside the probe connect to the concentric rings 44-51 to form the electrical connections with the arm. The second circuit board 32, uses switches (described in more detail below) , to electrically isolate the set-up buttons 14,16 from the arm and, in conjunction with the probe operation, emulates their functions. Thus no software or firmware change is required by the arm manufacturer to integrate the probe on the arm. The switches are preferably analogue switches which has the advantage that they are compatible with different logic voltages .

Schematically, the modified probe and button circuits are shown in Figure 5 and Figure 6. Fig 5 illustrates the modified probe and button connection schematic in the unconnected state (i.e. with no probe attached to the arm) .

The modified circuit illustrated in Fig 5 differs from the standard circuit in Fig 2 by the addition of an arm/probe interface 56 (provided by the connection rings in the 2^nd circuit board 32) and analogue switches 52,54.

As illustrated in Fig 5, when the probe is not connected to the arm (i.e. no connection at the interface) , switches 52 and 54 are normally closed and open respectively, maintaining the arm in its normal operation, i.e. as it would be without the additional circuit boards.

Fig 6 illustrates the modified probe and button connection in the connected state (i.e. with a probe attached to the arm) . This shows both the articulating arm circuitry and the probe circuitry.

The probe circuit includes a point enable control ring spring-pin contact 58, a set-up button sense ring spring-pin contact 60, contacts 61, 62 which connect to both split 5V ring sectors and a ground connection 64. The contacts 61,62 must be made up of at least 3 spring pin contacts (for example 2 spring pins to form the contact 61 and one spring-pin for contact 62) . By separating these three spring-pin contacts by 120 degrees it is guaranteed that both sectors of a ring split in to two approximately 180° sectors will have contacts upon them. The spring-pin contacts are connected to the interface in the following configuration ring 48 to spring pin at 58, ring 46 to spring pin at 60, ring 44 to spring pin at 64. Split ring sectors 50 and 51, and the three spring pins forming contacts 61 and 62 are all mutually connected when the probe is attached to the arm.

An FPGA (field programmable gate array) , or a similar device capable of controlling the probes operation, 66 receives an input from the set-up sense ring 46 via spring-pin contact 60 and sends an output to the point enable control ring 48 via spring-pin contact 58.

When the probe is connected to the arm, the +5V supply in the arm provides power to the probe via the split ring connection 50 in conjunction with spring-pin connections 61, 62, and ground connection 44 in conjunction with spring-pin 64. The +5V supply is also connected to the control line for switch 52 via the probe and the split ring 51 on the arm, thus opening the switch 52 when the probe is connected. Three electrically connected spring pins within the probe, spaced 120 degrees apart, ensure that a connection between the +5V supply and split ring of the arm exists, regardless of the probe's orientation on the arm's thread.

This action of mounting the probe on the arm isolates the set-up buttons from the arm and connects them to the probe via the normally open (i.e. not connected when there is no signal to the switch control line) contact of switch 52 and the ^Λset-up button sense ring' 46. This control line is electrically pulled up to a voltage which indicates high logic state via the spring-pin contact 60 within the probe, enabling the probe to sense the buttons' state.

The logic control output from the FPGA 66 for Switch 54 is connected via the spring-pin contact 58 and ^Λpoint enable control ring' 48 to the probe output 28. Closure of this switch will ground the arm/probe interface point taking input 28, emulating the set-up button.

The probe has two modes of operation, passive and active. The arm also has a third mode; "hard probe", where a probe is not connected to the arm, and the circuit reverts to the state where the set-up buttons work as in the original arm.

In passive probe mode, which is the default mode of the probe, the probe does not vibrate its piezoelectric stack. The probe mimics the arm's normal operation via monitoring the set-up buttons' input and reacting to activation and deactivations of the set-up button via control of switch 54, emulating the unmodified arm measuring system.

When changed ■ to active mode the probe will initially perform a full frequency sweep of its piezoelectric stack to determine the frequency for which optimum touch sensitivity will be achieved. The phase difference between the reference and the stack signals at this frequency will become the initial touch threshold. The function of the piezoelectric stack is described in international applications PCT/GB2007/001663 and PCT/GB2007/001667, which are incorporated by reference. Subsequent activation of the set-up button will result in the probe performing a much shorter sweep, centred on the last frequency, to compensate for temperature and other variations which affect the stack.

When in active mode, the probe is signalled to prepare to take measurements by the operator pressing the set- up button. With the set-up button pressed the probe monitors the phase difference changes caused when the probe's tip comes into contact with a surface; if this phase difference crosses the threshold, switch 54 will be closed by the probe, otherwise it will normally be open. The switch state will be sensed by the arm monitoring circuitry in the arm, and measurement points recorded as appropriate.

The probe allows the set-up buttons to be used as the "accept" mouse button when not on the surface (i.e. when the measurement software is waiting for a button press to confirm an action) . This is achieved through a measurement point being generated if the set-up button is no longer active on completion of the short frequency sweep. The sequence of events in this case is:

1. the operator depresses the set-up button, intending the measurement software to interpret this as an "accept" mouse button action 2. the probe electronics commences a short frequency sweep

3. the operator releases the set-up button

4. the short frequency sweep is completed

5. the probe electronics determine that the set-up button is not depressed and therefore an "accept" mouse button action was intended 6. the probe electronics generate a measurement point signal. 7. the measurement software interprets the measurement point signal as an "accept" mouse button action

In this situation the measurement point signal is made when the probe electronics closes switch 54 for a period long enough to signal a single point to the software. In this way, the operator can mimic the activation of the set-up button without the stylus having to be on the surface. This mode of operation is almost indistinguishable to the operator from using a hard probe.

In both active and passive modes the probe will continuously monitor the set-up button status for a certain sequence of button presses within a defined time. The sequence is designed to signal a mode change request, e.g. to change from passive mode to active mode, or vice-versa. The mode change would not normally be attempted when the arm software is in measuring mode, as button presses would produce points off the surface. It is normal practice, however, to re-configure the measurement software when changing a probe, so this mode change is not burdensome on the operator.

The mode change sequence might be, for instance, pressing the set-up button three times in the space of 0.5 seconds. In passive mode the probe monitors the set-up button in order to detect the required sequence, and three points are generated by the probe and ignored by the software.

In active mode, the first press starts the short sweep, and releasing before the end of this short sweep causes a point to be generated. Alternatively the button may have been pressed again before the sweep finishes so no point is generated. Subsequent button presses are monitored to see if two more occur within the required time, and may or may not generate points. However, with the software correctly configured, any point generated will be ignored as with the probe in passive mode.

After the required sequence is detected the mode is changed accordingly.

It is interesting to note that different styli can require significantly different excitation frequencies. Therefore when changing styli it is necessary to toggle from active mode, to passive, and then back to active again. This has the effect of forcing a full frequency sweep. This means that the stylus can be changed without the need to cycle the power or remove the probe in order to force the full sweep.

An alternative method to re-tuning when styli with different excitation frequencies are used is to automatically detect that the stylus has been changed in active mode, which would require no change to the mode of operation. Following a stylus change, a short frequency sweep would be performed. If a tuned frequency were not found, i.e. the frequency lay outside the swept short frequency range, the probe would automatically perform a full frequency sweep, find the new tuned frequency and be ready to measure.

If the frequency were within the short frequency range, the probe would set its new tuned frequency to that frequency and be ready to measure.

Fig 8 is a flow diagram showing the different modes of the probe. As illustrated in Fig 8, after the probe is powered up, it enters the passive mode 70. The set-up button is activated to generate point data and the system monitors for mode changes 72. If a mode change sequence is detected, the probe enters active mode 74 after performing a full frequency sweep. Otherwise, the probe remains in passive mode 70. In active mode, activation of the set-up button causes a short frequency sweep to be performed 76. After completion of the short frequency sweep, the set-up button state is checked 80. If the set-up button is inactive, a data point is generated and the system will monitor for mode changes 82 and enter passive mode 70 or remain in active mode 74 accordingly. If the set-up button is active and no new stylus is detected, the system will enter measurement- mode 82. Alternatively, if the set-up button is active and a new stylus is detected, a full frequency sweep is performed 84. Activation of the setup button enables the system to enter measurement mode 82.

Although the flow diagram of Fig 8 illustrates a preferred method of mode changing, it will be understood that alternative schemes are also possible.

This system therefore enables the existing buttons on the manually positionable arm to control the functions of the probe whilst keeping existing functionality on the manually positionable arm.

The above embodiment describes the integration of a contact sensing rigid probe on a manually positionable arm. Although the embodiments describe Renishaw' s MSP3 probe, it is also suitable for other contact sensing rigid probes. This system is also suitable for use with other types of probe and for machines other than manually positionable arms which use a switch, button or other device to take measurements.

Claims

1. A connection interface between a coordinate positioning apparatus and a surface sensing device connectable to the coordinate positioning apparatus, the coordinate positioning apparatus being provided with at least one selection device capable of being operated by a user, the connection interface comprising: interface circuitry, a connection between said interface circuitry and circuitry of the coordinate positioning apparatus; a connection between said interface circuitry and circuitry of the surface sensing device; wherein the interface circuitry has at least two modes of operation, a first mode in which operation of the at least one selection device creates an output signal; and a second mode, in which the selection device is isolated and wherein inputs received by the interface circuitry from the circuitry of the surface sensing device are output into the circuitry of the coordinate positioning apparatus as output signals which emulate the output signals from the selection device .

2. Α connection interface according to claim 1 wherein the interface circuitry comprises: a first switch which is connected to a voltage supply and acts to isolate said at least one selection device when power is supplied from the voltage supply; a second switch which when activated by an output from the surface sensing device, sends a signal to the coordinate positioning apparatus which emulates a signal generated by the at least one selection device.

3. A connection interface according to any preceding claim wherein operation of the at least one selection device changes modes in the surface sensing device.

4. A connection interface according to any preceding claim wherein the connection between said interface circuitry and circuitry of the surface sensing device comprises a plurality of concentric conductive rings.

5. A connection interface according to any preceding claim wherein one of said plurality of concentric conductive rings comprises two separate sectors.

6. A connection interface according to any preceding claim wherein the interface circuit provides power to the surface sensing device via the connection between said interface circuitry and circuitry of the surface sensing device.

7. A connection interface according to any preceding claim wherein the interface circuit receives power from the coordinate positioning apparatus via the connection between said interface circuitry and circuitry of the coordinate positioning apparatus.

8. A coordinate measuring system comprising: a coordinate positioning apparatus onto which a surface sensing device is connectable, the coordinate positioning apparatus being provided _.with at least one selection device capable of producing an output signal on operation by a user; a processor which receives said output signal; a connection interface according to any of claims 1-8 .

9. A coordinate positioning system comprising: a coordinate positioning apparatus onto which a surface sensing device is connectable, the coordinate positioning apparatus being provided with at least one selection device capable producing an output signal on operation by a user; a processor which receives said output signal; wherein the coordinate positioning system has at least two modes of operation, a first mode in which operation of the selection device causes an output signal to be sent to the processor, and a second mode in which the selection device is isolated and wherein signals produced by the surface sensing device emulate output signals from the selection device to the processor .

10. A coordinate positioning system according to claim 9 wherein the processor has at least two modes, a measurement mode in which input signals are used to take measurement points and a set-up mode in which input signals are used in a set-up process.

11. A coordinate measuring system according to any of claims 9 or 10 wherein the modes of the coordinate positioning system are selectable by operation of the selection device.

12. A coordinate measuring system according to any of claims 9 to 11 wherein the processor modes are selectable by operation of the at least one selection device .

13. A coordinate measuring system according to any of claims 9 to 12 wherein the surface sensing device is a contact sensing rigid probe.

14. A coordinate measuring system according to claim

13 wherein the contact sensing rigid probe has a vibrating surface contacting stylus and wherein change in the vibration characteristics is used to determine that the stylus has contacted a surface.

15. A coordinate measuring system according to claim

14 wherein the at least one selection device may be used to cause the contact sensing rigid probe to perform a frequency sweep.