WO2002103284A2

WO2002103284A2 - Probe for position determination

Info

Publication number: WO2002103284A2
Application number: PCT/GB2002/002599
Authority: WO
Inventors: David Collingwood; Geoffrey Salt; Jonathan Paul Fuge
Original assignee: Renishaw Plc
Priority date: 2001-06-16
Filing date: 2002-06-14
Publication date: 2002-12-27
Also published as: GB0114736D0; WO2002103284A3; AU2002314304A1

Abstract

The batteries of a probe (10) are replaced by a dummy battery (30) which is connected to a an external controller (44,45) by wires (32,134) leading from the dummy battery terminals (36,38). The external controller (44.45) supplies a constant voltage to the probe (10) and also sends messages to the probe consisting of pulses of higher voltage. A comparator circuit within the probe compares the voltage at the dummy battery terminals with a known reference and sets a logic level high or low, thus enabling a serial data stream to be communicated to a programmable device within the probe. The probe may respond by sending a message back to the external controller, for example by modulating the current drawn through the battery terminals, sending an optical signal or by other means.

Description

MACHINE TOOL PROBE

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 US Patent 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 .

It is known to have two-way communication established between a measuring probe on a machine spindle and the machine using only two wires between the probe and the machine. US Patent No. 4,817,362 discloses such a system wherein communication from the probe to the machine is achieved by causing current changes in an electrical circuit within the probe and communication from the machine to the probe is achieved by varying the voltage supplied to the probe circuit.

The present invention provides a probe for position determining apparatus having internal circuitry capable of operating in a plurality of modes; and a battery compartment suitable for containing a battery to power the probe; said internal circuitry of the probe having connection terminals which are adapted to connect with a battery in the battery compartment; characterised in that the internal circuitry includes a circuit for detecting signals received via said connection terminals which set one of said modes.

This permits an external controller to be connected to the probe via the battery terminals in order to set the mode .

Preferably a dummy battery is provided, for connection to the external controller, the dummy battery fitting in the battery compartment in place of the battery which powers the probe. This may then provide two-wire communication between the external controller and the probe via the battery terminals.

Preferably the external controller communicates with the probe by varying the voltage into the battery terminals. These variations in voltage may be pulses higher than a reference voltage. A comparator circuit within the probe may be used to compare these pulses with the reference voltage and set a logical level high or low.

Preferably data is sent from the probe to the external controller via variations in current. A programmable device within the probe may drive a transistor/resistor circuit and thus modulate current drawn from the positive battery terminal. A preferred embodiment of the invention will now be described with reference to the accompanying drawings, wherein:

Fig 1 is a diagrammatic view of the probe on a machine tool ;

Fig 2 is a schematic diagram of the dummy battery;

Fig 3 is a schematic diagram of the probe and the remote unit;

Fig 4 shows the variation of voltage input to the probe;

Fig 5 shows the variation of current output of the probe;

Fig 6 is a schematic diagram of the electronics in the probe; Fig 7 is a schematic diagram of the electronics in the remote unit ; and

Fig 8 is a schematic diagram of a second embodiment of the electronics in the remote unit .

Referring to Fig 1, the 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 a 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. Alternatively the measurement signals may be, for example, radio signals. 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.

The probe contains a battery compartment in which batteries to power the probe are located. The batteries are generally 3-volt batteries. The batteries may be replaced by a dummy battery 30 of the same physical dimensions as shown in Fig 2. The dummy battery 30 is held in the battery compartment 31 by a cap 40 and spring 42. The dummy battery 30 has battery terminals 36,38 which are held in contact with connection terminals on the battery compartment 33 and cap 40 respectively. Wires 32,34 lead from the battery terminals 36,38 to an external remote unit with a voltage supply.

Fig 3 shows the probe 10 and the connections 32,34 to the remote unit 4 . The remote unit 44 and/or the programmer 45 constitute an external controller. These may be separate as shown in Fig 3 or may be combined into a single device.

The remote unit 44 may be used to supply a constant voltage to the dummy battery terminals 36,38, for example this voltage may be about 6 volts (i.e. the same voltage as the batteries that have been replaced) . In addition, the remote unit 44 may send a message to the probe 10 consisting of pulses of higher voltage, for example 9 volts as shown in Fig 4. A comparator circuit within the probe compares the voltage at the dummy battery terminal with a known reference (e.g. 7.5V in this example) and sets a logic level high or low. A serial data stream can therefore be communicated to a programmable device within the probe from the remote unit. This is described in more detail below (Fig 6) .

The programmable device within the probe is programmed via the dummy battery by the pulsed input voltages. Series of pulses in the input voltage form codewords, and different codewords may be used to program different modes. The modes may be as described in the introduction.

The remote unit 44 is connected to a programmer 45 which may, for example, be a computer. The desired mode of the probe is selected at the programmer. The remote unit 44 sends a corresponding codeword to the probe consisting of voltage pulses.

Once the message has been received by the probe and/or the settings have been changed, the probe may respond by sending a message back to the remote unit. This message sent to the remote unit may be transmitted in the same manner as the measurement signals from the probe are transmitted, for example optically using LEDs or by radio signals. The message may be transmitted by other means for example by modulating the current drawn by the probe through its battery terminals. When working normally, the current drawn by the probe is well defined within a tolerance limit. However, the current drawn through the battery terminals may be modulated by allowing the programmable device within the probe to drive a transistor/resistor circuit. This additional current can be detected within the remote unit by measuring the voltage drop across a series resistor. This voltage drop is converted into a serial data stream. Fig 5 shows the output variation in current of the probe which corresponds to the input variation in voltage seen in Fig 4.

Fig 6 shows a possible circuit used in the probe for detecting signals received via the battery terminals 36,38. The battery terminals are connected at 36,38 and the probe receives its power supply at 56. A comparator 50 is provided to compare the input voltage with a reference voltage 52 and set a logic level high or low. The output of the comparator leads to a microcontroller 54 where the codewords are decoded. Outputs 55 from the micro-controller 54 lead to the probe circuitry to change the modes. The micro-controller sends pulses to a transistor 57 which allows more current to be drawn in response to the input voltage being higher than the reference voltage.

Figs 7 and 8 both show possible circuits for the remote unit. A micro-controller 64 controls a voltage regulator 60 which varies the voltage to form the desired pattern of pulses. The desired voltage is output to the dummy battery terminals 36,38. The varying current drawn by the probe through the positive battery terminal is detected within the remote unit by measuring the voltage change across a series resistor 62. This data is sent to the micro-controller 64 and then exported to the programmer (45 in Fig 3) .

This communication method overcomes the problems of DIP switches discussed in the introduction, and enables simple and accurate mode setting. It has the advantage that as the original battery compartment and battery contacts are being used, no additional contacts are required. In addition the battery compartment is sealed from the probe electronics .

This system allows fast programming of modes into the probe via a hand-held or PC-linked programmer. This would allow a standard probe to be mass-produced and then programmed to a particular customer's needs, thus reducing costs. This communication system allows certain modes to be incorporated into the probe for ease of probe testing and diagnostics. In addition this method lends itself to automatic testing equipment systems. For example the time-out mode may be selected to a very short time whilst testing and then reset to a longer time before being sent out to customers, thus reducing testing time and costs.

Changing the modes of the probe also includes configuring or updating the firmware of the probe. This comprises uploading serially encoded data to a memory inside the probe.

Claims

1. A probe for position determining apparatus having internal circuitry capable of operating in a plurality of modes and a battery compartment suitable for containing a battery to power the probe; said internal circuitry of the probe having connection terminals which are adapted to connect with a battery in the battery compartment; characterised in that the internal circuitry includes a circuit for detecting signals received via said connection terminals which set one of said modes.

2. A probe according to claim 1 wherein an external controller is connected to the probe via the battery terminals in order to set the mode.

3. A probe according to claim 2 wherein a dummy battery is provided for connection to the external controller, the dummy battery fitting in the battery compartment in place of the battery which powers the probe .

4. A probe according to claim 2 wherein the external controller communicates with the probe by varying the voltage into the battery terminals.

5. A probe according to claim 4 wherein the variations in voltage are pulses higher than a reference voltage.

6. A probe according to claim 5 wherein a comparator circuit within the probe is used to compare the voltage into the battery terminals with the reference voltage and set a logical level high or low.

7. A probe according to any of claims 2-6 wherein data is sent from the probe to the external controller.

8. A probe according to claim 7 wherein data is sent from the probe to the external controller by variations in current through the battery terminals.

9. A probe according to claim 7 wherein data is sent from the probe to the external controller via an optical signal.

10. A probe according to claim 7 wherein data is sent from the probe to the external controller via a radio signal .

11. A probe according to claim 8 wherein a programmable device within the probe drives a transistor/resistor circuit and thus modulates current drawn from the positive battery terminal .