GB2375026A

GB2375026A - Moveable articulated arm for coordinate measuring machine with position transducers connected to a controller via a serial network

Info

Publication number: GB2375026A
Application number: GB0218405A
Authority: GB
Inventors: Simon Raab; Joselito Parguian; Ali Seyed Sajedi
Original assignee: Faro Technologies Inc
Current assignee: Faro Technologies Inc
Priority date: 1998-07-08
Filing date: 1999-05-07
Publication date: 2002-10-30
Anticipated expiration: 2019-05-07
Also published as: GB0218405D0; GB2375026B

Abstract

An articulated arm of a coordinate measuring machine has position sensors which may be encoders 80. These are connected to interfaces 92 which each have unique addresses and include a memory 93 for storing position data. The interfaces are connected to a controller 24 via a serial bus 20 and a capture line 21. In use a signal on the capture line instructs the interfaces to store position data in the memory and the controller then serially addresses each interface in turn to transfer the stored position data from the memory to the controller over the serial bus. Transferred data may also include acknowledgement bits for handshaking. A temperature sensor 82 and other optional devices 110 may also be connected to the serial bus. This arrangement allows a reduction in the amount of wiring in the moveable arm.

Description

SERIAL ETWORX FOR COORDINATE MEASURErENT APARATL'S

lte i-ve-,,. ior X= ! a. es-e-eK i tc eo ~~ en. cn ? ! ccc----; e, zeas. t clL es (CQ rs). fore panicularly, this inveniicn relates M a three ieional C/fM mcludins a serial nerwork for rraRsniirdng dara from e ar to a coanroUerConventional CMM's use encoders to provide irbradon QBl the position of the arm in three dimensionai sace. FIGURE 1 is a side view. carnally ic cross-section. of an exemplary CvC/I 10 havis six degrees of freedom as described L'. S. Paict 3.-L02. J32.

At each joint, or degree of freedom, a transducer (such as a rotary encoder) 80 is used to produce signals indicating the rotation of each joint and thus the position of the arm. At the distal end of the CMM 10 is a probe/switch assembly 56 having two switches 150 and 152. Switch 150 is for taking data and switch 152 is for accepting data. As shown in Figure 1, six encoders 80 are used, one for each degree of freedom.

As described in U. S. Patent 5,402, 582 the CMM may also include an option port at the probe/switch assembly 56 for the attachment of a variety of

options and a temperature transducer.

A drlwback to the conventional CfM 10 is the large amount of wiring thnt must be housed within the ann. Each encoder 80 can require 7 or more wires. The option port, temperature transducer and control buttons 150 and 152 require additional wires. This large number of wires results in increased expense and reliability problems related to the increased

number of parts Preferably, the above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the articulated arm having a serial network of the present invention. The arm includes a serial network for communicating data from transducers

located in the arm to a controller. Each transducer is connected 10 a transducer interface having a memory which Stores transducer data. The controller serially addresses each transducer interface and handshaking is performed to transfer the data from the transducer interface memory to the controller- The above-discussed and other features and advantages of the present invention will be appreciated and undl-rstood bv those skilled in the an from the following detailed descrintion and drawing ? of embodiments of the invention.

B net Deser ion o Drav/inES Referring now 10 the drawings wherein like elements are numbered alike in the several FIGURES : FIGURE 1 is a side view, partially in cross-section of a conventional CfM : FIGURE 2 is a block diasram of the serial network of'he resent in''-'enticn : FIGURE 3 is a timing diagram illustrating the transfer cfdaia from multiole encoders : and FIGURE 4 is a timing diagram illustrating the transfer of data from a single encoder.

Detailed Description of the Embodiments FIGURE 2 is a block diagram of components of an arm including a serial network 20.

The serial network 20 is based on an IC format. As shown in FIGURE 2, a plurality of transducer interface boards 92 are connected to the serial network 20. The probe/switch module 56 is connected to the serial network 20 through a transducer interface 92. An LCD module 22 is connected to the serial network 20 and provides information to the operator. A separate capture line 21 is used to simultaneously instruct the transducer interfaces 92 to

store the current transducer data in memory 93. In the embodiment shown in FIGURE 2. the memory 93 is implemented using a register. It is understood that other types of memory may be used in the transducer interface. The separate capture line 21 is needed because the latency of the serial bus 20 is 1000 microseconds whereas the latency of the capture line 21 is 1 microsecond.

The serial network 20 is aiso connected to controller 24 which receives signais from the probe/swith module 56 and dat from the transducer interfaces 92 and sends information to the LCD module 22. A temperature transducer 82 is also connected to serial network 20

i 1=al to cor,-trolle,-Tre cont--oil-Ti to provide a temperature signal to controller 24. The controi'er 2- includes a microprocessor 25 and random access memory 23 for storing instructions to be executed by microprocessor '-6. A : nivc7al as,,-nc-T-L-onous the cuniversal asy1cto ous receiver/transmit er (U. ART) 30 enables cotnirur'. ic. . ticn Tern the controUer 2- to outside devices such as a host computer. Flash memory 32 stores program instructions and arm parameters permanently. A laities complex programmable logic device (CPLD) 36 and associated electrically erasable programmable read only memory (EEPROiY1) 34 are also included in the conuoller 24. Tne CPLD 36 contains interconnection logic between the components of controller 24.

Each transducer interface 92 is preferably a printed circuit board including memory 93 which stores the data from a transducer for a particular instant in time. The transducer interface circuit board may also include amplification circuitry to enhance the signal to noise ratio of the received data. FIGURE 2 illustrates seven transducer interfaces 92. Each transducer interface 92 can store any type ofdaia, including data from an encoder 80 or data from an alterative source. It is understood that the source of the data stored on each transducer interface can vary depending on the application The arm may also include an option port 110 such as that described in U. S. Patent

5 09 connected to the serial bus 20 as shown L'1 FIGURE 2. The option port 110 mav LTI I- include a number of voltage lines and analog-to-digital converter lines for general attachment to a number of options such as variable transducers, a laser scanning device or touch probe.

The CMIM 10 must store data indicating the position of each transducer for a particular instant in tune. Accordingly, upon depressing the''TAKE"bunon 150, the data 'or eacil for each transducer (e. g. encoder SO) is scored in memory 93 and the data is serially i transferred and stored in contoller 24 as described herein. It is understood that other methods may be used to acquire data other than pressing the TAKE button 150. For example, a touch probe may be mounted in the arm which initiates data acquisition upon contact. When the operator depresses the "ACCEPT" button 152, the transducer data stored into controller 24 is transferred to a host computer through UART 30.

I-i ta FIGURE 3 is a timing diagram illustrating the transfer of data from multiple transducer interfaces. When the operator initiates daia acquisition, (e. g. by pressing the TAKE button 150) this initiates a CAPTURE cycle having a duration of 10 msec. This allows the user to collect 100 data points per second. As indicated by the serial clock line

SCL, the data from each transducer interface 92 is transferred in intervals of 630 us. Each SCL, the data fcom each tm, ; duct * er.-L-1 m 0 event 40 represents the transfer of data from memory 93 to controller 24 and is described in event-'0 represents the tii'er o'L detail below with reference to FIGURE 4.

FIGURE 4 is a timing diagram illustrating one event 40 showing the bi-directional transfer of data on the serial data line (SDA) between controller 24 and one transducer interface 92. Upon initiation of a CAPTURE cycle (e. g. by the user depressing the TAKE button 150), each memory 93 stores the data from a respective transducer (e.g. endcoder 80).

The conrroller 24 then addresses each transducer interface 92 serially. As shown in FIGURE

es a ansducz : r' te.-i-ace 92 duouzia address for each event 40, the controller 24 addresses a transducer interface 92 through address bits Ad6-AdO and a read/write bit (R/W). The ninth bit ACK 42 is an acknowledge signal

from the transducer interface 92 Co the controller 2- indicating thai a valid address has been accessed. Bytes DO-D. 3 represent data transierred from the memory 33 to the coniroiler 24.

The nin h bit of each byte DO-D5 is an acknowledge bit from the controller 2- to the transducer interface 92 indicating that the cont-oller- 2 has received the byte. The handshaking shown in FIGURE 4 is performed for each transducer interlace 92.

The present invention provides a system for serially transferring data from the

plurality of transducers in a CMM to a controller. The use of a serial network significantly reduces rhe amount of wires needed m the CMM thereby reducing the number of pans and enhancing the reliability of the CMM.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not. limitation.

Further specific embodiments of the invention are laid out below.

A three dimensional coordinate measuring system comprising : d n ijaa : a movable arm including a plurality of joints with each joint corres-nondina to a j Lnt j lzt corres-oondincy to a degree of freedom such that said arm is movable within a selected volume, a plurality of said joints having a transducer, each said transducer producing position data; a controller for receiving said position data ; a capture line for transmitting a capture signal for initiating acquisition of said position data; and a serial network for transferring said position data to said controller.

The coordinate measuring system may also comprise: a transducer interface associated with each of said transducers, each said transducer interface including a memory for storing said position data ; wherein said capture line signals each said transducer interface to store said position data in said memory ;. wherein said serial network transfers said position data from each said memory to said controller.

The coordinate measuring system may be adapted so that each transducer interface is addressable and said controller serially addresses each transducer interface to transfer said position data from each said memory to said controller.

In the coordinate measuring system above, the transducer may be an encoder.

The coordinate measuring system may further comprise : a temperature transducer for generating temperature data ; wherein said temperature transducer is connected to said serial network.

The coordinate measuring system. above may also further comprise : The coordinate me an option port connected to said serial bus.

In a further embodiment there is provided a method of transferring position date from a plurality of transducers located in a movable arm to a controller comprising :

storing the position data for each transducer in a respective memory provided m a m a respec-ave memory transducer inienace ; serially accessing the position data in each memory ; and serially transferring the position data to the controller via a serial network.

In a development of the above method, said storing comprises providing a capture signal

to the transducer interface and storing position data for a specific instant m time in each i I I in I I I memory.

In a development of the above method, said serially accessing comprises addressing the transducer interface and sending an acknowledge bit to the controller upon validiv addressing the transducer interlace. in2 the transdi-, cer'mterfac.-.

In a development of the above method, said serially transferring comprises transferring position data from the transducer interface to the controller, wherein the controller sends an

acknowledge bit to the transducer interface upon receipt of the position data. z-l

Claims

CLAIMS 1. A three dimensional coordinate measuring system comprising : a movable arm including a plurality of joints with each joint corresponding to a degree of freedom such that said arm is movable within a selected volume, a plurality of said joints having a transducer, each of said transducers producing position data; a transducer interface associated with each of said transducers, each said transducer interface including a memory for storing said position data; a capture line for transmitting a capture signal for initiating acquisition of said position data and storage of said position data in memory; a serial network coupled to said transducers for serially transferring the stored position data to a controller, wherein said capture line signals each said transducer interface to store said position data in said memory ;. said serial network transfers said position data from each said memory to said controller; and each transducer interface receives position data from a single transducer.

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2. The coordinate measuring system of claim 1 further comprising: a display coupled to said serial network, said display providing information to an operator.
3. The coordinate measuring system of claim 1 wherein said memory lacks ability to execute instructions.
4. The coordinate measuring system of claim 1 wherein the memory is a register.
5. The coordinate measuring system of any one of claims 1-4 wherein each transducer interface is addressable and said controller serially addresses each transducer interface to transfer said position data from each said memory to said controller.
6. The coordinate measuring system of any one of claims 2-5 wherein said display is directly connected to a memory which is directly connected to the serial network.
7. The coordinate measuring system of claim 1 wherein said transducer is an encoder.
8. The coordinate measuring system of claim 1 further comprising:

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an option port connected to said serial network.
9. The coordinate measuring system of claim 1 wherein said controller transfers said position data to a host system.
10. The coordinate measuring system of claim 9 wherein said controller transfers said position data to a host system through a universal asynchronous receiver/ transmitter.
11. The coordinate measuring system of claim 1 wherein said movable arm is passive.
12. The coordinate measuring system of any of the above claims wherein said serial network includes means for addressing the transducer interface and means for sending an acknowledge bit to the controller upon validly addressing the transducer interface.
13. The coordinate measuring system of any of the above claims wherein said serial network includes means for transferring position data from the transducer interface to the controller and means for sending an acknowledge bit from the controller to the transducer interface upon receipt of position data by the controller.

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14. The coordinate measuring system of claim 1 wherein said serial network provides bi-directional communication between said controller and said transducer over a single line.
15. The coordinate measuring system of any one of the preceding claims further including a temperature transducer for generating temperature data, and wherein said temperature transducer is connected to said serial network for serially transferring the temperature data to the controller.
16. A method of transferring position data from a plurality of transducers located in a movable arm to a controller comprising: storing the position data for each transducer in a respective memory provided in a transducer interface; serially accessing the position data in each memory; and serially transferring the position data to the controller via a serial network, wherein each transducer interface receives position data from a single transducer.
17. The method of claim 16 further comprising serially

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transferring the position data to a display for presentation to an operator.
18. The method of claim 16 further comprising serially transferring temperature data from a temperature transducer to the controller.
19. The method of claim 16 wherein said memory is a register.
20. The method of claim 16 wherein said storing comprises providing a capture signal to the transducer interface and storing position data for a specific instant in time in each memory.
21. The method of claim 16 wherein said serially accessing comprises addressing the transducer interface and sending an acknowledge bit to the controller upon validly addressing the transducer interface.
22. The method of claim 16 wherein said serially transferring comprises transferring position data from the transducer interface to the controller, wherein the controller sends an acknowledge bit to the transducer interface upon receipt of the position data.

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23. The method of claim 16 wherein said movable arm is passive.
24. A measuring system substantially as any one embodiment herein described with reference to Figs.

2-4 of the accompanying drawings.
25. A method of transferring data substantially as herein described with reference to the accompanying drawings.