CA2183004A1

CA2183004A1 - Articulated-arm measuring machine and twist-net network

Info

Publication number: CA2183004A1
Application number: CA 2183004
Authority: CA
Inventors: Nino Camurri
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-23
Filing date: 1996-08-23
Publication date: 1998-02-24
Also published as: AU1587197A; WO1998008050A1

Abstract

The fields of design, manufacturing and inspection are rapidly evolving with theuse of advanced 3D software.
This trend accelerates and intensifies as the market demand for shorter productscycles, customized applications, and cost effective high quality products.
This evolution is creating a significant demand for apparatus that bridge the gap between the real 3D world of the product, and the virtual 3D world of the different software tools and electronic networks used to create them.
Unlike the existing "rigid" conventional CMM machines that can measure, with considerable capital expense, object of varying complexity, our invention is based on the immediate need that exist on the market today to inspect, re-engineer components, and to accurately measure assembled parts of varying size and geometry.

Description

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pa3e 2 INTRODUCTION

The present invention relates to a computerized apparatus which has been greatly modified, (from an existing similar apparatus), in order to provide, andco,~ "lly be able to obtain and accurately measure, spatiai position and angularoliellldtioll~ in different ",e~;l,a,liwl, structural, and other types of complex shaped members.
These changes resulted in a creation of an highly l~cl",ica,!y innovative machine that features the following (fig. 1):

~ Six degrees of freedom operation (this allows the operator the freedom to choose the best access condition for measuring and/or finding the X,Y,Z, COOldill~'~.3 in space).
~ Ability to measure cooldil~ points within a radius of 3 meters and more in any direction.
Apparatus is resting on wheels, to facilitate maneuverability and for best a:~ ~ y ~ Apparatus can be ~t . ' 'l~ leveled, indepel~ ly of the floor irregularities;
~ Machine pt)ssecsRs a dynamic automatic self recording of any absorbed shock loading.
~ Any possible distortions caused by the temperature gradients throughout the structure of the apparatus are eliminated due to the temperature c~ 5d~iOll feature.
~ The articulated arms are designed to be self-standing for highest sensibility.~ High precision encoders are used for accurately determine the orientation of the articulated arms and the measuring points.
~ A 3D touch trigger probe systems is utilized for consistent recording sensitivity.
Apparatus is battery-driven.
~ Radio data ball -n l~:llllology is used between the measuring machine and the central computing unit.
~ High speed data collection is performed by utilizing the TWIST-NET network.

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- page 3 DESCRIPTION OF THE TECHNICAL INNOVATIONS

The l~ullllologiual innovations that were created in relation to the already existing similar machines, were mainly co"ce"l,dLe:d in the areas of the Illeulld~ dl andelectronic aspects of the apparatus operation. These are:

1. Maneuverabilitv of the apparatus The machine is made to move on wheels (#2 - hg. 2). This facilitates the measuring and recording of data. The wheels are also designed with the option to be motorized in order to assure the extended measurement without any lateral and/or vertical deviation. This is also possibleby using an automatic mode that utilizes a laser alignment.
2. Stabilitv of the apparatus In our design we utilized electronic linear actuators (#1 - hg. 2), placed ~lldl~i~'ly throughout the base of the machine (#1 hg. 2), to assure and conserve perfect ho,i~u"' ' Iy. The dimension and the rigidity of themachine base is so designed to assure stability at any spatial position of the articulated arm structure.

3. Stiffness of the apparatus High precision angular contact (#4 and #5 - hg. 3)ball bearings (controlled pre-load) are used in all the apparatus articulated joints.
This design feature assures maximum system sensitivity, best circularity of movement, and ultimate flexibility in relieving the data points on complex geu,,,~llicdl parts including in recesses and internal hidden surfaces.

4. Articulated nodes To obtain the maximum possible precision in calculating the spatial positions, we have utilized high pe,ru",ldnce Phutueleullic Scanning-l~ ",eMdl Rotary Encoders (#6 - hg.3 and #7 - hg.4) that are rigidly asse",bled in each rotating axis. On the pnncipal nodes we have also ~ U~IJOI~ a type of integral coupling encoders able to generate 36,000 standard pulses/revolution.

5. Arms structural liahtness With the use of highly so~)l,iali~ dl~d analytical techniques, the articulated arms (#8, #9, #10 - hg. 5) have been optimized in order to assure their maximum structural and dynamic stability. The analysis wasperformed using a wide spectrum of composite and non-conventional materials.
The hnal arm configuration was selected based on the optimum calculated values for the arm stiffness, weight, Ille~,lldllicdl and thermal distortions.
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pa~e 4 6. Armselfstabilizer In the apparatus anms, we have illco,~o,~ d elastic SU~p~"Siul~ as well as pneumatic suspension cylinders. This design feature serves to counteract the effect of gravitational forces, as well as ",i"i",iN"g any additional loading during manual manipulation, while Illaillldil)illg anm linearity.

7. 3D touch probe The touch probe system (#11 - fig. 6) was illco,~uo,dL~d in this design in order to optimize the inspected measuring points. By so doing the l~p~ 1~ L "'y of measurements (better than 1 llm and maximum 4.5 N probing force) can be assured in all directions.
ô. TWIST-NET network The TWIST-NET (fig. 8) is a measuring system featuring illul~ ,,Ldl angular encoders (fig. 7). These encoders are connected to the network via local micro-controllers (fig. 9), that communicate with the control p,uct,s~i"g unit by following a network protocol. The major link between the measuring system and the central unit is assured by using radio-frequency.
Each micno-controller is so designed to recond at any time the instantaneous angular position value and it can also be easily ,u~u~ldlllllled to calculate the data average from several data inputs. This technique serves to minimize the enroneous readings derived from the possible l"e.;hdllical vibrations. In addition, each micro-controller can selectively be set to "zero" by the operating software, and/or be given a pne-dt:Le:l " ,i, led value that suits the potential ,, ' " 1.The advantage of this system is that the calculations use the proper values for each sensor, values that have been properly converted. This translates in extensive numerical time saving.
The TWIST-NET network has two distinct layers from the point of view of data transfer. One of them is one cable between the micro-controller, and the other, radio-frequency type, is between the machine and the computer. This allows the operator to minimize the distance between himself, working at the computer, and the machine~ even if the machine is at an d,U~ cidble distance.
The supply source of the lWlST-NET system is continuos and is supplied by Itluhdl~edlWe batteries that can furnish an autonomy of function of ap~.lu,~i",dl~ly 24 hours. The ,~-,I,d,yeable system of the batteries is an intelligent one and allows l~;l,ars~i"g during a neduced period oftime.

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pa~e 5 DESCRIPTION OF THE ELECTRONICAL TU115T-NET ~fig. 8) The output signal, provided by the sensor-encoder U1, is a sinusoidal curve 1 Vpp and the repetitiv period is ~hald~ , for all types os sensors: in this example it will be Iq~l~se"L~d by "N".
That means that 'Na is the number of impulses for a complete rotation of 360~.
The new method that we propose is to ~ lllilldlC: the i~ a"ediclL~ position between two consecutive positions; these last ones have been d~ ,ed previously.
The analogic signal between two positions is shown in fig.7: to calculate the final position in stationary rate means to calculate the "y' angle.
This is effectuated by resolving the equation y = arcsin U1 (y), where U1 sel ll~ a value of the analogic tension given by the sensor.
The U1 tension is analized by 16 bits analoyiJdiyildl convertor; the conversion in angle of the tension is done using a matrix that includes the lldll:~r~nlllaLion function and this part is realized by a single chip in the computer.
So we are able to increase the resolution to N x 256, i",,,~ossiL,le until now.
A module, as the one that we have described, will be assigned to each sensor, all of them being joined together to the same bifilar network.
The advantages are:
1. To detemmine the angle is an i"dt:pede"l process for each sensor.
2. The value of the angle is read by an exterior command.
3. If we need to eliberate the central unit and the communication system, in order to obtain an average of the values already read, this can be done by each controller.
4. Each controller reads and also transmets the temperature of one of the two branches of the network where we measure the angle (fig. 9).
5. We have the most accurate reading by a module of the SAMPLE & HOLD (fig. 9) of the an~loyiJdiyildl convertor (the advantage is that all values of all sensors are read in the same time).
6. The system needs a network communication cable and a supply cable only, that implies the reduction of the number of required wires (the same n,), ' " n wouldneed, conventionally, more than 48 wires (for a machine with 6 sensors), while our solution requests only 4, i"dependt~ y of the number of sensors.
7. The central unit ~"""and~ all micro-controllers in the same time (ex.: averaging the values command).

Claims

page 6 What is claim is:

1. A high precision computerized apparatus for measuring consistently and accurately coordinate points in spatial positions in different mechanical, structural, and other types of complex shaped systems, that apparatus comprising up to seven degrees of freedom operation with the ability to inspect coordinate points up to 3 meters and more in any direction, the apparatus is resting on wheels (with the option to be motorized utilizing a laser alignement) to facilitate best maneuverability and accessibility, the machine can be automatically leveled indipendently of the floor irregularities, also it possesses a dynamic automatic self recording of any absorbed shock loading, and the possible distortions caused by the temperature gradients throughout the structure of the apparatus are analytically minimized due to the temperature compensation feature, the articulated arms are designed to be self-standing for highest sensibility, high performance incremental rotary encoders means rigidly assembled on all the rotating axes and a 3D high sensitivity touch probe system are utilized, high speed articulated arms position data collection means is performed by the original TWIST-NET network and radio data transmission technology is used between the measuring machine and the central computing unit, the mobile apparatus will be battery driven.