Component measuring apparatus with multiple component multiple positioning device

A component inspection apparatus includes a component holder mounted on a compound slide structure. Two arrays of gauging elements are provided on a mutually perpendicularly movable slide. These arrays can be adjusted on the slide and each array includes a plurality of separate gauge elements movable by contact with the work and at least one linear transducer connected to each gauge element. In use, the slides are moved to a plurality of predetermined positions in a sequence. The displacements of the probe elements at each position are noted and compared with displacements obtained when the same sequence of positions is followed while a master componet is in the holder.

This invention relates to component inspection apparatus intended for use, 
for example, in the automatic inspection of gas turbine engine turbine 
blades. 
Generally speaking two types of inspection apparatus are currently in use 
in such automatic inspection applications. One type uses a single probe 
mounted for movement in a number of different directions by means of a 
suitable slide structure. The probe includes a switch element which is 
actuated when the probe touches the work piece or an analog probe the 
output of which is compared with a reference to detect when it is 
displaced. In an automatic measuring operation, the slides are driven in a 
predetermined sequence of movements and measurements are taken by noting 
the positions of the various slides when the probe contacts the workpiece. 
Such machines are inevitably relatively slow since measurements are made 
singly and slide movement at the instant of contact must be slow to ensure 
that the slide can be stopped without damage to the probe. 
The other conventional type of inspection apparatus utilises a plurality of 
independent analog measurement probes, one for each point of the workpiece 
where a measurement is required. The probes must be specially designed for 
the workpiece to be measured and a completely different set of probes will 
be required for each different workpiece design. Thus, when the measuring 
machine is to be used on a production line on which workpieces of 
different designs can be produced, the probe structure has to be changed 
at each change of workpiece and such changeover can be extremely time 
consuming. The manufacture must stock a set of measuring probes for each 
workpiece and maintenance of these sets of probes involves considerable 
time and highly skilled staff. 
In its broadest aspect the invention has as an object to provide a 
component inspection apparatus in which the above mentioned shortcomings 
of the conventioal machines are substantially overcome. 
In accordance with this broadest aspect of the invention there is provided 
a component inspection apparatus for inspecting a component by repeated 
and simultaneous contact of a plurality of gauging means with a plurality 
of points on the surface of the component, said apparatus comprising a 
component mounting device for receiving a component to be measured; a 
gauging means support; gauging means mounted on said support and 
comprising a plurality of probe elements independently movable relative to 
said support by contact with said component and at least one analog 
transducer associated with each probe element for providing an output 
representing displacement of the associated probe element from a rest 
position; adjustable means mounting said gauging means on said support 
whereby the rest positions of said probe elements are adjustable; 
positioning means for displacing the component mounting device and the 
gauging means support relative to one another in a plurality of different 
directions; sequence control means controlling said positioning means so 
as in use to cause the component mounting device and the gauging means 
support to be sequentially positioned in a series of different 
predetermined positions relative to one another; means for receiving the 
outputs of at least some of said transducers at each of said predetermined 
positions. 
With such an apparatus it is possible to set the positions of the probe 
means by utilising said adjustable means so as to prepare the apparatus 
for measurement of a specific type of component. Many different specific 
components can be inspected on the same apparatus without any need for 
time-consuming setting up procedures. After the positions have been 
adjusted, the positioning means is used, under the control of the sequence 
control means, to cause the probe elements to contact a multiplicity of 
points on the component, a plurality of readings being taken at each 
position. These readings are compared with readings previously taken using 
a master component of the same, or basically the same dimensions. 
Preferably said plurality of gauging means comprises a group of said probe 
elements and associated transducers and said adjustable means incorporates 
means for angularly adjusting the group as a whole relative to said 
support. 
The adjustable means may also comprise means for adjusting the position of 
at least one of the probe elements in the group independently of the 
remainder. 
With a view to preventing damage to probe elements, transducers, components 
under inspection etc., the apparatus prefereably includes a plurality of 
comparators connected respectively to said transducers and each arranged 
to produce an output signal if the associated transducer output exceeds a 
predetermined level, indicating that the probe has been moved beyond a 
normal measuring range, said comparator outputs being connected to said 
sequence control means and acting so as overridingly to stop operation of 
said positioning means if any one of said comparators produces said output 
signal. 
The invention also provides a method of inspecting components comprising 
causing a gauging means support to take up a series of positions relative 
to the component such that at each position of the support a plurality of 
probe elements arrange in an adjustably positioned array on the support, 
are displaced out of respective rest positions by contact between contact 
tips on the probe elements and different parts of the surface of the 
component, and comparing the outputs of analog transducers associated with 
the respective probe elements with previously recorded outputs of the same 
transducers obtained when the support is caused to take up the same series 
of positions relative to a master component. 
To allow simple and rapid exchange of individual probe elements when 
required, there is also provided, in accordance with a further aspect of 
the present invention a gauging device for use in a component inspecting 
machine, comprising a carrier, a linear analog transducer having a body 
mounted on a said carrier and a relatively movable part mounted on said 
body, an elongated probe element supported on said carrier, a first 
coupling part on one end of the probe element, a second coupling part on 
the movable part of the transducer, one of said first and second coupling 
parts being a spherical element and the other being a socket having three 
mutually inclined faces for contacting the spherical element, said first 
and second coupling parts being interengaged such that longitudinal 
displacement of the probe element by contact of a contact tip at its other 
end is transmitted to the movable part of the transducer, said transducer 
providing, in use, an electrical output signal related to the position of 
the movable part thereof, relative to the transducer body.

As shown in FIG. 1 and 2, the apparatus includes a base 10 on which there 
is provided a workpiece support means incoporating a compound slide 
structure 11, 12 whereby a workpiece holder 13 is movable in two 
perpendicular horizontal directions. Also mounted on tha base 10 are two 
columns 14, 15 on each of which a vertically movable slide, 16, 17 is 
mounted. The slide 16 has two probe arrays 18, 19 (as well as some further 
probes) mounted on it, each probe array being mounted on a separate 
turntable 22, 23 rotatable on an axis 22a, 22b parallel with one of the 
horizontal directions mentioned above. Each turntable 22, 23 may be 
manually turned using a manually rotatable rack 22b 22b engaging a gear 
segment 22c 23c on the turntable 22, 23. A locking device 22d 23d is 
provided for locking each turntable in its adjusted position in either 
case. All angular transducer (e.g. a ten-turn potentiometer ) 22e, 23e is 
provided to provide angular position data to a control computer to be 
described hereinafter. The slide 17 carries a single probe device 20. Also 
shown in FIG. 1 is a workpiece handling device 21 which forms no part of 
the present invention, but is used for loading and unloading the workpiece 
holder 13. 
Each array 18, 19 includes three substantially identical probe/transducer 
combinations arranged side by side in a spaced parallel relationship with 
one probe of each array transversely displaceable laterally by a lead 
screw arrangement 24, 25. Each lead screw has an associated angular 
transducer 24a, 25a providing positional data to the control computer. 
As shown in FIGS. 3 to 5, each such combination includes an elongated probe 
element 30 which has a contact tip 31 fitted at one end. The contact tip 
31 may take various forms according to the tasks it is required to 
undertake. The contact tip 31 shown in FIG. 4 simply has a tapered 
projection terminating in a hemispherical surface 31a. 
At the opposite end of the probe element 30 a seating is formed into which 
there is cemented a sphere 32 of rube or other hard material. This sphere 
co-acts with a socket 33 provided on the free end of the movable stem of 
an associated first transducer 34. This transducer, which is of the linear 
differential transformer type, has its body mounted on a suitable bracket 
16a. The socket 33 is of known form having three internal flat surfaces 
inclined to the axis of the transducer at substantially 45.degree. and 
equiangularly spaced around such axis to provide a stable three point 
contact with the sphere 32, thereby ensuring that the centre of the sphere 
32 lies precisely on the axis of the transducer. The bearings which 
support the movable member of the transducer on the body thereof ensure 
that the centre of the sphere can move only along the axis of the 
transducer. 
A slot 35 cut in the end of the probe element 30 receives (with ample 
clearance) a stop finger 36 on the bracket 16a. An abutment face 36a on 
this stop finger lies in a plane perpendicular to the transducer axis and 
is engageable by the sphere 32. The spring loading of the transducer 
itself causes the socket 33 to urge the sphere 32 against this abutment 
face so that, in a rest position, the sphere is held in a precise position 
against this abutment face. Thus far it will be seen that the probe 
element 30 is effectively universally coupled to the movable member of the 
transducer 34. 
To limit pivotal movement of the probe element 30 relatvie to the movable 
member of the transducer 34 about the axis of sphere 32, to a single 
plane, guide means are provided on the probe element 30 and the bracket 
16a. The guide means consists of two spheres 37, 38 of diameters larger 
than the local thickness of the probe element 30 cemented into cross bores 
in the probe element 30, which spheres lie between opposed planar guide 
surfaces 39, 40 on a guide plate assembly on the bracket 16. This guide 
plate assembly comprises guide plates 41, 42, etc. with their planar guide 
faces parallel to the desired plane of movement of the three probes, 
spaced apart by discs 45 of thickness only very slightly greater than the 
diameters of the spheres 37, 38. One of the spheres, i.e. sphere 37, has 
its centre lying on the axis of the probe element 30 (i.e. the line on 
which the centres of sphere 32 and hemispherical surface 31a both lie) and 
the other sphere 38 is spaced from sphere 37 in a direction perpendicular 
to this axis in the desired plane of movement. This last-mentioned 
direction is parallel to the axis of a second transducer 46 provided for 
each probe element. 
This second transducer 46 has its body mounted on the bracket 16a and a 
flat spaced end portion 46a on its movable member. This end portion 46a is 
urged by the spring loading of transducer 44 into engagement with yet 
another sphere 47 cemented in a recess in the probe element 30 adjacent 
the tip 31 (see FIG. 3). The spring loading of the transducer 46 thus 
urges the probe element 30 to turn in a clockwise direction as viewed in 
FIG. 3. To limit such clockwise movement the probe element 30 is fitted 
with a stop pin 48 which projects from both sides of the probe element 30 
and can engage a stop face on an extension 42a of the associated plate 42. 
It will be noted that the probe element itself is free from all connection 
to the bracket 16a or the transducers. It can therefore be readily removed 
by lifting it against the spring-loading of the transducer 34 until the 
pin 48 is clear of the extension 42a and then simply pulling the probe 
element to the left as seen in FIG. 4. To mount the same or a replacement 
probe element the socket 33 is manually lifted, the ball 32 at the end of 
the probe element is engaged in the socket, the probe element is swung to 
enter the spheres 37, 38 between the faces 39, 40 until the pin 48 is 
beyond the extension 42a and then the probe element is lowered until the 
sphere 32 seats on the stop finger 36. 
The single probe device 30 is shown in more detail in FIGS. 6 and 7. In 
this case there is an elongated probe element 50 which has a contact tip 
51 at one end and a cemented on sphere 52 overlying a lateral slot 53 in 
the opposite end just like the probe element 30. In this case however, the 
stop finger 54 against which the sphere 52 is urged by the spring loading 
of the associated longitudinal displacement transducer 55 is on a manually 
slidable member 56 which can be displaced to permit removal and 
replacement of the probe element 50, but which is spring loaded to its 
active position as shown in FIG. 6. 
As shown in FIG. 7 four linear transducer 60, 61, 62 and 63 are provided 
for measuring transverse displacements of the tip of the probe element 50. 
These four transducers are arranged in a cruciform configuration, i.e. 
with transducers 60 and 62 co-axial with one another and transducers 61 
and 63 coaxial with one another and perpendicular to the transducers 60 
and 62. The axes of the four transducers 60 to 63 lie in a plane 
perpendicular to the axis of the transducer 55 and intersect on the axis 
of transducer 55. Each transducer 60 to 63 has a flat face on the end of 
its movable member which is urged by the spring loading of the associated 
transducer towards a spherical surface 64 on the probe element adjacent 
the tip thereof. 
Since it would be unsatisfactory to allow the rest position of th probe 
element to be determined only by the spring loading of the four 
transducers 60 to 63, an arrangement is provided to hold any selected 
adjacent pair of the movable members of these transducers in a set 
position to determine the rest position of the probe element so precisely. 
This arrangement comprises, for each transducer 60 to 63 a retractor 
element 65 which has a head 65a at one end which is engageable with a 
projection 66 on the movable member of the transducer. This retractor 
element is spring loaded by a spring 67 in the same direction as the 
spring loading of the associated transducer to a position in which it does 
not interfere with free movement of the movable member of the transducer. 
A plate 68 on the other end of the retractor element 65 is acted upon by 
the piston rod of a pneumatic piston and cylinder unit 69 to displace the 
retactor element against its spring loading so as to move the projection 
66 on the movable member of the transducer into engagement with a stop 
member 70. This stop member 70 is itself slidable longitudinally of the 
retractor element 65, but is spring loaded by a spring 71 in the same 
direction as th spring-loading of the transducer and that of the retractor 
element 65. An adjustable stop 72 determines the position to which the 
stop member 70 is urged and the spring 71 is preloaded sufficiently to 
ensure that the stop member 70 cannot be displaced away from the 
adjustable stop 72 by the action of the unit 69 alone. 
Turning finally to FIG. 8, the electrical system of the apparatus includes 
a computer 80 which includes sufficient storage (e.g. disc drives) for all 
the program data for all components to be measured. On receipt of 
component number data from a production line management computer 81, the 
computer 80 calls up slide movement data from the storage and loads this 
into a slide position control 82 which is responsible for controlling 
movement of the various slides. The slide position system makes use of 
feedback from encoders provided on each slide to ensure that each slide is 
accurately positioned as required. The resolution of the slide positioning 
control need not be particularly fine provided that the size of the steps 
between positions is less than the normal measuring range of each 
transducer. The accuracy of position must, however, be extremely good, 
since actual dimensional measurements of the workpiece depend on the 
accuracy of both the transducers and the slide positioning system. The 
computer 80 also communicates with the operator of the apparatus via a 
cathode ray tube display 85 and a keyboard 86. For each new component to 
be measured, the computer causes data to be displayed indicating the probe 
elements required at each probe position and the settings required for the 
turntables supporting the two probe arrays 18, 19. The angular transducers 
22e, 23e, 24a, 25a provide position inputs to the computer 80 which must 
match the required positions for the workpiece to be meausred before 
measuring can commence. The computer also outputs appropriate control 
signals to a valve driver 88 which controls solenoid valves which in turn 
control air supply to the units 69. Each linear transducer is electrically 
connected to its own circuit which energises the transducer and converts 
its output signal to an analog voltlage linearly dependent on displacement 
in known manner. These analog voltages are supplied to an analog to 
digital converter 83 via a selector 84 under the control of computer 80. 
The computer receives the measurement data from the transducers and the 
slide position data from the slide position encoders and processes this 
data to establish the dimensions of the workpiece and, if necessary, pass 
corrective data to the computer 81. The individual data received from the 
tranducers at each position is compared with the data previously obtained 
when the same sequence of measurements was carried out on a master 
component. 
By way of example, when inspecting a turbine blade with a fir tree section 
root at one and a shroud position at the other end, the workpiece is 
mounted so that the inner and outer planar end surfaces of the blade are 
vertical, and the turntables are set so that the tips of the tree probes 
of each probe array are in a line parallel to the lengths of the grooves 
in the fir tree section root. Measurement on the end surfaces of the fir 
tree section root are made using the one array of probes, say array 19. 
the measurements being made by transverse displacement of the tips to 
displace the second transducer of each probe element. Measurements of the 
grooves are made using both arrays with the tips resting in the grooves. 
Outputs from both transducers associated with each probe element are used. 
The single probe 20 is used to make all the measurements required at the 
shroud end. Slide movements can be carried out rapidly and a large number 
of points on the componenet can be measured in a relatively short time as 
compared with a conventional single point measuring machine. Setting time 
between component runs is much less than that required for a conventional 
multi-point measurement machine. 
In order to avoid damage to the probes by collision as a result of program 
errors or the like, it will be seen from FIG. 7, that each transducer 
output voltage is applied to a voltage comparator, C.sub.1, C.sub.2, 
C.sub.3, C.sub.4 . . .C.sub.n to compare this output voltage with a 
reference level representing the normal maximum output voltage for the 
normal measuring range of the transducer (this measuring range being 
greater than the size of the steps of the slide positioning system). If 
any comparator is activated by overtravel of the associated probe element, 
an input signal is provided to an INTERRUPT input terminal of the computer 
80. This signal initiates an interrupt routine which immediately causes 
the computer 80 to pass a stop instruction to the slide position control 
to freeze all movements. Then the transducers are sequentially 
interrogated to ascertain which has caused the signal and the appropriate 
slide movement is reversed.