Abstract:
A hand-operated feeler includes a rod on a crossed movement table mounted on a support fitted with an immobilization device at a fixed reference as compared to the part to be measured and a processing unit configured to store and process the results. Such a device results in rapidly measuring the contours of parts including deep and sunken honeycomb cells.

Description:
BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present invention refers to a device and a process for profile measurement. 
   This can be used notably for complex contour parts such as turbine rotors, to measure the profiles of blade grooves or thin tightness tongues which are sharp peaks designed to etch the annular packing in material which can be sensitive to abrasion, to establish leaktightness by labyrinth seal. The profiles measured could be axial or circular on rotation parts. 
   (2) Description of Related Art 
   The metrological devices for profile measurement or more generally for surface contours comprise the following:
     the feeler rod comparators and penetration measurement dial, which allow only rudimentary measurements,   more accurate feelers but bulky and consequently costly, situated at the end of multiple articulation passive arms fitted with travelling encoders, an example of which is described in the document FR 2 702 043,   powered feelers mounted flexibly on a moving support where the movements are measured as and when the motor moves the feeler support and when a bending of the feeler is measured: an example is described in the document U.S. Pat. No. 4,622,751; but only simple movements are possible,
       non-mechanical devices using photogrammetry and based notably on the reflection of light by the surface to be measured; these are efficient but costly.   
       

   The situation is more complicated for the pronounced contour profiles, especially widening out under the surface of the part, which is the case of the blade grooves which are connected at the surface of the part only by a narrower neck. It thus creates a problem for reaching the profile points situated at the bottom of the cavity and above all those of the overhanging parts situated under the neck. Even the feeler mounted on an articulated arm is often insufficient in spite of its flexibility as the feeler must in practice have relatively wide sections in order to possess the required mechanical resistance, and to lodge the passive measuring and maintenance motors of the articulations in stable position. For checks of such profiles, the requester already used gauge sets which were moved up and down the grooves in search of a blocking point or excessive play if any. It is obvious that the gauge sets allow only basic measurements and have the disadvantage of being specific to a given section of grooving. Another method that the requester used consisted in moulding an impression of the groove section, then extracting the mould and measuring its profile under better conditions than the profile of the groove itself. This method, very long, produced good results but was not convenient. 
   A simple device is being sought after to measure complex or inaccessible profiles, with considerable or hollow contours. A device both simple and inexpensive is required, easy to use and sufficiently accurate—ten or so microns or a few microns for the applications mentioned above. 
   It has appeared that a hand-operated feeler was the only contour follower likely to offer these advantages although those already mentioned (the comparator and the articulated arm) are clearly insufficient for different reasons. 
   BRIEF SUMMARY OF THE INVENTION 
   The device suggested here comprises a feeler, a manipulation knob associated with the feeler, a support, a table with two perpendicular movements associating the support with the feeler, and the means of immobilizing the support as compared to the profile; a pair of displacement transducers situated between the mobile portions of the table and measuring the displacements according to the perpendicular movements; and means of reading and memory storage of the displacements measured. 
   The means of immobilization can, depending on the case, rest either on the part to be measured itself, or on a support of this part providing a position reference. The operator holds the knob and shifts the feeler right up to touching, then to following the profile. The operator uses the movements of the table in the two perpendicular movement directions whilst taking advantage of the absence of movement possible in the third perpendicular direction to remain in the plane of the profile to be measured. Mobile tables are available which are at the same time sufficiently rigid and fitted with sufficiently accurate displacement transducers to indicate the displacements movements of the feeler with very reduced uncertainty, in spite of the unknown force applied by the operator. In practice the device is flexible enough and does not require considerable manipulation effort, which allows the operator to work sensitively and therefore not to introduce notable deformation of the feeler or other elements of the device. 
   The invention is also remarkable through a profile measuring process of a part, involving a portable feeler device, comprising the following steps:
     calibration of the device,   assembly of the device in a fixed position as compared with the part,   manual displacement of the feeler along the profile,   automatic correction of measurement errors due to wear or deformation of the feeler, using the results of the calibration.   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to facilitate the understanding of the present invention, the description of the disclosed invention will be provided with reference to the embodiments illustrated in the appended drawings or figures, wherein like structures are identified with like reference designations. The invention will be described and explained with additional specificity and detail by the use of the accompanying drawings, wherein: 
       FIG. 1  illustrates an overall view of an embodiment of the invention in use; 
       FIG. 2  illustrates a perspective view of the device illustrated in  FIG. 1 ; 
       FIG. 3  illustrates details of a feeler of the instant invention with respect to other elements near to the device shown in  FIG. 1 ; 
       FIG. 4  illustrates an overall view of another embodiment of the invention in use; and 
       FIG. 5  illustrates a perspective view of the device illustrated in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Two fairly different realizations of the device are described hereunder using the following figures. The first  FIGS. 1 ,  2  and  3  illustrate therefore the first realization mode, and the last  FIGS. 4 and 5  another mode. The first realization mode applies notably to the control of the blade groove profiles or other deep honeycomb cells on a compressor hub or turbine disk. Please refer first of all to  FIG. 1  which is an overall view of the device in action. The disk  1  is mounted on a machining mandrel  3  in a known position. The cutting tool has been adjusted as accurately as possible and has carried out a run in one of the grooves  2 , of a blade which is now to be checked using the device. According to the control results of the groove  2 , machining of the other grooves  2  could follow, or on the contrary, the tool will be adjusted again. 
   The device comprises a feeler  4 , a support  5 , a crossed movement table  6  (also called X Y table) between the feeler  4  and the support  5 , and an operating system  7  of essentially computer data type. 
   The feeler  4  comprises a rod  8  terminating in a ball  9  which constitutes the feeler element. The rod  8  is bent at an angle ( FIG. 3 ) or more generally oblique for reasons that we will explain. Please see also  FIG. 2  which is a perspective view of the device. The crossed movement table  6  comprises an initial carriage  10  bearing the feeler  4  and mobile on an initial slide bar  11  in the direction of the rod unit  8 , and a second mobile carriage  12  perpendicular to the previous carriage and in the direction of the width of the groove  2  on a second slide bar  13 . The initial carriage  10  bears a gripper knob  14  for the operator; the second slide bar  13  is fixed on a support  5 . 
   The support  5  comprises, apart from a shank  15 , means of immobilization comprising in this case two pins of which one is circular and the other with bevelled sides  16  and  17 , two travel stops  18  and  19 , and lastly a screw  20 . All these means of immobilization are associated with complementary means fashioned on the mandrel  3 , which has been prepared to receive these means. The pin  16  penetrates a circular drill hole, the pin  17  in a recess of corresponding shape, the travel stops  18  and  19  rest on the two flat surfaces, and the extremity of the screw  20  is engaged in an internal screw thread. The pin  16  parallel to the rod  8  of the feeler  4  facilitates directing the rod when the feeler is pushed into the circular drill hole of the mandrel  3 ; the pin  17  prevents rotation of the support  5  around the gudgeon  16  (pin) and the lateral displacements of the rod  8  whilst giving acceptable precision of lateral and vertical reach; the travel stops  18  and  19 , themselves also directed in the same direction as the feeler  4 , limit the penetration of the support  5 ; and the screw  20  holds the support  5  during the check. The movements of the feeler  4  remain free in the directions of the slide bars  11  and  13 . 
   The carriages  10 ,  12  and the shank  15  of the support  5  are fitted at their junctions with line rules associated with optical encoders  21  and  22  which measure the displacements of the carriages  10  and  12  in their respective directions with a precision in the order of a micron. 
   The slide bars  11  and  13  are fitted with balls  23  which guarantee precise and rigid guiding, but with little friction. The processing unit  7  comprises a reading circuit  24  connected to optical encoders  21  and  22 , a memory  25  connected to the reading circuit  24  and recording its results, and a means of display  26  designed to retrieve the results received in the memory  25  as well as the reference results present in another memory  27 . A decision-aid circuit can be added to set out the results displayed more clearly. 
   The processing unit  7  comprises besides, but on the device, a control knob  28  allowing the start of memory storage of the signals from the optical encoders  21  and  22 , or on the contrary the temporary stoppage of these signals. Thus the processing unit  7  is only really active to receive and process these measurements on command from the operator, in practice when the profile to be measured is felt. The displacements other than from the feeler  4 , such as erratic displacements between 2 measurements of portions of measurement, are however read so as to continue to have knowledge of the position of the feeler  4 . The measurement can thus be interrupted and started again later. This is important in the case under study of the grooves  2 . We will now discuss  FIG. 3  which gives details of the feeler  4  and the elements near to the device. As we have mentioned, the rod  8  is bent at an angle and at first travels in a sideways direction, then in the other after a straight portion  29 . Furthermore, the straight portion  29  is mounted on a shaft  30  as an extension. The shaft  30  turns in the first carriage  10  around bearings  31 ; a manual rotation is made possible by a knob  32  extending from the first carriage  10  at the opposite end of the feeler  4 ; a clamping screw  33  facilitates keeping the feeler  4  in an invariable angle position. In practice two angle positions will be preferred and defined by thrust bearings of a stop  34  mounted on the shaft  30  extending radially on a pair of slugs  35  and  36  projecting from the first carriage  10  in the direction of the rod  8 . The two stop positions are diametrically opposed. They are suitable respectively for the two halves of the profile of the groove  2 , the elbow of the rod  8  being fairly significant to avoid any contact with the edges  37  of the neck  38  of the groove  2 . 
   A profile measurement will comprise therefore two runs, each allocated to travel over one half of the profile. Memory storage of the points is made for the determined shift or displacement steps of the carriages  10  and  12 . When one half of the profile has been covered completely, pressing the knob  28  stops memory storage and allows the return of the shaft  30  and the feeler  4  to cover the other half of the profile after having ordered once more the start of the memory storage. An overlap portion of the profile halves exists without this posing any difficulty as the processing unit  7  can superimpose the two readings or produce an average. If the ball  9  is perfectly in line with the shaft  30 , the readings of the two profile halves can be superimposed immediately, if not a correction calculation of its lateral displacement when the shaft  30  is turned, must be undertaken in the processing unit  7 . 
   The display means  26  can, in practice, give the shape of the profile controlled, indicate its intrinsic geometrical characteristics or as compared with the hub or disk  1  (as the control device and the hub  1  are both in specific positions on the mandrel  3 ), or compare the profile measured with admissible profiles. An operation both precise and less empirical than with existing procedures is possible. 
   A measurement standard  39  ( FIG. 2 ) can be added to the device to check its precision or the capabilities of the operator. The measurement standard itself also comprises complementary means identical to those of the mandrel  3  to hold the device in a particular position such as, for example, a honeycomb cell  40  where the profile slightly resembles the profile to be measured, without the similarity being really necessary. The operator recognizes the profile of the honeycomb cell  40  as in an ordinary measurement, and the processing unit  7  compares the results with the real profile, recorded previously. In this way the operator receives an indication of the accuracy of his work. It is possible to compensate for an excessive manipulation force, producing deformation, or wear of the ball  9  by calculating the average errors on each side of the honeycomb cell  40  and by subtracting these figures from the measurements obtained on the profile to be measured. A cause for uncertainty is in practice the penetration of the stops  18  and  19 ; comparators  141  can be mounted on the brackets of the shank  15  adjacent to the stops to check just the right penetration of the support  5 , in other words the beginnings of sensitivity of the comparators  141  when the travel stop has been set, but without appreciable movement of the rod of the comparators  141 . An interesting aspect of the invention is that the feeler  4  maintains its invariable and known directions and that poorly distributed wear of the ball  9  could be compensated for by an exact value for each portion of measurement due to the calibration and knowledge of the portion of ball  9  sliding on each portion of the profile of the part  1  as indeed of the profile of the measurement standard  39 . 
   A case  52  ( FIG. 1 ) surrounds the feeler  4  when the device is screwed in once again so as to provide protection; the feeler is retained on a screw thread  143  at the base of the rod  8 . 
   The other realization mode comprehensively described in this present description appears in  FIGS. 4 and 5  where the first is a general view and the second a detailed view. This comprises, in a similar manner to the previous realization, a feeler  4 ′, a support  5 ′ and an intermediary crossed movement table  6 ′. The part  1 ′ to be studied is a turbine disk with circular contours and notably thin tongues  41 . This is placed on a surface plate  42 , in other words, a perfectly smooth surface, in the same way as the support  5 ′. 
   The feeler  4 ′ can, in this type of realization, where the honeycomb cells separating the thin tongues  41  are not widened towards the bottom, could have a straight rod and fixed on the crossed movement table  6 ′; a realization similar to the previous realization could well be reworked. 
   The crossed movement table  6 ′ comprises, as previously, an initial carriage  10 ′ on which the feeler  4 ′ depends (which in this case is fixed to the carriage), a second carriage  12 ′ supporting an initial slide bar  11 ′ on which the first carriage  10 ′ slides, and a second slide bar  13 ′ fixed to a shank  15 ′ of the support  5 ′; while however the first slide bar  11 ′ which governs the penetration of the feeler  4 ′ is still oriented in the direction of its rod, the second slide bar  13 ′ which governs the run movement of the contour feeler  4 ′ is in this case vertical, examination of the profile  1 ′ being carried out in this direction. 
   As the movement of the table  6 ′ is still manual, due to a knob  14 ′ still fixed to the first carriage  10 ′, a fairly stable position of the table  6 ′ is provided by a counterweight  43  which balances the feeler  4 ′, the knob  14 ′ and the mobile parts of the table  6 ′; this is suspended on the end of a cable  44  held by a pulley  45  turning on the shank  15 ′; the second carriage  12 ′ is suspended on the other end of the cable  44 . Vertical movements of the feeler  4 ′ can in this way be imposed without any notable force, and the feeler  4 ′ can reciprocally be maintained easily at the required height. 
   The shank  15 ′ of the support  5 ′, carrier of the active parts of the device, comprises a collar  46  which allows this to slide on a column  47 ; a bolt  48  facilitates tightening this device on the column  47  to adjust the profile measurement to a required height. The column  47  rises from a base  48  resting on the surface plate  42  by three feet  40  which provide an initial immobilization (in both vertical and slanting directions) of the device as compared to the part  1 ′. The immobilization can be completed by travel stops  18 ′ and  19 ′, similar to the stops  18  and  19  already described, situated at the end of an arm  50  projecting from the two sides of the shank  15 ′. The travel stops  18 ′ and  19 ′ are positioned to hold the part  1 ′ during a measurement run, which completes the immobilization. 
   The measurement run consists therefore in realizing the immobilization of the device by placing the latter on the surface plate  42  next to the part  1 ′, and then in advancing the device towards the part up to contact with the travel stops  18 ′ and  19 ′. The shank  15 ′ is then installed at the required height. Lastly a measurement run is made by manually displacing the feeler  4 ′ and by moving the feeler along the surface contours of the part  1 ′. A processing unit similar to the unit described previously calculates the measurements. 
   It is clear that other realization modes are possible.