Gauging head for checking linear dimensions of mechanical pieces

A gauging head for checking linear dimensions of mechanical pieces includes a tubular outer casing having a square perimeter cross-section and an arm-set with a flat support element fixed to an internal side of the tubular casing. A movable arm supported by the support element passes through one of the ends of the tubular casing and carries a contact feeler movable substantially along a direction perpendicular to a longitudinal geometrical axis defined by the casing.

The present invention relates to a gauging head for checking linear 
dimensions of mechanical pieces, with an outer casing having lateral 
external faces that are substantially plane and parallel to a longitudinal 
geometrical axis of the casing; a movable gauging arm protruding from an 
end of the casing; a feeler fixed to the gauging arm to contact the 
surface of the piece to be checked, the feeler being movable along a 
direction that is substantially perpendicular to the geometrical axis; arm 
supporting means fixed to the casing; transducer means adapted to provide 
a signal depending on the position of the feeler; and sealing means for 
the closure of the casing. 
Many types of gauging heads for the inspection of mechanical parts on bench 
fixtures and/or during the machine tool machining and/or for inspection 
along transfer lines are already known. 
In most of these applications, it is required that the gauging heads, apart 
from guaranteeing high standards of accuracy and measurement 
repeatability, occupy little space and be of little weight, can be easily 
fixed to supports, ensure effective sealing and be relatively inexpensive. 
In the known gauging heads the compromise among these requirements, that 
are partly contrasting, isn't always satisfying. 
In fact the known gauging heads consist of many elements that are 
manufactured with great accuracy, are quite cumbersome and heavy, and are 
considerably expensive. 
An object of the invention is to provide a gauging head that achieves a 
better compromise among the aforementioned requirements with respect to 
the known gauging heads. 
This and other objects are obtained through a gauging head of the type 
outlined at the beginning of this description wherein, according to the 
invention, the casing basically consists of a single tubular element that 
is open at both its ends, the supporting means being fixed to an internal 
face of the tubular element and the sealing means being adapted to seal 
the ends or bases of the tubular element.

The gauging head shown in FIGS. 1 and 2 includes an outer casing consisting 
of a single tubular element 1 made of sheet steel, that is open at its 
ends and has cross-sections with outer and inner square perimeter. 
Element 1, which consists of a seamless drawn pipe or tube is clamped, in a 
way that will be described hereinafter, to a support 2 fixed to a base 3 
whereupon there is placed a piece 4 the height of which has to be checked 
or, more precisely, the height deviation from a nominal value. 
To the upper inner wall (FIG. 1) of tube 1 there is clamped by means of two 
threaded blind hole upset rivets 5, a longitudinal flat element 6 the 
width of which is slightly smaller than that of the wall. Element 6 ends 
at one end with a wing 7 that extends in a transversal direction with 
respect to the geometrical axis of tube 1. 
Wing 7 has a hole 8 for the passage of an electric cable 9. Cable 9 is 
housed in a sleeve 10, that is externally threaded and has a portion 11 
inserted in hole 8 of wing 7. To portion 11 there is connected a member 12 
providing a seat for housing a tear-resisting knot of cable 9. 
A threaded cap 13 closes the end of tube 1. Cap 13 has a hole for seating 
sleeve 10. The sealing is ensured by a resilient gasket 14 that is 
compressed against the outer face of cap 13 by a nut 15. 
At the other end of element 6 there is another wing 16 that forms, together 
with element 6 and with wing 7, a single piece of bent sheet steel for 
spring. 
Wing 16 includes a first portion 17 that extends in a transversal direction 
and a second portion 18 that extends in a substantially axial direction. 
The first portion 17 has a section 19 of considerably smaller thickness 
making section 19 resiliently flexible so as to act as a fulcrum. 
To the second portion 18 there is welded, by means of lateral seams, an 
L-shaped element 21 made of flat sheet steel, that has identical width as 
that of element 6. 
The longer leg of the "L" extends in a substantially axial direction with 
respect to tube 1 and the shorter leg of the "L" extends in a 
substantially transversal direction. 
In the shorter leg of element 21 there is a hole 22 wherein there is fixed 
an end of a cylindrical arm 23, that carries at its other end a feeler 
element 24 consisting of a threaded stem screwed to a hole of arm 23 and a 
feeler to contact the surface of piece 4. 
At the shorter leg of element 21, tube 1 is sealed by means of a flexible 
rubber gasket 25 and a protective diaphragm 26 made of multicellular 
rubber. Gasket 25 and diaphragm 26 have holes for the passage of arm 23 
and are adequately resilient in order to allow arm displacements, i.e. 
rotational movements about section 19. Normally these movements are of a 
small amplitude and it can therefore be assumed that feeler 24 
substantially moves in a direction that is perpendicular to the 
longitudinal geometrical axis of tube 1. 
The gauging head shown in FIGS. 1 and 2 also includes an inductive position 
transducer, of the so-called "pot-core" type that provides a measurement 
signal responsive to the position of arm 23 and consequently of the 
feeler. The first element, or "pot-core" 27 of the transducer contains an 
electrical winding and it is fixed to element 6, whereas the second 
element, or pot-core, 28, is coupled to element 21. 
Between elements 6 and 21 there is a spring 29 that has an end connected to 
a truncated cone support 30 housed in a seat 31 defined by element 6. The 
other end of spring 29 is connected to a screw 32 that has its head 
located in a seat 33 formed in element 21. The head of screw 32 is 
accessible through a hole 34 in tube 1, that is sealed by a threaded cap 
35. It is so possible, by turning the head of screw 32, to adjust the 
tension of spring 29 and consequently the contact force applied by the 
feeler to the surface of the piece to be checked. 
The wires of cable 9 and those of the transducer element 27 are connected 
to conductive areas 36 and 37 that consist in printed circuits on a board 
38. Board 38 is fixed to element 6 and it has a hole for the passage of 
one of rivets 5. For the passage of this rivet there are provided holes 
through element 6 and tube 1, whereas for the passage of the second rivet 
5 there are holes through tube 1, element 6 and element 21. 
The moving of feeler 24 towards piece 4 is delimited by the contacting of 
the two transducer elements 27 and 28 while that in the opposite direction 
is delimited by the contacting of the end of element 21 with the lower 
wall of tube 1. 
The shape of section 19 and the action of spring 29 are such as to cause, 
under rest conditions, the two elements 27 and 28 to contact each other 
and to make the feeler move the maximum permissible amount along the 
measurement direction. 
In the course of measurement taking, the action of spring 29 ensures the 
appropriate amount of contact force applied by the feeler to piece 4. 
The distances of the feeler displacement line and of the axis of the 
transducer from section 19 are identical; this enables achieving a 
displacement of the feeler equal to that (in the opposite direction) of 
pot-core 28. Between the head of each rivet 5 and tube 1 there is a 
sealing ring 39. 
The gauging head can be clamped to support 2 by means of two screws 40 that 
are screwed in the internal threads of the two rivets 5. In this way 
rivets 5, besides connecting element 6 with tube 1, i.e. the armset with 
the head casing, also allow the clamping of the latter to a support. The 
dimensions of the gauging head can be particularly small. For example, the 
cross-section of tube 1 can have external 12 mm sides and internal 10 mm 
sides. The width of elements 6 and 21 can be of 9 mm. 
The gauging head can be filled, through hole 35, with silicone fluid, or 
another suitable damping liquid. 
It is possible to disassemble in an easy way the gauging head by breaking 
first rivets 5 by using a drill, and then accomplishing any required 
repair work. Thereafter the gauging head is reassembled and by means of 
two new rivets element 6 is clamped to tube 1. 
The gauging head shown in FIGS. 3 and 4 has some variants with respect to 
the one illustrated in FIGS. 1 and 2, mainly as far as the transducer, the 
movable arm-set and connecting rivets are concerned. There is foreseen the 
use of a differential-transformer position transducer, including a casing 
41 with external plane faces, that houses the transformer windings 42, a 
movable core 43 and a printed circuit board 44 to which arrive the wires 
of cable 9 and those of the transducer. The transducer is of the type 
disclosed in Italian Patent Application No. 3365A/78 filed on Mar. 21, 
1978, now available to public inspection. 
With regard to the movable arm-set, instead of the two elements 6 and 21 of 
the gauging head shown in FIGS. 1 and 2, there is provided a single 
element 45 made of flat sheet steel for spring, substantially bent to a 
U-shape. Element 45 has a transversal portion 46 with a hole 47. Portion 
46 comprises two sections 48 of smaller thickness, that act as fulcrums. A 
square-sectioned arm 49 passes through hole 47 and is welded to the 
movable side 50 of element 45. 
Element 45 is clamped to a wall of tube 1 by means of two threaded rivets 
51. One of the two rivets 51 passes through two holes defined by opposite 
walls of tube 1 and a hole obtained through the longitudinal flat portion 
of element 45 that is fixed to tube 1. The second rivet 51 passes through 
two holes defined by tube 1, one hole in the longitudinal flat portion of 
element 45 and a further hole defined by side 50. 
Each rivet consists of two elements 52 and 53. Element 52 is upset to 
connect the longitudinal flat portion of element 45 to a wall of tube 1, 
the second element 53 is subsequently interference-fitted to element 52. 
Element 52 has a thread 54, accessible through the heads of the two 
elements 52 and 53 of the rivet. Thus it is possible to clamp the gauging 
head, by screws 55, to a support 2 in correspondence with both the upper 
face and also (as shown in FIG. 3) the lower face of tube 1. 
Arm 49 passes through a sealing gasket 56 and a protective membrane 57. 
Cable 9 passes through a threaded sleeve 58 connected with a wing 59 of 
element 45. A gasket 60 is placed between sleeve 58 and tube 1. A nut 61 
and a counternut 62 are screwed to sleeve 58 in order to keep it in 
position and compress gasket 60. 
It is evident from the previous description and from the drawings that the 
elements of the illustrated gauging heads are particularly simple and 
inexpensive. The use of sheet steel elements, for manufacturing both the 
casing of the head and parts of the arm-set, and also the particular 
structures shown in the drawings allow the mechanical processings to be 
reduced and simplified. Most of the necessary processings are of an 
inexpensive type, like forming, shearing, drawing, riveting, etc. 
Another basic advantage consists in the overall dimensions that, as 
formerly mentioned, can be reduced to dimensions similar to those of axial 
gauging heads of the type known as "pencil" or "cartridge".