Indicating instruments

An indicating instrument, particularly for indicating small displacements of a feeler for use in locating the precise position of notches in a program strip to set up a machine tool. The instrument has a lever arm fixed with respect to the feeler and an abutment member moved by the lever arm to give mechanical movement magnification, the degree of magnification being different for different ranges of movement so that the instrument is most sensitive at a predetermined zone of feeler movement, thereby allowing a condensed indicator scale.

This invention relates to an indicating instrument in which the movement of 
a feeler after magnification by a mechanical linkage, is applied to 
produce a corresponding movement of an indicator. Such indicating 
instruments find application for many purposes such for example as a 
position indicator or as a means for accurately setting up a mechanical 
tool to perform a machining operation. 
According to the present invention there is provided an indicating 
instrument comprising a first member which is mounted for pivotal movement 
about a first axis; a feeler secured to the first member; a lever arm 
mounted by one end to the first member and extending away from the first 
axis; a second member mounted for pivotal movement about a second axis 
which is parallel to and spaced from the first axis; a first abutment on 
the second member; a second abutment on the second member further from the 
said axis than the first abutment, and an indicator device coupled to give 
an indication corresponding to the angular movement of the second member, 
the arrangement being such that movement of the feeler rotates the first 
member, thereby swinging the lever arm which turns the second member by 
co-operation with firstly the second abutment to give a certain 
sensitivity and then with the first abutment to give a greater 
sensitivity. 
Such an arrangement enables the degree of magnification to be altered 
stepwise as the feeler is moved from its initial position. 
Thus, the instrument can be highly sensitive at a predetermined zone of 
operation of the feeler and less sensitive when the feeler is displaced to 
a position not as far as the predetermined zone. This means that the 
instrument can be sensitive where required without needing an unduly large 
indicator movement. 
In a preferred arrangement the first abutment is constituted by the 
intersection, with a substantially radially extending surface, of a 
cylindrical bore formed in the second member concentric with the second 
pivot axis. 
In such arrangement a second abutment may be constituted by the 
intersection of the surface with the outer periphery of the member or its 
part. Abutments formed in this manner enable the magnification to be 
determined very accurately since it is a simple matter to machine the bore 
and the outer diameter of the member or its part so as to provide 
abutments at precise distances from the pivotal axis. Also, one or more 
intermediate abutments may be provided by suitably angled faces. 
The invention also includes a system for use in setting up a machine tool 
comprising an instrument as above described adapted to be mounted on one 
part of the machine and a programme strip adapted to be mounted on another 
part of the machine for movement relative to the instrument, the programme 
strip having the predetermined positions along its length means for 
actuating the feeler of the instrument.

Referring firstly to FIGS. 1 and 2 the instrument comprises a first member 
10 which is mounted in bearings for pivotal movement about an axis B and 
is biased for movement in the direction shown by the arrow X by a spring 
arrangement. The member 10 carries a crank 12 from which a feeler 14 
projects parallel to the axis B and a short arm 16 projects at right 
angles to this axis; the purpose of this arm being explained below. One 
end of a layer arm 18 is secured to the member 10. 
The spring arrangement may be constituted by the arrangement shown in 
broken lines, where a leaf spring L co-operates with a pin P on an 
extension of a crank 12. When provided, the leaf spring may form part of a 
switch indicated schematically by a contact C which makes or breaks to 
allow an indication to be given electrically of when the feeler 14 is 
within a normal operating range of displacement. 
A second member 20 is mounted in bearings, not shown, for pivotal movement 
about an axis E which is parallel to and spaced from the axis B, and the 
member is biased in the direction shown by the arrow Y by spring means, 
not shown. The member carries a pointer 22 the free end of which 
co-operates with an arcuate scale (not shown). 
The illustrated instrument provides three degrees of magnification which 
come into operation in succession as the feeler 14 is moved. To this end 
the member 20 is provided with three abutments arranged at different 
distances from the axis E which are acted on in succession by the lever 
arm 18. The third abutment from the axis in constituted by a pin 24 which 
is carried on a crank 26 fast with the member 20. The second and first 
abutments are constituted by the intersection of a radially extending 
surface 28 with the outer surface of the member 20 at 30 and with a 
central bore 32 at 34. Since the member 20 can be machined accurately to 
provide a bore and outside diameter concentric with the axis E the radial 
distances from this axis of the abutments 30 and 34 can be precisely 
determined. 
It will be appreciated that in the illustrated arrangement and on account 
of the spring bias applied to the members 10 and 20 when the feeler 14 is 
in its initial position the abutment 24 will be engaged by the lever arm 
18 and that as the feeler moves this arm will act on abutment 24 to rotate 
the member 20 and thus move the pointer. After the member 20 has moved 
through a certain angle the lever arm will engage the abutment 30 to 
increase the magnification and finally will engage the abutment 34 to 
provide the highest magnification. 
It will be seen that the magnification ratio will be proportional to the 
distance between the axis B and the point on lever arm 18 which engages an 
abutment and inversely proportional to the distance of the abutment from 
the axis E so that in the illustrated arrangement the magnification ratios 
are BC3/ED3, BC2/ED2 and BC1/ED1 respectively. 
With this arrangement and in a compact instrument not more than about 10 
cms high it is found possible to obtain a degree of magnification in 
excess of 500/1 which enables measurements down to 1 micron to be made. 
FIGS. 3 and 4 illustrate diagrammatically how the instrument may be used 
for setting up a machine tool for a machining operation. The instrument 36 
is mounted on one part of a machine while an elongate bar 38 supporting a 
programme strip 40 in contact with the instrument feeler 14 is mounted on 
another part of the machine which moves relative to the first part, the 
direction of relative movement being normal to the plane of the paper as 
regards FIG. 4. 
The programme strip 40 is provided with notches 42 at predetermined 
positions along its length. When a notch comes above the feeler 14 this 
feeler will move upwards to cause the pointer 22, FIG. 2, to move over the 
scale 44 and by adjusting the machine for maximum deflection of the 
pointer the machine can be set very accurately to a position determined by 
the position of the notch on the programme strip 40. 
Since it is desirable to be able to change one programme strip for another, 
or to arrange more than one programme strip along the bar 38 this bar is 
conveniently arranged as illustrated so that the strip 40 can be clamped 
onto the bar by tightening the screw 46 on a clamp 48, as many clamps 
being provided as required. 
The notches 42 in the strip 40 may be ground or they may be made by means 
of a press and, if necessary, they can then be lapped accurately to shape. 
In some cases the machine may be provided with a suitable press so that 
the notches may be formed in situ, and exactly in the right place. 
For example, it is envisaged that the programme strip may be notched 
directly on the machine by mounting the press and the strip on the machine 
so that they move relative to each other in direct relation to the 
movements imparted by the lead-screw of the machine. Then, at appropriate 
positions determined, perhaps, by a prototype on the machine, the punch is 
operated to produce a notch. Thereafter, the use of the programme strip in 
the manner described will reproduce those positions to allow the 
predetermined operations to be carried out. This arrangement can also be 
used to copy programme strips, the master strip being used to determine 
the machine positions and the punch being used to those positions to 
produce a copy strip. 
Instead of using an on-machine press, a press remote from the machine and 
having its own lead screw may be used. 
FIGS. 5 and 6 illustrate alternative forms the notches may take. In the 
arrangement of FIG. 5 the notches are narrow and relatively shallow. In 
FIG. 6 however the notches are wider and deeper so that the feeler 14 will 
move linearly upwards along one side of the notch until it reaches a 
central position. It will be seen that with the instrument described, the 
sensitivity is greatest when the feeler is at the apex of the notch, so 
that precise location of the position of the apex is possible. However, 
since the sensitivity is less elsewhere, the instrument does not have an 
unduly large scale. 
It will be appreciated that it is possible to reverse the described 
arrangement by arranging the notches on the upper edge of the programme 
bar instead of on the lower edge as shown. In either case it is also 
possible that the feeler 14 could be arranged to carry a form of notched 
plate which would co-operate with pins arranged on the programme bar. 
In the use of this arrangement is may be difficult to observe movement of 
the instrument pointer as the machine is being adjusted and it would be 
possible for a notch to be passed unseen. The instrument is therefore 
provided with the arm 16, FIG. 1, which extends through the instrument 
casing as shown in FIGS. 3 and 4. By placing a finger on the end of this 
arm it is very easy to feel when the feeler 14 engages a notch and 
movement of the machine can then be stopped. 
The switch referred to above can be arranged to operate an audible or 
visible warning or in special cases this switch could be included in the 
control circuit of a motor arranged to provide the machine movement. 
The improved instrument of this invention has many possible applications. 
As an example it may be used for the accurate measurement or checking of 
angles. In such case the feeler would co-operate with a notch in the edge 
of a disc which is mounted on a blade. The blade may be urged against the 
face of a workpiece arranged on a base plate and the instrument will 
indicate the extent to which the angle of the workpiece departs from the 
prescribed angle, for example a right-angle. 
The notched programme strip may be bent around a circular drum so that 
accurate angles of rotation of the drum may be determined by the 
instrument. 
The instrument may have only two abutments instead of the three described. 
Alternatively it may have four or more abutments. 
In the embodiment described, the indicator device is a pointer. However, 
the indication may be given electronically and to this end there may be 
provided a digital read-out unit, one example of which is photo-electric. 
Thus, there may be provided a transparent scale coupled to be moved by the 
second member and carrying a track of alternate transparent and opaque 
marks. The track is interposed between a light source and a photo-cell so 
that movement of the scale gives a digital output which is counted and 
displayed by a digital display on the instrument. An improvement of this 
basic system is to arrange a set of parallel tracks on the scale 
associated with respective photo-cells, the tracks being arranged in 
asending order of digital significance, as in a Gray code scale, for 
example. In this way a digital output of position is derived without 
counting, and the possible errors associated therewith.