Apparatus for cutting or scoring sheet material

Glass scoring apparatus comprises a cutting tool, means for applying a cutting load to the cutting tool when the tool engages a glass surface to be scored, and a damping member arranged to absorb energy developed by reaction forces opposing the cutting load when the tool is moved into contact with the glass. The damping member has a loss factor tan .delta. which is high enough to prevent any substantial transient reduction in the cutting load.

BACKGROUND OF THE INVENTION 
The invention relates to apparatus for scoring sheet material, e.g. glass 
sheets or continuous glass ribbons, prior to breaking the sheet along the 
score line or lines. 
It is known, for the purposes of cutting or scoring a ribbon or sheet of 
glass, to use a cutter assembly carrying a cutting tool such as a wheel, 
the cutter assembly being attached to a mechanism for moving the cutter 
assembly towards and away from the glass to be cut. A previously proposed 
arrangement is described in our British Patent Specification No. 1323097 
and the arrangement described in that specification includes a double 
acting pneumatic cylinder and piston, the piston rod being connected to 
the cutter assembly and arranged to move the cutter assembly towards or 
away from the glass. 
When cutting speeds of 2 meters per second or less are employed known 
cutter assemblies and their operating mechanisms can be used to produce 
good results. However, difficulties can arise when cutting speeds are 
increased substantially above 2 meters per second. One of the difficulties 
encountered is that of keeping the cutting tool in contact with the glass 
surface. When increased cutting speeds, it is necessary to bring the 
cutting tool into contact with the glass with greater speed and this 
involves greater forces being applied to the cutting tool when moving it 
into contact with the glass. When the cutting tool engages the glass a 
reaction force is applied to the cutting tool by the glass tending to 
cause the tool to rebound from the glass after impact. This is 
particularly the case when scoring sheets of glass with a cutting wheel 
where substantial force is required. The force urging the wheel into 
contact with the glass sheet is known as the cutting load. When moving the 
tool into engagement with the glass surface, the reaction force from the 
glass and its means of support can substantially reduce the cutting load 
so that the tool moves out of contact with the glass surface. 
Alternatively, the reaction force may not be sufficient to move the tool 
out of contact but it may nevertheless severly reduce the cutting load so 
that an ineffective score is produced. In either case, a poor or 
unacceptable edge can be produced when the glass is eventually snapped to 
form a break along the score line. The effect of varying score quality 
along the cutting line can produce an effect known as "stitching" . 
The greater the cutting speed, the greater this problem can be. It is also 
found that when using cutting speeds in excess of 2 meters per second, any 
delay in response of the cutter mechanism to changes in the glass surface 
contour can cause problems in not permitting the cutting wheel to follow 
accurately the variation in glass surface contours. This delay is mainly 
created by friction in the mechanism used to move the cutting tool towards 
or away from the glass surface. 
SUMMARY OF THE INVENTION 
The present invention provides glass scoring apparatus comprising a cutter 
assembly for carrying a cutting tool, means connected to the cutter 
assembly for transmitting a cutting load to the cutter assembly, and a 
damping device for absorbing part of any energy developed by reaction 
forces opposing the cutting load when the cutting tool is moved into 
contact with the glass surface, the damping device having a sufficiently 
high loss factor tan .delta. as herein defined to prevent a substantial 
transient reduction of the cutting load. 
When a stress is applied to a damping device the stress is not 
instantaneously opposed by a degree of strain corresponding to that 
stress. The strain always lags slightly behind the stress. For example, if 
the stress variation is considered sinusoidal i.e. represented by a sine 
curve then the resulting strain can be represented by a similar sine wave 
with a phase difference, i.e. displaced in a positive direction on the 
time scale. An important consequence of the phase difference between 
strain and stress is that part of the energy put into the damping device 
during its deformation is not returned during the recovery of the damping 
device. To express this phenomena mathematically the effective stress 
acting on a damping device can be considered as made up of (i) an elastic 
stress component of magnitude A.sub.1 which varies strictly in-phase with 
the strain and (ii) a viscous component of magnitude A.sub.2 90.degree. 
out-of-phase with the strain. The magnitude A.sub.f of the total stress is 
then expressed: 
EQU A.sub.f =.sqroot.(A.sub.1.sup.2 +A.sub.2.sup.2) 
and the damping ability of the damping device can be expressed as a loss 
factor tan .delta. which is defined as follows: 
##EQU1## 
By subjecting a damping device to sinusoidal forced oscillations of 
constant frequency and amplitude it is possible to obtain values of tan 
.delta. for different damping devices. All numerical values of tan .delta. 
specified in this specification will be taken as values determined by 
applying the test conditions set out in British Standard BS903: Part A24: 
1976 operating at a temperature of 23.degree. C. and a frequency of 200 
Hertz. BS903: Part A24: 1976 is particularly applicable to damping devices 
consisting of a resilient material of circular or square cross-section. It 
will be appreciated that it may be possible to design an electromagnetic, 
penumatic, fluid or mechanical damping device, or combination of such 
damping devices which has equivalent damping characteristics, i.e. would 
have the same value of tan .delta., to that of a block of resilient 
material subjected to the test conditions defined above. It will be 
appreciated that when determining values of tan .delta. for such other 
damping devices it may not be possible to employ exactly the same test 
conditions set out in BS903: Part A24: 1976 because of the nature of the 
damping device. In such a situation the value of tan .delta. is determined 
by applying equivalent test conditions appropriate to the damping device 
being tested. It is to be understood therefore that the term damping 
device as used herein includes within its scope such equivalent damping 
devices as well as covering damping devices which consist solely or partly 
of a resilient material. 
British Standard BS903; Part A24; 1976 is available from the British 
Standards Institution, 2 Park Street, London WlA 2BS. 
This British Standard describes a method for measuring the dynamic 
properties of vulcanized rubber using forced sinusoidal oscillations. 
For low values of tan .delta. (.ltoreq.0.2) this method is not very precise 
and it is unlikely that the attainable accuracy will be better than 
.+-.0.02. 
For the purposes of this British Standard the following definitions apply: 
1. elastic shear modulus (in-phase modulus) G'. The component of applied 
shear stress which is in-phase with the shear strain, divided by the shear 
strain. 
EQU G'=.delta..sub.1 /S 
2. loss shear modulus (out-of-phase modulus) G". The component of applied 
shear stress which is 90.degree. out-of-phase with the shear strain, 
divided by the shear strain. 
EQU G"=.delta..sub.2 /S 
3. complex modulus G*. The resultant shear stress divided by the resultant 
shear strain where each is a vector which may be represented by a complex 
number. 
EQU G*=G'+iG" 
4. absolute value of the complex modulus .vertline.G*.vertline.. 
EQU .vertline.G*.vertline.=(G'.sup.2 +G".sup.2).sup.1/2 =.delta..sub.0 /S 
5. loss tangent (loss factor) tan .delta. tan .delta.=G"/G' 
where 
.delta. is the phase angle between the sinusoidal force and deformation. 
6. shear stress amplitude. The ratio of the maximum applied force, measured 
from the mean force, to the cross-sectional area of the unstressed test 
peice (zero to peak in one direction only). .delta..sub.0 =F.sub.0 /2A for 
a double shear test piece. 
7. shear strain amplitude (dimensionless). The ratio of the maximum 
deformation, measured from the mean deformation, to the free thickness of 
the unstrained test piece (zero to peak on one direction only). 
EQU S=x.sub.0 /h 
The terms given above are strictly applicable only to a linear material, 
i.e., one for which the stress is proportional to the deformation. For 
materials containing substantial quantities of filler this is not true, 
and the terms cannot therefore have a precise significance. However, if 
the amplitude of deformation is held constant, effective values of these 
quantities can be measured on the understanding that their magnitude 
depends on the deformation amplitude. 
Other terms, although not appearing in the body of the text, are frequently 
used in test procedures and design calculations. The more common 
expressions are described in Appendix A. 
The deformation used shall be simple shear. This deformation has the merits 
that (a) a substantial proportion of manufactured articles are used in 
this type of strain, and (b) the stress-strain behaviour is more nearly 
linear than in tension or compression, especially for rubbers containing 
little filler. Sinusoidal forced oscillations of a constant frequency and 
strain amplitude shall be employed as the method of measurement. Forced 
oscillations, rather than resonance or free oscillation methods, are used 
because this ensures control of the strain amplitude, which, as discussed 
below, is important. 
The test piece shall be of either circular or square cross section and 
shall be bonded to rigid end plates using a normal adhesion system. 
To avoid significant bending, the diameter (or side in the case of square 
test pieces) shall be at least four times the thickness. This will ensure 
that the deformation is essentially simple shear of the calculated 
magnitude and that the apparent shear modulus differs by less than 3% from 
the true value. 
No recommendation is made for absolute test piece dimensions because of the 
range of sensitivities of the testing machines available. However, the 
difficulties of ensuring uniform vulcanization in thick pieces suggests 
that thicknesses of more than 12 mm should be avoided. 
Double shear test pieces of the general form shown in FIG. 2 are preferred 
as being the most convenient. The measured properties are an average for 
the two segments of rubber. 
Any test machine whether mechanical, hydraulic or electromagnetic may be 
used provided the displacements and forces are adequate to give the forced 
oscillations of the necessary amplitudes over the required frequency 
range. The machine shall be such that the error in loss tangent (tan 
.delta.) of the order .+-.0.01 to .+-.5%, whichever is the greater, and 
the error in complex modulus (.vertline.G*.vertline.) is not more than 
.+-.2%. 
NOTE: It is important that apparatus should be thoroughly checked to ensure 
that these accuracies are met and maintained. 
For testing at elevated and sub-ambient temperatures the test piece shall 
be enclosed in a thermostatically controlled chamber. A gaseous heat 
transfer medium shall be used which is capable of maintaining the 
temperature anywhere in the test piece to within .+-.1.degree. C. Care 
shall be taken to minimize heat losses from the test piece caused by 
conduction through metal parts connected to the outside of the chamber. 
The temperature in the immediate vicinity of the test piece shall be 
measured by a thermocouple or resistance thermometer. 
The temperature of test may be chosen for the particular application in 
mind, but should preferably be one of the following: 
______________________________________ 
-55.degree. C. 70.degree. C. 
-40.degree. C. 100.degree. C. 
-25.degree. C. 125.degree. C. 
-10.degree. C. 150.degree. C. 
0.degree. C. 175.degree. C. 
23.degree. C. 200.degree. C. 
55.degree. C. 
______________________________________ 
The actual temperature of test shall not differ from the nominal value by 
more than the set tolerance. This should normally be .+-.2.degree. C. but 
may be tightened to .+-.0.5.degree. C. near a transition temperature, or 
relaxed when high frequencies or high amplitudes are involved. 
Materials containing substantial quantities of filler show viscoelastic 
behaviour that is dependent on the strain amplitude of test and on the 
strain history of the test piece. It is thus in general necessary to 
control these factors. 
Unfilled materials do not have these complications to a significant extent. 
A difficulty that can arise in testing materials of high loss angle is that 
heat generation in the test piece may rise the temperature significantly 
during the test and, as the properties of unfilled vulcanizates depend 
quite markedly on temperature, this introduces errors. A method of 
estimating the errors involved is given in Appendix B. Consideration of 
this factor, and the strains and frequencies met with in practical 
applications, have led to the recommendations that up to a frequency of 15 
Hz, the strain amplitudes of test shall be .+-.2% and .+-.10%. 
Observations at these two strains enable the magnitude to be determined of 
any strain amplitude effect that may be present. It may then be desirable 
to supplement the observations by tests at other strains if the 
application in mind demands this. For larger strains the possible 
temperature rise in the test piece should however be borne in mind. 
Above 15 Hz the amplitudes sustained by rubber components in use very often 
decrease with increasing frequency, approximately as the inverse of the 
square of the frequency (i.e. the maximum acceleration remains 
approximately constant). 
It is therefore recommended that the strain amplitudes applied to the test 
piece at frequencies above 15 Hz should be in accordance with table 1. 
TABLE 1 
______________________________________ 
STRAIN 
FREQUENCY (Hz) AMPLITUDE (%) 
______________________________________ 
15 2 and 10 
30 2.5 
50 1.0 
100 0.25 
150 0.10 
200 0.06 
______________________________________ 
The actual frequencies may be chosen for relevance to the particular 
application in mind, but should preferably be taken from table. 
NOTE: Superposed static strain. In practice many articles are used in a 
combination of strains, such as combined compression and shear. Because of 
the wide variety of combinations possible in practice no recommended 
values are given for static strains. However, the recommendations given 
here can be applied to the dynamic shear component whether or not a static 
strain is present. 
For all test purposes the minimum time between vulcanization and testing 
shall be 16 h. For non-product tests the maximum time between 
vulcanization and testing should be 4 weeks and for evaluations intended 
to be comparable the tests, as far as possible, should be carried out 
after the same time interval. For product tests, whenever possible the 
time between vulcanization and testing should not exceed 3 months. In 
other cases tests should be made within 2 months of the date of receipt by 
the customer of the product. 
Samples and test pieces shall be protected from light as completely as 
possible during the interval between vulcanization and testing. 
Test pieces shall be conditioned for not less than 3 h at 
23.degree..+-.2.degree. C. immediately before testing. 
Measurement of test piece dimensions. If the end pieces are bonded to the 
test rubber during vulcanization, measure their dimensions prior to 
moulding. This allows the determination of the rubber dimensions from 
measurements made on the complete moulded test piece. 
As an example, for the arrangement shown in FIG. 2, carry out the 
measurement as follows: 
(a) distances d.sub.1, d.sub.2 and d.sub.3 before moulding, 
(b) distance d.sub.4 after moulding, 
(c) calculate the mean thickness of the rubber from h=1/2[d.sub.4 -(d.sub.1 
+d.sub.2 +d.sub.3)] 
(d) determine the cross-sectional area A from the side length and breadth, 
or the diameter, measured after moulding. 
When the end pieces are bonded to a previously vulcanized rubber test 
piece, measure the thickness and cross-sectional area before attaching the 
end pieces. 
Take all measurements to a sufficient accuracy to allow determination of 
the test piece thickness and cross-sectional area to an accuracy of 
.+-.1%. 
Testing. Testing up to 15 Hz shall be carried out first at the lower strain 
of .+-.2%, and the strain should then be increased to .+-.10%. Because of 
the hazard of temperature rise, which may be significant at the higher 
strain at 15 Hz (see Appendix B), the period of oscillation at this strain 
should be kept to a minimum, consistent with obtaining accurate results. 
The temperature rise may be a particular problem at low temperatures where 
the materials are very much stiffer. If time dependent changes occur 
during the test which can be attributed to a temperature rise, the results 
should be extrapolated to zero time to obtain the dynamic properties 
appropriate to the nominal test temperature. At higher frequencies the 
test amplitude should be lower, as given in table 1. Temperature rise at 
these higher frequencies is unlikely to be a problem at the amplitudes 
recommended. It should be noted that the modulus at low deformation is 
depressed by prior oscillations at higher deformations, some hours of 
resting being necessary for the effect to disappear. Thus, if tests above 
15 Hz are required, it is desirable to begin at the high frequencies (and 
thus smaller amplitudes) and to reduce the frequency (increasing the 
amplitude), in order to avoid this possible complication. 
It is recommended that the results be presented as the variation of tan 
.delta. and .vertline.G* .vertline. with temperature, frequency and 
amplitude. Appendix C indicates how these quantities can be determined 
from a force-deflection curve. If both the force and displacement are 
sinusoidal with respect to time, the signals from the transducers can be 
analyzed by suitable electronic techniques to give the required 
information without recourse to recording the force-deflection loop. 
However, filled rubbers may exhibit some non-linearity in behaviour which 
complicates this treatment and measurement of the area of the 
force-deflection loop as described in Appendix C may be the most realistic 
procedure. 
We have tried using a coil spring in the cutter assembly to try and prevent 
a substantial transient reduction of the cutting load but surprisingly 
found that the springs we used had little or no damping influence and were 
unsuitable. We believe this is because the vast majority of springs used 
for cutter applications have a small hysteresis and a loss factor tan 
.delta. which is very small lying within the range 0 and 0.1. We have also 
tried blocks of natural rubber and neoprene both of which proved 
unsuitable for our particular application. We believe the natural rubber 
damping device has a tan .delta. lying between 0.1 to 0.15 whilst neoprene 
has a tan .delta. of approximately 0.2. 
Advantageously, therefore, the loss factor tan .delta. of our damping 
device has a loss factor greater than 0.2. In particular we have found 
that a block of resilient material having a 35% nitrile composition 
provides a suitable damping device. The loss factor tan .delta. of such a 
damping device has been estimated as approximately 0.3. 
Preferably the loss factor tan .delta. of the damping device is more than 
or equal to 0.3. 
We have found that the higher the loss factor tan .delta. the lower the 
resilience and the more efficient is the damping device. Blocks of butyl 
rubber and polyacrylate of inherently high hysteresis loss factors of 
approximately 0.7 and 0.8 respectively have been found suitable and 
preferable to blocks of resilient materials having lower loss factors. We 
believe that damping devices having loss factors higher than 0.8 are also 
suitable. 
Conveniently the damping device comprises a block of resilient material 
such as for example a rubber or synthetic plastics material or a composite 
structure of materials having the property of an elastomer with an 
inherently high hysteresis and high loss factor tan .delta.. Such 
materials may be deformed under load and subsequently recover their 
original form only releasing a part of the original energy input needed 
for deformation. Preferably the block of resilient material is in the form 
of a hollow block. 
Preferably the damping member is maintained continuously in a state of 
compression so that the damping member is preloaded for resisting any 
reduction in the load force of the cutting tool. 
A feature of the present invention is that of providing a glass scoring 
apparatus comprising a cutter assembly having a cutting tool for scoring a 
glass surface, moving means for moving the cutter assembly relative to the 
glass surface to be scored and means for applying a load force urging the 
cutting tool into engagement with the glass surface, and connecting means 
connecting the cutter assembly to the means for applying a load force, 
said connecting means including an untensioned damping device located 
between two parts of the connecting means having a sufficiently high loss 
factor tan .delta. to prevent a substantial transient reduction of the 
cutting load when the cutting tool is moved into contact with the glass 
surface. 
Conveniently the damping device is compressed between the two parts of the 
connecting means. 
The means for moving the cutter assembly towards and away from the glass 
surface and means for applying the cutting load can for example be an 
alectromagnetic, pneumatic, fluid or mechanical system, or a combination 
of such systems. The means we prefer comprises a double acting pneumatic 
cylinder and piston device. The pneumatic cylinder and piston device may 
be similar to that described in our British Patent Specification No. 
1323097. 
Our British Patent Specification No. 1323097 describes and claims glass 
scoring apparatus having a cutter assembly which can be moved towards and 
away from a glass surface to be scored by means of a double acting 
pneumatic cylinder and piston, there being a housing defining the cylinder 
in which the piston can slide, and a shaft connected with the piston and 
extending axially of the cylinder through a passageway in a wall of the 
housing so as to project therefrom, the cutter assembly being connected to 
the projecting end of the shaft, the relative dimensions of the piston and 
the cylinder and the relative dimensions of the shaft and the passageway 
being such as to permit flow of air between the piston and the cylinder 
wall and between the shaft and the passageway wall, thereby providing two 
spaced air bearings which facilitate controlled movement of the cutter 
assembly. 
The purpose of allowing air to bleed past the piston and piston rod is to 
reduce the friction normally associated with a pneumatic cylinder. In 
order to improve the response time of such an arrangement to allow for 
scoring operations at speeds greater than 2 meters per second, the piston 
and cylinder mechanism may be modified to reduce the friction further and 
decrease the response time of the apparatus. 
Preferably, at least two ducts are provided through a wall of the piston 
head to provide communication between a space defined between the piston 
head and the cylinder wall and the chamber in the cylinder above the 
piston head. Preferably the passageway wall is provided with two or more 
ducts for communication between the outside of the passageway wall and the 
space between the shaft and the passageway wall. 
Conveniently a source of pressurised air can be connected to the or each 
duct in the passageway wall for maintaining an airflow between the shaft 
and the passageway wall. 
Conveniently a source of pressurised air can be connected to the or each 
duct in the passageway wall for maintaining an airflow between the shaft 
and the passageway wall. 
A further modification to the apparatus described in our British Patent 
Specification No. 1323097 comprises mounting the top of the cylinder to a 
supporting bracket by means of a fulcrum pin located through a 
self-aligning bearing. A link including a self-aligning bearing may also 
be attached to the end of the piston rod, the link being attached to the 
cutter assembly by means of a fulcrum pin through the self-aligning 
bearing. 
The use of self-aligning bearings makes allowance for any misalignment 
between the cylinder support and cutter assembly and thereby further 
reduces friction between the piston head and the cylinder wall and between 
the piston rod and the passageway wall.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the arrangement shown in FIG. 1, a cutter assembly 11 is pivotably 
mounted on a supporting member 60. It is also attached by means of a 
self-aligning rod end 29 and a fulcrum pin 28 to a piston rod 31, which is 
part of a pneumatic piston and cylinder device 12. The device 12 is 
supported from a mounting bracket 13 by a self-aligning bearing 14 and 
fulcrum pin 14a. The mounting bracket 13 is attached to a support 13a to 
which the supporting member 60 is also attached by means not shown. The 
cutter assembly has on its underside a cutting wheel 15 such as a carbide 
wheel, and this is supported above a glass sheet or ribbon 16 which is to 
be scored on its upper surface. The pneumatic piston and cylinder device 
12, which is generally similar to that described in our British Patent 
Specification No. 1323097, can be operated to raise or lower the cutter 
assembly 11 relative to the glass sheet 16 so that the wheel 15 may be 
moved into contact with the surface of the glass sheet 16 and a suitable 
load force applied to the cutting wheel to achieve a satisfactory score. 
The wheel 15 is rotatably mounted on a carrier 17 which is held by a screw 
18 in a downwardly facing recess 19 in a cutter arm 20. The cutter arm has 
two spaced upstanding lugs 21 and an extension member 22 providing a flat 
surface supporting the damping member which in this case consists of a 
resilient block 23. The two lugs 21 are spaced on opposite sides of a 
generally horizontal arm 24 which is pivotally linked to the lugs 21 by 
means of a pivot pin 25. The right-hand end of the arm 24 is provided with 
an adjustable mechanical stop in the form of a screw 16 which passes 
through the arm 24 and engages at its lower end the upper surface of the 
member 22. The other end of the arm 24 bears against the upper part of the 
resilient block 23 and by suitable adjustment of the screw 26, the 
resilient block 23 can be preloaded to a desired degree of compression. 
The arm 24 has at its left hand end two lugs 27 which have a space between 
them into which the rod end 29 is located and held by means of a fulcrum 
pin 28. The rod end 29 is threaded (female) to mate with the end of piston 
rod 31 (threaded male) to allow for adjustment of the piston position in 
the cylinder relative to the cutter assembly. A nut 30 is used to lock the 
piston rod 31 to the rod end 29 after adjustment. 
In this example, the resilient block 23 comprises a hollow block of 
polyacrylate which has a loss factor tan .delta. of approximately 0.8 or 
above. The polyacrylate has an International Rubber Hardness (IRH) of 50. 
Materials with higher or lower IRH values than 50 can be used, 50 being a 
typical example. The polyacrylate has the advantage of having stable 
damping characteristics i.e., the percentage of energy absorbed during 
each cutting or scoring action should be the same. Other usable materials 
may, for example, comprise some rubbers, polyurethane or a cellular form 
of either rubber or plastics material or a combination of such materials. 
Preferably all such materials should have stable damping characteristics. 
Another type of material which can be used is butyl rubber which has a 
loss factor tan .delta. of approximately 0.7. The block has a hole in its 
centre to allow a greater degree of flexing and it is held continuously 
under a controlled amount of compression between the arm 24 and the 
surface of the member 22. The amount of compression is controlled by the 
stop 26. 
In use, the glass to be scored is normally supported on a cutting bed, 
typically a section of a roller conveyor. In order to prevent the cutting 
wheel hitting the conveyor rollers, an adjustable stop 32 (FIG. 2) is 
provided and arranged to cooperate with a projection 33 on the cutter 
assembly so as to ensure that the cutting wheel never falls below a level 
of for example, 1 mm above the level of the cutting bed. Also the stop 32 
ensures that the piston does not "bottom" in the cylinder when the cutting 
arm is in its lowest position. 
The piston and cylinder device 12 shown in FIGS. 1 and 2 is operated in a 
manner similar to that described in our British Patent Specification No. 
1323097. However, additional passages are provided to improve operation of 
the two air spaced bearings in the piston and cylinder device. A preferred 
arrangement for use in cutting at high speeds is shown in more detail in 
FIG. 3. Similar reference numerals have been used in FIGS. 1 and 2 for 
corresponding parts. The arrangement comprises a piston 34 connected to 
the shaft 31. The piston is surrounded by a cylinder 35. One air bearing 
is provided between the piston 34 and the surrounding wall of the cylinder 
35. A second air bearing is provided between the shaft 31 and the 
surrounding wall 36 at the lower end of the piston. In order to avoid 
depletion of air from these bearings when depressurisation occurs in the 
chamber 37 below the piston, additional ducts are provided adjacent to 
both air bearings. Four equally spaced ducts 38 are provided through the 
wall of the piston head thereby allowing air above the piston to flow 
through the ducts into spaces 39 between the wall of the piston and the 
wall of the cylinder. Similarly four equally spaced ducts 40 are provided 
through the wall 36 at the lower end of the cylinder where it surrounds 
the shaft 31. The ducts 40 lead to air supply passages 41 which may be 
connected to a high pressure air source. Air then flows to the air bearing 
as indicated by the arrows in FIG. 3. In operation a constant cutting load 
pressure is applied through duct 61 to the chamber above the piston. The 
pressurisation and depressurisation of the chamber below the piston head 
being controlled by a pressure controlling means connected to a duct 62. 
In use, the cutter assembly is moved to a suitable position for commencing 
a score line. Subsequent relative movement between the cutting wheel and 
the glass surface may be effected by moving the glass relative to the 
cutter or in some cases it may be preferable to move the cutting apparatus 
while the glass is held stationary. Normally, however, the glass and 
cutter are moved relative to one another such that bidirectional movement 
takes place so as to produce the required score line. When the cutting 
wheel has passed the edge of the glass, the cutter assembly is forced 
downwards by movement of the piston shaft 31 under the influence of 
pneumatic pressure acting above the piston head 34 so that the wheel is 
forced into contact with the glass surface and a suitable load force is 
applied to effect satisfactory scoring of the glass surface. As the 
cutting wheel engages the glass surface, the impact creates a reaction 
from the glass and its supporting cutting bed tending to cause the wheel 
and cutter assembly to rebound away from the glass surface. The travel of 
the piston rod 31 is preferably arranged such that when the wheel first 
engages the glass surface the piston still has a small downward stroke for 
example of the order of 5 mm. Consequently, at the time the cutting wheel 
receives a reaction force from the glass surface tending to cause it to 
rebound, the piston is still travelling in a downward direction. However, 
the connecting mechanism between the cutting wheel 15 and the piston shaft 
31 is arranged to absorb energy from the reaction force of the glass 
surface and to maintain the cutting wheel 15 in contact with the glass 
surface with sufficient load force to achieve satisfactory scoring. The 
upwards force on the wheel 15 is transmitted to the damping block 23 which 
absorbs some of the energy and continues to exert a force between the arm 
24 and extension 22 tending to maintain the cutting wheel in engagement 
with the glass surface. 
In order to achieve the best results, the cutter assembly is made of low 
density materials so as to reduce the overall mass of the cutter assembly. 
In typical operation conditions, the cutting load applied to the cutting 
wheel 15 may be between 3 and 4 kgs. 
The invention is not limited to the details of the foregoing examples. For 
example, FIG. 4 shows an alternative cutter assembly and like parts have 
been marked with the same reference numerals as used in FIGS. 1 and 2. In 
this particular example, the arm 20 of the cutter assembly has a shoe 50 
which provides the lower support surface for the resilient block 23. In 
place of the adjustable stop 26, a solid block of material 51 is used as a 
spacer between the arm 24 and the shoe 50 thereby providing the required 
compressive preload to the block 23. 
FIG. 5 shows a further alternative cutter assembly. In this arrangement, 
the cutter assembly 11 is connected to the shaft 31 by means of a linear 
lost motion connection rather than the pivoted arm connection mechanism 
described in the earlier examples. The cutter arm 20 is provided with lugs 
21 which fit on opposite sides of a block 53 attached to the lower end of 
the shaft 31. The block 53 is provided with an elongated slot 54 and the 
lugs 21 are connected to the block 53 by means of a pin 55 passing through 
the elongated slot 54. The lower end of the block 53 bears against the 
upper surface of the resilient damping block 23. It will be seen that when 
the shaft 31 is moved in a vertical direction, the cutter assembly will 
normally move with it. However, the location of the pin 55 in the 
elongated slot 54 permits compression of the block 23 to absorb energy 
from reactive forces on the cutting wheel 15 when the wheel is urged 
upwardly by the glass surface against the downward loading force applied 
by the shaft 31. 
It is to be understood that our invention can also be used for different 
cutting operations to the one described above in which problems of 
"stitching" and poor scoring can occur. The cutting of a glass ribbon or a 
glass sheet having saleable edges (i.e., from which the selvedge has been 
removed) involves charging the cutting tool transversely into the edge of 
the glass ribbon or glass sheet and then transversely over the surface of 
the glass ribbon or glass sheet. The initial impact between the tool and 
the edge of the glass can cause "stitching" and prior scoring and by 
employing a glass scoring apparatus having a damping device according to 
our invention these problems can be reduced or substantially eliminated. 
We believe that our invention has advantages even when low cutting speeds 
are used in that the presence of a damping member helps to increase the 
useful life of the cutting tool, and thereby substantially reduces glass 
loss because of the reduced number of changes of cutting tool required 
over a period of time.