Device and method for coating a rotating body with elastomeric wear layer

A control apparatus and method for a coating device utilize a measurement system to determine whether a body supplied to the coating device is acceptable for coating and/or to establish template data in preparation for a coating operation. The measurement system also obtains measurements of a body while the body is being coated, and these measurements are used to control the coating operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a control system for controlling a device which 
is adapted to coat a body with a wear layer and which comprises a frame on 
which the body can be rotatably arranged, a system for producing a mass of 
elastomeric material, a system for discharging the mass of elastomeric 
material and forming it into a strand, a system for applying the strand on 
the body so as to form the wear layer, and a system for automatic feedback 
control of the coating of said body. 
Coating a body, such as a tire carcass or a roller in a papermaking 
machine, with elastomeric material, such as rubber, in the form of strands 
(which are subsequently vulcanized), is not without its problems. 
Hitherto, it has not been possible to solve these problems in a 
satisfactory fashion. The present application concerns a technique for 
coating a hotly with rubber that aims at providing the rubber layer or 
tread with a certain profile, i.e. a certain outline and/or thickness. The 
profile is dependent on the dimensions of the rubber strand applied and on 
the closeness of the turns of rubber strand, which generally is identical 
with the degree of overlapping between one turn and the immediately 
preceding turn. 
2. Related Background Art 
There exist today control systems and methods aiming at achieving a 
certain, desired profile. In a prior-art method, the system controlling 
the coating machine is supplied with predetermined values of the closeness 
of the turns, and the machine i.. then operated according to these values 
with the aid of the control system, a predetermined rubber thickness being 
approximately achieved at each point on the body. 
In another prior-art method, a template for the final profile is arranged 
behind the body, and an operator controls, via the control system, the 
coating with rubber while watching the body and the template in order to 
ensure that a profile corresponding to the template is obtained. 
There are many problems associated with the above prior-art methods, and 
these problems are due to the control system itself as well as the way 
this is used. These problems are long standing, and the best efforts to 
find a solution have resulted in the control systems described above. 
Thus, the scrap percentage is embarrassingly high, and the quality of the 
end product leaves much to be desired, especially in certain applications, 
such as retreading and other sorts of recapping where the body is not new 
but merely reconditioned in view of the coating process. 
Additionally, in the prior art, the rubber consumption is far from optimal. 
In mass production of the type commonly used in this field, each saved 
gram of rubber is important, at least from the economic point of view, and 
there is thus a great demand for a technique enabling a minimization of 
the rubber consumption. 
These problems are primarily due to very approximate and inaccurate control 
of the rubber coating itself, the variations in a body or the variations 
between bodies of the same type being not taken into consideration, as in 
the first-mentioned prior-art technique, and/or the errors being 
overcompensated, as in both prior-art techniques described above. 
Consequently, an uneven body may result in an uneven rubber layer. 
Excessive amounts of rubber are applied to ensure that an aimed-at minimum 
thickness is achieved. Furthermore, the method using visual inspection for 
comparing the rubber layer with a template also involves an excessive 
rubber consumption, owing to the operators inability to assess the results 
correctly, for which reason the rubber layer will be thicker than is 
strictly necessary to ensure that the template is covered. 
Furthermore, there does not exist any efficient and cost-effective method 
for checking the quality of the body, which may vary within wide limits, 
primarily in certain applications, such as retreading. In combination with 
the above-mentioned control problems, this means that an unintentional 
irregularity of the body, such as an oval or crooked shape, affects also 
the rubber layer, resulting in an end product of irregular shape, which 
too often has to be scrapped. This leads to excessive production costs, a 
waste of raw material and energy, as well as complaints from customers, 
and may even result in a dangerous end product which, in the worse case, 
may pass the final inspection. In the second-mentioned prior-art 
technique, it is true that some irregularities may be compensated for, but 
also here are some irregularities, such as an oval shape as well as local 
irregularities not found in a whole turn, transferred to the rubber layer. 
When a portion of the body has a smaller or larger diameter than is 
assumed in the process, there is, furthermore, a risk that the rubber 
layer applied, which gives a profile approximately agreeing with the 
template, will be thicker or thinner in this portion than is deemed 
suitable. 
SUMMARY OF THE INVENTION 
One object of the invention is to provide a control system and a method for 
coating a body with a wear layer, for instance a rubber tread, resulting 
in a much-improved end product. 
Another object of the invention is to provide a control system and a method 
for coating a body with a wear layer, resulting in an optimum process with 
regard to material consumption. 
According to the invention, these objects are achieved by a control system 
and a method, which are of the type mentioned above in the Field of the 
Invention have the distinctive features recited appended claims. 
The control system and the method according to the invention enable much 
more reliable control of the coating of the body. The human factor in the 
form of the operator supervising the resulting profile has been eliminated 
and replaced with mechanical feedback recording the results of the coating 
as this proceeds and returning this information, such that the control 
parameters can be adjusted if need be. Such automatic feedback results in 
high accuracy in the coating process and reduces the material consumption. 
A special embodiment of the invention has the additional features of using 
measurement data to control the coating process in accordance with a 
template. 
This embodiment is advantageous in that the measurements and the computer 
in the feedback branch may be used for controlling the coating, as well as 
for rapidly checking the quality of the body before the wear layer is 
applied. As a result, a larger number of irregular bodies can be sorted 
out than in the prior art, which considerably reduces scrapping upon the 
final inspection and further enhances the quality of the end product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the drawings, the control system according to the invention is applied 
to a machine for retreading tires. This is but an example of a possible 
application of the control system according to the invention. This 
embodiment, as well as a method for implementing the invention, will now 
be described in more detail in order to illustrate the invention. 
FIG. 1 schematically illustrates converted components including a machine 1 
for retreading tires. This machine 1 comprises a unit 2, which is adapted 
to prepare rubber mass and which includes an extruder. An assembly 
comprising rollers 3 discharges the rubber moss and forms it into a strand 
4 of rectangular cross-section. A coating unit 5 applies the rubber strand 
to a carcass 6, whose periphery is indicated by a dash-dot line. The 
carcass 6 is rotatably arranged on a frame 7, more specifically on a hub 8 
forming part of the frame 7. The body 6 is rotated with the aid of a motor 
9. Also, the frame 7 is rotatably connected to the remainder of the 
machine 1. The axis of rotation is designated A--A and is referred to as 
the azimuth axis. When rotating about this axis A--A, the frame 7 obtains 
a certain azimuth angle in relation to its initial position. The 
inclination of the frame 7 may be adapted to different body diameters with 
the aid of a piston and cylinder unit 10, which pivots the frame 7 about a 
shaft 11. 
However, FIG. 1 also shows components that are characteristic of the 
control system according to the invention, namely a detector 12, here in 
the form of a camera, and a camera stand 13 which is connected to the 
frame 7 and on which the camera is displaceably arranged. 
FIG. 2 is a block diagram illustrating the main components of the control 
system according to the invention. These components may be divided into 
three groups, namely the camera 12 with an associated computer 14; a 
control unit 15 and the machine 1; and a personal computer 16. 
The control unit 15, which for instance may include a PLC system, is 
connected directly to the machine 1 and controls the coating process. The 
operation of the control unit 15 will be described in more detail below. 
The computer 14 receives picture information about the profile of the 
rubber tread from the camera 12, as well as information about the profile 
currently selected and the measurement tolerances of the selected profile 
from the personal computer 16. On the basis of the information received 
from the personal computer 16 and the camera 12, the computer 14 decides 
if the control need be amended in any way and, if necessary, transmits 
amendment signals to the control unit 15. The operation of the computer 14 
will be described in more detail below. 
The personal computer 16 is connected to the control unit 15 and the 
computer 14. By means of the personal computer 16, the operator 
communicates with the remainder of the system and, inter alia, selects a 
suitable program according to the type of body 6 at issue. Furthermore, 
the operator may, for instance, input Information on the tire dimensions, 
the tread design and the thickness of the rubber tread. The operator 
further obtains various sorts of status information via the personal 
computer 16, with the aid of which he runs the process. The operation of 
the personal computer 16 will also be described in more detail below. 
Furthermore, there are, of course, provided cabling for signal 
transmission, transducers, as well as motors actuated by the control unit 
for controlling parts of the process, such as the speed of rotation of the 
body and the azimuth angle of the frame. Some of these components are 
shown in FIGS. 3 and 4, but others have been left out for reasons of 
clarity. 
FIG. 3 schematically illustrates part of the control performed by the 
control unit 15, namely the control of the azimuth angle and thus of the 
rotation of the body 6. The frame 7 is schematically shown from below, the 
azimuth axis (A--A in FIG. 1), which is perpendicular to the plane of the 
drawing, being indicated by an x designated 30. The control unit 15 
controls a step motor (SM) 31. The step motor 31 causes the frame 7 to 
rotate via a gear (VXL) 32. The rotational movement is recorded as an 
azimuth angle by an angle sensor (.phi.) 33, and this information is 
forwarded to the control unit (15). 
FIG. 4 schematically illustrates another part of the control performed by 
the control unit 15, namely the control of the speed of rotation of the 
body 6 and hence of the peripheral speed thereof. A first pulse generator 
(P1) 40 gives a pulse frequency corresponding to the peripheral speed of 
the rollers 3 and hence to the rate of discharge V1 of the rubber strand 
4. A second pulse generator (P2) 41 gives a pulse frequency corresponding 
to the peripheral speed V2 of the body 6. The control unit 15 determines 
V1 and V2, while taking into consideration the diameter of the rollers and 
of the body as well as the transmission ratio of a gear 43, and then 
determines the relationship between V2 and V1. This relationship, which is 
referred to as SSR, should be essentially constant and have a certain 
value, usually approximately 1.1. The control unit 15 controls a motor 42, 
which causes the body to rotate in order to maintain the correct SSR 
value. A photocell 44 provides the control unit 15 with information 
verifying that the rubber strand is continuous. 
In the embodiment illustrated, which of course is but an example of a 
possible design of the control system according to the invention, and in 
the application to retreading, which also is but an example, the feedback 
control primarily consists of the control of the SSR relationship. The 
azimuth angle is altered according to a predetermined operation schedule 
with which the personal computer 16 loads the control unit 15. Unlike the 
SSR value, this schedule is not altered during the coating of the body 6. 
The feedback control of the SSR value, the feedback consisting of the 
camera 12 and the computer 14, is sufficient in this application to give 
excellent results in the form of a tire, whose profile agrees very well 
with the template, i.e. the aimed-at profile. 
As mentioned in the foregoing, a common SSR value is 1.1, i.e. the rubber 
strand 4 is stretched to a certain extent in order to obtain good adhesion 
to the body 6. The control of the SSR value is carried out as follows. If, 
when determining the current measuring point, the computer 14 finds that 
its value does not fall within the given tolerances, it determines a now 
SSR value, which it forwards to the control unit 15. If the rubber tread 
is too thick, the new value will be higher then the old, and vice versa if 
the rubber tread is too thin. Since the system operates with at least one 
measuring point per revolution of the body, the control of the thickness 
of the rubber tread in very exact. 
A mode of implementation of the inventive method for coating a body with 
rubber will now be described in detail. 
Assuming that the unit 2 is switched on, such that the rubber mass has the 
right temperature. The following operations result in a completed tire. 
Thus, the voltage to the control system in switched on, and the personal 
computer 16 is also switched on. On the display, the operator is then 
shown an image containing various process data, of which some may be 
altered by the operator in order to agree with the type of body to be 
coated. Then, the body 6 is mounted. Checking of the body is initiated, 
the personal computer 16 supplies the computer 14 with information, and 
the body is caused to rotate. On the basis of the information obtained, 
including the diameter of the body, the computer 14 sets the camera, and 
then measures the body 6 for control purposes, comparing measurement data 
deduced from the picture taken by the camera 12 with measurement data 
corresponding to the type of tire chosen. Should the measurement data of 
the body at any point fall outside the prescribed tolerances, which are in 
the order of .+-.1-2 mm, the computer 14 activates an alarm, causing the 
operator to scrap the body 6. If the body 6 is found to be acceptable, the 
operator initiate the coating process. The personal computer 16 supplies 
data in the form of an operation schedule to the control unit 15. This 
schedule includes information on SSR and a sequence of azimuth angles. For 
each azimuth angle of the sequence, the control unit 15 controls the step 
motor 31, such that the latter rotates the frame 7 to the desires 
position, which is monitored by the control unit 15 via the angle sensor 
33. Furthermore, the control unit continuously determines the SSR value as 
above and controls, with the aid of the motor 42, the speed of rotation of 
the body such that the given SSR value is maintained. 
At the same time, the computer 14 creates, on the basis of the information 
received from the personal computer 16, a template for the tire profile in 
the form of a large number of measuring points end, while the rubber tread 
is being applied, compares point by point the template with the results 
obtained from the camera. If there is a deviation falling outside the 
given tolerances, the computer 14 determines a new SSR value that is to 
compensate for the deviation and transmits this value to the control 
system 15. In this manner, the entire body 6 is coated, resulting in a 
tire whose profile on the whole is identical with the aimed-at profile. 
The minor differences that occur are without practical significance. 
Finally, the tire is vulcanized in known manner to a finished end product. 
Primarily owing to the exact control, but also owing to the initial 
checking of the body 6, the finished tire is of high quality, 
consequently, the scrap percentage is very low, and there should, to all 
appearances, be but a few complaints from the customers. 
The control system according to the invention has a further advantage. 
Instead of manual inputting of the measurements a certain type of body 6 
should exhibit, a carefully prepared, ideal body can be mounted on the 
frame 7, whereupon the system is ordered to determine the measurements of 
the body 6 and store these. This is done by having the computer 14 read a 
picture from the camera 12 and on the basis of this picture determine the 
measurements of the body 6, whereupon the computer 14 supplies these 
measurements to the personal computer 16 in order to draw up an operation 
schedule. 
It goes without saying that the embodiments described above are but 
examples and that modifications thus are conceivable within the scope of 
the invention as defined in the appended claims. Thus, the control system 
and the method according to the invention are applicable to the coating of 
many different sorts of bodies, which may be new as well as reconditioned. 
The detector, which is a camera in the embodiments described above, may 
consist of any detector able to record the outline of the body or the 
tread, the associated equipment for evaluating the information obtained 
from the detector being, of course, adapted to the type of detector 
employed. Also, the parameters controlled in the coating process may 
differ from those indicated above, depending on how the coating is carried 
out. It is also apparent that control of the SSR of FIG. 4 does not have 
to be provided along with azimuth control of FIG. 3 and each of the 
manifestations of control can be separately provided.