FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for indirectly measuring fabric roll diameter and sending a notification when specified diameter limit has been reached during unwinding of a roll.
BACKGROUND INFORMATION
Bag conversion machines are designed to provide solutions for conversion of tubular fabrics into bags which are affected by various form factors, i.e., bags having varied length and breadth, by cutting, stitching, welding etc. to achieve various bag geometries.
Nowadays, most of the applications require bag geometries such that bags can be efficiently stacked over each other, requires less storage space, and have more contact between two bag surfaces to avoid slippage. Processing such kind of bags needs processing of tubular fabric at different stages to form bags of desired contours. In addition to turning of tubular fabric in different angles and transporting it in various directions, formation of these kinds of bags may require pasting of multiple discrete fabric patches over openings of tubular pieces to close open ends and form desired bag geometries. Special geometry is major attribute of such bags which make them a potent player where space utilization is one of the prime concerns.
Each fabric patch sourcing unit is an independent unwinding unit. In detail, each patch sourcing unit consists of a fabric roll unwinding station, a fabric edge alignment system, a patch cutting system and a patch pasting system. In general, as the number of patch sourcing units increases, machine manufacturers usually use passive methods of controlling unwinding tension to save total machine cost. On one hand, passive methods of unwinding tension are multiple times cheaper than active methods at the same time they are much easy to maintain due to absence of complex closed loop control systems. However, on the flip side, passive tension

control systems are challenging to maintain and read real time running parameters like fabric tension, roll diameter etc.
As explained above when number of patch sourcing units increases on account of increasing complexity of bag geometry, it results in larger number of sub-units included in each patch sourcing station.
Mostly, passive tension control systems apply tension on fabric by overhanging belt lying on fabric roll carrying dead weight at one end. Since the purpose of a passive tension control system is to provide cost effective solution for measuring the diameter of a fabric roll, where it is not viable to employ existing ultrasonic, laser sensors to directly measure diameter of unwinding fabric roll especially when patch sourcing units are in multiple numbers.
Predominantly, operational issues arise in passive tension control system when machine is running during production and suddenly fabric get exhausted from any unwinding station without any prior notification. On the other hand, actively managed tension control systems change unwinding tension based on current diameter of an unwinding roll. Active tension control systems either uses loadcells or diameters sensors to maintain uniform tension throughout unwinding cycle. Basically, active system uses electronics to control tension. In the case of actively managed tension control systems, there are numerous methods to get notification of reducing fabric roll reserve but in case of passive tension control system which only consist of overlaying belt and dead weight, it is impossible to receive notification in any form thereby resulting in loss generated in terms of material wastage, power loss etc. which add up to significant value as number of unwinding stations increases. Therefore, machine designers are required to develop a system which must be cheaper by at least four times than the systems that employ well-known ultrasonic, laser sensor technologies by using cost effective, workable, and easily maintainable solution.

Therefore, there is an urgent need or requirement of a system/apparatus which continuously calculates fabric roll diameter of fabric roll and warns machine operator when diameter is decreased below the threshold level and at the same time raises emergency signals for systematic stoppage of machine to avoid material wastage. Threshold level is cutoff level after which systematic stoppage of machine would not be possible. So, in case diameter reaches below threshold level, it is more likely that fabric will get exhausted (i.e., the bobbin will run out of the fabric during unwinding) before operator can take necessary preventive action for systematic stoppage to avoid wastage or entanglement of fabric/bag even a single bag wastage due to sudden machine stop. Threshold level would be set by the operator based on experience or running material recipe.
There are various prior arts available mentioning about different types of fabric roll diameter measurement systems disclosed earlier. One of the relevant prior arts to current invention is referenced in US6168679. Here, inventor has also used an indirect method to determine roll diameter by using multiple sensors to monitor roll rotation cycle and speed of supporting roller and then mathematically calculated roll diameter. The limitation of invention disclosed in the '679 patent is precise positioning of sensors and use of number of such sensors to achieve the desired results. In detail, following are some of the limitations of referenced prior art:
• It is assumed that there is no slippage between web roll and supporting rollers because slippage causes error in calculation of angular speed and hence diameter calculation.
• Requirement of highly sensitive sensors to detect end of web material for time difference calculation. Sensors are required to check repetition of sensing point. If speed is high, then sensors must be capable of sensing the rotational points. Therefore, high frequency sensors are required.
• Web roll diameter calculation also depends upon supporting roller (5) of known diameter whose angular position is determined by encoder values.

So, resolution of selected encoder decides accuracy of calculated diameter value
In general, encoder pulses are used to calculate Angular velocity. This Angular velocity is used in fabric roll diameter calculation using V = r.w, where r is Roll Radii, 'w' is angular velocity & V = Linear speed. Therefore, if anyone incorrectly enters the radiuses of the roll, the calculation will generate error.
OBJECTS OF THE INVENTION
It is an object of the present invention is to provide an apparatus/system to measure diameter of unwinding rotating fabric roll where tension is maintained passively by overhanging belt lying on fabric roll carrying dead weight at one end.
Another aspect of the present invention is to provide a simple, easily maintainable & scalable system.
Yet another objective of the present invention is to provide an independent workable system which can be integrated with any machine or any other machine where the apparatus of the present invention can be used.
SUMMARY OF INVENTION:
The invention discloses an apparatus and a method for indirectly measuring fabric roll diameter and sending a notification when specified diameter limit has been reached during unwinding of a roll. The apparatus comprises a deflection sensing unit (7), overlay (or follower) belt (3) and dead weight (4). An inductive sensor (2) facing a cam block surface gives electrical output based on a positional gap (10) between inductive sensor (2) tip and profiled surface 1 (a) of the cam block (1). Curvature of the surface (la) of the cam block (1) facing inductive sensor (2) must be made such that positional gap (10) between cam block (1) and inductive sensor (2) varies linearly as fabric roll diameter changes from maximum to minimum level.

The inductive sensors (2) employed in the present invention are well known in industry as non-contact detection of metallic objects and widely used across applications.
LIST OF PARTS:
CAM Block (1)
Profiled surface 1 (a) of the cam block
Inductive Sensor (2)
Follower Belt (3)
Dead Weight (4)
Fabric Roll (5)
Support structure 6(a) & 6(b)
Deflection sensing unit (7)
Computing Module (8)
Transmitting Module (9)
Positional gap (10)
Unwinding shaft (11)
BRIEF DESCRIPTION OF FIGURES
Figure-1 illustrates front view of complete system or apparatus of the present
invention
Figure-2 illustrates block diagram of data flow architecture
Figure-3 illustrates detailed view of apparatus position at any instant
Figure-3 a illustrates detailed view of apparatus position when fabric roll is finished
Figure-3b illustrates detailed view of apparatus position when fabric roll is of
maximum diameter
Figure-4a illustrates system state when maximum fabric roll diameter is mounted
on unwinding shaft
Figure-4b illustrates system state when minimum fabric roll diameter is mounted
on unwinding shaft

DETAILED DESCRIPTION OF INVENTION:
The apparatus of the present invention will be mounted as an independent unit on any machine having unwinding station where tension of fabric roll is maintained by passive control methods.
The apparatus of the present invention comprises of deflection sensing unit (7), overlay (or follower) belt (3) and dead weight (4).
The deflection sensing unit (7) is not limited to CAM block (1) and inductive sensor (2) based arrangement as described in figure-1 but can also provide feasibility to employ other arrangements such as also those that are suitable to measure angular deflection of follower belt (3) and capable to mathematically calculate roll diameter accurately. Other arrangements which can be employed for this application include encoder, resolver, laser, ultrasonic, electrical contact-based concept, or any possible arrangement which can measure deflection of belt.
However, invention is explained by considering CAM block (1) and inductive sensor (2) as preferred components., However, it is important that the orientation of CAM block (1) profiled surface 1(a) should be facing inductive sensor (2) sensing area as shown in figure 3.
Inductive sensor (2) facing CAM block surface gives electrical output based on a positional gap (10) between inductive sensor (2) tip and Profiled surface 1 (a) of the cam block (1) as shown in figure 3. Curvature of the surface (la) of the CAM block (1) facing inductive sensor (2) must be made such that positional gap (10) between CAM block (1) and inductive sensor (2) varies linearly as fabric roll diameter changes from maximum to minimum level as shown in figures 3(a) & 3(b). Inductive sensors (2) employed in the present invention are well known in industry as non-contact detection of metallic objects and widely used across

applications. One of the well-known applications of inductive sensor (2) are metal detectors.
As shown in figure 3(a) & 3(b), relative position of CAM block (1) at extreme ends are shown when fabric roll (5) is at extreme limits.
Referring to Figure 1, the dead weight (4) attached to CAM block (1) via follower Belt(3) is one of essential element of passive tension control system. One end of belt (3) gets fixed at CAM block - profiled surface 1(a) while another end holds dead weight (4). Dead weight (4) used for belt tensioning basically applies opposing frictional force on rotating fabric roll (5) surface such that tension get applied during fabric unwinding. Belt (3) deflection continuously changes as fabric roll (5) diameter changes due to gravitational pull applied by dead weight (4). The purpose of providing a belt (3) is to apply tension to the fabric during unwinding. It is one of the traditional passive ways to apply tension on unwinding fabrics. The only requirement of the belt (3) is that it should not touch ground in case of the lowest roll diameter. Follower belt tension depends up on downward forced applied by dead weight (7), provided dead weight (7) does not touch ground.
In the preferred embodiment, block diagram as shown in Figure 2 the computing module (8) runs an algorithm to calculate fabric roll (5) diameter based on mapping of electrical signal magnitude done at minimum and maximum fabric roll (5) diameters.
It is important requirement that profiled surface 1 (a) of the cam block should follow predictable linear or curvilinear relationship with unwinding Fabric roll (5) diameter. However, it is always preferred that profiled surface 1 (a) of the cam block follows linear relationship with Unwinding fabric roll (5) diameter.

In reference to Figures 3(a) and 3(b) and based on various input value of E parameter, equation for fabric roll (5) diameter 'Dcai' calculation is done by computing module (8) as follows:
i-^cal — Umin ' (Umax ~ Umin)/(iimax ~ i^min) X ic, - limin)
Where, Dcai = Instantaneous calculated Fabric roll diameter at E electrical signal magnitude
Dmin = Minimum roll diameter mapped at Emin electrical signal magnitude Dmax= Maximum roll diameter mapped at Emax electrical signal magnitude
Evaluation of Deal may be in terms of either current or voltage. Equation given above can be used for calculating any instantaneous value. Instantaneous value of electrical signal will vary between Emin and Emax values.
Another aspect of the present invention is to inform/notify the operator once roll diameter has crossed threshold level and automatically initiate procedural shutdown of machine operation to avoid any wastages due to sudden machine stop.
As an example, the threshold level value could be Dmin +5mm or +10mm or as per the requirement of the operation by the operator. This threshold level value is desired to be kept at minimum level to obtain efficient system with no fabric wastage.
Yet another aspect of the present invention is transmission of computed fabric roll diameter 'Dcai' to remote controllers for processing. As shown in figure-2, Data flow path is shown from deflection unit (7) to transmitting module (9) which receives computed information from Computing module (8) and can transmit information through wired or wireless medium to remote central processing units.

The apparatus/system of the present invention offers an accurate roll diameter with continuous monitoring system at lower cost.
During initial setup before measuring the fabric roll diameter the computing module (8) to be calibrated by the following method:
a) Measuring initial and final diameter of the fabric roll which is Dmax and Dmin simultaneously and feeding into computing module (8).
b) Checking the position of the dead weight unit (4) which is mounted on the support structure (6b) such that the dead weight (4) does not touches the ground

c) Checking the position of the inductive sensor (2) such that it is facing the profiled surface 1 (a) of the cam block
d) Recording the initial position of the inductive sensor (2) with respect to the profiled surface 1 (a) of the cam block at the full fabric roll condition when the positional gap (10) is dl such that one extreme voltage limit coordinate Emax corresponding to Dmaxis obtained by the computing module (8).
e) Recording the final position of the inductive sensor (2) with respect to the profiled surface 1 (a) of the cam block just before the exhaust of the fabric when the positional gap (10) is d2 roll such that one extreme voltage limit coordinate Emin corresponding to Dmin is obtained by the computing module (8).
f) Computing module (8) will calculate real time diameter Dcai by following below equation -
i-^cal — Umin ' (Umax ~ l-AninJ/^iimax ~ iiminj X yc, - liminj
The method for measuring and estimating the roll diameter comprises of following
steps:
a) Feeding the threshold level value for the roll diameter into the computing module
(8).

b) Unwinding of the roll and measuring the Dcai by the computing module (8) continuously during the operation.
c) The computing module (8) continuously compare Dcai value with threshold value
d) As DCai value reaches threshold value, computing module (8) notifies machine operator either through acoustic signal or visual notifications like flashing light or any suitable means through which quick attention of operator can be obtained.
e) Computing module (8) can also initiate procedural shutdown of machine
operation to avoid any wastages due to sudden machine stop.
It is preferred that slope between two voltage points follow linear relationship and have constant slope throughout all measuring points.
Advantages of the device of the invention:
There are some places where you cannot mount direct measuring systems. In case
it is possible to mount direct measuring systems, it adds significantly to the cost of
the machine due to the additional hardware. The device and method of indirect
measurement proposed in the invention reduces the measurement costs
significantly.
While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.

We claim:

1. An apparatus for indirectly measuring fabric roll diameter characterized in that said device comprises a deflection sensing unit (7) attached to support structure(6b), an overlay belt (3) and a dead weight (4) connected or mounted to one of the ends od said belt(3), wherein said deflection unit (7) consists of at least one Cam block(l) with profiled surface and one inductive sensor (2) which generates electrical output based on a positional gap (10) between inductive sensor (2) tip and the profiled surface (la) of the cam block (1).
2. The apparatus as claimed in claim 1, wherein in the curvature of the profiled surface (la) of the cam block (1) facing inductive sensor (2) ensures that said positional gap (10) varies linearly or in a curvilinear relationship as fabric roll diameter changes from its maximum to minimum level.
3. The apparatus as claimed in claim 1, wherein said inductive sensor (2) is of the type of non-contact detection of metallic objects.
4. The apparatus as claimed in claim 1, wherein said deflection sensing unit (7) is selected from any one of the types consisting of encoder, resolver, laser, ultrasonic, electrical contact-based concept, or any possible arrangement capable of measuring deflection of said overlay belt (3).
5. A method for indirectly measuring fabric roll diameter using the apparatus as claimed in claims 1 to 4, characterized in that the method comprises the steps of:

a) measuring initial diameter (Dmax) and final diameter (Dmin) of the fabric roll simultaneously and feeding into a computing module (8);
b) checking the position of a dead weight unit (4) which is mounted on a support structure (6b)

c) positioning an inductive sensor (2) to face the profiled surface (la) of a cam block (1)
d) recording the initial position of the inductive sensor (2) with respect to the profiled surface (la) of the cam block (1) at full fabric roll condition and recording the positional gap (10) between the tip of said inductive sensor (2) and the profile surface (la) of the cam block (1) surface (la) termed as dl;
e) recording the final position of the inductive sensor (2) with respect to the profile surface (la) of said cam block (1) just before the exhaust of the fabric and recording said positional gap (10) termed as d2;
f) feeding a threshold level value for the roll diameter into said computing module (8);
g) unwinding the roll and measuring the Dcai by the computing module (8) continuously during the unwinding operation;
h) comparing continuously using said computing module (8) the value of Dcai
with said threshold value; i) notifying the operator using the computing module (8) as the value of Dcai
reaches the threshold value; j) optionally shutting down the machine operation based on such notification.
6.The method as claimed in claim 5, wherein said step (i) of notifying the operator is carried out using an acoustic signal or visual notification means such as flashing light or any other suitable means.
7.The method as claimed in claim 5, wherein the inductive sensors (2) is of the type of non-contact detector of metallic objects.
8.The method as claimed in claim 5, wherein said deflection sensing unit (7) is selected from any one of the types consisting of encoder, resolver, laser,

ultrasonic, electrical contact-based concept, or any possible arrangement capable of measuring deflection of said overlay belt (3).