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Title:
A DEVICE AND A METHOD FOR MOTION CONTROL OF A PUSHER ELEMENT IN AN AUTOMATED SACK MAKING APPARATUS
Document Type and Number:
WIPO Patent Application WO/2019/211685
Kind Code:
A1
Abstract:
Pusher elements that move forward and backward are used for forming valves in sack making. Their settings deteriorate over time causing wear and tear adversely affecting accuracy of pusher element's operation. The invention discloses a device for controlling the motion of a pusher element (1) in an automated sack making apparatus which is used for making a multi-angular fold at a corner of a tubular fabric (7) having separated individual layers. The device has an electro- magnetic device with discrete-step-motion (5) that controls the movement of said pusher element (1), and which in turn comprises a close-loop controller (6), and a motion driver (5 A). A method of controlling the motion of a pusher element (1) in an automated sack making apparatus is also disclosed where a step of controlling positioning of pusher element (1), and its acceleration during its forward movement, and its deceleration in its reverse movement precisely and accurately using an electro-magnetic device with discrete step motion (5) in relation to the travelling fabric (7) is disclosed.

Inventors:
LOHIA, Siddharth (D3/A, Panki Industrial Estate, Kanpur 2, 208 022, IN)
Application Number:
IB2019/053017
Publication Date:
November 07, 2019
Filing Date:
April 12, 2019
Export Citation:
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Assignee:
LOHIA CORP LIMITED (D3/A, Panki Industrial Estate, Kanpur 2, 208 022, IN)
International Classes:
B31B70/84; B31B70/74
Attorney, Agent or Firm:
TASE, Vijay (C/O Patent Cell, Lohia Corp Limited D-3/A, Panki,Industrial Estate, Kanpur 2, 208 022, IN)
Download PDF:
Claims:
Claims:

1. A device for controlling the motion of a pusher element (1) in an automated sack making apparatus, said pusher element (1) being used for making a multi-angular fold at a corner of a tubular fabric (7) having separated individual layers, characterized said device comprises an electro-magnetic device with discrete step motion (5) to control the movement of said pusher element (1), wherein said electro-magnetic device with discrete step motion (5) in turn comprises at least one close-loop controller (6), and a motion driver (5 A).

2. The device for controlling the motion of a pusher element as claimed in claim

1, characterized in that said motion driver (5 A) comprises a memory unit (5C), and an encoder unit (5D) that monitors the rotations of said electro- magnetic device with discrete step motion (5).

3. The device for controlling the motion of a pusher element as claimed in claims 1-2, characterized in that a second sensor (4 A) monitors the movement of a set of driving rollers (4) which are driven by a driving belt (3) and sends a control feedback to a programmable logic control unit, which, based on the control feedback, controls the movement of said electro-magnetic device with discrete step motion (5) to continue or stop the forward or reverse movements of the pusher element (1) through said motion driver (5 A).

4. The device for controlling the motion of a pusher element as claimed in claims 1-3, characterized in that each of said electro-magnetic device with discrete step motion (5) is directly coupled to said pusher element (1).

5. The device for controlling the motion of a pusher element (1) as claimed in claims 1-3, characterized in that each of said electro-magnetic device with discrete step motion (5) is connected to said pusher element (1) through a belt and link assembly and a driving roller (4).

6. The device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-5, characterized in that each of said electro-magnetic device with discrete step motion (5) is connected to said pusher element (1) through output shaft (4C) of speed reduction gear box (4B).

7. The device for controlling the motion of a pusher element (1) as claimed in claims 1-6 characterized in that said driving rollers (4) are coupled with said electro-magnetic device with discrete step motion (5) which in turn are controlled through real time electronically controlled closed loop controller unit (6)/system for accurate positioning of said pusher element (1).

8. The device for controlling the motion of a pusher element (1) as claimed in claimsl-7, characterized in that said pusher element (1) is capable of moving backwards and forwards along a linear motion guide (2) and in the plane of sack fabric (7) and in a direction that is substantially orthogonal to the direction of the movement of the sack fabric (7) on the sack conveyor belt (8)·

9. The device for controlling the motion of a pusher element (1) as claimed in claims 1-8, characterized in that said electro-magnetic device with discrete step motion (5) is oriented such that its rotational axis is substantially parallel to the direction of movement of the fabric (7) on the conveyor belt (8).

10. The device for controlling the motion of a pusher element (1) as claimed claims 1-9, characterized in that said driving rollers (4) and said driving belt (3) are respectively, pulleys and a belt, wherein the contact between said pulley and said belt is non-slipping.

11. The device for controlling the motion of a pusher element (1) as claimed claims 1-10, characterized in that said driving roller (4) has teeth on its outer surface and said driving belt (3) has a corresponding teethed inner surface for contact with said driving roller (4).

12. The device for controlling the motion of a pusher element (1) as claimed claims 1-11, characterised in that said multi-angular fold is triangular.

13. A method of controlling the motion of a pusher element (1) in an automated sack making apparatus characterized in that said method comprises a step of controlling positioning of pusher element (1), and its acceleration during its forward movement, and its deceleration in its reverse movement precisely and accurately using an electro-magnetic device with discrete step motion (5) in relation to the travelling fabric (7).

14. The method of controlling the motion of a pusher element as claimed in claim 13, wherein said method comprises the steps of: providing a device as claimed in any of claims 1 to 12,

sending via the encoder unit (5D), a signal with real-time angular position of the electro-magnetic device with discrete step motion (5) to the motion driver (5 A),

compared the real-time angular position of the electro-magnetic device with discrete step motion (5) with the desired value which is pre- stored/input/saved in the memory unit (5C),

close loop controller system (6), based on the outcome of comparison, sending a command to the electro-magnetic device with discrete step motion (5) for continuing the motion of the pusher element (1) or for stopping it.

Description:
A DEVICE AND A METHOD FOR MOT ION CONTROL OF A PUSHER ELEMENT IN AN AUTOMATED SACK MAKING APPARATUS

Field of Invention:

The present invention relates to an apparatus and mechanism facilitating precise motion in forward and reverse direction of a pusher element used in laying of individual layer of a tubular fabric for forming valve in sack making.

Background of Invention:

In the processing of tubular woven fabric for making sacks for packing applications, it is common to form valves for filling material such as cement or any other kind of powdery or granular raw materials such as sand, grain etc. into sacks. Conventionally, these valves are formed manually by opening the sacks at their one comer and forming a filling mouth. These conventional methods of making valves or creases at one end of tubular sacks are time consuming, especially as the production demand for the bags/sacks with valves increases.

In order to overcome this issue, conventionally, an apparatus is developed comprising a flat element known as pusher element, and a mechanism to drive these pusher elements linearly along a horizontal plane such that it pushes the sack fabric to form a multi-angular fold, which is later converted into a fold directed towards the inside of the bag body and ultimately a valve opening after further processing.

The flat element adapted for laying individual layers of tubular fabric, which can be woven polyolefin or any other kind of like materials suitable for sacks.

With the increase in demand for packaging sacks, there has been an increase in the automation of their manufacture, especially of the cutting and stitching stages. The tubular fabric is cut into pieces of required length, which are further transformed by stitching them at one end. At the other end of the cut pieces— the un-stitched end— the layers of the fabric are separated by using a parting mechanism. The pusher element is pushed forward such that it lays fabric layer to form multi-angular fold at the fabric corner and retracted back, thereafter facilitating transformation of the multi-angular corner folds into a fold directed towards the inside of the bag of tubular fabric. This forward and backward motion of the pusher element during folding process needs very precise synchronization with dynamics of entire cutting, stitching and valve forming machine. Any small phase lag between the motion of the pusher element and the motion of other parts of the sack forming apparatus can lead to distortion of shape or misalignment of tubular fabric which further results in faulty stitching or formation of incorrectly shaped valve. Traditionally, pusher elements are linked with various mechanical components to actuate their motion. Reliability and adjustment of these linkages play very important role in the positioning of the pusher elements and machine operations in general. However, the settings of pusher elements and linkages deteriorate over time leading to their wear and tear. This adversely affects desired accuracy of pusher element positioning with respect to travelling fabric.

There is a need for a reliable automated method to synchronize the movements of the pusher element and those of other moving parts of a sack making apparatus.

Objects of the invention:

It is, accordingly, an object of the present invention, to provide an efficient and precise mechanism in which the telescopic motion of the pusher element can be effectively controlled in real-time, maintaining utmost functional accuracy.

A further object of the invention is to develop a mechanism which requires minimum maintenance due to rapid reciprocating motion of assembly components.

The objects and advantages thereof may be understood by making reference to the following description, along with the accompanying drawings.

List of parts:

Pusher element (1) Linear motion guide (2) Driving belt (3) Central Processing Unit or a PLC (5B)

Driving Roller (4) Memory Unit (5C)

Second sensor (4A) Encoder Unit (5D)

Speed reduction gear box (4B) Close-loop controller (6)

Output shaft (4C)

Electro-magnetic device with discrete Tubular fabric (7)

step motion (5) Conveyor means (8)

Motion driver (5 A) Suction means (9)

Brief description of figures:

Figure 1 shows flow-diagram for process of valve making in a pillow-shaped sack Figure 2 shows the stages of sacks as it undergoes the manufacturing process Figure 3 shows the pre-operational position of a pusher element that operates in a linear mode

Figure 4 shows a schematic of pusher element forward motion

Figure 5 shows a schematic of pusher element reverse motion

Figure 6 shows a block diagram representation of the Electro-magnetic device with discrete step motion system with close-loop controller

Summary of Invention:

The present invention discloses a device and a method for facilitating precise motion in forward and reverse direction of the pusher element used in making multi-angular fold, preferably a triangular fold, from separated sheets of a tubular fabric used for sack making on an automated sack-making machine. The device uses a mechanism incorporating sensors, electro-magnetic devices with discrete step motion having close-loop control and drivers arranged to provide continuous monitoring of the pusher element motion and the sack fabric movement, and uses appropriate feedback loop to ensure synchronization between and alignment of the sack moving along the conveyor platform and the pusher element that is employed to lay the individual layers of the sack fabric in order to ultimately make a fold directed towards the inside of the bag for valve making. A method for accurate control of the pusher element motion is also proposed. The invention allows overcoming the problems of misalignment and helps prevent the damage caused by it, thereby increasing the operational life of the machine.

Detailed Description of invention:

The present invention is used in machines for processing of fabrics, papers and the like materials. The fabric may be non-woven or woven tubular fabric made from monoaxially stretched tapes. (In the upcoming description, we will use the term sack fabric or tubular fabric interchangeably.) Figure 1 shows flow-diagram for process of valve making in a pillow-shaped sack. The present invention - one that involving a pusher element (1) - comes into picture in conjunction with a fold forming and crease forming device. Figure 2 shows shows the stages of a typical sacks manufacturing process pictorially illustrating how a sack with a valve is formed. Here the pusher element (1) of the invention is used in forming stage E. The sequence may vary and what has been shown in Figure 2 is for illustrative purpose only.

In such machines it is often required to spread or open the tubular fabric (7) sheet mouth by separating its individual layers, or fold fabrics or carry out similar activities, as the tubular fabric (7) sheet travels from one processing point to another. Figure 3 illustrates the fabric (7) with separated layers and where the pusher element (1) is positioned. Figure 3 shows some of the typical parts used on a sack-making line - namely a conveyor platform, suction means (9) used to separate the individual fabric layers, and a stamper to form creases. Depending on the type of the sack making apparatus, different components may be used.

Conventionally, methods often used to advance a pusher element (1) into the opening between the individual sack layers, or to retract the pusher element (1) once the folding operation is over, are able to synchronize the pusher element (1) movement with moving components of other processing stations. So long as the pusher element (1) motion is aligned with the movement of fabric (7) including separation of individual layers of the fabric, the force applied by the flat element pushes the fabric (7) evenly and the multi-angular fold, preferably triangular, formed is perfect in shape. However, when the fabric (7) and the pusher element (1) are misaligned or are out of synchronization with each other, the force applied by the pusher element (1) forms undesired fold shape on fabric (7). In order to overcome the problem of misalignment and to prevent the damage caused by it, the present invention provides a pusher element (1) that is operated by electro- magnetic device with discrete step motion (5) to provide high operational accuracy.

For the purpose of this invention the terms 'synchronization' and 'alignment' are defined as thus:

synchronization indicates the state in time domain where the timing of events is such that a specific outcome is achieved. In the case of this invention, the timing of the movement of the pusher element (1) and the timing of its positioning at a desired location is such that it gets inserted in between the two separated layers of the sack fabric (7) with ease, forms a multi-angular fold, and retracts with ease.

Alignment indicates a state in spatial domain where the position of the pusher element (1) is such that it gets inserted in between the two separated layers of the sack fabric (7) with ease, forms a multi-angular fold, and retracts with ease. Figure 4 provides a partial view of invention comprising a pusher element mechanism, driven by an encoder-based rotary actuator drive system, which can be controlled by main programmable logic controller (PLC), also referred to as a close-loop discrete motion controller (6) (not shown in figure). In comparison to other proposed controlling systems, a close-loop discrete motion controller (6) provides a more precise and accurate positioning of the pusher element (1) in relation to the travelling fabric (7).

The close-loop discrete motion controller (6) may also be referred to as a close- loop (or closed loop) controller, or a closed loop controller unit (6) or a system.

Figure 4 shows a pusher element (1) that moves along the linear motion guide (2) as a driving belt (3) connected to the pusher element (1) moves on a set of rotating driving rollers (4), such that pusher element (1) motion along the linear motion guide (2) is perfectly aligned with travelling fabric (7) by using a PLC (5B) and a first sensor (which is a positional sensor - not shown in figures). The driving belt (3) maybe like a timing belt (a flexible belt with teeth moulded onto its inner surface), and correspondingly the driving rollers (4) are a timing type pulley (a pulley provided with toothed outer surface) such that the driving rollers (4) and the driving belt (3) have a non-slipping contact when the driving rollers (4) are being driven by the driving belt (3). In its operational state, the pusher element (1) moves in direction‘a’ (forward movement) as unstitched fabric-end reaches in front of the pusher element (1) and it pushes back the upper layer of the fabric to form a multi-angular fold (see Figure 2, stage E). The pusher element’s (1) initial positioning, its forward movement, and the positioning of the fabric (7) are all aligned with the help of the first sensors provided at appropriate location on the sack-making machine; the first sensors being used for indicating arriving position of fabric (7) when it reaches near to the pusher element (1). Similarly, the pusher element's (1) acceleration from its state of rest at its original position, its maximum forward speed, and decelerate to come to a state of rest at the end of the distance it's designed to travel on its way forward.

In the forward motion (indicated by the arrow 'a' in Figure 4) of the pusher element (1), the encoder (5D) (see Figure 6) monitors the rotations of the electro- magnetic device with discrete step motion (5). The PLC (5B) controls the start time of the pusher element (1) motion, following which there's continuous communication through a feedback loop between the close-loop discrete motion controller (6) and the electro-magnetic device with discrete step motion (5). The electro-magnetic device with discrete step motion (5) in turn drives, through an output shaft (4C), the driving rollers (4) that further provide movement to the pusher element (1). A set of second sensors (4A), also termed as driving sensors, is provided to monitor the movement of the driving rollers (4) and send a control feedback to the PLC (5B), which, based on the control feedback, controls the movement of the electro-magnetic device discrete step motion (5) to continue or stop the forward movement of the pusher element (1). One second sensor (4 A) is provided for each of the driving rollers (4). The reverse motion of the pusher element (1) is monitored along the same principle of comparing the feedbacks of the close-loop discrete step controller (6) and the actual measured movement of the pusher element (1).

Figure 5 shows the pusher element (1) in a retracted position. The driving rollers (4) are rotated in reverse direction (to the direction of rotation required for the forward motion of the pusher element) to retract the pusher element (1) along the linear guide (2) axis (i.e. in direction‘b’ shown in Figure 5). In a manner similar to its forward movement, in the reverse movement of the pusher element, the pusher element's (1) acceleration from its state of rest, its maximum travel speed, and decelerate to come to a state of rest at the end of the distance it's designed to travel on its way back to its original position. The reverse movement of the pusher element (1) (see Figure 5) is controlled using similar parameters (acceleration, deceleration and the distance travelled) by the electro-magnetic device with discrete step motion (5) and motion driver (5 A) of the invention.

Electro-magnetic devices with discrete step motion (5) are well known to a person skilled in the art. There are a number of applications, such as the present invention, where a limited rotation or movement (over a period of a few seconds or even a fraction of a second) of a motor-based component is required, rather than continuous repetitive movement over a long period of time. For such applications, specially designed motors are provided in special arrangements so that the motors move in certain angle under a given electric input. Some commonly known applications are robotics, CNC machinery. A closed loop feedback control system using a electro-magnetic device with discrete step motion (5) used for the present invention is shown in Figure 6. In an embodiment of the invention, the driving rollers (4) are coupled with electro-magnetic devices with discrete step motion (5) which in turn are controlled in real time by electronically controlled closed loop controller (6) system for accurate positioning. One of the preferred embodiments of the invention is the specially designed electro-magnetic device with discrete step motion (5), as indicated in the block diagram of Figure 5. It comprises of a motion driver (5 A) which further includes a memory unit (5C), an electro-magnetic device with discrete step motion (5) which further includes a motor unit and an encoder unit (5D). In general, a close-loop controller (6) system is a motion control system for position and acceleration/deceleration controlling through close loop feedback system completed based on the encoder unit (5D) feedback. The function of a motion driver (5A) along with the encoder unit (5D) is to provide a close loop control for the entire motion system. The data parameters of control of the electro-magnetic device with discrete step motion (5) are saved in memory unit (5C), included in motion driver (5 A).

The pusher element (1) positioning along the linear motion guide (2) is achieved by rotation of driving rollers (4). The function of driving rollers (4) is to provide driving force for pusher element (1) movement. These driving rollers (4) can be directly coupled to electro-magnetic device with discrete step motion (5) or by/ through speed reduction gear box (4B).

In the operational state of the pusher element (1), the encoder unit (5D) sends the real-time angular position of the shaft of the electro-magnetic device with discrete step motion (5) to the motion driver (5 A) of the electro-magnetic device with discrete step motion. As a result, the close-loop discrete motion controller (6) receives information on real-time position of the driving roller (4) which is further compared with the desired value which is already pre-stored/input/saved in the memory unit (5C). On the basis of this information, action is taken as to whether to command the motor unit of electro-magnetic device with discrete step motion (5) for motion or to stop it. This stepwise control of the electro-magnetic device with discrete step motion (5) in closed loop system increases accuracy of the position of the driving rollers (4), and as a result, the accuracy of the positioning of the pusher element (1).

The pusher element (1) movement may be orthogonal or perpendicular to the direction of movement of the fabric (7) that's fed on a conveyor system of the sack-making machine. In this case, the pusher element movement may be termed as axial movement.

In conventional sack making machines, the pusher element movement can be jerky, with sudden and haphazard acceleration/deceleration and starts and stops. The mechanical components of the conventional pusher element assemblies are liable to suffer unnecessary wear due to this, which results into reduced life. These problems are eliminated by the present invention which provides increased life of the pusher element assembly.

It is evident from the foregoing discussion that the invention has a number of embodiments as disclosed below.

1. A device for controlling the motion of a pusher element (1) in an automated sack making apparatus, said pusher element (1) being used for making a multi-angular fold at a corner of a tubular fabric (7) having separated individual layers, characterized said device comprises an electro-magnetic device with discrete step motion (5) to control the movement of said pusher element (1), wherein said electro-magnetic device with discrete step motion (5) in turn comprises at least one Close-loop controller (6), and a motion driver (5 A).

2. A device for controlling the motion of a pusher element as disclosed in embodiment 1, characterized in that said motion driver (5 A) comprises a memory unit (5C), and an encoder unit (5D) that monitors the rotations of said electro-magnetic device with discrete step motion (5).

3. A device for controlling the motion of a pusher element as disclosed in embodiments 1-2, characterized in that a second sensor (4 A) monitors the movement of a set of driving rollers (4) which are driven by a driving belt (3) and sends a control feedback to a programmable logic control unit, which, based on the control feedback, controls the movement of said electro- magnetic device with discrete step motion (5) to continue or stop the forward or reverse movements of the pusher element (1) through said motion driver (5A).

4. A device for controlling the motion of a pusher element as disclosed in embodiments 1-3, characterized in that each of said electro-magnetic device with discrete step motion (5) is directly coupled to said pusher element (1).

5. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-3, characterized in that each of said electro-magnetic device with discrete step motion (5) is connected to said pusher element (1) through a belt and link assembly and a driving roller (4). 6 A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-5, characterized in that each of said electro-magnetic device with discrete step motion (5) is connected to said pusher element (1) through output shaft (4C) of speed reduction gear box (4B).

7. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-6 characterized in that said driving rollers (4) are coupled with said electro-magnetic device with discrete step motion (5) which in turn are controlled through real time electronically controlled closed loop controller unit (6)/system for accurate positioning of said pusher element (1). 8. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-7, characterized in that said pusher element (1) is capable of moving backwards and forwards along a linear motion guide (2) and in the plane of sack fabric (7) and in a direction that is substantially orthogonal to the direction of the movement of the sack fabric (7) on the sack conveyor belt (8).

9. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-8, characterized in that said electro-magnetic device with discrete step motion (5) is oriented such that its rotational axis is substantially parallel to the direction of movement of the fabric (7) on the conveyor belt (8).

10. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-9, characterized in that said driving rollers (4) and said driving belt (3) are respectively, pulleys and a belt, wherein the contact between said pulley and said belt is non-slipping.

11. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-10, characterized in that said driving roller (4) has teeth on its outer surface and said driving belt (3) has a corresponding teethed inner surface for contact with said driving roller (4).

12. A device for controlling the motion of a pusher element (1) as disclosed in embodiments 1-11, wherein said multiangular fold is a triangular fold.

13. A method of controlling the motion of a pusher element (1) in an automated sack making apparatus characterized in that said method comprises a step of controlling positioning of pusher element (1), and its acceleration during its forward movement, and its deceleration in its reverse movement precisely and accurately using an electro-magnetic device with discrete step motion (5) in relation to the travelling fabric (7).

14. A method of controlling the motion of a pusher element as disclosed in embodiment 13, wherein said method comprises the steps of:

providing a device as disclosed in any of embodiment 1 to 12, sending via the encoder unit (5D), a signal with real-time angular position of the electro-magnetic device with discrete step motion (5) to the motion driver (5 A), compared the real-time angular position of the electro-magnetic device with discrete step motion (5) with the desired value which is pre- stored/input/saved in the memory unit (5C),

close loop controller system (6), based on the outcome of comparison, sending a command to the electro-magnetic device with discrete step motion (5) for continuing the motion of the pusher element (1) or for stopping it.

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.