WO2021209849A1

WO2021209849A1 - A cutting apparatus having a semi-automatically replaceable cutter rail and semi-automated method of replacing it

Info

Publication number: WO2021209849A1
Application number: PCT/IB2021/052729
Authority: WO
Inventors: Gaurav LOHIA
Original assignee: Lohia Corp Limited
Priority date: 2020-04-18
Filing date: 2021-04-01
Publication date: 2021-10-21
Also published as: TW202206247A

Abstract

The invention describes a cutting apparatus having a semi-automatically replaceable cutter rail (7) and semi-automated method of replacing it. The apparatus comprises a vertical frame (2) affixed to floor, a horizontal frame (3) affixed to said vertical frame (2) near its top end, a vertical guide rail (4) affixed to said vertical frame (2), a cutter rail carrier assembly (6) consisting of a cutter rail bracket (10) on which said cutter rail (7) is mounted, a geared motor (5) affixed to said vertical frame (2) to cause the up/down movement of said cutter rail carrier assembly (6), a set of guide roller (12) supported on a guide roller bracket (11) mounted on said horizontal frame (3) and capable of swivelling around a pivot (16). The cutter rail carrier assembly (6) is capable of moving up and down along said vertical guide rail (4) during replacement operation of said cutter rail (7).

Description

A CUTTING APPARATUS HAYING A SEMI-AUTOMATICAULY REPUACEABLE CUTTER RAIL AND SEMI-AUTOMATED METHOD OF REPLACING IT Field of Invention

The invention relates to a system and method for semi-automatic replacement of entire cutting unit on a plastic slit-film tape making extrusion system/machine. The invention preferably discloses a cutting unit having at least one cutting blade station, for the longitudinal cutting of moving sheet-like flat structure plastic films/webs into a multiplicity of tapes or flat threads of essentially selectable and constant width.

Background of Invention

In an extrusion slit film stretching line, generally known as a raffia tapeline, the longitudinal cutting of continuously moving wide width flat film coming from the film forming section, into multiple smaller width slit film tapes takes place at cutting unit. There are many known cutting systems used for this purpose.

In one of the widely adapted cutting systems, longitudinal cutting of the film is usually carried out by passing a film/web over several cutting blades arranged to suit the tape width and mounted over a cutter bar. With the increasing processing speeds, there is higher wear of these cutting blades, which requires to be replaced more frequently. For reducing the frequency of the replacement of cutter bars, there have been developed so-called rotational cutter bars, like the one disclosed in DE 31 37 826 Al. In the system disclosed in said patent application, there are provided cylindrical cutter bars and at the periphery of which are arranged six rows of cutting blades, which may be rotated further from one row of cutter blades to the next row of cutting blades, to carry out longitudinal cutting of film in the cutting plant.. When, however, eventually the blades of all blade rows become blunt, the entire production system has to be shut down to change or replace the complete cylindrical cutter bar with new bars..

With the use of such a rotational cutter bar, there will be achieved longer ran times of a system. However, the replacement of cutting bar or complete rotary cutting unit is done manually. More importantly, the replacement process is cumbersome and risk-laden involving higher downtime.

Further, with the increase in width of film/web, the cutting system weight would increase considerably making them significantly more difficult to handle by single person. Also, given that in the cutting system, there is plurality of sharp edges therefore the safe handling of cutting unit is also an area of one of the concern.

Also, in some tapeline configurations, the film/web longitudinal cutting unit is mounted at a considerable height above the ground level and also mounting area is considerably compact, these factor increases the risk to the person performing the changeover operation.

The cutting unit is a stationary object placed in the path of an advancing film of a slit film tape extrusion system. Cutters have a core on which a set of cutting blades - one blade corresponding to a single cut to be made in the film - is mounted. Individual blades from a blade set are placed next to each other at a distance equal to the width of the tapes. The blades have a definite cutting length - all of which needs to be fully utilized for cutting purpose. To achieve this, the position of blade relative to the plane of advancing film needs to vary, whereby unused part of the blade would come in contact with the film. Once the entire length of a blade gets blunted, the blades are no longer suitable for cutting purpose and the blade station needs to be changed. In order to minimize the downtime, it is desirable to reduce the number of occasions on which the entire cutter needs replacing. In this respect, it is advantageous to have multiple cutting locations on the cutter rail. Location of each blade set is termed as a station. For example, as shown in Figure 3, 4, 5 a six- station cutter has six sets of blades. Upon blunting of blades of a blade-set, the cutter rail is rotated so that a fresh blade-set may be deployed for cutting the advancing film. The cutter assembly is equipped with the facility for changing the blade stations for cutting. For replacing the cutter rail, the old cutter rail needs removing from the cutter rail carrier assembly and a new cutter rail needs to be put in its place.

The cutters rail is typically made of metal and depending on their own size and the width of the film, their weight may be significant. For example, for a film that is 1500 mm wide, and for a cutter rail with six-stations, the weight of the cutter rail could be as high as 150 kg. The machine operators have to manually remove the cutter rail and replace them. This activity is carried out in constrained space and pose substantial hazard to the operators and also to the machine itself. In the conventional systems, the operation of the cutter rail replacement is carried out at relatively high level, for example 6-8 feet above ground and involving substantial amount of bending on part of the operator while handling the cutter. Therefore, there is a need to provide a system that allows changing of cutters without significant risk to the operators and to the machinery. The invention discloses such system.

The system of the present invention ensures improved safety factor, reduces the downtime and eases the cutting rail changeover operations. Objects of Invention:

The main objective of the invention is to provide a cutting apparatus with a replaceable cutting rail on a plastic slit film tape making extrusion system / machine.

Another object of the invention is to provide system and method for replacing a cutter rail on a plastic slit film tape making extrusion system/ machine.

Another object of the invention is to reduce the downtime of cutting unit changeover operation.

Further object of the invention is to improve the safety during the changeover operation by semi-automation of the cutter handling process. A still further object of invention is to ensure perfect cutting operation of moving film web, with an improved blade life.

Yet another object of invention is to automate the changeover process from one cutting station to adjacent cutting station without interruption in moving film processing.

Summary Of Invention:

The invention discloses a system and method for semi-automatic replacement of entire cutting unit on a plastic slit-film tape making extrusion system/machine.

The present invention provides a semi-automated system wherein the cutter rail is disengaged from the cutting activity and brought from its normal working position to a level where it is more easily replaced by the operators by minimizing safety hazard to their own persons and to the machinery itself. In particular, the invention describes a cutting apparatus having a semi- automatically replaceable cutter rail (7) and semi -automated method of replacing it. The apparatus comprises a vertical frame (2) affixed to floor, a horizontal frame (3) affixed to said vertical frame (2) near its top end, a vertical guide rail (4) affixed to said vertical frame (2), a cutter rail carrier assembly (6) consisting of a cutter rail bracket (10) on which said cutter rail (7) is mounted, a geared motor (5) affixed to said vertical frame (2) to cause the up/down movement of said cutter rail carrier assembly (6), a set of guide roller (12) supported on a guide roller bracket (11) mounted on said horizontal frame (3) and capable of swivelling around a pivot (16). The cutter rail carrier assembly (6) is capable of moving up and down along said vertical guide rail (4) during replacement operation of said cutter rail (7).

The invention also discloses a semi-automated method of replacing a cutter rail (7) provided on a cutting apparatus uses the apparatus as described in foregoing paragraphs for cutting an advancing plastic film (1) into slit-film tapes (1A). The method discloses how to disengage the cutter rail (7) from the advancing film by moving the cutter rail carrier assembly (6) and then lowering the cutter rail assembly (6) to a position where the operator (19) can manually replace it, followed by raising the position of the cutter rail assembly (6) to its working position.

Brief Description of Figures:

Figure 1 shows conventional system of changing cutter assembly

Figure 2 shows the system of invention

Figure 3 shows a perspective view of cutter rail Figure 4 shows the different positions of cutting and direction of movement of cutter rail for changing blades

Figure 5 shows six different position of cutter

Figure 6 shows the part view of invention wherein movement of guide roller bracket is present

Figure 7 shows the part view of invention wherein cutter rail assembly and its movement is present

List of parts:

1. Advancing film 1A. Slit film

2. Vertical Frame

3. Horizontal Frame

4. Vertical Guide rail

5. Geared Motor

6. Cutter Rail Carrier assembly 6A. Top position

6B. Service position 6C. Working position

7. Cutter Rail (7)

7A. Cutter Core 7B. Blade (7B)

8. Motor

9. Pneumatic cylinder

10. Cutter rail bracket

11. Guide roller bracket

12. Guide roller 13. Stopper

14. Platform

15. Working position sensor

16. Pivot

17. Top position sensor

18. Service position sensor

19. Operator

Detail Description Of Invention:

Figure 2 shows apparatus of invention which comprises of vertical frame (2) and a horizontal frame (3) wherein said vertical frame (2) and horizontal frame (3) are joined together by joining means. The joining means can be of any type such as bolting, welding or by any means known to person skilled in art such that they he on the same plane.

Further, the vertical frame (2) comprises of a vertical guide rail (4) mounted on the said vertical frame (2) to form a one part. The vertical guide rail (4) can be of any material such as metal or non-metal or plastic to provide a smooth vertical to and fro movement of cutter rail carrier assembly (6) over it and can withstand the heavy weight of the said cutter rail earner assembly (6).

In another embodiment, cutter rail carrier assembly (6) slides over the vertical guide rail (4). The sliding motion can be achieved by any of the means such as rod bush arrangement, roller bearing arrangement, lead screw arrangement, rack and pinion arrangement, or can be controlled and moved by any kind of hydraulic or pneumatic mechanism.

As shown in figure 7, the cutter rail carrier assembly (6) comprises of a cutter rail (7), a cutter rail bracket (10) and a motor (8). The cutter rail (7) is mounted over mounting cutter rail bracket (10) and is connected with the motor (8) such that the motor (8) facilitates the rotational movement of the cutter rail (7). The motor (8) can be chosen from the set of electromagnetic drive system such that it can be servo motor or stepper motor to provide discrete step motion to the cutter rail (7). The said motor (8) can be remotely driven without any manual intervention. Such rotation is required to change the set of blades upon blunting, so that a fresh blade-set may be deployed for cutting the advancing film.

Further, cutter rail bracket (10) is engaged with the vertical guide rail (4). The said engagement is such that the cutter rail bracket (10) slides over the vertical guide rail (4).

In further embodiment, the friction between the vertical guide rail (4) and cutter rail bracket (10) should be as less as possible so that a smooth movement of the bracket (10) happens over vertical guide rail (4).

Again shown in figure 7, the movement of the cutter carrier rail assembly (6) over the vertical guide rail (4) is facilitated by geared motor (5). The cutter rail carrier assembly (6) is preferably moved to and fro in the vertical direction by any kind of motorised mechanism like geared motor (5) or stepper motor or such that a discrete step motion of the cutter rail carrier assembly (6) is achieved such that cutter rail carrier assembly (6) can be positioned at various distances as per the position of the advancing film.

Further, cutter rail (7) comprises of a cutter core (7A) on which set of cutting blades - one blade (7B) corresponding to a single cut to be made in the film - are mounted. Plurality of blade (7B) are set side by side at an equal distance equal to the width of tape to be achieved as shown in figure 1.

As shown in Figure 6, the horizontal frame (3) comprises of guide roller bracket (11) which is attached on the said horizontal frame (3) by a pivot (16) at one end and is connected by a pneumatic cylinder (9) at another end. Guide roller bracket (11) carries at least one set of rollers or preferably guide rollers (12) over which the advancing fdm (1) passes and thereby provides support to the advancing film

(1). A stopper (13) is present to limit the movement of the guide roller bracket

(11) in the upward direction, which can be set manually as per the contact formed by the advancing film (1) with the blade (7B). One such pre-set stopper (13) may be in the form of a linear structural member or a stud mounted on the horizontal frame (3). The pneumatic cylinder (9) facilitates the movement of the guide roller bracket (11) such that the guide rollers (12) carrying the advancing film (1) about pivot (16) while maintaining certain amount of tension in the advancing film (1), can be brought near to or in contact with the blade (7B). Such rotational movement about the pivot (16) can be achieved by any means such as hydraulically actuated means or a linear guide which provide linear motion to the guide roller bracket (11), such linear motion converts to rotational movement by pivot (16).

As shown in figures 2 and 7, positional sensors are present on the vertical frame

(2) as well as horizontal frame (3). These positional sensors determine the position of the cutter rail carrier assembly (6). The position of the cutter rail carrier assembly (6) can also be determined by any of the known sensing methods using proxy sensor, limit switch, potentiometer, laser beam, ultrasonic, infrared, sonar, laser, face shift sensor.

The said working positional sensor (15) is affixed to the horizontal frame (3) whereas top position sensor (17) and service position sensor (18) is affixed to the vertical frame (2).

As soon as the cutter rail carrier assembly (6) come in the vicinity of the working position sensor (15), a machine controller (not shown) commands the geared motor (5) to stop and ensure that the cutter rail carrier assembly (6) is now at the working position (6C). Further, as soon as the cutter carrier assembly (6) comes in the vicinity of the top position sensor (17), the geared motor (5) stops and ensures that the cutter carrier assembly (6) is in the top position (6A). Also, if the cutter carrier assembly (6) comes in the vicinity of the service position sensor (18), the geared motor (5) stops and ensures that the cutter carrier assembly (6) is in the service position (6B).

In another aspect of the invention, the position of the service position sensor (18) can be changed to alter the service position (6B) and stop the cutter carrier assembly (6) as per the operator (19) ease.

In a further aspect of the invention, the cutter carrier assembly (6) can be stopped at a desired height from the service platform (14) manually by a stop command wherein the service position sensor (18) can be bypassed, according to the height and ease of the operator (19).

The method of replacement of cutting rail (7) involve following steps: a. When it is time to change the cutter rail (7), the advancement of advancing film (1) is stopped. b. The cutter rail carrier assembly (6) along with cutter rail (7) moves upwards from its working position (6C) to its top position (6A) until it is, thereby disengaging it from the advancing film (1). c. As soon as the cutter carrier rail assembly (6) is sensed by a top position sensor (17), it is stopped. The upward movement of the cutter rail carrier assembly (6) is done by the geared motor (5). d. The advancing film (1) is then manually removed from the vicinity of the cutter rail carrier assembly (6). e. The guide roller bracket (11) is rotated down around a pivot (16) to take it out from the vicinity of the cutter rail carrier assembly (6). f. The cutter rail carrier assembly (6) moves downwards from its top position (6A) to a service position (6B). g. As soon as the cutter carrier rail assembly (6) is sensed by a service position sensor (18), it is stopped. The downward movement of the cutter rail carrier assembly (6) is done by the geared motor (5). h. The cutter rail (7) is then removed manually from the cutter rail carrier assembly (6) and placed on the service platform (14). i. The replacement cutter rail (7) is placed in the cutter rail carrier assembly

(6). j . The cutter rail carrier assembly (6) is now moved back to its top position (6 A) after replacement of cutter rail (7). k. As soon as the cutter carrier rail assembly (6) is sensed by a top position sensor (17), it is stopped. The upward movement of the cutter rail carrier assembly is done by the geared motor (5). l. The guide roller bracket (11) is rotated back to its working position (6C). m. The advancing film (1) is then passed over the guide rollers (12). n. The cutter rail carrier assembly (6) is lowered to its own working position (6C), until it is sensed by a working position sensor (15) and stops. o. Now the advancement of the film (1) begin to get output as a slit film (1A).

In a preferred aspect of the invention, the service position-2 (6B) may be anywhere from working position of rail carrier assembly (6) to approximately 0.5 meters above the ground level. In particular, it may be at a level at which a pair of operators (19) find it the easiest to remove the cutter rail (7) from the cutter rail carrier assembly (6), and replace it with a new cutter rail. The service position (6B) therefore depends on the ease of operators (19). The system of the invention is capable of determining the actual service position-2 (6B) to suit a particular operator (19) , depending on his height or other safety measures. It is evident from the foregoing description that the invention has a number of embodiments.

In the preferred embodiment, it provides a cutting apparatus having a semi- automatically replaceable cutter rail (7) for cutting an advancing plastic film (1) into slit-film tapes (1A). The characterising aspect of the invention is that, said apparatus comprises: a vertical frame (2) affixed to floor and a horizontal frame (3) affixed to said vertical frame (2) near its top end,

- a vertical guide rail (4) affixed to said vertical frame (2)

- a cutter rail carrier assembly (6) consisting of a cutter rail bracket (10) on which said cutter rail (7) is mounted,

- a geared motor (5) affixed to said vertical frame (2) to cause the up and down movement of said cutter rail carrier assembly (6) which takes place along the vertical guide rail (4),

- a set of guide roller (12) supported on a guide roller bracket (11), said bracket mounted on said horizontal frame (3) and capable of swivelling around a pivot (16).

The cutter rail carrier assembly (6) is capable of moving up and down along the vertical guide rail (4) during replacement operation of said cutter rail (7).

In another embodiment, the cutter rail carrier assembly (6) is positioned at a working position (6C) during its operation to cut said advancing film (1) into slit- film tapes (1A).

In a further embodiment, the up and down movement of the cutter rail carrier assembly (6) is limited between the top position (6A) and the service position (6B). Here, the top position (6A) is a position along said vertical guide rail (4) to which said cutter rail carrier assembly (6) is raised from its working position (6C) while it is being disengaged from the cutting operation, and the service position (6B), being at a variable location from ground, is a position to which said cutter rail assembly (6) is lowered from said top position (6A) for its manual replacement by an operator (19).

In a still further embodiment, the cutting apparatus has a top position sensor (17) mounted on the vertical frame (2) to sense arrival of said cutter rail assembly (6) to the top position (6A), a working position sensor (15) mounted on the horizontal frame (3) to sense arrival of the cutter rail assembly (6) at the working position (6C), and a service position sensor (18) mounted on the vertical frame (2) to sense arrival of the cutter rail assembly (6) at the service position (6B).

In another embodiment of the cutting apparatus the service position (6B) is a position at 0.5 metres above the ground level at which said operator (19) carries out the replacement operation of said cutter rail (7) and is determined by said operator (19).

In one more embodiment of the cutting apparatus, the swivelling movement of the bracket (11) around said pivot (16) is enabled by a pneumatic cylinder (9) mounted on said horizontal frame (2).

In the preferred embodiment of the invention, the semi-automated method of replacing a cutter rail (7) provided on a cutting apparatus uses the apparatus as described in foregoing paragraphs for cutting an advancing plastic film (1) into slit-film tapes (1A). The characterising aspects of the method comprise the following steps: a. stopping the advancement of the advancing film (1); b. disengaging the cutter rail (7) from the advancing film by moving the cutter rail carrier assembly (6) upward to the top position (6A), and stopping said cutter rail carrier assembly (6) at that position, c. manually removing the advancing film (1) from its operating path and out of the way of the downward path of the cutter rail carrier assembly (6), d. rotating downward the bracket (11) for guide roller around the pivot (16), e. moving the cutter rail carrier assembly (6) downwards from its top position (6A) to a service position (6B) and stopping said cutter rail carrier assembly (6) at that position, f. removing the blunt cutter rail (7) from the cutter rail carrier assembly (6), g. moving the cutter rail carrier assembly (6) to the top position (6A) and stopping said cutter rail carrier assembly (6) at that position, h. rotating the guide roller bracket (11) up around the pivot (16) to its working position, i. setting the film back to its working position (6C) by passing it over guide rollers (12) and into the path of the cutter rail (7), j . lowering the cutter rail carrier assembly (6) to its working position (6C) and stopping said cutter rail carrier assembly (6) at that position so as to produce slit film.

In an embodiment of the aforementioned method, the upward movement of steps b and g, and the downward movement of step e of said cutter rail assembly (6) are carried out by a geared motor (5).

In a further embodiment of the method, the rotational movement of the bracket (11) is carried out by a piston attached to the pneumatic cylinder (9). In another embodiment of the method, the stoppage of said cutter rail carrier assembly in steps b, e, g, and j is carried out upon a signal sent by respective sensors that sense the arrival of said cutter rail carrier assembly (6) at respective positions. In yet another embodiment of the method, the service position (6B) is a position from ground level at which said operator (19) carries out the replacement operation of said cutter rail (7) and is determined by said operator (19). In still another embodiment of the method, the service position (6B) is variable in its location from ground.

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.

Claims

Claims:

1. A cutting apparatus having a semi -automatically replaceable cutter rail (7) for cutting an advancing plastic film (1) into slit-film tapes (1A), characterised in that said apparatus comprises: a vertical frame (2) affixed to floor and a horizontal frame (3) affixed to said vertical frame (2) near its top end, a vertical guide rail (4) affixed to said vertical frame (2) a cutter rail carrier assembly (6) consisting of a cutter rail bracket (10) on which said cutter rail (7) is mounted, a geared motor (5) affixed to said vertical frame (2) to cause the up and down movement of said cutter rail carrier assembly (6) on said vertical guide rail (4), a set of guide roller (12) supported on a guide roller bracket (11), said bracket mounted on said horizontal frame (3) and capable of swivelling around a pivot (16), wherein said cutter rail carrier assembly (6) is capable of moving up and down along said vertical guide rail (4) during replacement operation of said cutter rail (7).

2. The cutting apparatus as claimed in claim 1, wherein said cutter rail carrier assembly (6) is positioned at a working position (6C) during its operation to cut said advancing film (1) into slit-film tapes (1A).

3. The cutting apparatus as claimed in claim 1, wherein said up and down movement of cutter rail carrier assembly (6) is limited between a top position (6A) and a service position (6B).

4. The cutting rail assembly as claimed in claim 2, wherein said top position (6A) is a position along said vertical guide rail (4) to which said cutter rail carrier assembly (6) is raised from its working position (6C) while it is being disengaged from the cutting operation, and said service position (6B) is a position to which said cutter rail assembly (6) is lowered from said top position (6A) for replacement of said cutter rail (7).

5. The cutting rail assembly as claimed in claim 4, wherein said replacement of said cutter rail (7) is carried out manually by an operator (19).

6. The cutting apparatus as claimed in claims 1 to 5, wherein said apparatus has positional sensors to sense the position of said cutter rail carrier assembly (6) during said up and down movement along said vertical guide rail (4).

7. The cutting apparatus as claimed in claims 3 to 5, wherein said service position (6B) is variable in its location from ground.

8. The cutting apparatus as claimed in claims 1 to 7, wherein a top position sensor (17) is mounted on said vertical frame (2) to sense arrival of said cutter rail assembly (6) to said top position (6A), a working position sensor (15) is mounted on said horizontal frame (3) to sense arrival of said cutter rail assembly (6) at said working position (6C), and a service position sensor (18) is mounted on said vertical frame (2) to sense arrival of said cutter rail assembly (6) at said service position (6B).

9. The cutting apparatus as claimed in claims 3 to 8, wherein said service position (6B) is a position from ground level at which said operator (19) carries out the replacement operation of said cutter rail (7) and is determined by said operator (19).

10. The cutting apparatus as claimed in claims 1 to 9, wherein said swivelling movement of said bracket (11) around said pivot (16) is enabled by a pneumatic cylinder (9) mounted on said horizontal frame (2).

11. The cutting apparatus as claimed in claims 8 to 10, wherein said sensors (15, 17, and 18) are selected from any of the types comprising proxy sensor, limit switch, potentiometer type, laser beam type, ultrasonic, infrared, sonar, laser, face shift sensor.

12. A semi -automated method of replacing a cutter rail (7) provided on a cutting apparatus as claimed in claims 1 to 12 for cutting an advancing plastic film (1) into slit-film tapes (1A), characterised in that said method comprises the steps of: a. stopping the advancement of said advancing film (1); b. disengaging the cutter rail (7) from the advancing film by moving the cutter rail carrier assembly (6) upward to the top position (6A), and stopping said cutter rail carrier assembly (6) at that position, c. manually removing the advancing film (1) from its operating path and out of the way of the downward path of the cutter rail carrier assembly (6), d. rotating downward the bracket (11) for guide roller about the pivot

(16), e. moving the cutter rail carrier assembly (6) downwards from its top position (6A) to a service position (6B) and stopping said cutter rail carrier assembly (6) at that position, f. removing the cutter rail (7) from the cutter rail carrier assembly (6) by an operator (19), g. moving the cutter rail carrier assembly (6) to the top position (6A) and stopping said cutter rail carrier assembly (6) at that position, h. rotating the guide roller bracket (11) to its working position, i. setting the film back to its working position (6C) by passing it over guide rollers (12) and into the path of the cutter rail (7), j . lowering the cutter rail carrier assembly (6) to its working position (6C) and stopping said cutter rail carrier assembly (6) at that position.

13. The method as claimed in claim 12, wherein the upward movement of steps b and g, and the downward movement of step e of said cutter rail assembly are carried out by a geared motor (5).

14. The method as claimed in claims 12 and 13, wherein the rotational movement of the bracket (11) is carried out by a piston attached to the pneumatic cylinder (9).

15. The method as claimed in claim 112, wherein the stoppage of said cutter rail carrier assembly in steps b, e, g, and j is carried out upon a signal sent by respective sensors that sense the arrival of said cutter rail carrier assembly (6) at respective positions.

16. The method as claimed in claims 12 to 15, wherein said service position (6B) is a position from ground level at which said operator (19) carries out the replacement operation of said cutter rail (7) and is determined by said operator (19).

17. The method as claimed in claims 12 to 16, wherein said service position (6B) is variable in its location from ground.