WEB CONVEYING APPARATUS WITH BRAKE

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2017-190228, filed on Sep. 29, 2017, the entire contents of which are incorporated herein by reference.

BACKGROUND
1. Technical Field

The disclosure relates to a conveying apparatus for conveying a web.

2. Related Art

Japanese Patent Application Publication No. 2011-79651 describes a printing apparatus that conveys a long-length web as a print medium while printing images on the web.

As such printing apparatuses, there are ones that convey a web, unwinding it from the web roll, which is the web rolled in a roll shape, while applying brakes to the rotation of the web roll, and eject ink from the inkjet head to print images on the web. Those printing apparatuses give the web appropriate tension for obtaining favorable print image quality by applying brakes to the rotation of the web roll.

SUMMARY

In the above printing apparatuses, during deceleration at the end of conveyance of the web, the inertia sometimes makes the rotation speed of the web roll high as compared with the conveyance speed of the web, which causes slack in the web. When slack occurs in the web, the web may come into contact with the inkjet head and damage it.

The disclosure is directed to a conveying apparatus capable of preventing slack in the web.

A conveying apparatus in accordance with some embodiments includes: a conveyor configured to convey a web while unwinding the web from a web roll; a brake configured to apply brakes to rotation of the web roll; and a controller configured to perform control to unwind the web from the web roll and convey the web with the conveyor while giving tension to the web by applying brakes to the rotation of the web roll using torque of the brake. The controller is configured to determine the torque of the brake during deceleration of the web to be a value depending on an inertial load of the web roll.

The configuration above makes it possible to prevent slack in the web.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a printing apparatus according to a first embodiment.

FIG. 2 is a control block diagram of the printing apparatus illustrated in FIG. 1.

FIG. 3 is a flowchart for explaining operation of the printing apparatus.

FIG. 4A is a diagram illustrating transition of the conveyance speed of the web.

FIG. 4B is a diagram illustrating transition of the roll diameter during conveyance of the web.

FIG. 4C is a diagram illustrating transition of the torque of a brake in the first embodiment.

FIG. 5 is a diagram illustrating an example of the relationships in the normal stop mode between the roll diameter at the time of starting deceleration of the web and the torque of the brake in accordance with the roll diameter at the time of starting the deceleration of the web, the magnitude of the inertial load of the web roll, and the torque of the brake in which the inertial load of the web roll is taken into account.

FIG. 6 is a diagram illustrating an example of the relationships in the emergency stop mode between the roll diameter at the time of starting deceleration of the web and the torque of the brake in accordance with the roll diameter at the time of starting the deceleration of the web, the magnitude of the inertial load of the web roll, and the torque of the brake in which the inertial load of the web roll is taken into account.

FIG. 7A is a diagram illustrating transition of the conveyance speed of the web.

FIG. 7B is a diagram illustrating transition of the roll diameter during conveyance of the web.

FIG. 7C is a diagram illustrating transition of the torque of a brake in the second embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

Description will be hereinbelow provided for embodiments of the present invention by referring to the drawings. It should be noted that the same or similar parts and components throughout the drawings will be denoted by the same or similar reference signs, and that descriptions for such parts and components will be omitted or simplified. In addition, it should be noted that the drawings are schematic and therefore different from the actual ones.

FIG. 1 is a schematic configuration diagram illustrating a printing apparatus 1 including a conveying apparatus according to a first embodiment of the disclosure. FIG. 2 is a control block diagram of the printing apparatus 1 illustrated in FIG. 1. Note that the upward, downward, right, and left directions in the following description are the same as those on the paper surface of FIG. 1. In addition, the direction orthogonal to the paper surface of FIG. 1 is defined as the front-rear direction. In FIG. 1, the right direction, left direction, upward direction, and downward direction are indicated by RT, LT, UP, and DN, respectively.

As illustrated in FIGS. 1 and 2, the printing apparatus 1 according to the first embodiment includes a web roll holder 2, a conveyor 3, printers 4A and 4B, a rewinder 5, and a controller 6. The web roll holder 2, the conveyor 3, and the controller 6 are included in the conveying apparatus.

The web roll holder 2 holds a web roll 7. The web roll 7 is a web W, which is a long-length print medium such as paper or film, rolled in a roll shape. The web roll holder 2 includes a web-roll supporting shaft 11, guide roller 12, brake 13, brake driver 14, speed reducer 15, and encoder 16.

The web-roll supporting shaft 11 rotatably supports the web roll 7.

The guide roller 12 guides the web W between the web roll 7 and a guide roller 21 of the conveyor 3 described later. The guide roller 12 is rotated by the web W being conveyed.

The brake 13 applies brakes to the rotation of the web-roll supporting shaft 11 to apply brakes to the rotation of the web roll 7. The brake 13 is constituted of a powder brake.

The brake driver 14 drives the brake 13.

The speed reducer 15 transmits the rotation of the web-roll supporting shaft 11 to the output shaft of the brake 13 at a specified speed reduction ratio.

The encoder 16 outputs a pulse signal at every specified rotation angle of the web-roll supporting shaft 11 (web roll 7).

The conveyor 3 unwinds the web W from the web roll 7 while conveying it. The conveyor 3 includes guide rollers 21 to 30, twenty under-head rollers 31, a meandering controller 32, a pair of conveying rollers 33, a conveying motor 34, a motor driver 35, a speed reducer 36, and an encoder 37.

The guide rollers 21 and 22 guide the web W between the web roll 7 and the meandering controller 32. The guide roller 21 is disposed at a left end of the lower portion of the conveyor 3. The guide roller 22 is disposed between the guide roller 21 and a meandering control roller 38 of the meandering controller 32 described later. The guide rollers 21 and 22 are rotated by the web W being conveyed.

The guide roller 23 to 29 guides the web W between the meandering controller 32 and the conveying rollers 33. The guide roller 23 is disposed slightly above the left side of a meandering control roller 39 of the meandering controller 32 described later. The guide roller 24 is disposed above the guide roller 23. The guide roller 25 is disposed at the same height as the guide roller 24 and on the right side of the guide roller 24. The guide roller 26 is disposed at a position below the guide roller 25 and higher than the guide roller 23. The guide roller 27 is disposed at a position on the left side of the guide roller 26, near the right side of the web W between the guide rollers 23 and 24, and at almost the same height as the guide roller 26. The guide roller 28 is disposed on the lower right side of the guide roller 27. The guide roller 29 is disposed below the guide roller 28 and slightly on the right side of the guide roller 28. The guide rollers 23 to 29 are rotated by the web W being conveyed.

The guide roller 30 guides the web W between the conveying rollers 33 and the rewinder 5. The guide roller 30 is disposed at a right end of the lower portion of the conveyor 3. The guide roller 30 is rotated by the web W being conveyed.

The under-head rollers 31 support the web W under head units 41 described later, between the guide rollers 24 and 25 and between the guide rollers 26 and 27. Ten under-head rollers 31 are disposed between the guide rollers 24 and 25; and ten, between the guide rollers 26 and 27. Two under-head rollers 31 are disposed immediately under each head unit 41. The under-head rollers 31 are rotated by the web W being conveyed.

The meandering controller 32 corrects meandering of the web W, which is fluctuation of the position in the width direction (front-rear direction) of the web W. The meandering controller 32 includes the meandering control rollers 38 and 39.

The meandering control rollers 38 and 39 are rollers for correcting the meandering of the web W while guiding the web W. The meandering control rollers 38 and 39 are rotated by the web W being conveyed. The meandering control rollers 38 and 39 are turned, by an unillustrated motor, and inclined relative to the width direction of the web W as viewed from the right-left direction to move the web W in the width direction to correct the meandering. The meandering control roller 38 is disposed on the right side of the guide roller 22. The meandering control roller 39 is disposed above the meandering control roller 38.

The pair of conveying rollers 33 nips the web W and conveys the web W toward the rewinder 5. One conveying roller 33 of the pair of conveying rollers 33 is rotationally driven by the conveying motor 34, and the other conveying roller 33 is rotated by the one conveying roller 33. The pair of conveying rollers 33 is disposed between the guide rollers 29 and 30.

The conveying motor 34 rotationally drives the one conveying roller 33 of the pair of conveying rollers 33.

The motor driver 35 drives the conveying motor 34.

The speed reducer 36 transmits the rotation of the output shaft of the conveying motor 34 to the one conveying roller 33 at a specified speed reduction ratio.

The encoder 37 outputs a pulse signal at every specified rotation angle of the output shaft of the conveying motor 34.

The printers 4A and 4B print images on the front surface and the back surface of the web W, respectively. The printer 4A is disposed above and near the web W between the guide rollers 24 and 25. The printer 4B is disposed above and near the web W between the guide rollers 26 and 27. The printers 4A and 4B each include five head units 41.

The head unit 41, having an inkjet head (not illustrated), prints images by ejecting ink to the web W through the nozzle of the inkjet head. In each of the printers 4A and 4B, the five head units 41 eject inks of different colors.

The rewinder 5 rewinds the web W subjected to printing by the printers 4A and 4B. The rewinder 5 includes a buffer 46, a brake roller 47, a brake 48, a brake driver 49, a rewinding shaft 50, a rewinding motor 51, a motor driver 52, and speed reducers 53 and 54.

The buffer 46 holds slack of the web W between the guide roller 30 of the conveyor 3 and the brake roller 47. The buffer 46 includes support rollers 56 and 57, and a dancer roller 58.

The support rollers 56 and 57 support the web W between the guide roller 30 and the brake roller 47. The support rollers 56 and 57 are apart from each other in the right-left direction and deposed at the same height. The support rollers 56 and 57 are rotated by the web W being conveyed.

The dancer roller 58 pushes down the web W between the support rollers 56 and 57 by its own weight. With this operation, the slack of the web W between the guide roller 30 and the brake roller 47 is absorbed by the buffer 46. The dancer roller 58 moves up and down by fluctuation of the slack amount of the web W between the guide roller 30 and the brake roller 47.

The brake roller 47 applies brakes to the web W being wound by the rewinding shaft 50. The brake roller 47 is rotated by the web W being wound by the rewinding shaft 50.

The brake 48 applies brakes to the web W via the brake roller 47 to give tension to the web W being wound by the rewinding shaft 50. This operation prevents wrinkles or the like from occurring in the web W being wound by the rewinding shaft 50.

The brake driver 49 drives the brake 48.

The rewinding shaft 50 winds the web W and holds it.

The rewinding motor 51 rotates the rewinding shaft 50 in the clockwise direction in FIG. 1. The rotation of the rewinding shaft 50 winds the web W on the rewinding shaft 50.

The motor driver 52 drives the rewinding motor 51.

The speed reducer 53 transmits the rotation of the brake roller 47 to the output shaft of the brake 48 at a specified speed reduction ratio. The speed reducer 54 transmits the rotation of the output shaft of the rewinding motor 51 to the rewinding shaft 50 at a specified speed reduction ratio.

The controller 6 controls operation of each section of the printing apparatus 1. The controller 6 is constituted of a programmable logic controller (PLC) or the like and includes a CPU and a memory.

In printing, the controller 6 performs control to unwind the web W from the web roll 7 and convey it with the conveyor 3 while applying brakes to the rotation of the web roll 7 using the torque of the brake 13 to give tension to the web W, and then wind the web W with the rewinder 5. The controller 6 makes the head units 41 of the printers 4A and 4B eject ink to print images on the web W being conveyed.

During deceleration at the end of conveyance of the web W for printing, the controller 6 performs control to set the torque of the brake 13 to a torque in which the inertial load of the web roll 7 is taken into account.

Next, operation of the printing apparatus 1 will be described.

FIG. 3 is a flowchart for explaining operation of the printing apparatus 1. FIG. 4A is a diagram illustrating transition of the conveyance speed of the web W driven by the conveyor 3. FIG. 4B is a diagram illustrating transition of the roll diameter Dr, which is the diameter of the web roll 7. FIG. 4C is a diagram illustrating transition of the torque of the brake 13 in the first embodiment.

When a print job is inputted, the controller 6 starts driving the conveyor 3 and the rewinder 5 to start conveyance of the web W for roll diameter calculation at step S1 in FIG. 3.

When starting the conveyance of the web W for roll diameter calculation, the controller 6 increases the conveyance speed of the web W driven by the conveying rollers 33 at a specified acceleration from time t1, which is the time when the conveyance starts, as illustrated in FIG. 4A.

After the controller 6 starts the conveyance of the web W, the conveyance speed of the web W driven by the conveying rollers 33 reaches a specified roll-diameter calculation conveyance speed Uc at time t2, at which the controller 6 makes the conveying rollers 33 start constant-speed conveyance of the web W at the roll-diameter calculation conveyance speed Uc.

The controller 6 drives and controls the conveying motor 34 via the motor driver 35 based on the conveyance speed of the web W calculated from the output pulse signal of the encoder 37 to control the conveyance speed of the web W driven by the conveying rollers 33.

The foregoing roll-diameter calculation conveyance speed Uc has been set in advance as the conveyance speed for conveying the web W for roll diameter calculation. The roll-diameter calculation conveyance speed Uc is set lower than the print conveyance speed Um, which is conveyance speed of the web W for printing.

After starting the constant-speed conveyance at the roll-diameter calculation conveyance speed Uc, the controller 6 calculates the roll diameter Dr at step S2 in FIG. 3.

The roll diameter Dr is calculated by the following formula (1), where U is the conveyance speed of the web W driven by the conveying rollers 33 and N is the rotation speed of the web roll 7.

Dr=U/(N×π) (1)

Here, Drs is the roll diameter during conveyance of the web W at the roll-diameter calculation conveyance speed Uc. At step S2, to calculate the roll diameter Drs, the controller 6 calculates the rotation speed Ns of the web roll 7 based on the output pulse signal of the encoder 16. Then, the controller 6 calculates the roll diameter Drs by substituting the calculated rotation speed Ns and the roll-diameter calculation conveyance speed Uc for N and U, respectively, in formula (1).

After finishing calculating the roll diameter Drs, the controller 6, at step S3 in FIG. 3, sets the torque of the brake 13 by switching it from an initial value τ0 to a torque τcs suitable for the roll diameter Drs (time t3).

Here, assuming that Tsb is a set tension of the web W in the printing apparatus 1, and that G is the speed reduction ratio of the speed reducer 15 connected to the brake 13, the torque τc of the brake 13 corresponding to the set tension Tsb is expressed by the following formula (2).

τc=Tsb×Dr/(2×G) (2)

The torque τcs suitable for the roll diameter Drs, calculated at step S2 is calculated by substituting Drs for Dr in formula (2).

Here, to control the brake 13, the controller 6 supplies voltage to the brake driver 14. The brake driver 14 converts the voltage into current and supplies the current to the brake 13. The brake 13 generates torque in accordance with the supplied current.

Assuming that Ic is current to cause the brake 13 to generate the torque τc corresponding the set tension Tsb, the relationship between τc and Ic is expressed by the following formula (3).

τc=a×Ic³+b×Ic²+c×Ic+d (3)

Here, a, b, c, and d are coefficients that are determined by the characteristics of the brake 13, which is a powder brake.

Assuming that Vc is the voltage converted into the current Ic by the brake driver 14, the relationship between Ic and Vc is expressed by the following formula (4).

Ic=Vc/Re (4)

Here, Re is a resistance value of a circuit that converts the voltage into the current, included in the brake driver 14.

Obtained from formulae (2) to (4) is the following formula (5).

Tsb=Ka×Vc
³
+Kb×Vc
²
+Kc×Vc+Kd (5)

Here, Ka to Kd are respectively expressed by the following formulae (6) to (9).

Ka=2×a×G/(Dr×Re³) (6)

Kb=2×b×G/(Dr×Re²) (7)

Kc=2×c×G/(Dr×Re) (8)

Kd=2×d×G/Dr (9)

The voltage Vc supplied to the brake driver 14 to set the torque of the brake 13 to the torque τc is obtained by solving formula (5) for Vc.

Accordingly, assuming that Vcs is a voltage supplied to the brake driver 14 for setting the torque of the brake 13 to the torque τcs suitable for the roll diameter Drs calculated at step S2, Vcs is determined by first obtaining Ka to Kd by substituting Drs for Dr in formulae (6) to (9) and then solving for Vcs formula (5) in which the obtained Ka to Kd are applied and Vcs is substituted for Vc.

After setting the torque of the brake 13 to the torque τcs suitable for the roll diameter Drs, the controller 6, at step S4 in FIG. 3, finishes the conveyance of the web W for roll diameter calculation.

Specifically, as illustrated in FIG. 4A, the controller 6 starts reducing the conveyance speed of the web W driven by the conveying rollers 33 at time t4, which is a time after time t3 when the torque of the brake 13 was set to the torque τcs, and stops conveying the web W at time t5. In addition, the controller 6 stops driving the rewinder 5.

Next, at step S5 in FIG. 3, the controller 6 starts driving the conveyor 3 and the rewinder 5 and starts the conveyance of the web W for printing.

When starting the conveyance of the web W for printing, the controller 6 increases the conveyance speed of the web W driven by the conveying rollers 33 at a specified acceleration from time t6, which is the time when the conveyance starts, as illustrated in FIG. 4A.

After the conveyance of the web W is started, the conveyance speed of the web W driven by the conveying rollers 33 reaches a specified print conveyance speed Um at time t7, at which the controller 6 makes the conveying rollers 33 start constant-speed conveyance of the web W at the print conveyance speed Um.

After starting the constant-speed conveyance of the web W at the print conveyance speed Um, the controller 6 starts printing with the printers 4A and 4B based on the print job at step S6 in FIG. 3.

Here, when the constant-speed conveyance of the web W at the print conveyance speed Um is started (time t7), the reduction amount of the roll diameter Dr from the time when the conveyance of the web W for roll diameter calculation is started (time t1) is small. In other words, the roll diameter Dr is almost constant until the time when the constant-speed conveyance of the web W at the print conveyance speed Um is started, as illustrated in FIG. 4B. Accordingly, as illustrated in FIG. 4C, the torque of the brake 13 remains set to the torque τcs suitable for the roll diameter Drs calculated during the conveyance of the web W for roll diameter calculation until the time when the constant-speed conveyance of the web W at the print conveyance speed Um is started.

However, as time passes from the start of the conveyance of the web W, the roll diameter Dr gradually decreases. To address this, the controller 6 calculates the roll diameter Dr in real time and sets the torque of the brake 13 to the torque τc in accordance with the calculation result in real time during the constant-speed conveyance of the web W at the print conveyance speed Um. With this operation, the tension of the web W is kept constant at the set tension Tsb.

Specifically, the controller 6 calculates the rotation speed N of the web roll 7 in real time based on the output pulse signal of the encoder 16 and calculates the roll diameter Dr in accordance with the rotation speed N based on the formula (1), substituting the print conveyance speed Um for U in the foregoing formula (1). Then, the controller 6 calculates the torque τc suitable for the roll diameter Dr using the foregoing formula (2) and sets the torque of the brake 13 to the torque τC. The voltage Vc supplied to the brake driver 14 to set the torque of the brake 13 to the torque τc is obtained by solving the formula (5) for Vc, as described above.

Returning to FIG. 3, the controller 6 determines at step S7 whether an emergency stop command has been inputted. Here, the emergency stop command is one that is inputted to the controller 6 in the case where the user presses an emergency stop button (not illustrated) or where an emergency stop switch (not illustrated) turns on due to a user's erroneous operation on the printing apparatus 1.

If the controller 6 determines that the emergency stop command has not been inputted (NO at step S7), the controller 6 determines at step S8 whether the printers 4A and 4B have finished printing based on the print job. If the controller 6 determines that the printing has not finished (NO at step S8), the controller 6 returns to step S7.

If the controller 6 determines that the printing has finished (YES at step S8), the controller 6 finishes conveying the web W with conveyance stop operation in a normal stop mode at step S9. The normal stop mode is a stop mode in which conveyance stop operation is performed such that the time taken for the web W to stop from the print conveyance speed Um is a specified normal deceleration time Sn.

Specifically, as illustrated in FIG. 4A, the controller 6 reduces the conveyance speed of the web W driven by the conveying rollers 33 at an acceleration to reduce speed for the normal stop mode from time t10, which is the time when the printers 4A and 4B finish printing. Then, the controller 6 stops the conveyance of the web W driven by the conveying rollers 33 at time t11, which is the time when the normal deceleration time Sn has passed after time t10. Here, the acceleration to reduce speed for the normal stop mode is set to a value at which the conveyance speed of the web W becomes zero when the normal deceleration time Sn passes after the start of deceleration from the print conveyance speed Um.

Along with the reduction of the conveyance speed of the web W driven by the conveying rollers 33 and the stoppage of the conveyance, the controller 6 makes the rewinder 5 reduce the rewind speed of the web W and stop rewinding.

In the conveyance stop operation in the normal stop mode, the controller 6 sets the torque of the brake 13 during deceleration of the web W to a torque τdn in which the inertial load Tan of the web roll 7 in accordance with the normal deceleration time Sn is taken into account, as illustrated in FIG. 4C.

Here, the inertial load Ta of the web roll 7 during deceleration from the print conveyance speed Um to the stoppage of the web W is the product of J, which is the moment of inertia of the web roll 7, and a, which is the angular acceleration of the web roll 7 from the print conveyance speed Um to the stoppage of the web W. In other words, the inertial load Ta is expressed by the following formula (10).

Ta=J×α (10)

Assuming that M is the mass of the web roll 7, and that the web roll 7 has a cylindrical shape, the moment of inertia J of the web roll 7 is expressed by the following formula (11).

J=M×Dr
²/8 (11)

The mass M of the web roll 7 is expressed by the following formula (12).

M=(Dr²−Dc²)×π×Wa×B/(4×H) (12)

Here, Dc is the diameter of the hollow core of the web roll 7. Wa is the width of the web W (the length of the web roll 7). B is the basis weight of the web W. H is the thickness of the web W.

The angular acceleration a of the web roll 7 from the print conveyance speed Um to the stoppage of the web W is expressed by the following formula (13).

α=−2×Um/(Dr×S×G) (13)

Here, S is the deceleration time, which is the time taken for the web W to stop from the print conveyance speed Um.

Using formulae (10) to (13), the inertial load Ta of the web roll 7 is expressed by the following formula (14).

$\begin{matrix} Ta = - \frac{({Dr}^{2} - {Dc}^{2}) \times π \times Wa \times B \times Dr \times Um}{16 \times H \times S \times G} & (14) \end{matrix}$

The inertial load Tan of the web roll 7 in accordance with the normal deceleration time Sn is calculated by substituting the roll diameter Dre at the time of the start of deceleration (time t10) from the print conveyance speed Um in the normal stop mode and the normal deceleration time Sn for Dr and S in formula (14), respectively.

The torque τdn in which the inertial load Tan of the web roll 7 in accordance with the normal deceleration time Sn in the normal stop mode is calculated using the following formula (15).

$\begin{matrix} \begin{matrix} τ dn = \langle Tan \rangle + τ ce \\ = \frac{({Dre}^{2} - {Dc}^{2}) \times π \times Wa \times B \times Dre \times Um}{16 \times H \times Sn \times G} + τ ce \end{matrix} & (15) \end{matrix}$

Here, as illustrated in FIG. 4C, τce is the torque of the brake 13 in accordance with the roll diameter Dre at the time of the deceleration start (time t10) from the print conveyance speed Um in the normal stop mode.

In other words, τdn is what is obtained by adding the magnitude (absolute value) of the inertial load Tan of the web roll 7 in accordance with the normal deceleration time Sn to the torque τce in accordance with the roll diameter Dre at the start time of deceleration from the print conveyance speed Um in the normal stop mode.

Assuming that Vce is the voltage supplied to the brake driver 14 to set the torque of the brake 13 to τce, Vce is determined by first obtaining Ka to Kd by substituting Dre for Dr in formulae (6) to (9) and then solving for Vce formula (5) in which the obtained Ka to Kd are applied and Vce is substituted for Vc.

Assuming that Icn is a current to cause the brake 13 to generate τdn, substituting τdn for τc and substituting Icn for Ic in the foregoing formula (3) yields the following formula (16).

τdn=a×Icn³+b×Icn²+c×Icn+d (16)

Icn is calculated by solving formula (16) for Icn.

Then, using the following formula (17), the voltage Vcn supplied to the brake driver 14 to set the torque of the brake 13 to τdn is obtained.

Vcn=Re×Icn (17)

The controller 6 changes the torque of the brake 13 from τce to τdn by changing the output voltage for the brake driver 14 from Vce to Vcn at the time of the deceleration start (time t10) from the print conveyance speed Um in the normal stop mode. Through the above operation, the torque of the brake 13 is set to the torque τdn in which the inertial load (torque for deceleration) Tan of the web roll 7 in the normal stop mode is taken into account.

Returning to FIG. 3, if the controller 6 determines at step S7 that the emergency stop command has been inputted (YES at step S7), the controller 6 finishes the conveyance of the web W with the conveyance stop operation in the emergency stop mode at step S10. The emergency stop mode is a stop mode in which conveyance stop operation is performed such that the time taken for the web W to stop from the print conveyance speed Um is an emergency stop deceleration time Sp, which is shorter than the normal deceleration time Sn.

Specifically, as illustrated in FIG. 4A, the controller 6 reduces the conveyance speed of the web W driven by the conveying rollers 33 at an acceleration to reduce speed for the emergency stop mode from time t8, which is a time after the emergency stop command is inputted. Then, the controller 6 stops the conveyance of the web W driven by the conveying rollers 33 at time t9, which is the time when the emergency stop deceleration time Sp has passed after time t8. Here, the acceleration to reduce speed for the emergency stop mode is set to a value at which the conveyance speed of the web W becomes zero when the emergency stop deceleration time Sp passes after the start of deceleration from the print conveyance speed Um.

In the conveyance stop operation in the emergency stop mode, the controller 6 sets the torque of the brake 13 during deceleration of the web W to a torque τdp in which the inertial load (torque for deceleration) Tap of the web roll 7 in accordance with the emergency stop deceleration time Sp is taken into account, as illustrated in FIG. 4C.

The inertial load Tap of the web roll 7 in accordance with the emergency stop deceleration time Sp is calculated by substituting the roll diameter Drf at the time of the start of deceleration (time t8) from the print conveyance speed Um in the emergency stop mode and the emergency stop deceleration time Sp for Dr and S in formula (14), respectively.

The torque τdp in which the inertial load Tap of the web roll 7 in accordance with the emergency stop deceleration time Sp in the emergency stop mode is calculated using the following formula (18).

$\begin{matrix} \begin{matrix} τ dp = \langle Tap \rangle + τ cf \\ = \frac{({Drf}^{2} - {Dc}^{2}) \times π \times Wa \times B \times Drf \times Um}{16 \times H \times Sp \times G} + τ cf \end{matrix} & (18) \end{matrix}$

Here, as illustrated in FIG. 4C, τcf is the torque of the brake 13 in accordance with the roll diameter Drf at the time of the deceleration start (time t8) from the print conveyance speed Um in the emergency stop mode.

In other words, τdp is what is obtained by adding the magnitude (absolute value) of the inertial load Tap of the web roll 7 in accordance with the emergency stop deceleration time Sp to the torque τcf in accordance with the roll diameter Drf at the start time of deceleration from the print conveyance speed Um in the emergency stop mode.

Assuming that Vcf is the voltage supplied to the brake driver 14 to set the torque of the brake 13 to τcf, Vcf is determined by first obtaining Ka to Kd by substituting Drf for Dr in formulae (6) to (9) and then solving for Vcf formula (5) in which the obtained Ka to Kd are applied and Vcf is substituted for Vc.

Assuming that Icp is a current to cause the brake 13 to generate τdp, substituting τdp for τc and substituting Icp for Ic in the foregoing formula (3) yields the following formula (19).

τdp=a×Icp³+b×Icp²+c×Icp+d (19)

Icp is calculated by solving formula (19) for Icp.

Then, using the following formula (20), the voltage Vcp supplied to the brake driver 14 to set the torque of the brake 13 to τdp is obtained.

Vcp=Re×Icp (20)

The controller 6 changes the torque of the brake 13 from τcf to τdp by changing the output voltage for the brake driver 14 from Vcf to Vcp at the time of the deceleration start (time t8) from the print conveyance speed Um in the emergency stop mode. Through the above operation, the torque of the brake 13 is set to the torque τdp in which the inertial load Tap of the web roll 7 in the emergency stop mode is taken into account.

Here, FIG. 5 illustrates an example of the relationships in the normal stop mode between the roll diameter Dre at the time of starting deceleration of the web W and the torque τce of the brake 13 in accordance with the roll diameter Dre at the time of starting the deceleration of the web W, the magnitude (|Tan|) of the inertial load (torque for deceleration) Tan of the web roll 7, and the torque τdn of the brake 13 in which the inertial load Tan of the web roll 7 is taken into account.

FIG. 6 illustrates an example of the relationships in the emergency stop mode between the roll diameter Drf at the time of starting deceleration of the web W and the torque τcf of the brake 13 in accordance with the roll diameter Drf at the time of starting the deceleration of the web W, the magnitude (|Tap|) of the inertial load (torque for deceleration) Tap of the web roll 7, and the torque τdp of the brake 13 in which the inertial load Tap of the web roll 7 is taken into account.

As FIGS. 5 and 6 illustrate, if the roll diameters are the same, the inertial load of the web roll 7 in the emergency stop mode is larger than that in the normal stop mode, and the torque of the brake 13 in which the inertial load of the web roll 7 is taken into account in the emergency stop mode is also larger than that in the normal stop mode. This is because the emergency stop deceleration time Sp is shorter than the normal deceleration time Sn, and the acceleration to reduce speed during the conveyance stop operation in the emergency stop mode is larger than that in the normal stop mode.

When the conveyance of the web W is stopped with the conveyance stop operation at step S9 or S10 in FIG. 3, a series of operations ends.

As described above, in the printing apparatus 1, the controller 6 sets the torque of brake 13 to the torque in which the inertial load of the web roll 7 is taken into account during deceleration at the end of conveyance of the web for printing. This operation prevents the web roll 7 from rotating fast compared with the conveyance speed of the web W due to the inertia of the web roll 7 during deceleration of the web W. Consequently, this operation prevents slack of the web W.

In addition, in the stop operation of conveying the web W in the normal stop mode and the emergency stop mode, the printing apparatus 1 sets the torque of the brake 13 during deceleration of the web W to a torque in which the inertial load of the web roll 7 in accordance with the normal deceleration time Sn or the emergency stop deceleration time Sp is taken into account, respectively. With this operation, even in the emergency stop mode, in which the inertial load of the web roll 7 is large due to the short conveyance stop operation, the torque of the brake 13 is set to a torque in accordance with the inertial load, which prevents slack of the web W.

Next, description will be provided for a second embodiment configured by changing a part of the first embodiment.

The general configuration of a printing apparatus 1A according to the second embodiment is the same as that of the printing apparatus 1 according to the first embodiment illustrated in FIGS. 1 and 2.

The second embodiment is different from the first embodiment in that when the torque of the brake 13 is changed to be set to a torque in which the inertial load of the web roll 7 is taken into account at the deceleration at the end of conveyance of the web for printing, the torque of the brake 13 is gradually changed.

FIG. 7A is a diagram illustrating transition of the conveyance speed of the web W driven by the conveyor 3. FIG. 7B is a diagram illustrating transition of the roll diameter Dr, which is the diameter of the web roll 7. FIG. 7C is a diagram illustrating transition of the torque of the brake 13 in the second embodiment. Note that FIGS. 7A and 7B are similar to FIGS. 4A and 4B. However, on FIGS. 7A and 7B, time t22 is indicated for comparison with FIG. 7C.

As descried in FIG. 7C, in the stop operation of the conveyance of the web W in the normal stop mode, the controller 6 gradually increases the torque of the brake 13 from the start time of deceleration (time t10) of the web W when changing the torque of the brake 13 from τce to τdn. The torque of the brake 13 reaches τdn at time t22, from which the controller 6 keeps the torque of the brake 13 at τdn.

Also in the stop operation of the conveyance of the web W in the emergency stop mode, the controller 6 gradually increases the torque of the brake 13 from the start time of deceleration (time t8) of the web W when changing the torque of the brake 13 from τcf to τdp. The torque of the brake 13 reaches τdp at time t21, from which the controller 6 keeps the torque of the brake 13 at τdp.

Note that also in changing the torque of the brake 13 from τ0 to τcs during the conveyance operation for roll diameter calculation, the controller 6 gradually changes the torque of the brake 13 from time t3 as illustrated in FIG. 7C.

The reason why the torque of the brake 13 is changed gradually as described above is to prevent the occurrence of slack in the web W caused by a tension change of the web W that occurs due to a sudden change of the torque of the brake 13.

Here, as can be seen from the foregoing formula (14), the larger the roll diameter Dr is, the larger the magnitude (absolute value) of the inertial load Ta of the web roll 7 in reducing the conveyance speed of the web W is. For this reason, the larger the roll diameter Dr is in deceleration of the web W, the larger the range of change when changing the torque of the brake 13 in the normal stop mode and the emergency stop mode is. Then, the larger the range of change in the torque of the brake 13 is, the more likely the tension change of the web W is to occur.

Accordingly, the controller 6 adjusts the torque change rate in gradually changing the torque of the brake 13 in accordance with the roll diameter Dr at the time of deceleration of the web W. Specifically, the larger the roll diameter Dr at the time of deceleration of the web W is, the smaller the controller 6 makes the torque change rate for gradually changing the torque of the brake 13. In other words, the larger the roll diameter Dr at the time of deceleration of the web W is, the more gently the controller 6 changes the torque when gradually changing the torque of the brake 13. With this operation, the torque change rate of the brake 13 is made appropriate in accordance with the roll diameter Dr, which prevents more the occurrence of tension changes of the web W due to changes in the torque of the brake 13.

As described above, in the second embodiment, the controller 6 gradually changes the torque of the brake 13 when changing the torque of the brake 13 to set it to a torque in which the inertial load of the web roll 7 is taken into account at the deceleration at the end of conveyance of the web for printing. This operation prevents sudden changes in the torque of the brake 13, and thus prevents the occurrence of slack in the web W caused by tension changes in the web W.

In addition, since the controller 6 adjusts the torque change rate for gradually changing the torque of the brake 13 in accordance with the roll diameter Dr at the time of deceleration of the web W, this prevents more the occurrence of slack in the web W caused by tension changes due to changes in the torque of the brake 13.

In the first and second embodiments described above, description has been provided for a case where there are the two stop modes, the normal stop mode and the emergency stop mode; however, there may be three or more stop modes each having different time for decelerating the web W.

In the first and second embodiments described above, description has been provided assuming that the brake 13 is constituted of a powder brake; however, the brake 13 may be a brake of another type.

An embodiment according to the disclosure, for example, includes the following configuration.

A conveying apparatus includes: a conveyor configured to convey a web while unwinding the web from a web roll; a brake configured to apply brakes to rotation of the web roll; and a controller configured to perform control to unwind the web from the web roll and convey the web with the conveyor while giving tension to the web by applying brakes to the rotation of the web roll using torque of the brake. The controller is configured to determine the torque of the brake during deceleration of the web to be a value depending on an inertial load of the web roll.

The controller may be configured to: upon stopping conveyance of the web by the conveyor, control a stop operation of the conveyance of the web based on one of different stop modes each having different deceleration time of the web; and in the stop operation of the conveyance of the web in each stop mode, determine the torque of the brake during the deceleration of the web to be a value depending on the inertial load of the web roll in accordance with the deceleration time of the stop mode.

Upon changing the torque of the brake to set the torque of the brake at the deceleration of the web to the value depending on the inertial load of the web roll, the controller may be configured to gradually change the torque of the brake.

The controller may be configured to adjust a torque change rate for gradually changing the torque of the brake in accordance with a diameter of the web roll at the deceleration of the web.

The conveying apparatus may further include a web roll holder including a web-roll supporting shaft rotatably supporting the web roll. The brake may be configured to apply brakes to rotation of the web-roll supporting shaft.

The controller may be configured to calculate the inertial load of the web roll used for calculation of the torque of the brake during the deceleration of the web, using a diameter of the web roll at a start timing of the deceleration of the web.

The inertial load of the web roll during the deceleration of the web may be a product of a moment of inertia of the web roll and an angular acceleration of the web roll from a print conveyance speed of the web to stoppage of the web.

Embodiments of the present invention have been described above. However, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Moreover, the effects described in the embodiments of the present invention are only a list of optimum effects achieved by the present invention. Hence, the effects of the present invention are not limited to those described in the embodiment of the present invention.

WEB CONVEYING APPARATUS WITH BRAKE

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