Conveyance apparatus of web print medium

A conveyance apparatus includes a conveyance roller, a conveyance motor, a back tension roller, a conveyance speed detector, a brake, and a controller. The controller is configured to: based on a conveyance speed of a web detected by the conveyance speed detector, control a value of a drive control parameter of the conveyance motor such that the conveyance speed of the web is equal to a target speed; and, based on an output torque of the conveyance motor corresponding to the value of the drive control parameter, adjust a braking force of the brake applied to the back tension roller which applies a tension to the web such that the tension of the web is equal to a target tension.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-067650, filed on Mar. 30, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The disclosure relates to a conveyance apparatus which conveys a web.

2. Related Art

Japanese Unexamined Patent Application Publication No. 2013-71323 proposes a printing apparatus which continuously conveys a long web as a print medium and, at the same time, performs printing on the web by ejecting ink from an inkjet head.

Among printing apparatuses of the aforementioned type, there is one which includes a conveyance roller arranged downstream of the inkjet head and a back tension roller arranged upstream of the inkjet head. The conveyance roller is driven by a motor and conveys the web. A brake is connected to the back tension roller and the back tension roller applies tension to the web by receiving the braking force of this brake.

In such a printing apparatus, the conveyance speed of the web is detected by an encoder or the like provided in the motor and the motor is controlled based on the detected conveyance speed to maintain the conveyance speed of the web at fixed speed. The conveyance speed of the web is maintained at the fixed speed to prevent deviation of ink landing positions and obtain good print quality.

However, when the aforementioned motor control is performed to maintain the conveyance speed of the web at the fixed speed, the output torque of the motor changes and the tension of the web between the conveyance roller and the back tension roller changes. When the tension of the web changes, the web vibrates and the distance between the inkjet head and the web changes in some cases. When the distance between the inkjet head and the web changes, there is a risk that the ink landing positions deviate and the print quality decreases.

In view of this, in such a printing apparatus, a tension detector is installed between the conveyance roller and the back tension roller, and the brake is controlled such that the tension is constant, based on the tension of the web detected by the tension detector.

SUMMARY

Meanwhile, providing the tension detector leads to complicated apparatus configuration. Moreover, the tension detector sometimes causes conveyance failure such as meandering of the web. Accordingly, it is desirable to suppress the tension change of the web without the tension detector.

An object of the disclosure is to provide a conveyance apparatus which can suppress tension change of a web without a tension detector.

A conveyance apparatus in accordance with some embodiments includes: a conveyance roller configured to convey a web and arranged downstream of an inkjet head for ejecting ink to the web in a conveyance direction of the web; a conveyance motor configured to drive the conveyance roller; a back tension roller arranged upstream of the inkjet head in the conveyance direction and configured to apply a tension to the web; a conveyance speed detector configured to detect a conveyance speed of the web; a brake configured to apply a braking force to the back tension roller; and a controller configured to control the conveyance motor and the brake. The controller is configured to: based on the conveyance speed of the web detected by the conveyance speed detector, control a value of a drive control parameter of the conveyance motor such that the conveyance speed of the web is equal to a target speed; and, based on an output torque of the conveyance motor corresponding to the value of the drive control parameter, adjust the braking force of the brake such that the tension of the web is equal to a target tension.

In the aforementioned configuration, it is possible to control the conveyance motor such that conveyance speed of the web is maintained at fixed speed and, at the same time, control the braking force of the brake such that the tension of the web is fixed, without directly detecting the tension of the web. Accordingly, tension change of the web can be suppressed without a tension detector for detecting the tension of the web.

The brake may include: a base brake configured to generate a base braking force; and an adjustment brake with a maximum output smaller than a maximum output of the base brake and with a response speed higher than a response speed of the base brake. The controller may be configured to adjust the braking force of the brake by adjusting a braking force of the adjustment brake.

In the aforementioned configuration, it is possible to finely adjust the braking force of the brake while providing required braking force.

Depending on a type and a size of the web, instead of adjusting the braking force of the brake such that the tension of the web is equal to the target tension, the controller may be configured to control the braking force of the brake such that the braking force of the brake is maintained constant at a braking force predetermined depending on the type and the size of the web.

In the aforementioned configuration, it is possible to omit the adjustment of the braking force while providing braking force required to suppress the oscillation of the web. As a result, it is possible to simplify the brake control while suppressing the oscillation of the web W.

The base braking force may be a constant force predetermined depending on a type and a size of the web.

DETAILED DESCRIPTION

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. 1is a schematic configuration diagram of a printing apparatus1including a conveyance apparatus according to an embodiment of the present invention.FIG. 2is a control block diagram of the printing apparatus1illustrated inFIG. 1. Note that, inFIG. 1, the rightward direction, the leftward direction, the upward direction, and the downward direction are denoted by RT, LT, UP, and DN, respectively. Moreover, the direction orthogonal to the sheet surface ofFIG. 1is referred to as a front-rear direction.

As illustrated inFIGS. 1 and 2, the printing apparatus1includes a feeder2, a printer3, a winder4, and a controller5. Note that the controller5and a conveyer21to be described later form the conveyance apparatus.

The feeder2feeds a web W which is a long print medium made of paper, film, or the like, to the printer3. The feeder2includes a web roll support shaft11, a feed motor12, and an upstream buffer13.

The web roll support shaft11supports a web roll14in a rotatable manner. The web roll support shaft11is formed in a long form extending in the front-rear direction. The web roll14is a roll of the web W.

The feed motor12rotates the web roll support shaft11clockwise inFIG. 1. The rotation of the web roll support shaft11causes the web roll14to rotate in the same direction and the web W is fed downstream (toward the right side).

The upstream buffer13absorbs a slack of the web W between the web roll14and the printer3. The upstream buffer13includes support rollers16,17and a dancer roller18.

The support rollers16,17support the web W between the web roll14and a pair of back tension rollers31of the printer3to be described later. The support rollers16,17are arranged at the same height at an interval in a left-right direction.

The dancer roller18pushes down the web W with its own weight between the support rollers16,17. The dancer roller18thereby absorbs the slack of the web W. The dancer roller18moves up and down depending on the amount of slack in the web W.

The printer3prints an image on the web W while conveying the web W. The printer3includes the conveyer21and a head unit22.

The conveyer21conveys the web W fed by the feeder2. The conveyer21includes the pair of back tension rollers31, a brake32, guide rollers33,34, ten under-head support members35, a pair of conveyance rollers36, a conveyance motor37, and an encoder38.

The pair of back tension rollers31are rollers for applying tension to the web W. The pair of back tension rollers31are arranged upstream of the head unit22in a conveyance direction of the web W. The pair of back tension rollers31rotate by following the web W conveyed by the pair of conveyance rollers36, while nipping the web W. The brake32applying brake to the back tension rollers31causes tension to be applied to the web W between the pair of the conveyance rollers36and the pair of back tension rollers31.

The brake32applies braking force for applying tension to the web W, to the back tension rollers31. The brake32includes a base brake41and an adjustment brake42.

The base brake41generates base braking force to be applied to the back tension rollers31. The base braking force is set (predetermined) depending on the type and size (width) of the web W. The base brake41is a brake with maximum output high enough to generate base braking force corresponding to various types of webs W used in the printing apparatus1. The base brake41is, for example, a powder brake.

The base brake41includes an output shaft41aconfigured to output braking force. The braking force of the base brake41is transmitted from the output shaft41ato a pulley47via a brake belt46, the pulley47coaxially connected to one of the back tension rollers31. The braking force of the base brake41is thereby applied to the back tension rollers31. The brake belt46is an annular belt wound around the pulley47, the output shaft41aof the base brake41, and an output shaft42aof the adjustment brake42to be described later.

The adjustment brake42is a brake for adjusting the braking force of the brake32which is to be applied to the back tension rollers31. The adjustment brake42is a brake with maximum output smaller than the maximum output of the base brake41and with higher response speed to control than response speed of the base brake41. The adjustment brake42is, for example, a powder brake.

The adjustment brake42includes the output shaft42aconfigured to output braking force. The braking force of the adjustment brake42is transmitted from the output shaft42ato the pulley47via the brake belt46. The braking force of the adjustment brake42is thereby applied to the back tension rollers31.

The guide roller33guides the web W between the pair of back tension rollers31and the most upstream under-head support member35. The guide roller34guides the web W between the most downstream under-head support member35and the pair of conveyance rollers36.

The under-head support members35support the web W under the head unit22. The ten under-head support members35are arranged in an arch shape protruding upward. The web W is thereby set to a tensioned state between the adjacent under-head support members35and is maintained in a stable attitude.

The pair of conveyance rollers36convey the web W toward the winder4while nipping the web W. The pair of conveyance rollers36are arranged downstream of the head unit22.

The conveyance motor37rotationally drives the conveyance rollers36. The conveyance motor37includes a drive shaft37aconfigured to output rotational drive force. The rotational drive force of the conveyance motor37is transmitted from the drive shaft37ato a pulley49via a drive belt48, the pulley49coaxially connected to one of the conveyance rollers36. The conveyance rollers36are thereby rotationally driven.

The encoder38outputs a pulse signal every time the drive shaft37aof the conveyance motor37rotates by a predetermined angle. The pulse signal outputted by the encoder38is used to detect the conveyance speed of the web W. The encoder38corresponds to a conveyance speed detector.

The head unit22prints an image on the web W conveyed by the conveyer21. The head unit22includes inkjet heads51A to51E.

The inkjet heads51A to51E each have multiple nozzles (not illustrated) aligned in the front-rear direction (main scanning direction) and eject ink from the nozzles. The inkjet heads51A to51E are arranged above the web W conveyed by the conveyer21.

The winder4winds the web W subjected to printing by the printer3. The winder4includes a downstream buffer56, a winding shaft57, and a winding motor58.

The downstream buffer56absorbs a slack of the web W between the printer3and the winding shaft57. The downstream buffer56includes support rollers61,62and a dancer roller63.

The support rollers61,62support the web W between the pair of conveyance rollers36and the winding shaft57. The support rollers61,62are arranged at the same height at an interval in the left-right direction.

The dancer roller63pushes down the web W with its own weight between the support rollers61,62. The dancer roller63thereby absorbs the slack of the web W. The dancer roller63moves up and down depending on the amount of slack in the web W.

The winding shaft57winds and holds the web W. The winding shaft57is formed in a long form extending in the front-rear direction.

The winding motor58rotates the winding shaft57clockwise inFIG. 1. The rotation of the winding shaft57causes the web W to be wound by the winding shaft57.

The controller5controls operations of various units in the printing apparatus1. The controller5includes a CPU, a RAM, a ROM, a hard disk, and the like.

In the printing, the controller5drives the inkjet heads51A to51E to eject the inks and perform printing on the web W, while driving the feeder2, the conveyer21, and the winder4to convey the web W.

While the web W is being conveyed, the controller5controls the conveyance speed of the web W. Specifically, the controller5controls a value of a drive control parameter of the conveyance motor37such that the conveyance speed of the web W is equal to print conveyance speed which is target speed, based on the conveyance speed of the web W detected by the encoder38. In this case, the drive control parameter of the conveyance motor37is a parameter for controlling power supplied to the conveyance motor37, and is specifically current, voltage, or the like. In the following description, the drive control parameter of the conveyance motor37in the embodiment is assumed to be the current.

Moreover, while the web W is being conveyed, the controller5performs brake control in a braking force variable mode or a braking force fixed mode, depending on the type and size of the web W.

The braking force variable mode is a mode in which the braking force of the brake32is changed such that the tension of the web W is maintained at target tension. In the braking force variable mode, the controller5adjusts the braking force of the brake32such that the tension of the web W is equal to the target tension, based on the output torque of the conveyance motor37corresponding to the current supplied to the conveyance motor37.

The braking force fixed mode is a mode in which the braking force of the brake32is fixed. In the braking force fixed mode, the controller5performs control such that the braking force of the brake32is fixed (constant) at braking force set (predetermined) depending the type and size of the web W.

Next, operations of the printing apparatus1are described.

When a print job is inputted, the controller5first executes brake control mode selection processing. The brake control mode selection processing is processing in which the braking force variable mode or the braking force fixed mode is selected as the brake control mode in the conveyance of the web W. The brake control mode selection processing is described with reference to the flowchart ofFIG. 3.

When the print job is inputted, in step S1ofFIG. 3, the controller5determines whether the web W to be subjected to printing in this operation is a web being a target of the braking force variable control, based on setting information included in the print job.

In this case, the web being the target of the braking force variable control is a web other than a web being a target of the braking force fixed control. The web being the target of the braking force fixed control is a web of such type and size that a stretch amount between the inkjet head51A and the inkjet head51E is within an allowable range when tension high enough to suppress oscillation due to vibration within an allowable range is applied to the web. In other words, the web being the target of the braking force variable control is a web of such type and size that the stretch amount between the inkjet head51A and the inkjet head51E cannot be maintained within the allowable range when the tension high enough to suppress the oscillation due to vibration within the allowable range is applied to the web.

When the web W to be printed in this operation is determined to be the web being the target of the braking force variable control (step S1: YES), the controller5selects the braking force variable mode and terminates the brake control mode selection processing in step S2.

When the web W to be printed in this operation is determined not to be the target of the braking force variable control, that is, to be the web being the target of the braking force fixed control (step S1: NO), the controller5selects the braking force fixed mode and terminates the brake control mode selection processing in step S3.

After the brake control mode selection processing, the controller5starts the conveyance of the web W. Specifically, the controller5starts the drive of the feed motor12, the brake32, the conveyance motor37, and the winding motor58. The web W is thereby conveyed from the feeder2to the winder4. In the printer3, the brake32applies brake to the back tension rollers31and this causes the web W to be conveyed with the tension applied to the web W.

After the conveyance of the web W is started, the controller5controls the inkjet heads51A to51E based on the print job and causes the inkjet heads51A to51E to print an image on the web W.

Here, the conveyance speed of the web W changes in the conveyance of the web W due to unevenness in the thickness of the web W and the like. To counter this, the controller5performs the conveyance speed control to suppress the speed change of the web W in the printer3and maintain the print conveyance speed. The conveyance speed control of the web W is performed as follows.

While the web W is being conveyed, the controller5obtains the conveyance speed of the web W detected by the encoder38. Specifically, the controller5calculates the number of revolutions of the conveyance motor37based on the pulse signal outputted by the encoder38and calculates the conveyance speed of the web W corresponding to the calculated number of revolutions. Then, the controller5controls the current supplied to the conveyance motor37such that there is no difference between the calculated conveyance speed and the print conveyance speed (target speed). The conveyance speed detected as illustrated in, for example,FIG. 4is thereby controlled to match the print conveyance speed.

Moreover, while the web W is being conveyed, the controller5performs the brake control in the braking force variable mode or the braking force fixed mode selected in the brake control mode selection processing. InFIG. 5, the bold solid line depicts the output torque of the base brake41, the thin solid line depicts the output torque of the adjustment brake42, the broken line depicts the output torque of the conveyance motor37, and the alternate long and short dash line depicts a target torque difference described below.

First, the brake control in the braking force variable mode is described.

In the braking force variable mode, the controller5controls the base brake41such that the base brake41generates and maintains the base braking force depending on the type and size of the web W. As illustrated inFIG. 5, the output torque (braking force) of the base brake41is thus constant.

Moreover, the controller5calculates the output torque of the conveyance motor37corresponding to the current supplied to the conveyance motor37. The value of the output torque of the conveyance motor37corresponding to the supplied current can be calculated from the motor characteristics of the conveyance motor37. Then, the controller5adjusts the braking force (output torque) of the adjustment brake42such that the difference between the output torque of the conveyance motor37and the output torque of the brake32is equal to the target torque difference corresponding to the target tensile of the web W.

As illustrated inFIG. 5, the braking force (output torque) of the adjustment brake42is thus adjusted to cancel out the change in the output torque of the conveyance motor37which is caused by the conveyance speed control of the web W. As a result, the tension of the web W is maintained at the target tension. This suppresses vibration due to the change in the tension of the web W, and decrease in print quality is thereby suppressed.

Next, the brake control in the braking force fixed mode is described.

In the braking force fixed mode, the controller5controls the base brake41and the adjustment brake42such that, during the conveyance of the web W, the braking force of the brake32is fixed at the braking force preset depending on the type and size of the web W.

The braking force in the braking force fixed mode is set (predetermined) such that the tension high enough to suppress the oscillation due to vibration within the allowable range can be applied to the web W and the stretch amount of the web W between the inkjet head51A and the inkjet head51E is maintained within the allowable range when such tension is applied. In this case, the allowable ranges of the oscillation and stretch amount of the web W are set depending on an allowable range of a deviation amount of an ink landing position which is used to maintain good print quality.

Fixing the braking force of the brake32to the braking force described above can suppress the oscillation of the web W within the allowable range even when the output torque of the conveyance motor37changes due to the conveyance speed control of the web W. Accordingly, the decrease of print quality is suppressed.

When the printing based on the print job is completed, the controller5terminates the conveyance of the web W. Specifically, the controller5stops the feed motor12, the brake32, the conveyance motor37, and the winding motor58. The series of operations are thereby completed.

As described above, in the printing apparatus1, the controller5controls the current supplied to the conveyance motor37such that the conveyance speed of the web W is equal to the print conveyance speed which is the target speed, based on the conveyance speed of the web W detected by the encoder38. Moreover, in the braking force variable mode, the controller5adjusts the braking force of the brake32such that the tension of the web W is equal to the target tension, based on the output torque of the conveyance motor37corresponding to the current supplied to the conveyance motor37. As a result, the printing apparatus1can control the conveyance motor37such that conveyance speed of the web W is maintained at the fixed speed and, at the same time, control the braking force of the brake32such that the tension of the web W is constant, without directly detecting the tension of the web W. Accordingly, the printing apparatus1can suppress tension change of the web W without being provided with a tension detector for detecting the tension of the web W.

Moreover, in the printing apparatus1, the brake32includes the base brake41configured to generate the base braking force and the adjustment brake42with maximum output smaller than the maximum output of the base brake41and with higher response speed than response speed of the base brake41. In addition, the controller5adjusts the braking force of the brake32by adjusting the braking force of the adjustment brake42. Accordingly, it is possible to finely adjust the braking force of the brake32while providing required braking force.

Moreover, in the braking force fixed mode, the printing apparatus1controls the braking force of the brake32depending on the type and size of the web W, such that the braking force of the brake32is fixed at the braking force set depending on the type and size of the web W. It is thus possible to omit the adjustment of the braking force while providing braking force required to suppress the oscillation of the web W. As a result, it is possible to simplify the brake control while suppressing the oscillation of the web W.

Note that, although the configuration in which the brake32includes two brakes of the base brake41and the adjustment brake42is described in the aforementioned embodiment, the brake32may include one brake.

Although the configuration in which the braking force variable mode and the braking force fixed mode can be selectively used as the brake control mode is described in the aforementioned embodiment, the braking force fixed mode may be omitted. That is, only the braking force variable mode can be used for the web W of all types and sizes (i.e. both the web being the target of the braking force variable control and the web being the target of the braking force fixed control explained above).

Although the current is described as the drive control parameter of the conveyance motor37in the aforementioned embodiment, the drive control parameter is not limited to this and may be voltage or the like.

Although the encoder38is used to detect the conveyance speed of the web W in the aforementioned embodiment, the conveyance speed detector is not limited to this and a laser Doppler velocimeter or the like may be used.

Although the configuration in which the feeder2and the winder4are incorporated in the printing apparatus1is described in the aforementioned embodiment, a feeding apparatus and a winding apparatus which are separate apparatuses may be connected to the printing apparatus.

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.