Patent Description:
Some background information can be found in <CIT>, which relates to a transportation belt for a printer driven by a driving roller. Some further background information can be found in <CIT> which relates to a print apparatus transportation mechanism and a processor configured to control the transportation mechanism in accordance with a setting value acquired based on a machine-learning model.

The same part numbers designate the same or similar parts throughout the figures.

In some large industrial inkjet printers, a vacuum belt is used to hold down media flat for printing. The vacuum belt forms a loop driven by a pulley at one end of the loop around an idler pulley at the other end of the loop. The print media is carried along the upper run of the belt loop through a print zone where ink is
dispensed on to the media from a printing unit above the belt. The printing unit may include multiple print bars that extend across the full width of the belt to print each of multiple corresponding color planes on to the media in a single pass. The vacuum holding down the print media applies strong normal forces to the belt as it moves through the print zone, creating friction that can cause small jumps in belt speed. Also, in response to the substantial operating stresses in an industrial printing environment, a belt drive pulley may develop an eccentric wobble that causes unwanted variations in belt speed through the print zone. An encoder gives feedback to a controller to try to correct for unwanted changes in belt speed, and thus synchronize the position of the print media on the belt to the printing unit dispensing ink, so that that ink is dispensed at the proper locations on the print media. Uncorrected changes in belt speed can adversely affect print quality.

Belts can pull but not push. If the encoder indicates the belt should speed up in the print zone, then the drive pulley is accelerated to pull forward on the upper run of belt. If the encoder indicates the belt should slow in the print zone, then the drive pulley is decelerated to pull back on the lower run of belt. The lower run of belt travels further to the print zone than the upper run of belt. Consequently, it takes longer to slow the belt in the print zone than it does to speed up the belt in the print zone. As a result of this deceleration delay, the belt speed control system is slower to correct changes in belt speed, operating at a lower gain with more dynamic errors than it might without a deceleration delay.

A new drive system has been developed to help more quickly correct the speed of a conveyor belt that carries print media through the print zone in a printer. Rather than driving the belt from one end of the loop, the belt is driven from both ends of the loop with independent drivers. According to the invention, a pair of pulleys circulates the belt from opposite ends of the belt loop at the urging of a respective pair of drive motors, an encoder measures movement of the belt through the print zone, and the drive motor for each pulley is controlled based on measurements from the encoder. For steady state operation, one pulley pulls the upper run of belt forward through the print zone and the other pulley simultaneously pulls the lower run of belt back at the same linear speed to circulate the belt.

If the encoder indicates the belt should speed up in the print zone, then one pulley is accelerated to pull forward faster on the upper run of belt. If the encoder indicates the belt should slow in the print zone, then the other pulley is decelerated to pull back on the upper run of belt. One pulley pulls forward on the upper run of belt for acceleration and the other pulley pulls back on the upper run of belt for deceleration, so that deceleration occurs without delay compared to acceleration, allowing the speed control system to operate at higher gain with lower dynamic errors.

These and other examples described below and shown in the figures illustrate but do not limit the scope of the patent, which is defined in the Claims following this Description.

As used in this document: "and/or" means one or more of the connected things; and a "computer readable medium" means any non-transitory tangible medium that can embody, contain, store, or maintain instructions and other information for use by a processor and may include, for example, circuits, integrated circuits, ASICs (application specific integrated circuits), hard drives, random access memory (RAM), read-only memory (ROM), and flash memory.

<FIG> is a block diagram illustrating one example of a dual drive print media conveyor system <NUM>. Referring to <FIG>, system <NUM> includes an endless belt <NUM> in a loop to convey print media for printing, a pair of drivers <NUM>, <NUM> to circulate belt <NUM> from opposite ends of the loop, and an encoder unit <NUM> located under the print zone to measure movement of belt <NUM> through the print zone. System <NUM> also includes a controller <NUM> operatively connected to drivers <NUM>, <NUM> and encoder unit <NUM>. Controller <NUM> represents the processing and memory resources and the programming, electronic circuitry and components needed to control the operative elements of system <NUM>. Controller <NUM> may include distinct control elements for individual system components. In the example shown in <FIG>, controller <NUM> includes a processor <NUM> and a computer readable medium <NUM> with control instructions <NUM> that represent programming to control drivers <NUM>, <NUM>, and thus the speed of belt <NUM>, based on belt movement measured by encoder unit <NUM>. Controller <NUM> may also include programming to control a printing unit dispensing ink based on movement measured by encoder unit <NUM>, for example as described below with reference to <FIG>.

While any suitable drivers <NUM>, <NUM> may be used to circulate belt <NUM>, it is expected that each driver <NUM>, <NUM> usually will be implemented with a pulley and a motor to turn the pulley at the direction of controller <NUM>, for example as described below with reference to <FIG>. Where conveyor belt <NUM> is implemented as a vacuum belt, system <NUM> may include a vacuum chamber <NUM> operatively coupled to belt <NUM> to hold down print media flat on belt <NUM>.

<FIG> illustrates an example implementation for a print zone encoder unit <NUM> shown in <FIG>. Referring to <FIG>, encoder unit <NUM> includes an encoder pulley <NUM>, a rotary encoder <NUM> operatively connected to encoder pulley <NUM>, and an endless belt <NUM> engaging print media conveyor belt <NUM> in the print zone so that encoder belt <NUM> moves with conveyor belt <NUM>. Encoder belt <NUM> wraps encoder pulley <NUM> to turn pulley <NUM> in response to conveyor belt <NUM> moving through the print zone. Encoder belt <NUM> converts linear movement of belt <NUM> through the print zone to rotation of encoder pulley <NUM> that is measured by rotary encoder <NUM>. The encoder measurements are used by controller <NUM> in <FIG> to control the speed of conveyor belt <NUM> and/or the timing of a printing unit dispensing ink based on the movement of conveyor belt <NUM> in the print zone.

<FIG> are plan and elevation views illustrating an example implementation for a print media conveyor system <NUM> shown in the block diagram of <FIG>. <FIG> are plan and elevation views illustrating an example inkjet printer with a print media conveyor system <NUM> from <FIG>. <FIG> is a plan view detail from <FIG>. <FIG> is an elevation view of the detail of <FIG>.

Referring to <FIG>, print media conveyor system <NUM> includes an endless print media conveyor belt <NUM> in a loop <NUM> and a pair of drivers <NUM>, <NUM> to circulate belt <NUM> from opposite ends of loop <NUM>. Drivers <NUM>, <NUM> circulate belt <NUM> clockwise in <FIG> to convey print media to the right for printing, as indicated by direction arrows <NUM> and <NUM>. First driver <NUM> pulls forward (to the right) on an upper run <NUM> of conveyor belt <NUM> in <FIG> and second driver <NUM> pulls back (to the left) a lower run <NUM> of conveyor belt <NUM>. Belt <NUM> includes vacuum holes <NUM> operatively connected to a vacuum chamber <NUM> along upper run <NUM>.

In the example shown in <FIG>, each driver <NUM>, <NUM> includes a pulley <NUM>, <NUM> at opposite ends of belt loop <NUM> and a motor <NUM>, <NUM> to turn the corresponding pulley <NUM>, <NUM>. Teeth <NUM> on pulleys <NUM>, <NUM> engage teeth <NUM> on belt <NUM> to circulate belt <NUM> at the urging of motors <NUM>, <NUM>. As shown in <FIG>, a controller <NUM> from <FIG> may include distinct control elements for each driver <NUM>, <NUM> - a controller <NUM> for first motor <NUM> and a controller <NUM> for second motor <NUM>. Both motor controllers <NUM>, <NUM> control the speed of motors <NUM>, <NUM> based on measurements from encoder unit <NUM>. Although conveyor belt <NUM> is shown as a single belt in <FIG>, a print media conveyor belt <NUM> could be implemented as a series of multiple belts spaced apart from one another laterally across the print zone, with the belts circulated together with drivers <NUM>, <NUM>.

Referring to <FIG>, an inkjet printer <NUM> includes a printing unit <NUM> with print bars <NUM>, <NUM>, <NUM>, <NUM> over belt <NUM>. Printing unit <NUM> defines a print zone <NUM> in which ink is dispensed on to print media <NUM> moving with conveyor belt <NUM> under the print bars. Print media <NUM> is shown in phantom lines to not obscure belt <NUM>. Each print bar <NUM>-<NUM> includes one or multiple inkjet printheads that dispense ink on to print media <NUM> according to "firing" signals timed to produce the desired images at the desired locations on media <NUM>.

Referring to <FIG>, an encoder unit <NUM> is positioned under belt <NUM> in print zone <NUM> to measure belt movement through the print zone. In the example shown in <FIG>, encoder unit <NUM> includes a toothed encoder pulley <NUM>, guide pulleys <NUM>, and a toothed encoder belt <NUM> wrapping pulleys <NUM> and <NUM>. Encoder unit <NUM> also includes a rotary encoder <NUM> operatively connected to encoder pulley <NUM> to measure the rotation of encoder pulley <NUM>. Pulleys <NUM>, <NUM> are mounted to a frame <NUM> and configured to make the upper run of encoder belt <NUM> parallel to print media conveyor belt <NUM>. A first guide pulley <NUM> has a first axis of rotation <NUM>, a second guide pulley <NUM> has a second axis of rotation <NUM>, and encoder pulley <NUM> has a third axis of rotation <NUM> between first axis <NUM> and second axis <NUM>. Teeth on encoder belt <NUM> engage teeth on conveyor belt <NUM> and teeth on encoder pulley <NUM> so that the linear movement of conveyor belt <NUM> is transferred to encoder belt <NUM> which is converted to rotation of encoder pulley <NUM>.

Rotary encoder <NUM> measures the rotation of encoder pulley <NUM> which represents the linear movement of conveyor belt <NUM> in print zone <NUM>. Accordingly, rotary encoder <NUM> measures movement of conveyor belt <NUM> in print zone <NUM> indirectly through encoder pulley <NUM> and belt <NUM>. While it is expected that rotary encoder <NUM> usually will be implemented as an incremental encoder, any suitable rotary encoder may be used. Also, the configuration of an encoder unit <NUM> in <FIG> is just one example. Other configurations are possible. For one example, it may be possible in some implementations to use a linear encoder to directly measure the movement of a print media conveyor belt <NUM> through the print zone. For another example, it may be possible in some implementations to drive an encoder pulley <NUM> directly by a print media conveyor belt <NUM>.

<FIG> is a plan view illustrating another example of a dual drive print media conveyor system <NUM>. Referring to <FIG>, system <NUM> includes multiple print media conveyor belts <NUM> and a pair of drivers <NUM>, <NUM> to circulate each belt <NUM>. Each belt <NUM> includes vacuum holes <NUM> operatively connected to a vacuum chamber <NUM> along the upper run of belt <NUM>. Each driver <NUM>, <NUM> includes a pulley <NUM>, <NUM> at opposite ends of the corresponding belt loop and a motor <NUM>, <NUM> to turn the respective pulley <NUM>, <NUM>. An encoder unit <NUM> located under each belt <NUM> in print zone <NUM> measures movement of the corresponding conveyor belt <NUM> through the print zone. Motor controllers <NUM>, <NUM> control the speed of motors <NUM>, <NUM> based on measurements from encoder unit <NUM> for each belt <NUM>.

<FIG> is a block diagram illustrating an inkjet printer <NUM> implementing one example of a dual drive print media conveyor system <NUM>. Referring to <FIG>, printer <NUM> includes a printing unit <NUM> with printheads <NUM>-<NUM> that define a print zone where ink is dispensed on to print media carried by system <NUM>. Each printhead <NUM>-<NUM> may be implemented, for example, as a print bar <NUM>-<NUM> shown in <FIG>. In this example, each printhead <NUM>-<NUM> dispenses cyan, magenta, yellow, and black ink, respectively. Each printhead <NUM>-<NUM> is operatively connected to a controller <NUM> executing control instructions <NUM> to dispense ink according to firing signals timed to produce the desired images at the desired locations on the print media.

Encoder unit <NUM> measures the movement of conveyor belt <NUM> in the print zone and communicates the measurements to controller <NUM>. Processor <NUM> on controller <NUM> executing control instructions <NUM> controls drivers <NUM> and <NUM> to maintain the desired speed of media conveyor belt <NUM> through the print zone based on movement of media conveyor belt <NUM> measured by encoder unit <NUM>, for example by correcting for jumps in belt speed and/or wobble in the driver pulleys. If the encoder in unit <NUM> indicates belt <NUM> should speed up in the print zone, then controller <NUM> controls driver <NUM> to pull forward faster on the upper run of belt <NUM>. If the encoder in unit <NUM> indicates belt <NUM> should slow in the print zone, then controller <NUM> controls driver <NUM> to pull back on the upper run of belt <NUM>. One driver pulls forward on the upper run of belt for acceleration and the other driver pulls back on the upper run of belt for deceleration. In one example, if the encoder in unit <NUM> indicates belt <NUM> should speed up in the print zone, then controller <NUM> controls drivers <NUM> and <NUM> to simultaneously pull forward faster on the upper run of belt <NUM> and back faster on the lower run of belt <NUM> and, if the encoder in unit <NUM> indicates belt <NUM> should slow in the print zone, then controller <NUM> controls drivers <NUM> and <NUM> to simultaneously pull back on the upper run of belt <NUM> and forward on the lower run of belt <NUM>.

To further reduce the risk of speed changes adversely effecting print quality, processor <NUM> on controller <NUM> executing control instructions <NUM> may also control the firing signals for printheads <NUM>-<NUM> based on movement of media conveyor belt <NUM> measured by encoder unit <NUM>, to produce the desired images at the desired locations on the print media, for example by synchronizing the firing signals to changes in belt speed. While it is expected that belt movement will usually be measured by an encoder located in the print zone, for example as shown in <FIG>, it may be possible or even desirable in some implementations to use an encoder located away from the print zone.

<FIG> illustrates a process <NUM> for circulating an endless belt in a loop, such as might be implemented in a dual drive conveyor system <NUM> shown in <FIG>. Part numbers in the following description of <FIG> refer to <FIG>. Referring to <FIG>, process <NUM> includes a first pulley <NUM> pulling forward on an upper run of belt <NUM> from one end of the loop (block <NUM>) and a second pulley <NUM> simultaneously pulling back on a lower run of belt <NUM> from the other end of the loop (block <NUM>), with both pulleys <NUM>, <NUM> pulling the respective run of belt <NUM>, <NUM> at the same linear speed. Process <NUM> also includes measuring movement of the belt <NUM> (block <NUM>), for example print zone encoder unit <NUM> measuring an unwanted burst of speed, and, based on the measuring, the second pulley <NUM> pulling back on the upper run of belt <NUM> to slow the belt <NUM> (block <NUM>).

The examples shown in the figures and described above illustrate but do not limit the patent, which is defined in the following Claims.

Claim 1:
A system (<NUM>) configured to convey print media through a print zone in an inkjet printer, the system comprising:
an endless conveyor belt (<NUM>) in a loop;
a pair of drivers (<NUM>, <NUM>) configured to circulate the conveyor belt through the print zone from opposite ends of the loop;
an encoder (<NUM>) configured to measure movement of the conveyor belt; and
a controller (<NUM>) programmed to control both drivers driving the conveyor belt based on measurements from the encoder;
characterized in that the controller is programmed to:
control the first driver (<NUM>) to pull forward on an upper run of the conveyor belt from one end of the loop;
control the second driver (<NUM>) to pull back on a lower run of the conveyor belt from the other end of the loop simultaneously with the first driver pulling forward on the upper run of the conveyor belt; and
control both drivers to pull the respective run of the conveyor belt at the same linear speed.