Linear Rotary Encoder

Abstract

A linear rotary encoder includes a pair of rotary surfaces. A contact strip has a first end coupled to a first rotary surface of the pair and a second end coupled to a second rotary surface of the pair. The contact strip is driven to rotate around the pair of rotary surfaces by a driving force applied to a medium to move the medium from the first end toward the second end. An encoding scale is coupled to an inner surface of the contact strip. A reader is positioned to read the encoding scale as the contact strip rotates around the pair of rotary surfaces. The reader generates an output signal representative of the position of the medium based on the reading of the encoding scale.

Description

Technical Field

[0001] The present technology relates to a linear rotary encoder. Background Art

[0002] Many mechanical systems use encoders to track the movement of system components. For example, printing systems use encoders to track the position of ink heads or printing media in the system. The encoder enables the printing system to track the relative positions of the ink head and the media to ensure that patterns are printed correctly onto the media. Encoders used in mechanical systems are typically linear encoders that track position along a straight line, or rotary encoders that measure angular distance. However, especially when used in printing systems, rotary encoders are affected by tolerance stacking, which reduces measurement accuracy. The practicality of linear encoders in printing systems is limited because the media typically moves in one direction in the system, so the linear encoder must periodically bounce back to a reset position. Therefore, there is a need for an encoder that more accurately tracks position in a printing system. Brief Description of the Drawings

[0003] Figure 1 is a block diagram showing the components of an exemplary printing system.

[0004] Figures 2A - 2B shows an exemplary embodiment of a linear rotary encoder.

[0005] Figure 3 is a diagram showing an example of a contact strip and a coding strip.

[0006] Figure 4 is a schematic diagram showing an example operation of a reader. Detailed Description

[0007] Embodiments of a linear rotary encoder are described herein. In some embodiments, the linear rotary encoder includes a pair of rotating surfaces, such as wheels or bearings. The linear rotary encoder may also include a contact strip having a first end coupled to a first rotating surface of the pair and a second end coupled to a second rotating surface of the pair. The contact strip can be driven to rotate around the pair of rotating surfaces by a driving force applied to the media to move the media from the first end towards the second end. A coding scale can be coupled to the inner surface of the contact strip. The position of a reader can be set to read the coding scale when the contact strip rotates around the pair of rotating surfaces. The reader can generate an output signal representing the position of the media based on the reading of the coding scale.

[0008] In some embodiments, the linear rotary encoder can be used in a printer system. In addition to the linear rotary encoder, the printer system can also include a driver configured to drive the media through the printer system and one or more print heads configured to deposit ink on the media.

[0009] By way of example, embodiments of a linear rotary encoder are described herein, including its use in a printing system. The linear rotary encoder described herein beneficially reduces the tolerance stack-up present in a pure rotary encoder and can also be used in printers with limited space and generally unidirectional linear motion. However, the linear rotary encoder can be used in any of a variety of systems that require information about the position of a mechanical component.

[0010] Figure 1 is a block diagram showing the components of an example printing system 100. The example printing system 100 has a conveyor system 110 for transporting a medium 115 relative to one or more print bars 120 (e.g., print bars 120A, 120B, and 120C). The conveyor system 110 can include a drive belt 112 and a pair of rollers 114. The rollers are rotatably mounted on shafts ( Figure 1 not shown). One or both of the rollers 114 can be powered by a drive mechanism 130 to drive the movement of the drive belt 112. Specifically, the drive mechanism 130 can controllably rotate a roller 114, such as roller 114B, to produce movement of the drive belt 112, thereby moving the medium 115. In some embodiments, the conveyor system 110 transports the medium 115 unidirectionally through the printing system 100, e.g., moving the medium 115 only in direction 119.

[0011] Each print bar 120 includes one or more print heads 122. In some embodiments, the print bar 120 is fixedly locked relative to other components of the printing system 100. When the medium 115 is transported relative to the print bar 120, the print heads 122 deposit ink 117 on the medium 115. The ink 117 can be deposited according to any text, image, pattern, or other specific data, and the medium can include any substrate, including, for example, paper, film, cardboard, tile, or cloth. In some embodiments, the medium 115 can be constrained on the drive belt 112 (e.g., by a clamp or vacuum) to flatten the medium 115 against the belt 112 or to ensure that the medium 115 does not move relative to the belt 112 during printing.

[0012] A controller 140 controllably powers the components of the printing system 100 (e.g., the print bar 120 and the drive mechanism 130). The controller 140 can include one or more processors 142 and a storage device 144 (e.g., a memory). In some embodiments, the controller 140 is configured to control any movement and operation in the printing system 100, such as moving the drive belt 112 via the drive mechanism 130, feeding the medium 115 via a feed system (not shown), or coordinating the operation of the print heads 122.

[0013] In some embodiments, to print content onto the medium 115, the controller 140 receives a print job (e.g., a Tagged Image File Format (TIFF) file). The controller 140 can then generate a raster image, which can be divided into separations that are sent to the print bars 120. Based on these separations, the controller of each print bar 120 or a slave computer can control its corresponding print head 122 to print the corresponding color or other coating onto the medium 115.

[0014] The linear rotary encoder 160 measures the movement of the drive belt 112 through the printing system 100. The encoder 160 generates a signal representing the position of the belt 112, which can be output to the controller 140 to control the drive mechanism 130 and / or the print bars 120 based on this signal. For example, the information about the position of the belt 112 output by the encoder 160 can be used as feedback to control the rate at which the drive mechanism 130 drives the drive belt 112. Similarly, the position of the belt 112 can be used to control the position of the print bars 120 to ensure that the print job is correctly printed onto the medium 115. The encoder 160 will be further described with reference to Figures 2A - 2B Further.

[0015] The printing system 100 is shown by way of example only. The linear rotary encoder 160 according to the embodiments described herein can be used in any of a variety of systems that benefit from precise tracking of mechanical components. Additionally, when the encoder 160 is used in a printing system, these systems can have more, fewer, or different components than those Figure 1 shown, or the arrangement of these components can be different from that Figure 1 shown. For example, the printing system can have a roller that feeds the medium directly through the system relative to the print head, rather than a drive belt 112 that drives and then supports the medium through the system.

[0016] Figures 2A - 2B An example embodiment of the linear rotary encoder 160 is shown. As Figures 2A - 2B shown, the encoder 160 can include a pair of rotary surfaces 205, having a first rotary surface 205A and a second rotary surface 205B. In some embodiments, each rotary surface 205 can be a wheel mounted on a corresponding shaft 210A, 210B. The shafts 210A, 210B can be coupled by a bracket 215, or each shaft 210 can be coupled to the housing of the encoder 160 or another structure in the printing system 100 that can support the encoder 160. In other embodiments, the rotary surfaces 205 are bearings. The bearings can be low-friction bearings, such as air bearings, liquid bearings, magnetic bearings, or ball bearings.

[0017] The linear rotary encoder 160 may also include a contact strip 220 and a coding strip 225. The contact strip 220 may have a first end 222A coupled to (e.g., partially surrounding) the first rotary surface 205A and a second end 222B coupled to (e.g., partially surrounding) the second rotary surface 205B. When the medium 115 is driven by the printing system 100, the contact strip 220 may rotate relative to the axis 210 about the rotary surface 205. In some embodiments, the contact strip 220 is in direct contact with the medium 115 (e.g., as Figure 2A shown). However, in other embodiments, the contact strip 220 instead contacts the drive belt 112, where the drive belt 112 in turn drives the medium 115 through the printing system 100.

[0018] Figure 3 is a diagram showing the contact strip 220 and the coding strip 225 in more detail. As Figure 3 shown, the contact strip 220 may have an outer surface 262 and an inner surface 264. The outer surface 262 may contact the medium 115, e.g., Figure 3 shown. However, in other embodiments, the outer surface 262 may contact the drive belt 112. To ensure that the contact strip 220 does not slide relative to the medium 115, the coefficient of friction between the outer surface 262 and the medium 115 (or the drive belt 112) may be relatively high. That is, the coefficient of friction may be high enough such that the force required to overcome the static friction force (i.e., the maximum static friction force) between the contact strip 220 and the medium 115 is greater than the driving force applied transversely to the medium 115.

[0019] Return Figures 2A - 2B , the position of the coding strip 225 may be set between the contact strip 220 and the rotary surface 205 and coupled to the inner surface 264 of the contact strip 220. The coding strip 225 may have a scale readable by the reader 230 to measure the distance the contact strip 220 moves. In various embodiments, the coding strip 225 may be a strip separate from but coupled to the contact strip 220 (e.g., by glue, by one or more fasteners such as brads, tacks, or clamps, or by a high coefficient of friction between the contact strip 220 and the inner surface 264 of the contact strip 220). In other embodiments, the coding strip 225 may be integrated into the contact strip 220. For example, the coding strip 225 may be a readable scale printed on the inner surface 264 of the contact strip 220.

[0020] At least one of the contact band 220 and the encoding band 225 may have a relatively high overall stiffness to reduce the amount of expansion or contraction of the band as it rotates around the rotating surface 205. Additionally, each band 220, 225 may include a single material or multiple layers with different materials for each layer. For example, the contact band 220 may have a first layer with a relatively rigid material to reduce tension or compression, and a second layer at the outer edge 262 with a material having a high coefficient of friction (such as rubber).

[0021] In some embodiments, the rotating surface 205 rotates around its corresponding axis 210. In such cases, the contact band 220 and the encoding band 225 do not slide relative to the rotating surface 205, but instead cause the rotating surface 205 to rotate as the bands rotate. Additionally, the coefficient of friction between each rotating surface 205 and the corresponding axis 210 may be relatively low to ensure that the rotating surface 205 rotates freely. For example, the coefficient of friction may be low enough such that the torque applied by the band to the rotating surface 205 is greater than the reaction frictional force applied by the axis 210 to the rotating surface. In some cases, the rotating surface 205 and the axis 210 are configured such that the frictional force is significantly lower than the applied torque, for example, by at least one order of magnitude.

[0022] In other embodiments, the rotating surface 205 is fixedly coupled to the axis 210 and does not rotate around the axis. In these cases, the contact band 220 and the encoding band 225 slide around the rotating surface 205. The coefficient of friction between the rotating surface 205 and the bands 220, 225 may be low enough such that the bands 220, 225 can slide freely without significantly resisting the movement of the tracking medium 115 through the printing system 100. For example, the coefficient of friction may be low enough such that the driving force applied to drive the bands 220, 225 around the rotating surface 205 is greater than the reaction frictional force applied by the rotating surface 205 to the bands 220, 225. In some embodiments, the frictional force may be significantly lower, for example, by at least one order of magnitude.

[0023] In other embodiments, one rotating surface 205 may be fixed relative to its corresponding axis 210, while the other rotating surface 205 may rotate freely around its axis 210. For example, the contact band 210 may drive the first rotating surface 205A to rotate relative to the axis 210A (the contact band 210 does not slide relative to the first rotating surface 205A), while the contact band 210 slides around the second rotating surface 205B that is fixed relative to the axis 210B.

[0024] The position of at least one reader 230 is set between the rotating surfaces 205 such that the reader can read the encoding scale on the encoding band 225. Figure 2A An example embodiment is shown where the encoder 160 has a single reader 230, while Figure 2BAn example embodiment of an encoder 160 having two readers 230A, 230B is shown. The readers 230 are configured to read a scale on an encoded tape 225 to measure the linear distance that the encoded tape 225 (and correspondingly, the medium 115) has been moved.

[0025] Figure 4 is a schematic diagram showing an example operation of the reader 230. As Figure 4 shown, the encoded tape 225 can have a series of scale lines 405 spaced at a known regular distance. The reader 230 can include an optical emitter 410 (e.g., an LED) and an optical detector 415 (e.g., a photodetector). The optical emitter 410 emits an optical signal 420 towards the encoded tape 225. The optical detector 415 detects a reflection 425 of the optical signal 420. Based on the reflected signal 425, the reader 230 can detect the scale lines 405. When the encoded tape 225 passes by the reader, the scale lines 405 can be counted, and the known spacing between the lines 405 can be used to convert the number of lines into a distance. Thus, by counting the scale lines 405, the position change of the medium 115 can be measured.

[0026] Other embodiments of the reader 230 can be configured to detect distance using methods other than optical measurement. For example, the reader 230 and the encoded scale can be magnetic, capacitive, or inductive.

[0027] In an embodiment where the encoder 160 has multiple readers 230, each reader 230 can output a signal representing the distance that the contact tape 220 has moved. The controller 140 can compare these signals to determine the actual distance that the contact tape 220 has moved. For example, if the encoded tape 225 has a seam, gap, or other irregularity that interferes with the encoded scale, the measurement result of a single reader 230 may be inaccurate when the reader 230 reads the scale portion affected by the irregularity. Thus, for example, if the controller 140 detects that the measurement of the first reader is disrupted while the measurement of the second reader is not, the controller 140 can use the signal output by the unaffected reader 230 until the disruption has passed the first reader.

[0028] In summary, for purposes of illustration, specific embodiments of the present technology have been described herein, but various modifications can be made without departing from the scope of the present technology. Therefore, the present technology is not limited except as by the appended claims.

Claims

1. A linear rotary encoder system, comprising: A pair of wheels, including a first wheel and a second wheel spaced apart from the first wheel; A contact belt having a first end coupled to the first wheel and a second end coupled to the second wheel, and being driven to rotate around the pair of wheels by a driving force applied to a medium to move the medium from the first end towards the second end; Wherein, the maximum static friction force between the contact belt and the medium is greater than the driving force applied to the medium; A coding scale coupled to the inner surface of the contact belt; and A reader positioned to read the coding scale when the contact belt rotates around the pair of wheels, the reader generating an output signal representing the position of the medium based on the reading of the coding scale; Wherein, the reader is a first reader that generates a first output signal, and wherein the linear rotary encoder system further includes a second reader that generates a second output signal, and the position of the medium is determined based on the first output signal and the second output signal.

2. The linear rotary encoder system according to claim 1, further comprising a coding tape coupled to the inner surface of the contact belt, wherein the coding scale is located on the coding tape.

3. The linear rotary encoder system according to claim 1, wherein the coding tape is located on the inner surface of the contact belt.

4. The linear rotary encoder system according to claim 1, wherein the coding tape includes a series of scale lines, and counting them is used to measure the change in the position of the medium.

5. The linear rotary encoder system according to claim 1, wherein each of the first wheel and the second wheel is caused to rotate about an axis by the contact belt.

6. The linear rotary encoder system according to claim 1, wherein the contact belt slides around the first wheel and the second wheel.

7. The linear rotary encoder system according to claim 1, wherein the reader is located between the first wheel and the second wheel.

8. A printer system, comprising: A driver configured to drive a medium through the printer system; One or more print heads configured to deposit ink on the medium; And A linear rotary encoder that generates an output signal representing the position of the medium in the printer system when the driver drives the medium relative to the print heads, the linear rotary encoder including: A pair of rotating surfaces, including a first rotating surface and a second rotating surface spaced apart from the first rotating surface; A contact belt having a first end coupled to the first rotating surface and a second end coupled to the second rotating surface, and being driven to rotate around the pair of rotating surfaces by a driving force applied by the driver to the medium to move the medium from the first end towards the second end; A driving belt that supports the medium, wherein the driver applies the driving force to the driving belt, Wherein, the contact belt touches the driving belt, and the maximum static friction force between the contact belt and the driving belt is greater than the driving force A coded scale, which is coupled to the inner surface of the contact strip; and A reader, whose position is set to read the coded scale when the contact strip rotates around the pair of rotating surfaces, and the reader generates an output signal representing the position of the medium based on the reading of the coded scale, wherein the reader is a first reader that generates a first output signal, and wherein the linear rotary encoder further includes a second reader that generates a second output signal, and the position of the medium is determined based on the first output signal and the second output signal.

9. The printer system according to claim 8, further comprising a controller configured to receive the output signal from the reader and control the print head to deposit the ink on the medium based on the output signal.

10. The printer system according to claim 8, wherein the contact strip touches the medium, and wherein the maximum static friction between the contact strip and the medium is greater than the driving force.

11. The printer system according to claim 8, further comprising a coded strip coupled to the inner surface of the contact strip, wherein the coded scale is located on the coded strip.

12. The printer system according to claim 11, wherein the coded strip includes a series of scale lines, and the number of these scale lines is counted to measure the change in the position of the medium.

13. The printer system according to claim 8, wherein each of the first rotating surface and the second rotating surface includes a wheel, and wherein the contact strip causes each wheel to rotate about an axis.

14. The printer system according to claim 8, wherein the position of the reader is set between the first rotating surface and the second rotating surface.

15. The printer system according to claim 8, wherein the driver drives the medium unidirectionally through the printer system.

16. The printer system according to claim 8, wherein the first rotating surface and the second rotating surface include low-friction bearings.

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