Capacitive sensing for paper tray

Priority is claimed under USC § 119(e) to: (a) U.S. Provisional Application 61/915,036, filed 12 Dec. 2013, and (b) US Provisional Application 61/932,394, filed 28 Jan. 2014.

This Patent Document relates generally to printing systems/products that include sheet feeding from a paper tray.

Printing systems/products that provide printed (paper) output, typically include sheet feeding apparatus. The sheet feeding apparatus feeds paper to a printing apparatus from a paper tray.

These printing systems/products commonly include various mechanical or electronic mechanisms to determine the condition or characteristics of paper in the tray. For example, paper tray sensing mechanism can be used to determine paper quantity and paper size.

This Brief Summary is provided as a general introduction to the Disclosure provided by the Detailed Description and Figures, summarizing some aspects and features of the disclosed invention. It is not a complete overview of the Disclosure, and should not be interpreted as identifying key elements or features of the invention, or otherwise characterizing or delimiting the scope of the invention disclosed in this Patent Document.

The Disclosure describes apparatus and methods for capacitive sensing for paper tray status (paper condition/characteristics), such as paper size, paper stack height, page count and paper dielectric.

According to aspects of the Disclosure, measuring paper characteristics for paper within a paper tray using capacitive sensing. The paper tray is configured with at least two capacitive sensors with respective capacitive electrodes CIN 1 and CIN 2 , each with a ground plane at a paper tray bottom, with CIN 1 and CIN 2 at a top of the paper tray oriented relative to a width dimension of the paper in the paper tray such that the paper covers CIN 1 , and partially covers CIN 2 , and with CIN 2 having a length a2=a2p+a2a, where a2p is a portion of the CIN 2 length a2 that is over the paper, and a2a is a portion of the CIN 2 length a that is not over the paper. The method can include: (a) with no paper in the paper tray, measuring a capacitance CA 0 =CIN 1 to the ground plane; (b) with paper in the paper tray, measuring a capacitance CA 1 =CIN 1 to ground; (c) measuring a capacitance CA 2 =CIN 2 to ground; and (d) determining CDIFF_w=CA 1 *(1−a2p/a2)−CA 0 *(aa/a); and (e) determining paper width based on (1) a2=a2p+a2a, (2) a2p=a2−a2a, and (3) a2a=(a2*CDIFF_w)/(CA 1 −CA 0 ). Paper width corresponds to a percentage (a2p/a) of CIN 2 covered by paper.

Other aspects and features of the invention claimed in this Patent Document will be apparent to those skilled in the art from the following Disclosure.

FIG. 1 is an example functional illustration of a capacitive sensing system based on projected self-capacitance, adaptable for use in printing systems/products to sense the condition/characteristics of paper in the paper tray, such as paper size and paper stack height (page count), and to determine paper type (paper dielectric).

FIGS. 2A, 2B and 2C illustrates an example embodiment of a paper tray with capacitive sensing for measuring paper size/width, including: ( 2 A/B) top and side views illustrating a paper tray incorporating a capacitive sensor, including capacitive electrodes CIN 1 and CIN 2 , and ( 2 C) example capacitive sensing results.

FIGS. 3A, 3B and 3C illustrate an example embodiment of a paper tray with capacitive sensing for measuring paper stack height/page count, including: ( 2 A/B) top and side views illustrating a paper tray incorporating a capacitive sensor, including capacitive electrode CIN 1 , and ( 3 C) example capacitive sensing results.

FIG. 4 illustrates and example embodiment of a paper tray with a capacitive sensing for measuring paper dielectric, including example inter-digitated (co-planar) capacitive and ground electrodes E 1 and G 1 .

This Description and the Figures disclose example embodiments and applications that illustrate various features and advantages of a capacitive system for sensing paper tray status.

In brief overview, a capacitive sensing system is based on projected self-capacitance. In example embodiments, the capacitive sensing system can be configured with one or more shielded capacitive sensors incorporated into the paper tray, and oriented relative to the paper according to the paper condition/characteristic sensed.

FIG. 1 is an example functional illustration of a capacitive sensing system 100 suitable for use in printing systems/products, and in particular, for use in sensing paper tray status. More particularly, capacitive sensing system 100 is adapted to embodiments of the invention used to sense the condition/characteristics of paper in the paper tray, such as paper size, paper stack height, page count and paper dielectric.

Capacitive sensing system 100 includes a capacitive sensor 110 and capacitance acquisition/conversion 130 formed by a capacitance-to-digital conversion (CDC) unit 150 , and a data processor 170 .

In example embodiments, capacitive sensor 110 is adapted for incorporation into a paper tray, and configured for capacitive sensing of condition/characteristics of paper 120 . The capacitive sensor 110 need not be co-located with the CDC unit 150 , but to reduce the effects of parasitic capacitance, CDC 150 is preferably located as close as possible to capacitive sensor 110 .

Capacitive sensing system 100 is configured for capacitive sensing based on projected self-capacitance. Capacitive sensor 110 includes a sensor electrode 111 and a driven sensor shield 113 , separately coupled to CDC 150 (Acquisition Channel input CH and Shield Excitation/Driver output SHIELD).

Capacitive sensor 110 includes a driven sensor shield 113 , also coupled to a shield driver in CDC 150 . Sensor shield 113 is disposed over, and insulated from, sensor electrode 111 . Shield drive can be provided synchronously with sensor excitation frequency, and can be used to focus sensing direction, and to counteract parasitic capacitance.

CDC 150 acquires capacitance measurements from capacitive sensor 110 , and converts these capacitance measurements to digital sensor data representative of paper condition/characteristics. The CDC sensor data can be input to data processor 170 , and processed to provide paper tray status information.

FIGS. 2A, 2B and 2C illustrates an example paper tray 201 with capacitive sensing adapted for measuring paper size/width, including a capacitive sensor with example capacitive electrodes CIN 1 and CIN 2 ( 211 and 212 ). The example capacitive electrodes CIN 1 and CIN 2 are substantially identical in configuration with a length a (a1 and a2) and width b, with an area A=a*b. The capacitive sensing system includes a capacitive sensor structure with (shielded) capacitive electrodes CIN 1 and CIN 2 configured for capacitance measurements of paper size/width based on projected self-capacitance.

FIGS. 2A and 2B are top and side views that illustrate an example arrangement for the elements of the capacitive sensor incorporated with a paper tray 201 , and in particular, the placement of the capacitive electrodes CIN 1 and CIN 2 relative to the paper 220 , which is aligned within the tray at 203 . Specifically, capacitive sensor/electrode CIN 1 is positioned so that it is covered by paper 220 in tray 201 , and capacitive sensor/electrode CIN 2 is positioned relative to the width dimension of the paper so that it is partially covered by paper 220 in tray 201 : CIN 2 has a length a2=a2p+a2a, where a2p is a portion of the CIN 2 length a2 that is over the paper, and a2a is a portion of the CIN 2 length a that is not over the paper.

Referring to FIG. 2B , a capacitive sensor includes capacitive electrodes CIN 1 and CIN 2 ( 211 and 212 ), shield 213 and insulator 214 , integrated or mounted within tray 201 . A ground plane 219 is spaced from the capacitive sensors CIN 1 and CIN 2 in the projection direction. As illustrated ground plane 219 is on the bottom side of tray 201 —alternatively, the ground plane can be located within the tray, adjacent paper 201 .

For paper size/width measurement, CIN 1 measurements are used to calibrate for the type of paper, and combined CIN 1 and CIN 2 measurements are used to determine paper size/width. If CIN 1 and CIN 2 are not identical, CIN 2 can be calibrated.

An example methodology for determining paper size/width based on capacitive sensing involves first calibrating for tray thickness and sensor size/position based on a capacitive measurement CA 0 =CIN 1 to ground (with no paper present).

For paper size/width measurement operations, with paper present, CIN 1 and CIN 2 measurements are captured:

CA 1 =CIN 1 to ground

CA 2 =CIN 2 to ground

C DIFF= CA 1 −CA 2

Paper width can be determined from a percentage of CIN 2 covered by paper, as represented by CDIFF.

An example methodology for determining paper size/width is based on measuring CA 0 , CA 1 , and CA 2 , and using the following relationships:

a 2= a 2 p+a 2 a

where C DIFF_ w=CA 1*(1− a 2 p/a 2)− CA 0*( aa/a )

a 2 p=a 2− a 2 a

a 2 a =( a 2 *C DIFF_ w )/( CA 1− CA 0).

This methodology for determining paper size/width is independent of the dielectric of paper ε p .

Referring to FIG. 2B , the capacitive sensor (shield 213 , insulator 214 , electrodes CIN 1 /CIN 2 is mounted above tray 201 and paper 220 , so that the sensing field projects through the paper 220 toward the ground plane 219 . In an alternate configuration, the sensor can be mounted on the tray, oriented 180 degrees to the orientation illustrated, with the sensor electrodes CIN 1 /CIN 2 adjacent paper 220 .

A third capacitive sensor/electrode CIN 3 can be used to measure paper length using a similar method. Capacitive sensor/electrode C IN3 can be positioned so that it is partially covered in the length dimension by paper 220 in tray 201 (substantially as illustrated for CIN 2 for the width dimension).

FIG. 2C provides example measurement results based on the following parameters:

CIN 1 and CIN 2 electrode length is a=104 mm (a1+a2)

Letter paper is approximately 6 mm wider than A4

Cdiff_nopaper accounts for non-identical electrodes and is subtracted from CDIFF.

Example design modifications for the configuration of the capacitive electrodes CIN 1 and CIN 2 include, in addition to size/perimeter, different shapes/profiles, such as spiral.

FIGS. 3A, 3B and 3C illustrates an example paper tray with capacitive sensing for measuring paper stack height and page count. The capacitive sensing system includes a capacitive sensor structure with a (shielded) capacitive electrode CIN 1 ( 311 ) configured for capacitance measurements of paper stack height/page count based on projected self-capacitance.

FIGS. 3A and 3B are top and side views that illustrate an example arrangement for the elements of the capacitive sensor incorporated with a paper tray 301 , and in particular, the placement of the capacitive electrode C IN1 relative to the paper 320 , which is aligned within the tray at 303 . Specifically, capacitive sensor/electrode C IN1 is positioned so that it is covered by paper 220 in tray 201 .

Referring to FIG. 3B , a capacitive sensor includes a capacitive electrode CIN 1 ( 311 ), shield 313 and insulator 314 , integrated or mounted within tray 301 . A ground plane 319 is spaced from the capacitive sensor CIN 1 in the projection direction. As illustrated ground plane 319 bottom side of tray 301 —alternatively, the ground plane can be located within the tray, adjacent paper 301 .

An example methodology for sensing paper stack height involves first calibrating for tray thickness and sensor size/position based on a capacitive measurement CA 0 =CIN 1 to ground with no paper present.

For stack height measurement operation, with paper present, the CIN 1 measurement is captured: CA 1 =CIN 1 to ground, which is proportional to a total thickness of paper between CIN 1 and ground, i.e., total paper stack height.

Page count can be determined from an initial sheet feed. An example methodology for calculating the number of pages in the paper stack includes: (a) feed one paper sheet, and determine from capacitive measurements the change in stack height, so that (b) page count=previous stack height/change in stack height.

An example methodology for determining page count includes two determinations from the capacitance measurement CA 0 . First, determine capacitance CA 1 , 0 :

CA ⁢ ⁢ 1 , 0 = ⁢ ( CAIR - 1 + CPAPER - 1 ) - 1 = ⁢ [ 1 CA ⁢ ⁢ 0 + dp ɛ ⁢ ⁢ 0 ⁢ ⁢ A ⁢ ( 1 ɛ ⁢ ⁢ P - 1 ɛ ⁢ ⁢ A ) ] - 1

where dp is the total thickness of paper between sensor CIN 1 and ground; and where:

CA ⁢ ⁢ 0 = k * ɛ 0 * ɛ A * A d CAIR = k * ɛ 0 * ɛ A * A d - dp CPAPER = k * ɛ 0 * ɛ P * A dp

and where

da is the total thickness of air between the sensor and ground

d=dp+da

da=d−dp

ε A is the dielectric constant of the air

k accounts for fringing

A is sensor area.

Then feed one page of paper, and determine capacitance CA 1 , 1

CA ⁢ ⁢ 1 , 1 = [ 1 CA ⁢ ⁢ 0 + ( dp + d ⁢ ⁢ 1 ⁢ page ) ɛ ⁢ ⁢ 0 ⁢ ⁢ A ⁢ ( 1 ɛ ⁢ ⁢ P - 1 ɛ ⁢ ⁢ A ) ] - 1

where d 1page is the thickness of one sheet of paper.

Capacitance CA 1 , 0 can be used to determine dp as the total thickness of paper between sensor CIN 1 and ground (total stack height), and CA 1 , 1 can be used to determine d1page is the thickness of one sheet of paper. Then page count can be determined as: page count=dp/(d1page).

This initial-sheet-feed methodology, which provides sheet thickness d1page does not require prior knowledge of the dielectric constant of the paper ε p .

The dielectric constant of the paper ε p (paper type) can be determined from the above measurement for paper stack height and page count, including the determination of sheet thickness d 1page , which enables computation of the average dielectric ε eff between C IN1 and GND.

Average dielectric ε eff and the dielectric constant of the paper ε p are related by:

ɛ eff = 1 nw / d ⁡ ( 1 / ɛ paper - 1 / ɛ air ) + 1 / ɛ air

where n=number of pages, w=sheet thickness (d1page), so that nw is stack height (dp), and d is the distance between the capacitive electrode CIN 1 and GND.

Based on the known values:

Distance between CIN 1 and GND, d

Average dielectric between CIN 1 and GND, ε eff

Number of pages in the stack n (d1page/d)

Thickness of a single sheet of paper w

paper dielectric ε paper (paper type) can be determined from:

FIG. 3C provides example page count measurement results, comparing expected to actual results.

As an alternate embodiment for determining page count using an initial sheet feed (i.e., to determine sheet thickness d1page), the dielectric of the paper ε paper can be capacitively sensed, and page count determined if sheet thickness is known, or assumed.

FIG. 4 illustrates an example capacitive sensor arrangement adapted for measuring paper stack height/page count based on capacitively sensing paper dielectric. Two capacitive sensors are used. A capacitive sensor/electrode CIN 1 ( 411 ) is used as in the embodiment in FIGS. 3A /B. An inter-digitated (co-planar) capacitive sensor with capacitive/ground electrodes E 1 /G 1 is used for measuring paper dielectric ε paper .

Capacitive electrode CIN 1 is operable for the capacitive measurement CA 1 , 0 as described in connection with FIGS. 3A / 3 B—the capacitive measurement CA 1 , 1 after an initial sheet feed (to obtain d1page) need not be taken. The CIN 1 ground plane 419 can be disposed relative to CIN 1 as described above in connection with FIGS. 3A / 3 B.

For capacitive sensing in connection with determining paper dielectric ε paper , the inter-digitated (co-planar) capacitive/ground electrodes E 1 /G 1 are disposed on the interior surface of a paper tray, for example at the alignment corner (in FIG. 3A , at 303 ). The sensor/ground electrodes E 1 /G 1 are configured and oriented in an inter-digitated co-planar arrangement, preferably so that the projected fringe fields are confined to the typical thickness of one sheet of paper (approximately 100 microns).

Capacitance CD is measured with and without paper, to obtain the paper dielectric ε paper .

For this embodiment, which does not require an initial sheet feed to determine paper thickness (i.e., d1page), page count requires knowledge of paper dielectric ε paper and paper sheet thickness. Paper thickness can be determined by, for example, separate input, or based on assumption, for example, a standard paper thickness of approximately 100 microns.

The Disclosure provided by this Description and the Figures sets forth example embodiments and applications, including associated operations and methods, that illustrate various aspects and features of the invention. Known circuits, functions and operations are not described in detail to avoid unnecessarily obscuring the principles and features of the invention. These example embodiments and applications can be used by those skilled in the art as a basis for design modifications, substitutions and alternatives to construct other embodiments, including adaptations for other applications. Accordingly, this Description does not limit the scope of the invention, which is defined by the Claims.