# US 10,308,457 B2 · Capacitive sensing for paper tray

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- Number: US 10,308,457 B2
- Document ID: US10308457B2
- Status: Granted
- Kind: B2
- Application number: 14/568,675
- Filed: 2014-12-12
- Published: 2015-06-18
- Granted: 2019-06-04
- Earliest claimed: 2013-12-12
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Evgeny Fomin; Alfred Gomes; Domenico Granozio; Matthew Christopher Kessler; Scott D. Kulchycki
- Web page: https://patentgrep.com/patent/US10308457B2

## CPC

- B65H 7/02: by feelers or detectors
- G01B 7/082: {Height gauges}
- B65H 2511/10: Size; Dimensions
- B65H 2511/11: Length
- B65H 2511/12: Width
- B65H 2511/15: Height, e.g. of stack
- B65H 2511/30: Numbers, e.g. of windings or rotations
- B65H 2515/70: Electrical or magnetic properties, e.g. electric power or current
- B65H 2553/23: Capacitive detectors, e.g. electrode arrangements
- B65H: HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A capacitive sensing system based on projected self-capacitance is suitable for use in printing systems/products to sense paper tray status. In example embodiments, a capacitive sensing system is adapted for sensing the condition/characteristics of paper in the paper tray, such as paper size, stack height and page count and paper dielectric. 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.

## Claims

### Claim 1

A method of measuring paper characteristics for paper within a paper tray using capacitive sensing, the paper tray including at least two capacitive sensors with respective capacitive electrodes CIN1 and CIN2, each with a ground plane at a paper tray bottom, with CIN1 and CIN2 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 CIN1, and partially covers CIN2, with CIN2 having a length a2=a2p+a2a, where a2p is a portion of the CIN2 length a2 that is over the paper, and a2a is a portion of the CIN2 length a that is not over the paper, the method comprising
with no paper in the paper tray, measuring a capacitance CA0=CIN1 to the ground plane;
with paper in the paper tray,
measuring a capacitance CA1=CIN1 to ground;
measuring a capacitance CA2=CIN2 to ground; and
determining CDIFF w=CA1*(1−a2p/a2)−CA0*(aa/a); and
determining paper width based on:
a2=a2p+a2a
a2p=a2−a2a
a2a=(a2*CDIFF w)/(CA1−CA0)
with paper width corresponding to a percentage (a2p/a) of CIN2 covered by paper.

### Claim 2 (depends on 1)

The method of claim 1, further comprising calibrating for tray thickness, sensor size/position and sensor ground plane position, based on CA0.

### Claim 3 (depends on 1)

The method of claim 1, further including a third capacitive sensor CIN3 at the top of the paper tray, oriented relative to a length dimension of the paper in the paper tray such that the paper partially covers CIN3, with CIN3 having a length a3=a3p+a3a, where a3p is a portion of the CIN2 length a3 that is over the paper, and a3a is a portion of the CIN3 length a that is not over the paper, and further comprising:
measuring a capacitance CA1=CIN1 to ground;
measuring a capacitance CA3=CIN3 to ground; and
determining CDIFF I=CA1*(1−a3p/a3)−CA0*(a3a/a3); and
determining paper length based on:
a3=a3p+a3a
a3p=a3−a3a
a3a=(a3*CDIFF I)/(CA1−CA0)
with paper length corresponding to a percentage (a2p/a) of CIN3 covered by paper.

### Claim 4 (depends on 1)

The method of claim 1, further comprising determining page count by:
measuring capacitance CA1,0
CA
⁢
⁢
1
,
0
=
(
CAIR
-
1
+
CPAPER
-
1
)
-
1
=
[
1
CA
⁢
⁢
0
+
dp
ɛ
⁢
⁢
0
⁢
⁢
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
]
-
1
where
CA
0
=
k
*
ɛ
0
*
ɛ
A
*
A
d
⁢
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 εA is the dielectric constant of the air, εp is the dielectric constant of paper, k accounts for fringing, A is sensor area; and
determining dp as the total thickness of paper between sensor CIN1 and ground (total stack height), where da is the total thickness of air between the sensor and ground, so that d=dp+da, and da=d−dp
feeding one page of paper d1page, and measuring capacitance CA1,1 where
CA
⁢
⁢
1
,
1
=
[
1
CA
⁢
⁢
0
+
(
dp
-
d
⁢
⁢
1
⁢
page
)
ɛ
⁢
⁢
0
*
⁢
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
]
-
1
determining d1page; and
determining page count=dp/(d1page).

### Claim 5 (depends on 1)

The method of claim 1, further comprising determining paper dielectric εp according to:
1
/
ɛ
pape
⁢
r
_
_
⁢
d
⁢
⁢
ɛ
air
+
(
nw
-
d
)
⁢
ɛ
eff
nw
⁢
⁢
ɛ
eff
⁢
ɛ
air
where εeff is the average dielectric between CIN1 and GND; n=number of pages, w=sheet thickness (d1page), and stack height=nw (dp); and (d) is the distance between the capacitive electrode CIN1 and GND.

### Claim 6 (depends on 1)

The method of claim 1, wherein the paper tray includes a capacitive sensor with co-planar interdigitated capacitive E1 and ground G1 electrodes (together the E1/G1 interdigitated electrodes, disposed in the paper tray such that paper contacts the E1/G1 electrodes, the E1/G1 electrodes configured such that during capacitive sensing a fringing electric field is substantially confined to one sheet of paper, the method further comprising:
measuring capacitance CD_nopaper with the E1/G1 electrodes with no paper present;
measuring capacitance CD_paper with the E1/G1 electrodes with paper present;
determining paper dielectric εp based on CD_nopaper and CD_paper, and a thickness w of one sheet of paper.

### Claim 7

A system for measuring paper characteristics for paper within a paper tray using capacitive sensing, comprising:
the paper tray including at least two capacitive sensors with respective capacitive electrodes CIN1 and CIN2, each with a ground plane at a paper tray bottom, with CIN1 and CIN2 at a top of the paper tray
CIN1 and CIN2 oriented relative to a width dimension of the paper in the paper tray such that the paper covers CIN1, and partially covers CIN2, with CIN2 having a length a2=a2p+a2a, where a2p is a portion of the CIN2 length a2 that is over the paper, and a2a is a portion of the CIN2 length a that is not over the paper;
a capacitance-to-digital converter (CDC) configured to acquire capacitance measurements from the capacitive sensors, and to convert capacitance measurements into sensor date representative of paper width;
the CDC configured to acquire capacitance measurements based on:
with no paper in the paper tray, measuring a capacitance CA0=CIN1 to the ground plane, and
with paper in the paper tray,
measuring a capacitance CA1=CIN1 to ground,
measuring a capacitance CA2=CIN2 to ground; and
the CDC is configured to convert these capacitance measurements into sensor data for:
determining CDIFF_w=CA1*(1−a2p/a2)−CA0*(aa/a), and
determining paper width based on:
a2=a2p+a2a,
a2p=a2−a2a,
a2a=(a2*CDIFF_w)/(CA1−CA0);
with paper width corresponding to a percentage (a2p/a) of CIN2 covered by paper.

### Claim 8 (depends on 7)

The system of claim 7, wherein the CDC is configured to convert the capacitance measurements CA0 into sensor data for calibrating for tray thickness, sensor size/position and sensor ground plane position.

### Claim 9 (depends on 7)

The system of claim 7, further including a third capacitive sensor CIN3 at the top of the paper tray, oriented relative to a length dimension of the paper in the paper tray such that the paper partially covers CIN3, with CIN3 having a length a3=a3p+a3a, where a3p is a portion of the CIN2 length a3 that is over the paper, and a3a is a portion of the CIN3 length a that is not over the paper, and wherein:
the CDC is configured to acquire capacitance measurements, including:
measuring a capacitance CA1=CIN1 to ground, and
measuring a capacitance CA3=CIN3 to ground; and
the CDC is configured to convert these measurements into sensor data for determining paper length based on determining CDIFF_I=CA1*(1−a3p/a3)−CA0*(a3a/a3),
where,
a3=a3p+a3a,
a3p=a3−a3a, and
a3a=(a3*CDIFF_I)/(CA1−CA0);
with paper length corresponding to a percentage (a2p/a) of CIN3 covered by paper.

### Claim 10 (depends on 7)

The system of claim 7, wherein:
the CDC is configured to convert capacitance measurements CA0 into sensor data for determining page count based on:
determining capacitance CA1,0
CA
⁢
⁢
1
,
0
=
(
CAIR
-
1
+
CPAPER
-
1
)
-
1
=
[
1
CA
⁢
⁢
0
+
dp
ɛ
⁢
⁢
0
⁢
⁢
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
]
-
1
where
CA
0
=
k
*
ɛ
0
*
ɛ
A
*
A
d
⁢
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 εA is the dielectric constant of the air, εp is the dielectric constant of paper, k accounts for fringing, A is sensor area; and
determining dp as the total thickness of paper between sensor CIN1 and ground (total stack height), where da is the total thickness of air between the sensor and ground, so that d=dp+da, and da=d−dp;
feeding one page of paper d1page, and determining capacitance CA1,1,
CA
⁢
⁢
1
,
1
=
[
1
CA
⁢
⁢
0
+
(
dp
-
d
⁢
⁢
1
⁢
page
)
ɛ
⁢
⁢
0
⁢
*
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
]
-
1
determining d1page; and
determining page count=dp/(d1page).

### Claim 11 (depends on 7)

The system of claim 7, wherein:
the CDC is configured to provide sensor data for determining paper dielectric εp according to:
1
/
ɛ
pape
⁢
r
_
_
⁢
d
⁢
⁢
ɛ
air
+
(
nw
-
d
)
⁢
ɛ
eff
nw
⁢
⁢
ɛ
eff
⁢
ɛ
air
where εeff is the average dielectric between CIN1 and GND; n=number of pages, w=sheet thickness (d1page), and stack height=nw (dp); and (d) is the distance between the capacitive electrode CIN1 and GND.

### Claim 12 (depends on 7)

The system of claim 7, wherein the paper tray includes a capacitive sensor with co-planar interdigitated capacitive E1 and ground G1 electrodes (together the E1/G1 interdigitated electrodes, disposed in the paper tray such that paper contacts the E1/G1 electrodes, the E1/G1 electrodes configured such that during capacitive sensing a fringing electric field is substantially confined to one sheet of paper, and wherein:
the CDC is configured to acquire capacitance measurements
CD_nopaper with the E1/G1 electrodes with no paper present, and
CD_paper with the E1/G1 electrodes with paper present; and
the CDC is configured to provide sensor data for determining paper dielectric εp based on CD_nopaper and CD_paper, and a thickness w of one sheet of paper.

### Claim 13

A capacitance-to-digital converter (CDC) for use in a system for measuring paper characteristics for paper within a paper tray using capacitive sensing, the paper tray including at least two capacitive sensors with respective capacitive electrodes CIN1 and CIN2, each with a ground plane at a paper tray bottom, with CIN1 and CIN2 at a top of the paper tray, and with CIN1 and CIN2 oriented relative to a width dimension of the paper in the paper tray such that the paper covers CIN1, and partially covers CIN2, with CIN2 having a length a2=a2p+a2a, where a2p is a portion of the CIN2 length a2 that is over the paper, and a2a is a portion of the CIN2 length a that is not over the paper, the CDC comprising:
acquisition circuitry configured to acquire capacitance measurements, including:
with no paper in the paper tray, a capacitance CA0=CIN1 to the ground plane, and
with paper in the paper tray,
a capacitance CA1=CIN1 to ground,
a capacitance CA2=CIN2 to ground; and
conversion circuitry configured to convert these capacitance measurements into sensor data for:
determining CDIFF_w=CA1*(1−a2p/a2)−CA0*(aa/a), and
determining paper width based on:
a2=a2p+a2a,
a2p=a2−a2a,
a2a=(a2*CDIFF_w)/(CA1−CA0);
with paper width corresponding to a percentage (a2p/a) of CIN2 covered by paper.

### Claim 14 (depends on 13)

The CDC of claim 13, wherein:
the conversion circuitry is configured to convert the capacitance measurements CA0 into sensor data for calibrating for tray thickness, sensor size/position and sensor ground plane position.

### Claim 15 (depends on 13)

The CDC of claim 13, further including a third capacitive sensor CIN3 at the top of the paper tray, oriented relative to a length dimension of the paper in the paper tray such that the paper partially covers CIN3, with CIN3 having a length a3=a3p+a3a, where a3p is a portion of the CIN2 length a3 that is over the paper, and a3a is a portion of the CIN3 length a that is not over the paper, and wherein:
the acquisition circuitry is configured to acquire capacitance measurements:
a capacitance CA1=CIN1 to ground, and
a capacitance CA3=CIN3 to ground; and
the conversion circuitry is configured to convert these measurements into sensor data for determining paper length based on determining CDIFF_I=CA1*(1−a3p/a3)−CA0*(a3a/a3),
where,
a3=a3p+a3a,
a3p=a3−a3a, and
a3a=(a3*CDIFF_I)/(CA1−CA0);
with paper length corresponding to a percentage (a2p/a) of CIN3 covered by paper.

### Claim 16 (depends on 13)

The CDC of claim 13, wherein:
the conversion circuitry is configured capacitance measurements CA0 into sensor data for determining page count based on:
determining capacitance CA1,0
CA
⁢
⁢
1
,
0
=
(
CAIR
-
1
+
CPAPER
-
1
)
-
1
=
[
1
CA
⁢
⁢
0
+
dp
ɛ
⁢
⁢
0
⁢
⁢
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
-
1
]
where
CA
0
=
k
*
ɛ
0
*
ɛ
A
*
A
d
⁢
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 εA is the dielectric constant of the air, εp is the dielectric constant of paper, k accounts for fringing, A is sensor area; and
determining dp as the total thickness of paper between sensor CIN1 and ground (total stack height), where da is the total thickness of air between the sensor and ground, so that d=dp+da, and da=d−dp;
feeding one page of paper d1page, and determining capacitance CA1,1,
CA
⁢
⁢
1
,
1
=
[
1
CA
⁢
⁢
0
+
(
dp
-
d
⁢
⁢
1
⁢
⁢
page
)
ɛ
⁢
⁢
0
⁢
*
A
⁢
(
1
ɛ
⁢
⁢
P
-
1
ɛ
⁢
⁢
A
)
]
-
1
determining d1page; and
determining page count=dp/(d1page).

### Claim 17 (depends on 7)

The system of claim 7, wherein:
the conversion circuitry is configured to provide sensor data for determining paper dielectric εp according to:
1
/
ɛ
pape
⁢
r
_
_
⁢
d
⁢
⁢
ɛ
air
+
(
nw
-
d
)
⁢
ɛ
eff
nw
⁢
⁢
ɛ
eff
⁢
ɛ
air
where εeff is the average dielectric between CIN1 and GND; n=number of pages, w=sheet thickness (d1page), and stack height=nw (dp); and (d) is the distance between the capacitive electrode CIN1 and GND.

### Claim 18 (depends on 13)

The CDC of claim 13, wherein the paper tray includes a capacitive sensor with co-planar interdigitated capacitive E1 and ground G1 electrodes (together the E1/G1 interdigitated electrodes, disposed in the paper tray such that paper contacts the E1/G1 electrodes, the E1/G1 electrodes configured such that during capacitive sensing a fringing electric field is substantially confined to one sheet of paper, and wherein:
the acquisition circuitry is configured to acquire capacitance measurements CD_nopaper with the E1/G1 electrodes with no paper present, and CD_paper with the E1/G1 electrodes with paper present; and
the conversion circuitry is configured to provide sensor data for determining paper dielectric εp based on CD_nopaper and CD_paper, and a thickness w of one sheet of paper.