# US 2014/0190811 A1 · Methods and apparatus for capacitively detecting key motion and finger presence on a magnetic keyboard key

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- Number: US 2014/0190811 A1
- Document ID: US20140190811A1
- Status: Published application
- Kind: A1
- Application number: 14/146,811
- Filed: 2014-01-03
- Published: 2014-07-10
- Earliest claimed: 2013-01-04
- Assignees: Synaptics Incorporated
- Applicants: Synaptics Incorporated
- Inventors: Robert J. Bolender; Joseph Kurth Reynolds
- Web page: https://patentgrep.com/patent/US20140190811A1

## CPC

- H03K 17/9622: {using a plurality of detectors, e.g. keyboard}
- G01R 27/2605: {Measuring capacitance (capacitive sensors G01D5/24)}
- G06F 3/0202: {Constructional details or processes of manufacture of the input device}
- H01H 3/122: {with enlarged actuating area, e.g. of the elongated bar-type; Stabilising means therefor}
- H01H 13/7065: characterised by the mechanism between keys and layered keyboards
- H01H 2217/01: Off centre actuation
- H01H 2221/04: magnetic
- H03K 17/98: having a plurality of control members, e.g. keyboard
- H03K 2217/96079: using a single or more light guides
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H01H: ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES (contact cables H01B7/10; electrolytic self-interrupters H01G9/18; emergency protective circuit arrangements H02H; switching by electronic means without contact-making H03K17/00)

## Abstract

Devices and methods for capacitively sensing key cap position during the initial and latter stages of a keystroke. A key assembly includes a stationary key guide magnet, a movable key cap magnet, and a transmitter/receiver electrode pair. One or both of the electrodes underlies the key cap. The capacitance change between the electrodes during a keystroke includes the capacitance change between the key cap and the electrode pair, and the change in capacitance between the key cap and the key guide. Key cap position may thus be accurately detected throughout the entire keystroke.

## Claims

### Claim 1

A keyboard comprising a plurality of key assemblies, wherein each of at least a subset of the key assemblies comprises:
a key guide having a first conductive portion;
a key cap having a second conductive portion;
a transmitter electrode; and
a receiver electrode disposed underneath the second conductive portion;
wherein the first and second conductive portions cooperate magnetically to return the key cap to a nominal position following a keystroke; and
wherein the first transmitter electrode and first receiver electrode form a variable capacitance in response to the keystroke.

### Claim 2 (depends on 1)

The keyboard of claim 1, wherein the transmitter electrode is disposed beneath the key guide.

### Claim 3 (depends on 1)

The keyboard of claim 1, wherein the transmitter electrode, the receiver electrode, and the first and second conductive portions are configured to form:
a first capacitance between the receiver electrode and the second conductive portion;
a second capacitance between the first and second conductive portions; and
a third capacitance between the transmitter electrode and the first conductive portion;
wherein the variable capacitance comprises the first, second, and third capacitances.

### Claim 4 (depends on 1)

The keyboard of claim 1, wherein the transmitter electrode is disposed beneath the key cap, and wherein the first conductive portion is configured to be maintained at a substantially constant electrical potential.

### Claim 5 (depends on 1)

The keyboard of claim 1, wherein at least one of the first and second conductive portions comprises a magnet.

### Claim 6 (depends on 1)

The keyboard of claim 1, wherein each of the subset of key assemblies further comprises a planar-translation-effecting (PTE) mechanism configured to impart planar, vertical, and lateral motion to the key cap when pressed by a user.

### Claim 7

A key assembly for use in a keyboard, the assembly comprising:
a key guide including a first magnetic component;
a key cap including a second magnetic component and configured to be pressed downwardly relative to the key guide; and
a keystroke sensor configured to measure a variable capacitance between the first and second magnetic components during a keystroke.

### Claim 8 (depends on 7)

The key assembly of claim 7, wherein the keystroke sensor comprises a transmitter electrode and a receiver electrode, wherein at least one of the transmitter electrode and the receiver electrode is disposed underneath the key cap.

### Claim 9 (depends on 7)

The key assembly of claim 7, wherein one of a transmitter electrode and a receiver electrode is disposed underneath the key cap, and one of the transmitter electrode and receiver electrode is disposed underneath the key guide.

### Claim 10 (depends on 7)

The key assembly of claim 7, wherein the keyboard comprises at least two key assemblies, and further wherein the same transmitter is associated with the at least two key assemblies.

### Claim 11 (depends on 7)

The key assembly of claim 7, wherein the variable capacitance further comprises a first capacitance between the first and second magnetic components, and a second capacitance between the keystroke sensor and the second magnetic component.

### Claim 12 (depends on 11)

The key assembly of claim 11, wherein the first capacitance decreases during a downward keystroke, and wherein the second capacitance increases during a downward keystroke.

### Claim 13

A method of detecting keystroke motion of a keyboard key responsive to applied force by an input object, the method comprising:
determining the keystroke motion based on a first and second capacitance;
wherein the first capacitance is formed between a stationary key guide and the key, and the second capacitance is formed between a stationary keystroke sensor and the key.

### Claim 14 (depends on 13)

The method of claim 13, wherein the first and second capacitances each comprise a variable capacitance.

### Claim 15 (depends on 13)

The method of claim 13, wherein the stationary keystroke sensor comprises a transmitter and receiver electrode pair, wherein at least one of the transmitter and receiver electrode is disposed underneath the key.

### Claim 16 (depends on 13)

The method of claim 13, wherein the first capacitance decreases with downward motion of the key.

### Claim 17 (depends on 13)

The method of claim 13, wherein the second capacitance increases with downward motion of the key.

### Claim 18 (depends on 13)

The method of claim 13, wherein determining the keystroke motion based on a first and second capacitance comprises measuring a composite third capacitance.

### Claim 19 (depends on 13)

The method of claim 13, wherein the same transmitter is associated with at least two keyboard keys.

### Claim 20 (depends on 13)

The method of claim 13, further comprising imparting planar, vertical, and lateral motion to the key during the keystroke.