INPUT DEVICE AND POSITION DETERMINING METHOD

• US 20120265485A1
• Filed: 04/17/2012
• Published: 10/18/2012
• Est. Priority Date: 04/21/2011
• Status: Active Grant

• Current Assignee: TRW Automotive Electronics & Components GmbH & Co. KG
• Original Assignee: TRW Automotive Electronics & Components GmbH & Co. KG
• Inventors: Backes, Ulrich
• Granted Patent: US 9,513,738 B2
• Time in Patent Office: Days
• US Class Current: 702/150
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

An input device (10) has a contact plate (12) having a contact surface (14) and being least partially coated with an electrical resistive layer (16) on a surface opposite the contact surface (14). The electrical resistive layer (16) has at least two electrically conducting contacts (18). A measuring circuit (20) is provided for measuring a sensing capacitor (24) formed by the electrical resistive layer (16) and an electrostatically chargeable object (22) arranged at a contact position on the contact surface (14). Further, a processing unit is provided for determining coordinates (X, Y) of the contact position of the electrostatically chargeable object (22) on the contact surface (14) by means of a determination of the ohmic resistances (R_n) between the contact position of the electrostatically chargeable object (22) and the electrically conducting contacts.

Claims

1. An input device (10), comprising:

a contact plate (12) which comprises a contact surface (14) and is at least partially coated with an electrical resistive layer (16) on a surface facing away from the contact surface (14), the electrical resistive layer (16) comprising at least two electrically conducting contacts (18),

and a measuring circuit (20) for measuring a sensing capacitor (24) formed by the electrical resistive layer (16) and an electrostatically chargeable object (22) arranged at a contact position on the contact surface (14),

a processing unit being provided with which coordinates (X, Y) of the contact position of the electrostatically chargeable object (22) on the contact surface (14) can be determined by determining the ohmic resistances (R₁, R₂, R₃, R_n) between the contact position of the electrostatically chargeable object (22) and the electrically conducting contacts (18).

2. The input device according to claim 1, characterized in that at least three electrically conducting contacts (18) are provided on the electrical resistive layer (16).

3. The input device according to claim 1, characterized in that the measuring circuit (20) comprises a reference capacitor (32).

4. The input device according to claim 3, characterized in that the measuring circuit (20) comprises several switches (28, 30, 34) for charging a sensing capacitor (24) formed by the electrical resistive layer (16) and the electrostatically chargeable object (22), for equalization of charge between the sensing capacitor (24) and the reference capacitor (32) and for discharging the sensing capacitor (24) and the reference capacitor (32).

5. The input device according to claim 1, characterized in that the electrical resistive layer (16) is formed so as to fully cover a surface area or so as to be ring-shaped.

6. A method of determining the position of an electrostatically chargeable object (22) on a contact plate (12) of an input device (10) according to any of the preceding claims, comprising the process steps:

measuring an RC element with the sensing capacitor (C_f) and the ohmic resistance (R_n) between the contact position of the electrostatically chargeable object (22) and each one of the electrically conducting contacts (18) when the sensing capacitor (C_f) is fully electrically charged;

measuring the RC element with the sensing capacitor (C_f) and the ohmic resistance (R_n) between the contact position of the electrostatically chargeable object (22) and each one of the electrically conducting contacts (18) when the sensing capacitor (C_f) is partially electrically charged;

determining the ohmic resistance (R_n) between the contact position of the electrostatically chargeable object (22) and each one of the electrically conducting contacts (18) by measuring the corresponding RC element;

determining the contact position of the electrostatically chargeable object (22) by means of the ohmic resistances (R_n) between the contact position of the electrostatically chargeable object (22) and the electrically conducting contacts (18).

7. The method according to claim 6, wherein the capacitance of the sensing capacitor (C_S) is determined in a process step.

8. The method according to claim 6, wherein a voltage (U_S) across a reference capacitor (C_S) is measured during measuring the RC element.

9. The method according to claim 8, wherein measuring the RC element comprises the process steps:

fully discharging the sensing capacitor (C_f) and the reference capacitor (C_S);

fully charging the sensing capacitor (C_f);

equalizing charge between the sensing capacitor (C_f) and the reference capacitor (C_S);

measuring the voltage (U_S) across the reference capacitor (C_S);

repeating the process steps with partially charging the sensing capacitor (C_f) for a charging duration (t).

10. The method according to claim 9, characterized in that the ohmic resistance (R_n) between the contact position of the electrostatically chargeable object (22) and each one of the electrically conducting contacts (18) is calculated according to the formula:

11. The method according to claim 6, characterized in that the coordinates (X, Y) of the contact position of the electrostatically chargeable object (22) are calculated according to the formulas: