Pressure-sensitive input apparatus

• US 4,929,934 A
• Filed: 09/22/1988
• Issued: 05/29/1990
• Est. Priority Date: 09/28/1987
• Status: Expired due to Fees

• Current Assignee: Nippon Telegraph and Telephone Corporation, OKI Electric Industry Company Limited
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Inohara, Kazuyoshi, Hattori, Kouji, Ueda, Kenichi, Terada, Akihiko
• Primary Examiner(s): OBERLEY, ALVIN E
• Application Number:
  US07/247,782
• Time in Patent Office: 614 Days
• Field of Search: 340/706, 340/709, 340/712, 178/18, 178/19
• US Class Current: 345/174
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

In a pressure-sensitive input apparatus comprising an X-coordinate detection resistive member connected to mutually parallel vertical electrodes and a Y-coordinate detection resistive member connected to mutually parallel horizontal electrodes, for detecting the position of a point depressed by a stylus or the like, by detecting changes in the resistance values of these resistive members, switches are provided for on-off control of the current flowing into or out of both ends of the X-coordinate detection resistive member and the Y-coordinate detection resistive member, and a voltage detection circuit detects the voltage between the X-coordinate detection resistive member and the Y-coordinate detection resistive member. Multiple inputs can be detected according to the results obtained from the voltage detection circuit when the currents are switched by the switches.

Claims

1. A pressure-sensitive input apparatus comprising:

vertical electrodes which are parallel with each other;

horizontal electrodes which are parallel with each other, intersect said vertical electrodes and are separated from the vertical electrodes;

the electrical resistance between said vertical electrodes and said horizontal electrodes being reduced at a location where a pressure is applied;

an X-coordinate detection resistive member connected to the vertical electrodes;

a Y-coordinate detection resistive member connected to the horizontal electrodes;

current supply means for supplying an electric current through said vertical electrodes, said horizontal electrodes, said X-coordinate detection resistive member and said Y-coordinate detection resistive member;

coordinate calculating means for detecting currents through said X-coordinate detection resistive member and said Y-coordinate detection resistive member and calculating the positional coordinate at which a pressure is applied;

switching means for on-off control of the current flowing through both ends of the X-coordinate detection resistive member and the Y-coordinate detection resistive member;

voltage detection means for detecting the voltage between the X-coordinate detection resistive member and the Y-coordinate detection resistive member;

judgment means responsive to the voltage detection means for detecting multiple input according to the results obtained from the voltage detection means when the currents are switched by the switching means.

2. An apparatus according to claim 1, wherein said judgment means detects the multiple input according to the results obtained from the voltage detection means when the switching means are in respective states.

3. An apparatus according to claim 2, further comprising control means for controlling said switching means, wherein said judgment means is responsive to the control means to determine the states of the switching means.

4. An apparatus according to claim 1, wherein said current supply means has a first output terminal connected to first and second ends of said X-coordinate detection resistive member, and a second output terminal connected to first and second ends of said Y-coordinate detection resistive member.

5. An apparatus according to claim 4, wherein said X-coordinate detection resistive member and said Y-coordinate detection resistive member have a uniform lengthwise resistivity.

6. An apparatus according to claim 5, wherein said switching means comprises:

a first switch interposed between said first output terminal of said current supply means and said first end of said X-coordinate detection resistive member,

a second switch interposed between said first output terminal of said current supply means and said second end of said X-coordinate detection resistive member,

a third switch interposed between said second output terminal of said current supply means and said first end of said Y-coordinate detection resistive member, and

a fourth switch interposed between said second output terminal of said current supply means and said second end of said Y-coordinate detection resistive member.

7. An apparatus according to claim 6, wherein said voltage detection means is connected to detect the voltage across said first output terminal and said second output terminal of said current supply means, and said judgment means makes said judgment in accordance with whether or not the following relationship holds:

space="preserve" listing-type="equation">|(v.sub.1 +v.sub.2)-(v.sub.3 +v.sub.4)|<

e

where

v₁ is the voltage detected by said voltage detection means when said first switch is on, said second switch is off, said third switch is on and said fourth switch is off,

v₂ is the voltage detected by said voltage detection means when said first switch is off, said second switch is on, said third switch is off and said fourth switch is on,

v₃ is the voltage detected by said voltage detection means when said first switch is on, said second switch is off, said third switch is off and said fourth switch is on,

v₄ is the voltage detected by said voltage detection means when said first switch is off, said second switch is on, said third switch is on and said fourth switch is off, and

e is a predetermined value.

8. An apparatus according to claim 7, wherein the pitch of the electrode is so small that the probability of erroneous input at multiple locations where either the X-coordinate values or the Y-coordinate values are identical is negligible.

9. An apparatus according to claim 7, wherein said coordinate calculating means determines the X-coordinate x and the Y-coordinate by performing the following calculation:

space="preserve" listing-type="equation">x=L.sub.x ·

i.sub.2 /I.sub.0

space="preserve" listing-type="equation">y=L.sub.y ·

i.sub.4 /I.sub.0

where

L_x is the length of the effective input area in the direction of the horizontal electrodes,

L_y is the length of the effective input area in the direction of the vertical electrodes,

I_o is the current value of the current supply means when said first, second, third and fourth switches are all on,

i₂ is the current through one end of the X-coordinate detection resistive member when said first, second, third and fourth switches are all on, and

i₄ is the current through one end of the Y-coordinate detection resistive member when said first, second, third and fourth switches are all on.

10. An apparatus according to claim 9, wherein said current supply means is a constant-current supply means.

11. An apparatus according to claim 1, wherein said vertical electrodes and said horizontal electrodes are separated from each other by a pressure-sensitive sheet or air gap.