TOUCH STICK CONTROLLER USING CAPACITANCE TOUCHPAD CIRCUITRY AS A MEASUREMENT SYSTEM

Abstract

Capacitance-sensitive touchpad circuitry used for detecting and tracking an object on the surface of a touchpad now receives as inputs to the circuitry the voltage divider signals from each axis of a strain gauge used as a touch stick input device, wherein the touchpad circuitry is far less sensitive to noise, and wherein touch stick control circuitry can be eliminated through the use of existing touchpad circuitry.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a typical prior art touch stick strain gauge measurement circuit.

FIG. 2 is a block diagram of a touchpad as taught by the prior art.

FIG. 3 is a block diagram of the circuitry of the present invention.

FIG. 4A is a conceptual circuit diagram that is representative of touchpad circuitry when measuring charge transfer from electrodes of a touchpad.

FIG. 4B is a conceptual circuit diagram that is representative of touchpad circuitry when measuring charge transfer from voltage divider circuitry of a touch stick.

FIG. 5 is a detailed circuit diagram of a touch stick circuit that is modified to include an external resistor that is used when making a measurement in the Z axis, and the measurement points for making measurements in the X, Y and Z axes.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow.

A first embodiment of the present invention is shown in FIG. 3 as a block diagram, wherein a signal 30 from an X-axis voltage divider circuit 32 is sent to a sense line input 38 of a capacitance sensitive touchpad circuit 62, and a signal 34 from a Y-axis voltage divider circuit 36 is sent to the sense line input 38 of the capacitance sensitive touchpad circuit 62. P and N signals 70, 74, 76 and 78 are also taken from the X-axis and Y-axis voltage divider circuits 32 and 36. An output signal 60 from the touchpad circuit 62 is the proportional value of the capacitive coupling between the sense electrodes and the P and N electrodes. A positive value indicates greater coupling between the P electrodes and the sense electrode, and a negative result indicates greater coupling between the N electrodes and the sense electrode.

From the output signal 60, it is possible to determine the amount of force being applied to a strain device, such as a touch stick, in both the X and Y axes. This signal can be used, for example, by a notebook computer to control the position and movement of a cursor on a display screen.

It should be understood that the system-level measurement methods for touch sticks and touchpads are different, but both methods rely on measuring the charge transfer measured by the sense electrode when P and N signals are toggled. Thus beginning with FIG. 4A, this figure is a schematic diagram that describes the nature of the circuit but not the actual circuit that exists when the touchpad circuitry is operating with a touchpad. Thus conceptually, in the touchpad measurement method, the P and N signals are coupled to the sense electrode by variable parasitic capacitors whose capacitive values are modulated by user modulation of the capacitor dielectrics. In other words, the presence of a finger enables the capacitive coupling between the P and N signals and the sense line.

When user modulation of the parasitic capacitors results in greater capacitive coupling between the P signal and the sense electrode, the resulting signal on the sense electrode is more positive. Thus, the finger is nearer to an electrode with a P signal. Likewise, when user modulation of the parasitic capacitors results in greater capacitive coupling between the N signal and the sense electrode, the resulting signal on the sense electrode is more negative.

In contrast, the conceptual circuit that is created when the touch stick is being used is different. FIG. 4B is a circuit diagram that shows that the touch stick creates a user modulated voltage divider between the P and N signals. In other words, pushing on the touch stick changes the resistance being measured in the X and Y voltage dividers. The output of the voltage dividers is then capacitively coupled to the sense electrode via a capacitive component (sense capacitor) having a static value.

For example, consider a touch stick that has a P signal in a left direction and an N signal in a right direction. If the touch stick is pushed to the left, the resistance connected to the P signal is less than the resistance connected to the N signal, and the resulting signal on the sense electrode will be more positive. The system then knows that the user is pushing the touch stick to the left. The situation is the same when the touch stick is pushed towards the right. The result will be more negative on the sense electrode.

The circuit of a touch stick coupled to touchpad circuitry is now described in FIG. 5 to show more detail of the circuitry of FIG. 3, but in a schematic diagram. Before addressing the specific circuit, in general, the voltage dividing resistors of the touch stick are still used in the present invention, as these are typically a part of the touch stick apparatus itself. Therefore there is no need to design a new touch stick or modify those already existing. The same touch sticks that are presently being manufactured can be used in this first embodiment.

In FIG. 5, what is shown is the voltage divider circuitry within dashed line 80 that is already part of existing touch sticks. Signal measurements are taken from any one of five different locations on the circuit, depending on what value is being determined. To assist in understanding and summarizing the measurements, Table 1 is provided below.

	TABLE 1
	X Measurement	Y Measurement	Z Measurement
X	Sense	No Connection	No Connection
Y	No Connection	Sense	No Connection
Z	P Signal	P Signal	Sense
A	No Connection	No Connection	P Signal
B	N Signal	N Signal	N Signal

An X measurement is a measurement that provides information regarding how hard the touch stick is being pushed relative to an X axis. In other words, the measurement determines if there is an X axis component to the force being applied to the touch stick. Similarly, a Y measurement is a measurement that provides information regarding how hard the touch stick is being pushed relative to a Y axis. Thus, this measurement determines if there is a Y axis component to the force being applied to the touch stick. It should be apparent that a force may be applied in only one axis, but is more likely to be applied in at least two axes at the same time.

According to Table 1, X is coupled to the sense 100, Y has no connection, Z has is coupled to P 102, A has no connection, and B is coupled to N 104. The connections for making a Y measurement should now be apparent from Table 1.

It should also be apparent from Table 1 that a Z measurement is also possible. A Z measurement is a measurement for determining if the touch stick is being pressed down, or if there is at least some component of force that is downward on the touch stick. A Z measurement can be used, for example, to detect what a touchpad would interpret as a tap or double tap. Constant force may also be applied to the touch stick if some type of drag gesture were to be performed.

For example, if RZ is, for example, made equal to the resistance of the touch stick resistors, or in other words, the combination of RX1 in series with RX2 in parallel with RY1 in series with RY2, then a force applied on the touch stick would result in a decrease in the resistance of the touch stick resistors, and the circuit is again a voltage divider at location Z.

It should now be apparent that using touchpad control circuitry to receive and measure signals from the touch stick is performed without having to amplify any signals coming from the touch stick resistors. Accordingly, the system is much less sensitive to noise on the signals. Furthermore, the touchpad circuitry does not have to be altered to perform the function of measuring charge transfer.

In another aspect of the present invention, the axes can be operated independently of each other. In other words, a touch stick may only operate in only one axis, either the X or Y axis. Accordingly, only RX1 and RX2 would be present in the voltage divider if only the X axis is being used.

In another alternative embodiment, a touch stick could also operate in either the X or Y axis, in combination with the Z axis.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements.

Claims

1. A touch stick system that is operated by transmitting signals to a charge transfer measurement device, said touch stick system comprised of: a first touch stick voltage divider for a first axis; anda charge transfer measurement device coupled to the first touch stick voltage divider to thereby determine a degree of force applied to the touch stick system in the first axis.

2. The touch stick system as defined in claim 1 wherein the first touch stick voltage divider is coupled to the charge transfer measurement device at three locations.

3. The touch stick system as defined in claim 2 wherein the first touch stick voltage divider has a Z connection point at a top of said divider, an X connection point between resistors of said divider, and a B connection point at a bottom of said divider.

4. The touch stick system as defined in claim 3 wherein the touch stick system is further comprised of a second touch stick voltage divider for a second axis.

5. The touch stick system as defined in claim 4 wherein the second touch stick voltage divider is coupled to the charge transfer measurement device at three locations.

6. The touch stick system as defined in claim 5 wherein the second touch stick voltage divider has a Z connection point at a top of said divider, a Y connection point between resistors of said divider, and a B connection point at a bottom of said divider.

7. The touch stick system as defined in claim 6 wherein said system is further comprised of the first touch stick voltage divider being coupled in parallel with the second touch stick voltage divider.

8. The touch stick system as defined in claim 7 wherein the charge transfer measurement device is further comprised of a positive signal input, a negative signal input, and a sense input.

9. The touch stick system as defined in claim 8 wherein to make a measurement relative to the first axis, the X connection point is coupled to the sense input, the Z connection point is coupled to the positive signal input, and the B connection point is coupled to the negative signal input.

10. The touch stick system as defined in claim 8 wherein to make a measurement relative to the first axis, the X connection point is coupled to the sense input, the Z connection point is coupled to the negative signal input, and the B connection point is coupled to the positive signal input.

11. The touch stick system as defined in claim 8 wherein to make a measurement relative to the second axis, the Y connection point is coupled to the sense input, the Z connection point is coupled to the positive signal input, and the B connection point is coupled to the negative signal input.

12. The touch stick system as defined in claim 8 wherein to make a measurement relative to the second axis, the X connection point is coupled to the sense input, the Z connection point is coupled to the positive signal input, and the B connection point is coupled to the negative signal input.

13. The touch stick system as defined in claim 8 wherein the touch stick system is further comprised of a third touch stick voltage divider for a third axis that is orthogonal to the first and second axes.

14. The touch stick system as defined in claim 13 wherein the third touch stick voltage divider is comprised of a top resistance that is comprised of a resistor that is external to the touch stick system, wherein the bottom resistance is a combination of the first touch stick voltage divider and the second touch stick voltage divider.

15. The touch stick system as defined in claim 14 wherein the Z connection point is coupled to the sense input, an A connection point above the top resistance is coupled to the positive input signal, and the B connection point is coupled to the negative input signal.

16. The touch stick system as defined in claim 14 wherein the Z connection point is coupled to the sense input, an A connection point above the top resistance is coupled to the negative input signal, and the B connection point is coupled to the positive input signal.

17. A measurement system for determining the amount of force applied to a strain gauge, said measurement system comprised of: a first strain gauge voltage divider for a first axis; anda charge transfer measurement device coupled to the first strain gauge voltage divider to thereby determine a degree of force applied to the first strain gauge voltage divider in the first axis.

18. A method for measuring the amount of force applied to a touch stick, said method comprising the steps of: 1) providing a first touch stick voltage divider for a first axis and a charge transfer measurement device that is coupled to the first touch stick voltage divider; and2) determining a degree of force applied to the touch stick system in the first axis by measuring a charge that is transferred to the first touch stick voltage divider.

19. The method as defined in claim 18 wherein the method further comprises the step of providing a positive and a negative signal from the first touch stick voltage divider to the charge transfer measurement device.

20. The method as defined in claim 19 wherein the method is further comprised of the step of capacitively coupling an output of the first touch stick voltage divider to a sense input of the charge transfer measurement device.

21. The method as defined in claim 19 wherein the method is further comprised of the step of modulating a resistance of the first touch stick voltage divider to thereby enable the charge transfer measurement device to determine in which direction a force is being applied along the first axis.