Fail safe design for a stylus that is used with a touch sensor

A system and method for enabling a stylus to be used with a touch sensor even after it has failed in an open mode or a closed mode, wherein the tethered stylus activates the inking function when the stylus is in contact with the touch sensor and deactivates the inking function when the stylus is lifted off the surface of the touch sensor when the switch is functioning properly, but when there is a failure of the switch in the open mode or the closed mode, enabling the tethered stylus to continue functioning by using a timer to activate the inking function when the tethered stylus is close enough to be detected by a touch sensor, and to deactivate the inking function when the tethered stylus is no longer detectable by the touch sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a tethered stylus that is used with a touch sensor. More specifically, the invention is a change to operation of the tethered stylus so that a hardware failure of the tethered stylus does not prevent use of the touch sensor.

2. Description of Related Art

There are several designs for capacitance sensitive touch sensors. It is useful to examine the underlying technology to better understand how any capacitance sensitive touchpad can be modified to work with the present invention.

The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated as a block diagram inFIG. 1. In this touchpad10, a grid of X (12) and Y (14) electrodes and a sense electrode16is used to define the touch-sensitive area18of the touchpad. Typically, the touchpad10is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these X (12) and Y (14) (or row and column) electrodes is a single sense electrode16. All position measurements are made through the sense electrode16.

The CIRQUE® Corporation touchpad10measures an imbalance in electrical charge on the sense line16. When no pointing object is on or in proximity to the touchpad10, the touchpad circuitry20is in a balanced state, and there is no charge imbalance on the sense line16. When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area18of the touchpad10), a change in capacitance occurs on the electrodes12,14. What is measured is the change in capacitance, but not the absolute capacitance value on the electrodes12,14. The touchpad10determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line16to reestablish or regain balance of charge on the sense line.

The system above is utilized to determine the position of a finger on or in proximity to a touchpad10as follows. This example describes row electrodes12, and is repeated in the same manner for the column electrodes14. The values obtained from the row and column electrode measurements determine an intersection which is the centroid of the pointing object on or in proximity to the touchpad10.

In the first step, a first set of row electrodes12are driven with a first signal from P, N generator22, and a different but adjacent second set of row electrodes are driven with a second signal from the P, N generator. The touchpad circuitry20obtains a value from the sense line16using a mutual capacitance measuring device26that indicates which row electrode is closest to the pointing object. However, the touchpad circuitry20under the control of some microcontroller28cannot yet determine on which side of the row electrode the pointing object is located, nor can the touchpad circuitry20determine just how far the pointing object is located away from the electrode. Thus, the system shifts by one electrode the group of electrodes12to be driven. In other words, the electrode on one side of the group is added, while the electrode on the opposite side of the group is no longer driven. The new group is then driven by the P, N generator22and a second measurement of the sense line16is taken.

From these two measurements, it is possible to determine on which side of the row electrode the pointing object is located, and how far away. Using an equation that compares the magnitude of the two signals measured then performs pointing object position determination.

The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes12,14on the same rows and columns, and other factors that are not material to the present invention.

The process above is repeated for the Y or column electrodes14using a P, N generator24

Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes12,14and a separate and single sense electrode16, the sense electrode can actually be the X or Y electrodes12,14by using multiplexing.

The proliferation of portable electronic appliances such as tablet computers and smart phones has also created new problems with keeping these power hungry and portable devices charged. It would be an advantage to be able to provide new and more convenient means for charging portable electronic appliances that use rechargeable batteries.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention is a system and method for enabling a stylus to be used with a touch sensor even after it has failed in an open mode or a closed mode, wherein the tethered stylus activates the inking function when the stylus is in contact with the touch sensor and deactivates the inking function when the stylus is lifted off the surface of the touch sensor when the switch is functioning properly, but when there is a failure of the switch in the open mode or the closed mode, enabling the tethered stylus to continue functioning by using a timer to activate the inking function when the tethered stylus is close enough to be detected by a touch sensor, and to deactivate the inking function when the tethered stylus is no longer detectable by the touch sensor.

These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.

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.

It should be understood that use of the term “touch sensor” throughout this document may be used interchangeably with “capacitive touch sensor”, “touch panel”, “touchpad” and “touch screen”.

A touch sensor is provided for use as a means of data input to an electronic appliance such as a computer or some type of related computational device. Touch sensor circuitry receives input from electrodes of the touch sensor and provides information regarding objects that are touching or in proximity of the touch sensor. However, there may be unused inputs on the touch sensor circuitry. A tethered stylus may be coupled to an unused input of the touch sensor circuitry. Input signals from the tethered stylus are sent to the touch sensor circuitry that enable the position regarding the tethered stylus relative to the touch sensor to be determined. Other information may also be obtained from the touch sensor circuitry regarding the tethered stylus. Such information may include pressure, tilt and rotation of the tethered stylus.

FIG. 2is provided to illustrate how the first embodiment of the present invention may operate. Consider a touch sensor30and a tethered stylus32. The path that may be followed by the tethered stylus32is shown as line34. The tethered stylus32may approach the touch sensor30along the path34. The tethered stylus32includes a switch. When the tethered stylus32makes contact with the touch sensor30at location36, the tethered stylus32may begin inking or activate an inking function on an associated display screen that is showing input received from the tethered stylus32and the touchpad30. After the tethered stylus32has traveled along the surface of the touch sensor30, it may be lifted off the surface of the touch sensor30at point38. At this time, the tethered stylus32may stop inking or deactivate the inking function on the display screen.

It is understood that the touch sensor30may be a touch screen, and thus the display is directly under or on top of the touch sensor. The touch sensor30may also be a touch panel or touchpad, and thus the display screen is separated from the touch panel or the touchpad.

FIG. 3shows in a block diagram that the touch sensor circuitry40receives input from the touch sensor30and the tethered stylus32. The touch sensor circuitry40may send data to the display screen42.

It was determined that there are two potential fail modes for the tethered stylus32. These failure modes are failing open (fail open) and failing closed (fail closed). In other words, the switch in the tethered stylus32may fail where the switch is stuck in an open or a closed position. In a stuck open position, the tethered stylus32may not be able to send a signal to the touch sensor circuitry40indicating that the tethered stylus is on the touch sensor30and that inking should occur. In a stuck closed position, the tethered stylus32may not be able to send a signal to the touch sensor circuitry40indication that the tethered stylus is no longer on the touch sensor30. This mode may interfere with operation of the touch sensor30because, for example, all contact may be ignored if it is not coming from the tethered stylus32.

The different failure modes present potential problems to the system. In the fail open mode, the touch sensor30may not recognize the tethered stylus32, and it may be impossible to perform inking. In the fail closed mode, the touch sensor30may believe that input may only be accepted from the tethered stylus32, and thereby ignore all other touch data from the touch sensor, such as a finger moving on a surface of the touch sensor. The present invention may enable the tethered stylus32to perform inking regardless of which failure mode has occurred, and for the touch sensor30to accept touch input from an object other than the tethered stylus32when it is appropriate.

It should be understood that operation of the switch in the tethered stylus32is well known to those skilled in the art and is not considered to be a patentable aspect of the present invention. What is important to understand is that the switch can break, and the tethered stylus may continue to operate using the embodiments of the present invention.

The first embodiment teaches that the tethered stylus32may continue to operate by being able to bypass the failure of a faulty switch by providing the capability of tracking the tethered stylus using the touch sensor30. In other words, the tethered stylus32must also be capable of being tracked by the touch sensor30in order for the first embodiment to function as desired.

FIG. 4is a flowchart that is provided to illustrate the first embodiment of the present invention. The algorithm begins at item50. The first step at item52is to turning inking off to reset the system. In other words, the touch sensor circuitry40should send a command so that no inking should be taking place on a display screen42.

The next step is to take a time stamp at item54and to add a predetermined amount of time to the current time and to store that value in the variable XTIME. The default value in the variable XTIME is zero. The purpose of this time stamp and the XTIME variable is not clear until addressing the issue of a fail open mode as will be explained.

The next step at item56is to check and see if the Z threshold46(the Z threshold depicting an approach of the tethered stylus towards the touch sensor30) has been crossed by the tethered stylus32as shown inFIG. 2. The Z threshold46is not a set distance, and it may even vary for a particular tethered stylus32because of changes in the properties of the components being used. The Z threshold46is defined as the earliest detection of the tethered stylus32as it approaches the touch sensor30. If the Z threshold46is not reached, then the algorithm stops tracking at item58, and then returns to the step at item52where inking is turned off. The term Z threshold is used to reference the movement of the tethered stylus32in the Z axis, which is the axis away from the surface of the touch sensor30.

In the event that the Z threshold46is reached and the tethered stylus32is detected by the touch sensor30, then the algorithm proceeds to the next step where tracking begins in item60. The step of tracking may not mean that inking begins, depending on the functionality of the tethered stylus32.

As the tethered stylus32is likely to be descending towards the touch sensor30, the next step is to determine if the inking switch (just “switch” hereinafter) on the tethered stylus32has been activated in item62. The switch may be activated when the tip of the tethered stylus32not only makes contact with but physically presses against a spring loaded tip that completes a circuit in the switch in the tethered stylus32. However, any means for activating the switch when the tethered stylus32makes contact with the touch sensor30is also considered to be within the scope of the present invention.

If the switch is not yet triggered, the algorithm proceeds to the step of checking to see if the variable XTIME is less than the current time in item64. If this is analyzed from the perspective that the tethered stylus32is assumed to be functioning properly and the switch is working, it is unlikely that the value of the variable XTIME will be less than the current time. The assumption is being made that that the switch will be activated before XTIME is greater than the current time. It is assumed that the switch will be activated or closed, and that the algorithm will proceed from item62to item66instead of to64. Thus, when the tethered stylus32makes contact with the touch sensor30at location36inFIG. 2, two events take place in item66. Namely, the variable XTIME may be reset to a predetermined value such as zero, and the variable STUCK COUNTER is also cleared and may be set equal to zero.

The next step in item68may be to turn on inking. The position of the tethered stylus32is being tracked, and an inking trail may be shown on the display screen42. The algorithm then returns to item56. The algorithm will proceed through the steps in items56,60,62,66and68and then back to item56as long as the switch on the tethered stylus32is activated. In other words, the tethered stylus32is in contact with the surface of the touchpad30, causing the switch to be closed.

When the tethered stylus32is lifted off the touch sensor30, and shown here by example as being at location38, the switch is deactivated which means that the switch is now open. As the tethered stylus is pulled away from the touch sensor30, it will eventually pass the Z threshold48which means that the tethered stylus32is no longer being detected. The algorithm will then proceed through the steps in items52,5456,58and back to item52. This loop continues until the Z threshold is crossed again when the tethered stylus32is again made to approach the touch sensor30to perform inking.

So far, the algorithm has been directed to what takes place when the switch in the tethered stylus32is functioning properly. However, it should be recognized that if the switch is stuck in a closed position, or it is in a fail closed mode, the Z threshold step in item56now controls operation of inking for the tethered stylus32. In other words, the tethered stylus32is sending a signal indicating that it is in contact with the touch sensor30and that inking should commence as soon as the inking function is activated.

Looking atFIG. 2, it can be seen that the tethered stylus32would now begin inking earlier than touchdown at location36, and continue inking after lift-off at location38. Inking would now be controlled by passing the Z threshold46.

The other failure mode of the tethered stylus32is when the switch is stuck open. When the tethered stylus32pressed down on the touch sensor30but the switch is broken and does not close, the algorithm follows a path that still allows inking.

When the Z threshold46fromFIG. 2is passed in item56(FIG. 3), the tethered stylus32is waiting for the switch to close before inking. If the switch is never closed because it is broken, the algorithm is able to compensate. In this embodiment, the algorithm only waits a set period of time before the system turns inking on based on the assumption that the tethered stylus was going to make contact with the touch sensor30because it was headed in that direction. This set period of time is going to be the value stored in the variable XTIME. Experimentation may be used to adjust the timing, but for the purposes of this example, it will be assumed that a value of 50 milliseconds accurately describes the amount of time that the tethered stylus might take to move from the Z threshold46to location36on the touch sensor30.

In step54, a start time is recorded. In other words, a time stamp is taken, and at the same time, the variable XTIME is set to be equal to the current time plus a set period of time. For example, it may be determined that if the switch has not closed 50 milliseconds after the Z threshold46has been crossed, the tethered stylus32should activate inking, even if the switch has not been closed or activated.

The assumption is made that this is the likely intent of the user, and if the switch is stuck open, then inking begins. Therefore, in item54, the time stamp is recorded, a value is added to that time stamp, such as 50 ms, and this value is recorded as the variable XTIME.

Thus, as the algorithm repeats the steps in items56,60,62,64and back to56, this cycle will be repeated as many times as it takes until XTIME is not less than the current time. When item64is true and XTIME is less than the current time, the algorithm proceeds to item70where the variable STUCK COUNTER is incremented. The next step in item72is to determine if the variable STUCK COUNTER is at a maximum value. This maximum value is the number of times that the algorithm will see an open switch and increment the stuck counter. If the value MAX is set to the number 5, then the steps56,60,62,64,70,72and68will be repeated 5 times. After being repeated 5 times, then the STUCK COUNTER now equals 5, and the algorithm proceeds from the step in item72to the step in item74. In item74, the variable XTIME is set equal to zero or some set period of time, and then proceeds to the step in item68.

The result is that as long as the Z threshold is not passed again, the tethered stylus32will continue to ink, but the algorithm will now be repeating the cycle of the steps in items56,60,62,64and back to56because XTIME was set equal to zero. Because the variable XTIME will always be less than the current time, the tethered stylus32will continue to ink until the Z threshold is passed in item56, and the system will stop tracking and stop inking.

It should be understood that the present invention is not limited to the exact algorithm as shown inFIG. 4. What should be understood is that the present invention is the use of a tethered stylus that can be tracked by a touch sensor. This ability to be tracked enables the tethered stylus to enable the system to continue inking even if a switch on the tethered stylus has failed. Furthermore, the failure can be in a fail open or a fail closed mode.

If the tethered stylus fails in a fail closed or activated mode, then the operation of the tethered stylus is controlled by the ability to be tracked. There may be a slight delay in turning inking on or off, or there may even be a premature activation of the inking mode, but the tethered stylus will continue to operate.

However, when the tethered stylus has a switch that is stuck open, a slight delay is created before inking is turned on after the tethered stylus is close enough to the touch sensor to pass the Z threshold. But as long as the tethered stylus is not pulled away from the touch sensor far enough to pass the Z threshold48, then inking will continue uninterrupted.

FIG. 5is a graph that shows how the Z level or Z strength of the tethered stylus32may vary as a function of distance of the tethered stylus from different touch sensors,80and82. The reason for the variability in how far above the touch sensors80,82that the tethered stylus32may be detected is a function of the capabilities of the touch sensors, the materials from which the tethered stylus is manufactured, and differences in the sensing capabilities of the touch sensor circuitry. This figure illustrates that the Z threshold when the tethered stylus32is detectable will simply vary, but not change the outcome of the algorithm ofFIG. 4.