Capacitive sensing trackpad with force sensing and haptic features

Abstract

The utility model relates to a capacitive sensing track pad with force sensing and tactile features. A capacitive sensing trackpad that uses force sensing to determine an approximate location of a touch on the trackpad and uses that location as an inspection of the location determined by the capacitive touch in order to exclude potential noise generating signals. The locations resolved from the inductive force sensing measurements may also be used to assist in generating a uniform haptic experience for the user. The force sensing measurement is also used to determine whether a threshold for "click" is satisfied.

Description

Technical Field

[0001] The present invention relates generally to the field of track pads, and more particularly, to a capacitive sensing track pad having force sensing and tactile features. Background Art

[0002] Track pads are widely used in computers, vehicles, and other applications for user interface functions. The prior art features capacitive sensing for tracking. A single dome switch (or other type of electromechanical switch) combined with capacitive sensing is sometimes used for selective switching (left, right). Multiple switches are also used, or capacitive methods or strain gauges are used to measure the force from the user's finger. When force sensing is used, the system is usually characterized by tactile feedback to the user to produce a tactile sensation.

[0003] Electromechanical switches have a single, non-adjustable "click" point, are subject to wear and degradation, and importantly require movement that creates an opening for liquids or dust to enter. Both of these factors can be considered disadvantages.

[0004] Haptic feedback is traditionally expensive, such that typically only a limited amount of haptic feedback is present in use per product. Summary of the invention

[0005] The purpose of the present invention is to enable a reliable and cost-effective force sensing implementation for a track pad with adjustable sensing levels for "click" activation and good tactile feel using a minimum number of haptic engines. Additionally, force sensing can be used as a track pad redundancy check to prevent false or spurious touch events from entering the system due to RF or other electromagnetic noise.

[0006] The primary target application of the present invention is capacitive track pads as found, for example, in laptop and notebook computers, but also for other track pads and touch screens. For any of these track pads, it is proposed to use inductive force sensing to determine the level of pressure applied by the user to the track pad, and also determine the location where the pressure is acting.

[0007] In this specification, "pressure" and "force" are used interchangeably unless the context clearly indicates otherwise.

[0008] In an embodiment of the present invention, force sensing is performed on a track pad that includes a bracket that flexes under pressure and is constructed in a manner that changes the proximity between the inductive coil(s) and the metallic or ferrite object(s). The resulting change in distance between the inductor and the interfering member is reflected in a change in inductance, which in turn is directly related to the pressure acting on the track pad.

[0009] In a particular exemplary embodiment, the track pad is supported by support structures with inductive force sensing features only in the four corners. If the user presses right on top of the support structure, the force is sensed primarily (or depending on the structure - entirely) in the attached single force sensing structure. If the user presses right in the center between all the force sensing support structures, the force sensors (if properly calibrated) reflect equal or very similar measurements.

[0010] Force sensing by, for example, strain gauges is known in the art. Inductance measurement techniques are known in the art, and the present invention is directed to the use of inductive force sensors in capacitive track pad systems to achieve certain functions / features, and in particular, a means of producing changes in inductance that can be measured and related to pressure and displacement experienced on the track pad.

[0011] In an embodiment of the present invention, detection of force applied to the track pad (e.g., by a user's finger) is used to support the authenticity of the capacitive touch sensor system. If an electromechanical switch is used for the track pad "click", this redundant functionality is not possible. The switch only provides information when the pressure is high enough to activate it, and normal track pad operation is performed at much lower pressure levels. According to the present invention, for example, if the capacitive sensor system detects a signal on the track pad, but the force sensing system does not measure pressure, the capacitive signal can be rejected.

[0012] In an embodiment of the present invention, the relative force between four force sensing measurements made at the four corners of the track pad is used to make a determination of the location of the pressure point. This location is then correlated to the location determined by the capacitive touch sensing system. This can be used to achieve a higher confidence level in the capacitive sensing operation. For example, if an icon is selected on the screen, false selection of some functions may be problematic. Capacitive sensing track pads are known to be affected by liquids, radio frequency interference or other electromagnetic noise, and also liquids on the touch surface. For example, if the capacitive sensor measures a completely wrong event, the force sensor will most likely not reflect the corresponding event. The force measurements and the locations derived from the force sensor measurements can be used to support and in a sense verify the capacitive sensing track pad results.

[0013] Position verification or redundancy can also be applied to lines being drawn on a track pad. For example, as the line moves from the left front to the right back of the track pad, the position derived from the force sensor measurements must correlate.

[0014] In further embodiments, post-decision information from the capacitive and force sensors is used to train and / or fine tune the algorithms in either sensor system. This is particularly helpful if some of the mechanical parameters change over time due to, for example, wear and tear. Using AI techniques and adaptive software, these changes can be tracked and compensated.

[0015] In embodiments of the present invention, a force sensing system may be used to make a determination regarding the equivalent action of a user pressing a tactile switch such as found in "single click" and "click anywhere" capacitive track pads. Even though a very small displacement is required, the determination of a "click" in accordance with the present invention is made based on a pressure metric. This means that at a certain pressure, the force sensor system makes the determination that the equivalent action of a switch activation "click" has occurred, such as at the bottom left or right of the track pad. The force sensor alone makes the pressure determination, but the left, right, or other position may be determined by either the capacitive touch system or the force sensing system.

[0016] The location of the press by the user's finger on the track pad can also be used to influence the sense of touch to balance the tactile sensation or tactile feedback at the location of the press. For example, if a single tactile stimulator is used and the tactile stimulator is located in the middle and front of the track pad, a press on the middle front of the track pad may require the tactile stimulator (e.g., LRA) to be driven at a much reduced level. Pressing the right front or left front may require a slightly reduced drive level, while pressing at the right rear or left rear of the track pad may require the maximum drive force to the tactile stimulator. By using the derived press location information, the same technique is applicable to balancing the perceived effects from multiple tactile stimulators.

[0017] The level of force or pressure required in terms of deciding when the equivalent action of switch activation (click) has occurred may be regulated, for example, in the left front sensor, or may depend on combined readings from multiple sensors.

[0018] For example, if the user presses right at the far left front corner, the left front inductive sensor should reflect almost all of the force applied to the track pad. If the user presses between the left front corner and the front middle, the force reading will be a ratio between the two front corner sensors. This means that if the decision as to "click" depends only on the reading from a single sensor, more pressure may be required if the pressure is not exactly at the corner.

[0019] So if consistent pressure is required for making a click decision, the readings from all force sensors (the four corners) need to be combined when making the decision. Different configurations and / or numbers of force sensors can be used. For example, 3 sensors are needed for triangulation. A fifth sensor in the middle might help with accuracy and support, but might be difficult to implement for something like a touchscreen, and in fact the method can be extended to any number of force sensors, albeit with increased software complexity.

[0020] It is also proposed to provide tactile feedback (tactile or click sensation) when the pressure is sufficient to activate the click decision and again when the pressure is released (tactile or click sensation). This may be during a short press, where it will be experienced as a single tactile click, or it may be a period during which the user presses and maintains pressure for an extended period before releasing. The signal provided to the linear resonant actuator (LRA) motor or other actuator may differ between the two signals for engagement and disengagement.

[0021] The bracket(s) that hold the track pad in place and also the stacking of the system can be very simple to save cost and reduce thickness. The same bracket(s) can be used for force sensing and for mounting the track pad into a notebook or laptop computer.

[0022] The technique of using inductive force sensing measurements to determine user clicks reported by haptic components can also be extended to gain further flexibility and advantages, such as:

[0023] When two or more finger gestures are used, there is automatically more pressure from the user onto the track pad, and in accordance with the present invention, when two or more fingers are identified as being in contact with the track pad, the pressure trigger level used to decide that a click has occurred or must occur can be increased. This will reduce the chance of accidental click decisions during multi-finger gestures such as pinching or zooming. Similarly, for gestures such as dragging or swiping, the required level for deciding that a click has occurred can be increased, or clicks can be prevented during this time.

[0024] Haptics may also be used to report the use of a tap gesture.

[0025] It is also possible to implement the use of haptics to report two finger or sidebar scrolling. This means that for example when two fingers are used to scroll up / down in a document, such scrolling and scrolling speed can be announced using haptics similar to what would occur when scrolling with a computer mouse. The same approach can also be applied when a sidebar or top bar is used to scroll up / down or sideways.

[0026] Similar to standard palm rejection, force sensing / haptics can be deactivated for anomaly detection.

[0027] Force sensing can be calibrated during production, but it is also possible to recalibrate after a period of use by indicating where the user must press and then correlating that information with the measurements of the four sensors. Again, the system can activate a recalibration procedure or can advise the user of this after a period of time or if it determines that a violent event has occurred (such as a heavy object being dropped on the track pad). Correlation with capacitive touch information can also be used from time to time or continuously to calibrate the force sensing system.

[0028] The inductive sensing system of the track pad can also be used to monitor the lid closure of a product such as a laptop or notebook computer.

[0029] According to the present invention, force sensing can be used to assist with "palm rejection" functionality. This is done when capacitive sensing on a track pad is used to sense a touch but the force seems too great for a single finger.

[0030] In further embodiments, the track pad inductive sensing system may be a multi-sensor system that may also monitor ambient light and assist in activating or deactivating the keyboard backlight.

[0031] It is also proposed that another novel construction method can be used, in which the bracket is used only to act in an opposite direction to the force applied by the user, i.e. the bracket determines the displacement of the tracking pad in relation to the force applied by the user. For example, if the pressure acts just above the bracket support structure, 10 Newtons must produce a force of about 10um, or 50 Newtons must move the tracking pad by about 50um. If the pressure acts in the center of the tracking pad, the pressure will be shared between the various support structures and there will be less movement on each individual sensing structure. The inductive sensor structure comprises at least an inductor, such as a coil connected to an integrated circuit (e.g. a tracking pad pcb). The construction comprises a conductive or ferrite member. The conductive or ferrite member is oriented so that when the tracking pad moves under the pressure applied by the user, it penetrates into the core of the inductor (or vice versa when the pressure is released) and in this way affects the inductance of the coil.

[0032] In this construction, the bracket is not part of something that affects / changes the inductance associated with movement.

[0033] In this specification, a "click" is an event in which a user presses hard enough on the track pad (eg, the front left) to activate a switch to make a selection. This is used in accordance with prior art in laptop computers and the like.

[0034] In each embodiment, the signals generated by the sensors are fed to a suitable processor which, by using appropriate algorithms as known in the art, calculates the force level on the track pad, the pressure period, determines a "click", and makes such comparisons and evaluations as may be required. These aspects are within the capabilities of those skilled in the art. As indicated, the important inventive step provided herein is a means of generating a measurable inductance change associated with pressure and displacement on a capacitive track pad. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 - Simple click track pad, which is a prior art track pad that utilizes a single electromechanical switch to determine left / right front clicks by the user.

[0036] The present invention is further described with reference to the following drawings:

[0037] Figure 2 - Track Pad Stack-Up for Force Sensing, which describes an embodiment of the invention having a tactile LRA and force sensing structure located on the front of the track pad.

[0038] Figure 3 ——Inductive force sensing configuration, example of inductive force sensing configuration in a track pad application.

[0039] Figure 4 ——Force sensing bracket construction with coil penetration.

[0040] Figure 5 Bottom view: track pad, bracket, haptic actuator, and layout.

[0041] Figure 6 - Side view: Tracking board, bracket and stop.

[0042] Figure 7 - Circuit diagram showing a measurement circuit (processor) connected to an inductor. DETAILED DESCRIPTION

[0043] The following description presenting the drawings is only for illustrating the spirit and scope of the present invention, and is not intended to limit such scope. These are merely embodiments in exemplary applications, and there may be numerous alternative or equivalent embodiments and applications, which will still fall within the scope of the claims of the present invention.

[0044] exist Figure 2In , an embodiment of the invention is described with reference to a capacitive track pad comprising four inductive force sensors and an LRA (Linear Resonant Actuator) tactile actuator. A cover layer such as glass or polyester film 2.1 is located on top of a pcb 2.1A having a capacitive sensing electrode pattern 2.2. A bracket 2.3 is used to mount the track pad to a product such as a laptop computer (not shown) at a fastening point 2.5.

[0045] In this embodiment, a compressible film or strip 2.7 is used to create space between the pcb and each coil (inductor) 2.6 and the bracket 2.3. When pressure is applied to the track pad (such as a user's finger (digit)), the film 2.7 is compressed and the coil 2.6 moves closer to the metal of the bracket 2.3. This change in proximity causes a change in the inductance of the coil 2.6. The change in inductance is a measure of the displacement caused by the pressure. Similarly, the change in pressure is reflected and measured by the change in the inductance of the coil (such as 2.6). In another embodiment, the strip 2.7 is solid (incompressible), but the bracket bends under force to allow changes in the distance between the coil 2.6 and the metal bracket 2.3. In both cases, the bracket 2.3 acts as an interference member, which affects the inductance of the coil 2.6 in a way that allows the inductance measurement to give a measure related to the force applied to each sensor.

[0046] In this example, the haptic actuator (LRA) 2.4 is located in the middle and front of the track pad 2.2. Pressure applied at the left front 2.9 or right front 2.10 is at a shorter distance from the LRA 2.4 than a pressure point at, for example, the right rear 2.11.

[0047] In an embodiment of the present invention, inductive sensing information from four sensors placed at the four corners of the track pad is used to resolve the location of a single pressure point on the track pad. In applications where the user desires to experience (through the user's finger) uniform or equal tactile force or tactile feedback regardless of the pressure point, the resolved location can be used to calculate the distance between the LRA 2.4 and the pressure point. The driving force of the tactile actuator can be adjusted accordingly to balance the degradation of the tactile force with distance. For example, if the pressure point is at the top of the LRA 2.4, the driving force is lowest, and if the pressure point is at the right-most rear corner, the driving force is highest. If the adjustment for tactile energy dissipation with distance is properly programmed and the calibration is done well, a single tactile actuator or multiple tactile generators (unequally distributed across the track pad) can be used to present a more uniform user feel everywhere on the track pad.

[0048] In another embodiment of the present invention, the pressure applied by the user on the track pad and measured by the force sensing system is used to gate a capacitive touch sensing event. For example, if no pressure is measured, a low probability may be placed on a touch sensing event. In this context, force sensing (or lack of force sensing) may verify or disqualify a touch sensing event.

[0049] In another embodiment of the present invention, the location of a single pressure point on the track pad can be resolved using the combined force sensing measurements and can be mapped into a grid 2.8 on the track pad. This location can be used as a redundant measurement to specifically check the capacitive touch location. If the two measurements are substantially different, a decision can be made to reject the data, retake the measurement, etc. In essence, the force sensing data can be used to enhance or improve the capacitive touch data. This is particularly important for key functions selected through the track pad user interface in applications such as in automobiles or medical devices.

[0050] It is possible to make decisions based solely on force sensing data, such as, for example, a swipe gesture or a fragment selection (such as a digitizer), ie, no capacitive sensing data is required.

[0051] exist Figure 3 , another example configuration of an inductive track pad force sensing stackup is shown. A cover layer 3.1 is attached to a capacitive track pad pcb 3.3 having an inductive coil 3.2 wired flat on the pcb 3.3. A mechanical bracket 3.5 similar to 2.3 is configured in the portion that moves under pressure and in the portion 3.4 that is not subject to pressure applied by the user on the track pad. The bracket is located at the top of the spacer and is fastened to the chassis of a laptop or other product housing 3.6 at fastening points 3.8.

[0052] When pressure is applied to the track pad cover 3.1, for example above the inductive coil 3.2, the portion of the bracket 3.5 supporting the track pad bends towards the housing. The thickness of the spacer determines the maximum displacement of the bracket. Blocks or spacers can be used to further limit the maximum bending. As the bracket 3.5 bends towards the chassis 3.6, the distance between the coil 3.2 and the metal bracket portion 3.4 decreases. This change in proximity results in a change in the inductance of the coil 3.2. The applied pressure results in a related change in the measured inductance.

[0053] according to Figure 4 , other constructions are possible where an interfering metal or ferrite piece 4.9 is positioned on a non-moving bracket component 4.4 or attached to the product chassis (component 4.8 of 4.6) to move into a hole 4.10 in the center / core of the flat coil inductor 4.2 when pressure is applied by a user to the track pad top layer 4.1.

[0054] Figure 5A track pad unit 5.1 with various features according to the invention is shown. The track pad (cover and pcb) is divided into regions left (L), center (M) and right (R), front (F), middle (M) and back (B). There are four brackets (5.2). These can also be designed as part of a single structure.

[0055] Each bracket is attached to the pcb (5.4) and has a portion adjacent to but removed from the inductor coil on the PCB. The portion 5.3 of the bracket used to mount the tracking pad inside the product varies from product to product.

[0056] It is beneficial to mount the track pad in a floating manner to better transfer energy from the haptic actuator to the user. Likewise, a shock absorbing mechanism between the stand portion 5.3 and the product (eg, laptop chassis) may be beneficial.

[0057] According to the present invention, force sensing can determine the location of the force applied by the user on the track pad, and based on the tactile actuator location 5.6, adjust the tactile energy to produce a similar feeling across the entire track pad. For example, when the user presses directly above the actuator 5.6, the tactile energy is lowest. When the distance between the tactile actuator and the touched location is greater, the energy of each area can be adjusted or adjusted to be stronger. This will compensate for the loss of tactile energy with distance. In this example, when the user presses in LB or RB, the actuator will be driven at its highest energy level.

[0058] This concept is obviously linked to the location where one or more tactile actuators are located.

[0059] exist Figure 6 In more details of an exemplary inductive force sensing bracket which may be located at a corner of a track pad 6.1 are given. The track pad has a cover layer (glass or other layer) 6.2 and a multilayer pcb 6.3 with an inductive coil 6.5, for example in the form of a track on the pcb. The bracket 6.4 must be able to move close to the coil 6.5 under the force of the member 6.6. The part above the coil may be a conductive metal or may be a ferrite. Changing the distance between the bracket 6.4 and the coil 6.5 will change the inductance measured for the coil 6.5 and in this way movement / pressure can be determined.

[0060] If the track pad is supported by member 6.6 only at the four corners, the net force applied by the user to the track pad is the aggregate of the four inductive force sensors. Moreover, the location of a single pressure point can be derived from the pressure ratio between the four sensors. This is similar to triangulation, but with four reference points.

[0061] The bracket is securely attached to the pcb, e.g. using double sided tape or epoxy / glue.

[0062] In order to prevent the bracket from being permanently deformed, a block or stop 6.7 may be used which will receive the force from the bracket after moving beyond a certain distance.

[0063] exist Figure 7 In the embodiment of the present invention, there is shown a measurement circuit processor 701, which is an electronic component and may be a microprocessor circuit, which also includes sensor circuitry suitable for measuring the inductance of inductors 702A, B, C, D. The inductors are variable relative to the pressure applied to the capacitive tracking pad. Resistors 703A, 703B are used for current limiting (if necessary), and capacitors 704A, 704B may be included for filtering radio frequency noise.

Claims

1. A capacitive sensing tracking pad, characterized in that: The capacitive sensing track pad determines a level of force applied by a user on the capacitive sensing track pad having four corners, the capacitive sensing track pad comprising: a respective inductive force sensor at or near each corner, the respective inductive force sensor generating a respective signal dependent on the level of force measured by such sensor; and a processor, responsive to the signal, the processor configured to determine the level of force applied on the track pad by using information from all of the inductive force sensors.

2. The capacitive sensing tracking pad according to claim 1, wherein: A track is included on the capacitive sensing track pad, the track being used to implement an inductor used in the inductive force sensor, and wherein the processor is configured to determine an approximate location of a pressure point on the track pad.

3. The capacitive sensing tracking pad according to claim 2, wherein: The processor is configured to compare the approximate position to a reference position determined by measurements of the capacitive sensing track pad and to reject the reference position as invalid if the comparison fails to exceed a predetermined degree.

4. The capacitive sensing tracking pad according to claim 2, wherein: The capacitive sensing track pad includes a tactile generator that generates tactile forces at levels related to the determined locations in response to the pressure point determinations to achieve a more uniform tactile sensation everywhere on the track pad.

5. The capacitive sensing tracking pad according to claim 2, wherein: The processor is configured to determine at least one of the following based on the pressure point location and force level measurement: If a predetermined level of force is reached, then a "click" is determined to have been made, and The location of the "click" made by the track pad.

6. The capacitive sensing tracking pad according to claim 2, wherein: The processor is configured to vary the magnitude of the force level required for a “click” event to be recognized when the capacitive sensing track pad measurement detects multiple contact points on the track pad.

7. The capacitive sensing tracking pad of claim 1, wherein: Each inductive force sensor includes an inductor having a core and an interfering member movable to the core in response to a force applied to the track pad so as to affect an inductance of the inductor.

8. The capacitive sensing tracking pad according to claim 5, wherein: The processor is configured to adjust in software the force level required for a click to be recognized in response to user input.

9. The capacitive sensing tracking pad of claim 1, wherein: The capacitive sensing track pad includes a bracket for mounting the track pad to a product, and wherein each inductor includes a track on a printed circuit board, and wherein a force on the track pad produces a change in inductance in the inductor, the change in inductance being attributable solely to at least one of: the material from which the stent is made, and Deformation or change of shape of the stent.

10. The capacitive sensing track pad of claim 1, wherein: The processor is configured to implement at least one of the following: (a) using force sensing information to improve palm rejection performance; or (b) Use force sensing information about the gesture being performed to prevent recognition of a "click".

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