1. Technical Field
The present invention generally relates to a method for calibrating stylus pressure mapping curve, and more particularly to a method for calibrating stylus pressure mapping curve for matching Microsoft® Window 10 standard in mass production.
2. Description of Related Art
Capacitive touch input technology is the mainstream of the input technologies applied to the widely used touch panel. A typical capacitive touch panel includes substrates on which transparent electrode patterns are coated thereon. When a finger or a stylus touch or hover on the touch panel, coupling capacitance is formed between the finger or the stylus and the transparent electrode patterns because the finger or the tip of the stylus is a conductive to establish capacitive coupling with the transparent electrode patterns. Meanwhile, the capacitance of the electrode pattern under the finger or the stylus on the touch panel will change, thus the voltage or the current in the electrodes of the electrode patterns will change. By comparing a voltage difference between the electrode under the finger or the stylus and the adjacent electrodes, the coordinate of the finger or the stylus can be determined.
However, the fingers of user are not suitable for a more delicate writing input operation, such as the writing input operations with stroke thickness changes. Moreover, input operation by using user's fingers also lacks various functions. Thus a stylus instead of user's fingers is used to perform exquisite input operation upon a touch panel with a capacitive touch input function. The stylus can further allow user to depict lines with various stroke thicknesses on a touch panel. The stylus can also detect the force which a user applies upon the stylus against the touch panel.
The stroke thickness of a stylus displayed on the touch panel is a result of signals generated from a pressure sensing module of the stylus. The stroke thickness of a stylus displayed on a touch panel should be proportional to the pressure applied on the tip of the stylus in an ideal condition. However, due to various issues, such as physical and mechanical errors of pressure detection components of the stylus or non-uniform characteristics of a pressure sensor of the stylus, the signals generated from the pressure sensing module of the stylus do not always match the pressure applied on the tip of the stylus. Thus since styluses usually have different physical and mechanical errors of pressure detection components and slightly different characteristics of pressure sensors, the styluses may have various tip pressure sensitivities. Obviously, the styluses will need to be calibrated before leaving the factory. Thus the invention provides a method for calibrating stylus pressure mapping curve for matching Microsoft® Window 10 standard in mass production.
The invention provides a method for calibrating stylus pressure mapping curve. First of all, data of average pressure sensing signal values are generated. Then data of standard pressure levels are generated. Next a standard pressure level mapping curve of average pressure sensing signal values via standard pressure levels is generated. Then a pressure sensing signal value of a stylus under calibration is generated. Next the calibrated pressure sensing signal value is compared with the average pressure sensing signal value to generate a calibration reference value, wherein the calibrated pressure sensing signal value and the average pressure sensing signal are corresponding to the same weight applied on the stylus. Finally, data of pressure sensing signal values of the stylus is calibrated by the calibration reference value, thereby mapped to the pressure levels matching the standard pressure curve via the standard pressure level mapping curve.
The invention further provides a stylus with pressure mapping function. The stylus comprises a control unit with embedded non-transitory computer readable medium storing executable instructions for performing a method for calibrating stylus pressure mapping curve. The method comprises generating data of average pressure sensing signal values; generating data of standard pressure levels; generating a standard pressure level mapping curve of average pressure sensing signal values via standard pressure levels; generating a pressure sensing signal value of the stylus under calibration; comparing the calibrated pressure sensing signal value with the average pressure sensing signal value to generate a calibration reference value, wherein the calibrated pressure sensing signal value and the average pressure sensing signal value are corresponding to the same weight applied on the stylus; and calibrating data of pressure sensing signal values of the stylus by the calibration reference value, thereby mapping to the pressure levels matching the standard pressure curve via the standard pressure level mapping curve.
Embodiment of this invention will be described in detail below. However, in addition to as described below, and this invention can be broadly implemented in the other cases the purpose and scope of this invention is not affected by the application of qualified, claim after its prevail. Furthermore, to provide a description more clear and easier to understand the invention, the pieces within the schema and not in accordance with their relative size of drawing, compared to certain dimensions to other scales have been exaggerated; details not related nor completely drawn in part in order to schematic simplicity.
In this embodiment, the conductive nib 104, the nib holder 105, the elastomer 108, the pressure sensor 110 and the pressure sensor circuit board 112 are configured to provide the stylus 100 with tip pressure detection. Some components can be further included to enhance the performance, such as a spring to restore the conductive nib 104 back to the original position after tip pressure is removed. In other embodiments, various pressure sensing modules can be used to provide the stylus 100 with tip pressure detection.
The stylus further comprises a control unit (not shown) on the control circuit board 114. The control unit comprises a microprocessor unit or MCU with embedded non-volatile memory or non-transitory computer readable medium such as flash memory. The control unit calculates the tip pressure applied on the stylus 100 via signals from the pressure sensor 110. The signals from the pressure sensor 110 may fluctuate due to various reasons. For example, physical and mechanical errors or size inaccuracy of the conductive nib 104, the nib holder 105, the elastomer 108 or the spring to restore the conductive nib 104 resulting from manufacture issues or assembling causes, and the fluctuated contact condition between the elastomer 108 and the pressure sensor 110 amid the use of the stylus 100. The control unit outputs pressure sensing signals via the conductive nib 104 to the touch panel 10. The touch panel 10 displays strokes of the stylus 100 according to coordinates of the stylus 100 and stroke thicknesses according to pressure sensing signals. The pressure sensing signals may be converted to a digital value by an ADC (Analog Digital Converter) in the touch panel 10. Ideally, the pressure sensing signals should be proportional to the tip pressure applied on the tip of the conductive nib 104. However, the physical and mechanical errors of pressure sensing modules of different styluses may cause diversified pressure sensitivities. The relation between the pressure sensing signals and the tip pressure applied on the tip of the conductive nib 104 forms a pressure sensing signal curve of the stylus 100.
V
s(x)=V(x)−V(0)
Vs is a shifted pressure sensing signal value and x is a weight applied on the styluses, while V is a pressure sensing signal value from the styluses and V(0) is the pressure sensing signal value without adding any weight on the styluses. The pressure sensing signal curves can be easily obtained by using a spreadsheet or an interactive computer application program.
V
a(x)=SUM(V1(x)+ . . . +Vn(x))/n
Va is an average pressure sensing signal value, while V1(x) and Vn(x) represent pressure sensing signal values of stylus 1 and stylus n with weight x applied thereon. For example, the data of the shifted pressure sensing signal values shown in
P(x)=LN(x)*71.723−165.15
P(x) is pressure level of a stylus with weight x applied thereon LN(x) is the Natural Logarithmic function. The value of pressure level is from 0 to 255 and thus there are 256 levels. The pressure levels are corresponding to stroke thicknesses displayed on a touch panel.
V
c(x)=V(x)−(V(xc)−Va(xc))
Vc is the calibrated pressure sensing signal value after mapping, xc is the weight of the mapping point applied on the stylus being calibrated. In
V
c(x)=V(x)−(V(450 g)−Va(450 g))
The mapping of pressure sensing signal curve of stylus set forth can be performed by a program encoded in the non-volatile memory of the control unit. Thus after production, quality control personnel can use the tool 12, the holder 14 and the weight 16 to calibrate newly produced styluses on the touch panel 10.
Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.