1. Field of the Invention
The present invention relates to a device for varying capacitance, and reflecting pressure-variation on it by means of the variation of the capacitance, which pertains to the field of the application of electronic devices and components.
2. Description of the Related Art
With the increasing improvement in the design of the consumptive electronic products as well as the increment of the demand of the user, there are more and more occasions in which a varying external physical quantity needs to be measured, controlled and responded. Pressure sensing techniques are examples adopted in such occasions, which are widely used in many technical fields, such as a handwriting pen in the input apparatus of a computer. When the writer uses the handwriting pen, a real time feedback to the pressure is required. That is, the variation of the magnitude of the acting force upon writing should be quickly and timely reflected on an apparatus or an application software and displayed on the computer screen so that a status of force applied by the user upon writing, for example, whether a light, heavy, quick, or slow writing is done, can be reflected.
In order to achieve the aforesaid purpose and effect, several solutions have been provided. In particular, the Japanese patent No. JP2001319831 provides a solution which relates to a pressure measurement device wherein a dielectric has two end faces with one end face having two electrodes and the other end face having one flexible electrode; a predetermined gap is provided between the flexible electrode and the other end face; While being applied with an external force, the flexible electrode can generate a relative variation with respect to the other end face; and when the relative variation is generated, a parameter associated with the applied external force can be obtained.
The above solution has obvious defects which are mainly represented as below: two electrodes are connected to one dielectric, which is equivalent to one porcelain dielectric capacitor. Therefore, there is an initial value of capacitance. When the flexible electrode is brought into contact with the dielectric and the contacting area varies, the amount of the variation of the capacitance is established on the basis of the initial capacitance value as the minimum capacitance value. In fact, the capacitance value when the flexible electrode just contacts the dielectric is identical to the initial capacitance value, and it is difficult to distinguish between variation value and the initial value, which causes inconvenience in the sensing and controlling operation. Therefore, the manufacturing level must be improved, and in particular, the requirement for manufacturing the devices tends to be much more stricter. In addition, the Japanese patent No. JP1990-0206774 is slightly different from the previous solution. Although there is a zero initial value, the structure of the latter Japanese patent is complicated and troublesome for manufacturing and production, and the reliability of the product is reduced.