Inductive touch sensor and method for operating such a sensor

Abstract

Inductive touch sensor (10), with at least one magnetic field generating element (12a, 12b) for generating a magnetic field, at least one resonance element (14a, 14b) arranged in the magnetic field of the magnetic field generating element (12a, 12b), a positioning element (16) for positioning the at least one resonance element (14a, 14b) relative to the at least one magnetic field generating element (12a, 12b), wherein the position of the resonance element (14a, 14b) relative to the at least one magnetic field generating element (12a, 12b) is changeable, so that the resonance generated by the magnetic field in the resonance element (14a, 14b) changes, an evaluation circuit for evaluating the change in the amplitude of the electrical signal of the resonance element (14a, 14b) and for comparing it with a reference amplitude, so that an actuation of the inductive touch sensor is detected.

Description

[0001] The invention relates to an inductive touch sensor and a method for operating such a sensor.

[0002] In modern robotic applications and other industrial applications, haptic feedback is often required, for example, when grasping an object or operating machinery. To detect whether an object has been grasped, a capacitive sensor, also used in smartphone displays, could be employed. Resistive and inductive sensors are also common. A problem with these sensors is that they can only detect certain materials. For example, a capacitive touch sensor will not detect a piece of plastic. Resistive sensors have the disadvantage of being highly temperature-dependent.

[0003] Oscillating circuit-based sensors are known from the following publications: SHINODA H. ; OASA, H. : Wireless Tactile Sensing Using Stress-Sensitive Resonator. In: IEEE / ASM Transactions on Mechatronics, Vol. 5, No. 3, Sept. 2000, pp. 258 - 265. ISSN 1941-014X US 2014 / 0 350 348 A1 ZHENG C., LI W., LI A., : Design and Manufacturing of a Passive Pressure Sensor Based on LC Resonance. In: Micromachines 2016, 7, 87; doi: 10.3390 / mi7050087

[0004] The object of the invention is to provide a touch sensor that can detect all materials and allows for more accurate measurement.

[0005] Furthermore, a method for operating such a sensor should be provided.

[0006] This problem is solved according to the invention by the features of claims 1 and 8.

[0007] The inductive touch sensor according to the invention has at least one magnetic field generating element for generating a magnetic field. This can be a coil to which an alternating voltage is supplied via an excitation circuit, thereby generating a magnetic field.

[0008] The inductive touch sensor according to the invention further comprises a resonant element arranged in the magnetic field of the magnetic field-generating element. This element can, for example, be a capacitor. Alternatively, an inductor connected to a circuit can be used. This circuit could, for example, contain identification codes for each resonant element. In all embodiments of the invention, it is preferred that the evaluation circuit can identify the resonant element whose resonance has been changed. Any element that is excited to resonance by the magnetic field of the magnetic field-generating element can serve as the resonant element. Preferably, this occurs after the magnetic field-generating element has been switched off, that is, after no voltage is supplied to it by the excitation circuit.

[0009] The inductive touch sensor also includes a positioning element for positioning the at least one resonant element relative to the magnetic field generating element. This positioning element can be, for example, a compliant medium, such as silicone, within which the resonant element is arranged. The position of the resonant element relative to the magnetic field generating element is thus changeable, thereby altering the resonance generated by the magnetic field in the resonant element.

[0010] This change in the resonance of the resonant element is evaluated by an evaluation circuit, thereby triggering detection and activation of the inductive touch sensor. Compared to sensors known from the prior art, the sensor according to the invention is not temperature-dependent and is also less susceptible to manufacturing inaccuracies. Furthermore, this sensor can detect all materials.

[0011] It is preferred that a shielding element be arranged on the side of the inductive touch sensor that is touched by the user. This can improve the measured signal. The shielding element preferably serves to shield integer multiples of the resonant frequency used.

[0012] Furthermore, it is preferred that a separate measuring branch of the excitation circuit, which generates the magnetic field of the magnetic field generating element, is used as the evaluation circuit. Alternatively, a separate circuit can also be used as the evaluation circuit.

[0013] Furthermore, it is preferred that at least two magnetic field generating elements are provided, which are excited at different frequencies. For example, the first magnetic field generating element can be excited at a higher frequency, while the second magnetic field generating element is excited at a lower frequency. In this embodiment, at least two resonant elements are also used.

[0014] The invention further relates to a method for operating an inductive touch sensor, in particular as previously described. The method according to the invention can have all the features of the device according to the invention, and vice versa.

[0015] In the method according to the invention, a magnetic field is generated by at least one magnetic field generating element. Subsequently, the magnetic field generating element is switched off by no longer supplying it with voltage via the excitation circuit.

[0016] The changing resonance of at least one resonance element positioned in a magnetic field is then measured. The resonance generated by the magnetic field in the resonance element changes because the position of the resonance element relative to the magnetic field-generating element can be altered. Depending on the position of the resonance element relative to the magnetic field-generating element, the resonance in the resonance element will therefore change.

[0017] An evaluation circuit analyzes this change in the resonance of the resonance element, thereby detecting an activation of the inductive touch sensor.

[0018] In a preferred embodiment, at least two magnetic field-generating elements are excited at different frequencies. The resonance of at least two resonant elements arranged in the magnetic field is then measured. Based on the different resonances of the two resonant elements at the different frequencies, the position where the touch sensor was touched is determined. The rationale behind this embodiment of the method is that the resonant elements respond only to the specific frequency for which they were designed. The resonant elements are thus excited at different frequencies (frequency division multiplexing), and their respective resonances are then measured. This makes it possible to identify and locate each individual resonant element.For this purpose, for example, a change in the amplitude of the electrical signal of the respective resonant element in the evaluation circuit is compared with a reference amplitude, so that information about a movement of the resonant element relative to the magnetic field generating element can be derived. It is further preferred that several magnetic field generating elements are distributed across a touch sensor, enabling the entire surface of the touch sensor to be scanned.

[0019] Preferred embodiments of the invention are explained below with reference to figures.

[0020] They show: Fig. 1 a first embodiment of the touch sensor according to the invention, Fig. 2 and Fig. 3 two different operating modes of the touch sensor according to the invention.

[0021] According to Fig. The inductive touch sensor 10 has a first coil (12a) and a second coil (12b), each of which generates a magnetic field. The resonator (14) is located in this Fig. 1 common magnetic field (not shown). It is located in the compliant material 16, which can be, for example, a silicone material and which serves as a positioning element by which the resonator 14 is positioned relative to the coils 12a, 12b.

[0022] The outward-facing side of the sensor 10 is provided with a shielding element 18.

[0023] If an object now touches this shielding element 18, the compliant medium 16 is compressed, thus reducing the distance between the resonator 14 and the coils 12a and / or 12b. This changes the resonance in the resonator 14, which is induced by the magnetic field of the coils 12a and 12b. This change in resonance is detected and evaluated by an evaluation circuit (not shown), so that it can be determined whether and, preferably, at which point the inductive touch sensor has been touched by the object.

[0024] In Fig. Figure 2 illustrates how a measurement process can take place. In the middle of the Fig. Figure 2 shows the excitation, which is caused by a pulse and supplied to the two coils 12a, 12b by an excitation circuit (not shown). The coils are then immediately switched off. The excitation creates a magnetic field. This, in turn, causes the resonator 14 to also oscillate. This is shown in the right part of the Fig. Figure 2 shows that by switching off coils 12a and 12b, the strength of the resonance field of the resonance element 14 can now be measured using a measuring circuit.

[0025] Another embodiment of the device and method according to the invention is described in Fig. Figure 3 shows two coils 12a, 12b, each excited at a different frequency. Furthermore, at least two resonator elements 14a, 14b are used, arranged in the common magnetic field of the two coils. As shown in the lower part of the Fig.As can be seen in Figure 3, the two resonance elements react differently to the different frequencies.

Claims

[1] Inductive touch sensor (10), with at least one magnetic field generating element (12a, 12b) for generating a magnetic field, at least one resonance element (14a, 14b) arranged in the magnetic field of the magnetic field generating element (12a, 12b), a positioning element (16) for positioning the at least one resonance element (14a, 14b) relative to the at least one magnetic field generating element (12a, 12b), wherein the position of the resonance element (14a, 14b) relative to the at least one magnetic field generating element (12a, 12b) is changeable, so that the resonance generated by the magnetic field in the resonance element (14a, 14b) changes, an evaluation circuit for evaluating the change in the amplitude of the electrical signal of the resonance element (14a, 14b) and for comparing it with a reference amplitude, so that an actuation of the inductive touch sensor is detected. [2] Inductive touch sensor according to claim 1, characterized by , that the magnetic field generating element (12a, 12b) is a coil. [3] Inductive touch sensor according to claim 2, characterized by , that the resonance element (14a, 14b) is a capacitor. [4] Inductive touch sensor according to one of claims 1 to 3, characterized by , that the positioning element (16) has a compliant medium within which the resonance element (14a, 14b) is arranged. [5] Inductive touch sensor according to one of claims 1 to 4, characterized by , that a shielding element (18) is arranged on the side of the inductive touch sensor (10) that is touched by the user. [6] Inductive touch sensor according to any one of claims 1 to 5, characterized by , that a separate measuring branch of the excitation circuit is used as the evaluation circuit, through which the magnetic field of the magnetic field generating element (12a, 12b) is generated. [7] Inductive touch sensor according to any one of claims 1 to 6, characterized by , that at least two magnetic field generating elements (12a, 12b) are provided which are excited at different frequencies, and furthermore at least two resonance elements (14a, 14b) are provided. [8] Method for operating an inductive touch sensor (10) wherein the method comprises the following steps: Generating a magnetic field by at least one magnetic field generating element (12a, 12b), Measuring a changing amplitude of the electrical signal of at least one resonant element arranged in a magnetic field (14a, 14b), Comparing the measured amplitude with a reference amplitude, wherein the position of the resonance element (14a, 14b) relative to the at least one magnetic field generating element (12a, 12b) is changeable, so that the resonance generated by the magnetic field in the resonance element (14a, 14b) changes, Evaluating the change in the resonance of the resonance element (14a, 14b) so that an actuation of the inductive touch sensor is detected. [9] Method according to claim 8, characterized by the steps: Excitation of at least two magnetic field generating elements (12a, 12b) with different frequencies, Measuring the resonance of at least two resonance elements arranged in a magnetic field (14a, 14b), where, due to the different resonance of the two resonance elements (14a, 14b) at the different frequencies, the position at which the inductive touch sensor (10) was touched is determined.

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