DE102007016818B4 - Method for determining the polarity of a piezoelectric component - Google Patents

Abstract

Method for determining a polarity of a piezoelectric component (1) which has at least one capacitance (C), in which the component is subjected to a varying voltage (U) and a change in the measured capacitance of the component caused thereby indicates the polarity of the component, in which the capacitance (C) is measured electrically using a basic AC voltage, with the varying voltage (U) being superimposed on the basic AC voltage.

Description

A method for determining the polarity of a piezoelectric component which has at least one capacitance is specified.

The pamphlet DE 10 2004 001 692 A1 describes a test method for determining a polarity of a piezo actuator, the piezo actuator being mechanically loaded and the polarity being determined from an electrical response signal.

The publication of McCALLUM, Stephen; RESMER, Frank: "Automatic coupling control system for radio frequency in vivo electron paramagnetic resonance based on a piezoelectric controlled capacitor." (In: Review of scientific instruments, Vol. 70, No. 12, December 1999, pp. 4706-4710) describes a use of a piezoelectric actuator in electron spin resonance measurements.

The pamphlet DE 40 18 308 A1 describes a method for determining a polarity of a locally poled area of a piezoelectric film, a voltage being applied locally to the film and the polarity being determined from a change in thickness of the film.

In the publications by HAMI, Khalil El [et al.]: "Organic variable capacitor as direct application of piezoelectric effect." (In: Thin solid films, Vol. 393, 2001, pp. 343-346) and BIRK, H. [et al.]: "The local piezoelectric activity of thin polymer films observed by scanning tunneling microscopy." (In: Journal of Vacuum Science & Technology B, Vol. 9, 1991, No. 2, Part II, p. 1162- 1165) describes the determination of the piezoelectric properties of ultra-thin copolymer films from their change in thickness when a voltage is applied.

One problem to be solved is to specify a method by means of which the polarity of an electrical component can be determined in a particularly simple manner.

A method for determining the polarity of a piezoelectric component, which has at least one capacitance, is specified, a voltage being applied to the component and the capacitance of the component being measured.

The piezoelectric component has a basic polarity which is already present when it is measured.

In the method, the polarity of the component is determined or ascertained on the basis of a change in the measured capacitance of the component caused by the variation in the voltage. The voltage can be varied continuously or stepwise.

The method has the advantage that the polarity of the component does not have to be identified by means of written characters, shapes or other optical or pictorial means of identification. The polarity of the component can thus already be determined in its form suitable for installation, without it having to be provided with additional polarity markings.

The polarity of a piezoelectric multilayer component can be determined, which has a stack of dielectric layers and electrode layers arranged one on top of the other. Capacities can arise between respectively adjacent electrode layers of the multilayer component.

According to one embodiment of the method, a varying bias voltage is applied to the component. In this case, the component is preferably subjected to at least two bias voltages, one negative and one positive. In addition, the component can also be measured for its capacitance value with a bias voltage of 0.

The bias voltage is preferably subject to a basic voltage that is as low as possible, preferably between 0.5 and 1.5 V. The bias voltage can be an AC voltage of approx. 0.5 to 1.5 V at a frequency of approx 1.5 kHz are subject or the bias voltage is superimposed on the AC voltage.

A reduction in the capacitance of the piezoelectric component during the application of different, for example increasing, voltages can indicate a plus-plus polarity of the component. A plus-plus polarity means that a plus contact of a measuring device is contacted with a plus contact of the component.

An increase in capacitance during the application of different voltages to the electrical component indicates a plus - minus polarity of the component. A plus-minus polarity means, for example, that a plus contact of a measuring device is contacted with a minus contact of the component.

Varying bias voltages of between -25 and 25 V or between -10 and 10 V are preferably applied to the piezoelectric component. An AC voltage underlying the bias voltage with an amplitude of between 0.5 and 1.5 V, preferably 1 V, can be applied.

The polarity of a piezoelectric component that has externally accessible external contacts is preferably determined. This makes it easier to apply the selected voltage to the component.

According to an advantageous embodiment of the method, the piezoelectric component can be touched by a measuring device. This preferably has electrical contacts or contact pads, which are contacted with the component in such a way that the polarity of the multilayer component is measured using the measuring device. In this case, the contacts or contact pads of the measuring device are brought into contact with external electrical contacts of the component.

According to one embodiment, the measuring device can comprise a transport means which moves the component into a desired orientation as a function of the determined polarity.

The transport means preferably comprises a mechanical arm which has electrical contacts. The electrical contacts of the mechanical arm are contacted with the component to determine the polarity. The electrical contacts can be arranged on or in a clamping device or on a gripper of the arm.

A device for determining the polarity of a piezoelectric component is also specified, the component having at least one capacitance and externally accessible electrical external contacts.

The device includes a transport means with two differently polarized electrical contacts, which are arranged in such a way that they can be contacted with electrical connections of the piezoelectric component.

The electrical contacts of the means of transport can be connected to electrical supply lines that are connected to an electrical voltage supply.

The device preferably comprises an electronic evaluation unit, by means of which electrical characteristic values of the component picked up by the transport means can be evaluated and the polarity of the component can be determined. The evaluation unit is preferably designed such that it controls the device or the means of transport depending on the determined polarity of the component in such a way that it moves or transports the component into a position in which it is favorable in a container, in a housing or on a mechanical bearing or can be mounted on an electrical circuit board.

The objects described are explained in more detail with reference to the following figures and exemplary embodiments.

• 1 ein elektrisches Bauelement,
• 2A bis 2D Grafiken zur Darstellung des Verhältnisses zwischen der Änderung einer Kapazität des Bauelements und der Polarität des Bauelements,
• 3 eine Messvorrichtung zur Bestimmung der Polarität eines piezoelektrischen Bauelements, die ein Transportmittel umfasst.

It shows or shows:

• 1 an electrical component,
• 2A until 2D graphs showing the relationship between the change in a capacitance of the component and the polarity of the component,
• 3 a measuring device for determining the polarity of a piezoelectric component, which comprises a transport means.

1 shows a piezoelectric actuator 1 with a base body 2 which includes a plurality of dielectric layers 3 and electrode layers 4 . External contacts 5 and 6 are arranged on the surface of the piezoelectric actuator. Alternatively, the piezo actuator could be designed with electrical connections in the form of electrically conductive wires that contact the electrode layers. The contacting of the electrode layers with the electrical connections can take place inside the base body.

A varying bias voltage is applied to the component via the electrical external contacts or electrical connections. The capacitance C of the component changes in the process. An increase or decrease in the capacitance of the device is a measure of the polarity of the device.

Related to the 2A until 2D 10 piezo actuators were measured in one test. Capacities of the piezo actuators were recorded in µF, measured with 1V amplitude and 1 kHz AC voltage. The following measurement sequence was carried out in relation to the application of a bias voltage to the piezo actuators: positive bias voltage, no bias voltage (bias voltage=0), negative bias voltage.

In the case of the piezo actuators A1 to A5, the plus pole of the respective piezo actuator was placed on the plus pole of the measuring output of a measuring device. In the case of the piezo actuators A5 to A10, the minus pole of the respective piezo actuator was connected to the plus pole of the measuring output of a measuring device. The graphics show that the polarity of the respective piezo actuators can be clearly seen in the course of the bias-voltage-dependent capacitance.

2a shows a graphic showing a reduction in the capacitances C of several piezo actuators A1 to A5 as a function of a bias voltage U varying from -8 to +8 V. It is shown how the capacitances of the piezo actuators A1 to A5 fall from 2.3 µF to approx. 2.21 µF when the component is loaded at a bias voltage of -8V and ends at a bias voltage of 8V. The falling of the capacities of the piezo actuators is a sign of a plus - plus polarity of the respective piezo actuators. A plus-plus polarity means that a plus contact of a measuring device is contacted with a plus contact of the component.

2 B shows a graphic showing an increase in the capacitances C of several piezo actuators A6 to A10 as a function of a bias voltage U varying from -8 to +8 V. It is shown how the capacitances of the piezo actuators A1 to A5 increase from approx. 2.20 µF to approx. 2.35 µF when the component is charged at a bias voltage U of -8 V and at a bias voltage of 8 V ends. The increase in the capacity of the piezo actuators is a sign of a plus - minus polarity of the respective piezo actuators. A plus - minus polarity means that a plus contact of a measuring device is contacted with a minus contact of the component.

2c shows a graphic showing a reduction in the capacitances C of several piezo actuators A1 to A5 as a function of a bias voltage U varying from -20 to +20 V. It is shown how the capacitances of the piezo actuators A1 to A5 fall from 2.35 µF to approx. 2.16 µF when the component is charged at a bias voltage U of -20 V and at a bias voltage of 20 V ends. The falling of the capacities of the piezo actuators is a sign of a plus - plus polarity of the respective piezo actuators.

2d shows a graphic showing an increase in the capacitances C of several piezo actuators A6 to A10 as a function of a bias voltage U varying from -20 to +20 V. It is shown how the capacitances of the piezo actuators A1 to A5 increase from approx. 2.16 µF to approx. 2.37 µF when the component is charged at a bias voltage of -20 V and at a bias voltage of 20V ends. The increase in the capacity of the piezo actuators is a sign of a plus - minus polarity of the respective piezo actuators.

The following table shows the measurement results of the test: orientation plus on plus plus on minus Bias [V] A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 8th 2.24 2.24 2:21 2:21 2.25 2.25 2.3 2.6 2.24 2.34 0 2.27 2.27 2.23 2.24 2.28 2.22 2.27 2.23 2.22 2:31 -8th 2.28 2.29 2.25 2.26 2.3 2:21 2.26 2.22 2.2 2.3 20 2:19 2.2 2:17 2:18 2:21 2.28 2.34 2.29 2.27 2.38 0 2.25 2.25 2.22 2.23 2.27 2.22 2.28 2.24 2.22 2.32 -20 2:31 2.32 2.28 2.29 2.34 2:16 2:21 2:17 2:16 2.25

3 shows a measuring device 7, which has a transport means 7a, which moves the measured piezoelectric components 1 into a desired orientation and position. The transport means preferably has rotatable and/or pivotable mechanical arms 8 . At the end of an arm or joint 8 there is a gripper 9 with which piezoelectric components can be gripped. The gripper has electrical contacts 10, which are contacted with externally accessible electrical external contacts 5, 6 of the component.

The measuring device comprises an evaluation unit 11, which is connected to the electrical contacts of the gripper by means of electrical supply lines 12, 13. Measured values obtained from the transport means 7a and simultaneously subjected to a bias voltage from piezoelectric components are conducted via the electrical contacts of the gripper and the feed lines 12 and 13 to the evaluation unit.

This evaluates the measured values in order to determine the polarity of the component held by the means of transport. The transport means is controlled on the basis of the evaluation result or on the basis of the evaluated polarity information in such a way that it moves the held component into a desired orientation and position. The end position and end orientation of the piezoelectric component reached by the transport means is preferably a position or an orientation in which the component is already in an installation position suitable for assembly with other components in relation to the polarity of the component.

Reference List

1

Piezoelectric component

2

body

3

dielectric layer

4

electrode layer

5

first outside contact

6

second outside contact

7

measuring device

7a

Mode of Transport

8th

mechanical arm

9

gripper

10

contact pads

11

evaluation unit

12

Electrical supply

13

Electrical supply

u

bias voltage

Claims (14)

Method for determining a polarity of a piezoelectric component (1) which has at least one capacitance (C), in which the component is subjected to a varying voltage (U) and a change in the measured capacitance of the component caused thereby is the Pola ity of the component in which the capacitance (C) is measured electrically using a basic AC voltage, with the varying voltage (U) being superimposed on the basic AC voltage. procedure after claim 1 , in which a reduction in capacitance (C) indicates the polarity of the component (1). procedure after claim 1 , in which an increase in capacitance (C) indicates the polarity of the component (1). A method according to any one of the preceding claims, wherein the fundamental AC voltage has a frequency of between 0.8 and 2 kHz. Method according to one of the preceding claims, in which the amplitude of the basic alternating voltage is between 0.5 and 1.5 V. Method according to one of the preceding claims, in which the varying voltage (U) is varied in steps. Procedure according to one of Claims 1 until 5 , in which the varying voltage (U) is varied continuously. Method according to one of the preceding claims, in which the varying voltage (U) is between -25 and 25 V. Method according to one of the preceding claims, in which the component (1) has externally accessible electrical external contacts (5, 6) via which the varying voltage (U) is applied to it. Method according to one of the preceding claims, in which the piezoelectric component (1) is touched by a measuring device (7) having contacts (10) which are contacted with the component such that the polarity of the component is measured using the measuring device . procedure after claim 10 , in which the measuring device (7) comprises a transport means (7a) and the transport means transports the component (1) into a desired orientation and position depending on the polarity determined. procedure after claim 11 , in which the means of transport comprises a mechanical arm (8) with a gripper (9), the gripper having the electrical contacts (10) which are contacted with the component (1) to determine the polarity. Procedure according to one of Claims 10 until 12 , In which the measuring device (7) comprises an evaluation unit (11) which determines the polarity of the component (1). procedure after Claim 13 , in which, using polarity information of the component (1) evaluated by the evaluation unit (11), the evaluation unit controls the transport means (7) by means of electronic signals in such a way that the component is transported in the desired orientation and position.

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