DE102005022178B4 - Positioning device and method for compensation of acceleration forces - Google Patents

Abstract

Positioning device (100), which comprises a first actuator (12) which is arranged on a carrier element (14) and whose extension can be changed in a direction perpendicular to the surface of the carrier U1 (t) (16), on the carrier element (14) At least one second actuator (22) is arranged, the extent of which can be changed in a direction perpendicular to the surface of the carrier element (14) as a function of a compensation signal U2 (t) (28), characterized in that the actuators have different masses or material properties and that Compensation signal (28), with the exception of a constant offset U0, is essentially proportional to the control signal (16) (U2 (t) = U0 + αU1 (t)), the changes in the expansion of the first actuator (12) and the second actuator ( 22) at least partially cancel out the forces exerted on the carrier element (14) and the proportionality constant α is set accordingly, ci di e coefficients of change in length and m ~ i are the effective masses of the actuators (12, 22) and the proportionality constant α positive ...

Description

The invention relates to a positioning device according to the preamble of claim 1 and to a method for compensating acceleration forces in a positioning device according to the preamble of claim 8.

Positioning devices are known from the prior art, in which a Feinstpositionierung at a control range between a few micrometers and a few hundred micrometers at a resolution or step down to a nanometer and below to be guaranteed. Although movements made in these systems should be small, they should be able to be executed as quickly as possible and as precisely as possible. In addition, such systems should be small and light, whereby the structure is indeed sufficiently stable against static forces, but not against high forces, which occur due to the accelerations required to execute the movements.

A typical example of such a positioning system is a displacement sensor in a scanning probe microscope. Scanning probe microscopy uses a piezo actuator to move the probe. As the piezo actuator contracts or expands under the action of the voltage applied to its electrodes, the probe is moved to a desired position of the sample. However, there are several factors that make accurate location determination difficult. Thus, the piezo actuator does not move linearly but with some hysteresis which causes the actuator not to return to its original position upon resetting the voltage to zero. Another non-linear effect is the so-called creep of the piezo actuator.

The DE 43 03 125 C1 discloses a circuit arrangement in which two similar piezoelectric actuators are connected to the same supply voltage generator, wherein the second actuator is coupled to a length measuring device which senses the movement of the first actuator and generates an output signal which is linearly associated with the actuating movement of the actuator of the first actuator , This feedback eliminates the effects of hysteresis, creep or temperature change.

In addition to the non-linear effects mentioned, differences in the amplitude and phase position occur between the control signal at the input and the real trajectory of the piezoactuators in the positioning devices. One reason for this is that the base on which the piezoactuator is arranged can not be made sufficiently rigid, as a result of which it is elastically deformed under the action of the acceleration forces and excited to damped oscillations, which overlap the positioning movement. This problem is particularly noticeable in multi-axis systems, since higher masses have to be moved here and rigidity is more difficult to realize in all spatial directions.

The effect of movement of the piezoactuator on the base is highly frequency dependent. Since the acceleration which occurs in a vibration with a fixed amplitude is proportional to the square of its frequency, the forces exerted on the basis of strong increase with increasing frequency. In addition to the mentioned effect on the positioning accuracy, the materials of the base are subject to high fatigue.

From the DE 199 23 462 C1 a positioning device is known in which the control signal provided for positioning a piezoactuator is modified by a filter. The calculation of the coefficients of the filter is carried out in real time, which can be responsive to system changes. The aim of such an arrangement is to pre-process in amplitude and phase the frequency components applied to the actuator in such a way that the position of the probe actually proceeds in a manner proportional to the original control signal. However, this is only approximately possible with a causal filter, so that a satisfactory result can only be expected in limited frequency ranges.

From the DE 101 48 60 A1 a positioning device with the features of the preamble of claim 1 is known in which the forces exerted by two symmetrically arranged identical actuators cancel forces approximately. It is not intended that the actuators have different masses or material properties.

From the DE 200 05 563 U1 a piezo-scanner for a scanning tunneling microscope is known in which is achieved by using a counterweight that occur at a time-dependent change in length of the scanner tube no forces at its attachment point.

The object of the invention is to provide a positioning device which can be used in situations where high speeds in the movement of the actuators and a high resolution are required.

According to the invention this object is achieved by means of a positioning device with the in claim 1 mentioned features or by means of a method with the features mentioned in claim 7.

Characterized in that on the carrier element at least a second actuator is arranged, whose extension in a direction perpendicular to the surface of the carrier element in response to a compensation signal is changeable, wherein the compensation signal with the exception of a constant offset U ₀ is substantially proportional to the control signal (U ₂ ( t) = U ₀ + αU ₁ (t)) and wherein the forces exerted by the expansion changes of the first actuator and the second actuator on the carrier element cancel at least partially, the elastic deformation of the carrier element is counteracted. In addition to an increase in the positioning accuracy, a reduction in the mechanical stress on the carrier element is achieved. In addition, the carrier element can be made extremely lightweight, which can be particularly advantageous in multi-stage positioning of great economic advantage, since here the mass of the carrier element at the same time constitutes a substantial part of the transport mass of the previous positioning stage.

The positioning device according to the invention can be designed such that the two actuators are arranged on the same surface of the support element or surfaces facing away from the support element. In this case, the latter arrangement is generally preferable because it can also prevent the occurrence of shear forces.

eingestellt ist, wobei c_i die Längenänderungskoeffizienten und m ~_i die effektiven Massen der Stellglieder sind und wobei die Proportionalitätskonstante α positiv ist, wenn die beiden Stellglieder auf einander abgewandten Oberflächen des Trägerelementes angeordnet sind. Dadurch überträgt das zweite Stellglied eine Kraft auf das Trägerelement, welche dem Betrag nach der ursprünglichen Kraft des ersten Stellglieds gleicht, aber die entgegengesetzte Richtung aufweist. Etwaige Schwingungen des Trägerelementes werden gedämpft und sterben ab.The actuators have different masses or material properties. It is provided that the proportionality constant α in accordance with

where c _{i are} the coefficients of extensional change and m ~ _{i are} the effective masses of the actuators and where the proportionality constant α is positive when the two actuators are arranged on opposite surfaces of the support element. Thereby, the second actuator transmits a force on the carrier element, which is equal to the amount of the original force of the first actuator, but has the opposite direction. Any vibrations of the carrier element are damped and die.

In a preferred embodiment of the invention, it is provided that the positioning device comprises a control loop for controlling the proportionality constant α, the control loop comprising a position sensor arranged on the carrier element, a multiplication step for multiplying a signal supplied by the position sensor with the control signal and a filter for averaging one of the multiplication step supplied signal includes. As a result, a controlled tracking of the control of the compensation actuator is also possible in cases in which the masses moved by the actuators are variable or unknown.

gewählt wird, wobei c_i die Längenänderungskoeffizienten und m ~_i die effektiven Massen der Stellglieder (12, 22) sind und wobei die Proportionalitätskonstante α positiv ist, wenn die beiden Stellglieder (12, 22) auf einander abgewandten Oberflächen des Trägerelementes (14) angeordnet sind. Potentielle Einsatzbereiche für ein solches Verfahren sind alle Antriebe im Bereich der Rastersondenmikroskopie sowie in der Mikroelektronik, wo mittels eines Greifers Chips oder Wafer schnell bewegt werden sollen. Außerdem lässt sich das Verfahren auch zur aktiven Schwingungsunterdrückung und somit zur Verhinderung von unerwünschter Schallerzeugung an schwingenden Flächen vieler Maschinen einsetzen.In the method according to the invention for compensating acceleration forces in a positioning device, it is provided that at least one second actuator is arranged on the carrier element whose extent in a direction perpendicular to the surface of the carrier element is controlled by a compensation signal U ₂ (t) such that the forces exerted on the carrier element by the expansion changes of the first actuator and the second actuator, at least partially, wherein the actuators have different masses or material properties, wherein the compensation signal ( 28 ) with the exception of a constant offset U ₀ substantially proportional to the control signal ( 16 ) is (U ₂ (t) = U ₀ + αU ₁ (t)), where the proportionality constant α in accordance with

where c _{i is} the coefficient of change in length and m _{i is} the effective mass of the actuators ( 12 . 22 ) and wherein the proportionality constant α is positive when the two actuators ( 12 . 22 ) on opposite surfaces of the support element ( 14 ) are arranged. Potential applications for such a process are all drives in the field of scanning probe microscopy and in microelectronics, where by means of a gripper chips or wafers are to be moved quickly. In addition, the method can also be used for active vibration suppression and thus to prevent unwanted sound generation on vibrating surfaces of many machines.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The invention will be explained in more detail in embodiments with reference to the accompanying drawings. Show it:

1a a conventional uncompensated piezoactuator;

1b Trajectories of the mass moved by the uncompensated piezoactuator;

2a a positioning device according to the invention with compensation;

2 B a trajectory of the moving of the positioning device according to the invention mass and

3 a positioning device according to the invention with control loop.

1a shows a piezo actuator 12 according to the prior art, which on a support element 14 is attached and a mass 10 in response to a control signal 16 move on a given path or make a vibration of given frequency and amplitude. At the same time, the piezoactuator expands 12 upon application of a suitable voltage or contracts, whereby a change in length is achieved, which is used to position the mass 10 serves. Should a movement of the mass 10 from position A to position B, the piezoactuator expands 12 according to the change of voltage. In 1a three times are shown during the adjustment process - the initial position at rest (left), a point in time during the expansion of the piezo actuator 12 in which the carrier element 14 is deformed (center), and the final state at rest (right).

1b shows the timing of the control signal 16 with the corresponding trajectories 18 the moving mass 10 , The control signal increases 16 ideally ramped. The two illustrated courses 18 the moving mass 10 correspond to different stiffnesses of the carrier element 14 , The dashed line is for comparison with the control signal 16 , The shape of the tracks 18 the moving mass 10 is due to the fact that by accelerating the moving mass 10 a force is created which the carrier element 14 deformed. This delays the deflection of the moving mass 10 in the desired direction and also induces a ringing of the system whose frequency is determined by the geometric structure and rigidity of the system. While a delayed start of the position, except for time-critical path adjustments, would still be tolerated, the Nachschwingvorgang is absolutely unacceptable because the moving mass 10 is temporarily moved across the desired position B and thereby can collide destructively with another body.

2a shows a positioning device according to the invention 100 in which on the back of the support element 14 a compensation actuator 22 is arranged, which is also a piezoelectric actuator and a compensation mass 20 emotional. In the simplest case, the properties of the two piezoactuators would be 12 . 22 and the moving masses 10 . 20 equal. Then it would suffice, the compensation actuator 22 by the same control signal 16 head for. That way, the compensation mass would 20 moved exactly in the opposite direction with the same amount and the same acceleration, so that the support element 14 only symmetrically compressed, but not deflected down. Thus, the time required for the bending of the carrier, and the moving mass would be eliminated 10 would reach its desired deflection B faster. Furthermore, there would be no relaxation of the bending of the carrier element 14 instead, so that in 1b Repeated swinging omitted and the deflection of the moving mass 10 would not exceed the point B.

In the present case, the properties of the two piezo actuators 12 . 22 different. For example, piezoactuators 12 . 22 may be used, which consist of a different number of individual plate or disc-shaped piezo elements, which are lined up in sandwiched together and electrically connected in parallel. In addition, the moving masses can 10 . 20 differ. In this case, the compensation actuator must 22 with a modified compensation signal 28 be controlled, which is proportional to the control signal 16 is.

In order to determine the associated proportionality constant α, the length of the piezoactuators becomes 12 . 22 It is assumed that the time scale on which the length of an actuator adjusts to an applied voltage is very small compared to the time scale on which the applied voltage changes. The movement of the piezoactuators 12 . 22 successes in the x-direction. The rest position of the support element 14 Let X = 0 be the lengths of the piezoactuators 12 . 22 without applied voltage let L ₁ and L ₂ . The approximately linear changes in length due to the applied voltages are ΔL _i = c _i U _i . The masses m _{i of} the piezoactuators 12 . 22 are distributed uniformly over their length, so that they can be summarized at half the length at x _i . The to the from the support element 14 remote ends of the piezoactuators 12 . 22 masses attached to x ' _i 10 . 20 be designated with m ' _i . Then the constraints are: x ₁ = X + (L ₁ + c ₁ U ₁ ) / 2 x ' ₁ = X + (L ₁ + c ₁ U ₁ ) x ₂ = X - (L ₂ + c ₂ U ₂ ) / 2 x' ₂ = X - (L ₂ + c ₂ U ₂ ).

The only external forces are the damping force -δẊ and the restoring force -kX. Thus, the equation of motion for the gravity movement is: m ₁ ẍ ₁ + m ' ₁ ẍ' ₁ + m ₂ ẍ ₂ + m ' ₂ ẍ' ₂ + Mẍ = -δẊ - kX.

After two derivations of the constraints and insertion into the equation of motion, the following equation results: (m ₁ + m _'1 + m ₂ + m' ₂ + M) x + (m _1/2 + m _'1) c ₁ P ₁ - (m _2/2 + m' ₂₎ c ₂ P ₂ = - δẊ - kX respectively μẍ + m ~ ₁ c ₁ P ₁ - m ~ ₂ c ₂ P ₂ = -δẊ - kX, where μ = m ₁ + m ' ₁ + m ₂ + m' ₂ + M is the total mass of the system and m ~ _i = m _i / 2 + m ' _{i are} the effective masses of the actuators. In the following, only these effective masses are taken into account, which consist of shares of the moving masses 10 . 20 and the piezoactuators 12 . 22 consist.

After execution of a Fourier transformation results: [-Μω ² + iδω + k] X = ω ² [m ~ ₁ , c ₁ U ₁ -m ~ ₂ c ₂ U ₂ ].

zu X = 0. Dies ist die Trivialbedingung, bei welcher eine vollständige Kompensation erreicht wird.

ist somit die erforderliche Proportionalitätskonstante α, mit welcher das Steuersignal 16 multipliziert werden muss, um ein Kompensationssignal 28 zur Ansteuerung des Kompensationsaktuators 22 zu ergeben, so dass sich die auf das Trägerelement 14 ausgeübten Kräfte zu Null addieren.With it leads

to X = 0. This is the trivial condition where complete compensation is achieved.

is thus the required proportionality constant α, with which the control signal 16 must be multiplied by a compensation signal 28 for controlling the compensation actuator 22 to give, so that the on the support element 14 Add applied forces to zero.

Often at least one of the variables m _i , m ' _i and c _{i is} not known, so that the proportionality constant α has to be determined from measurements on the system. In an embodiment not shown is to the support element 14 a position sensor attached. Now in a test mode, a sinusoidal control signal 16 and a compensation signal proportional thereto 28 according to U ₂ (t) = αU ₁ (t) used. The measurement of X (ω) by the position sensor at the fixed frequency for two different values of the proportionality constant α leads to a clear solution of the α, for which the trivial condition is fulfilled, because of the linearity of the condition mentioned above in Fourier space.

In order to achieve a suitable compensation during operation, the positioning device 100 operated in a closed loop. The aim of the control is to approximate the trivial condition even in situations in which the masses or linear expansion properties of the actuators used change over time.

3 shows a control loop which tracks the proportionality constant α. A control signal input device 24 generates a control signal 16 , which is used to control the piezoactuator 12 serves. At the same time the control signal 16 a proportionality controller 26 which is the control signal 16 multiplied by the proportionality constant α and thereby the compensation signal 28 for controlling the compensation actuator 22 generated. On the support element 14 is a position sensor 30 arranged, which constantly the position X (t) of the support element 14 determines and a measurement signal to a multiplication stage 32 conducts, in which the signal X (t) with the control signal 16 , U ₁ (t), is multiplied. The thus determined product of the two time signals is a temporal integration element (I controller) 34 supplied, which integrates the product signal X (t) U ₁ (t) suitably and thereby measures its DC component. This DC component is the controlled variable of the control circuit according to the invention. Its setpoint is 0, and the manipulated variable is α. On the basis of the manipulated variable α, the proportionality controller becomes 26 controlled to achieve a change to the trivial condition. The change in the DC component of the signal X (t) U ₁ (t) indicates the direction in which the manipulated variable α is to be changed.

In a non-illustrated embodiment, a second position sensor to the compensation mass 20 or to the compensation actuator 22 appropriate. By subtraction of the signals of the second position sensor and the position sensor 30 can change the length of the compensation actuator 22 getting closed. By comparing the measured change in length with the control signal 16 conclusions about non-linear effects like hysteresis and creep can be drawn. By suitable regulation, the control signal 16 be modified so that the non-linear effects are eliminated.

LIST OF REFERENCE NUMBERS

10

moving mass

12

first actuator / piezo actuator

14

support element

16

control signal

18

Trajectory of the moving mass

20

compensating mass

22

second actuator / compensation actuator

24

Control signal input means

26

Proportionalitätssteller

28

compensation signal

30

position sensor

32

multiplication stage

34

temporal integration element

100

positioning

Claims (8)

Positioning device ( 100 ), which is a first actuator ( 12 ), which on a support element ( 14 ) is arranged and its extension in a direction perpendicular to the surface of the support element ( 14 ) in response to a control signal U ₁ (t) ( 16 ) is variable, wherein on the support element ( 14 ) at least one second actuator ( 22 ) whose extent is in a direction perpendicular to the surface of the carrier element ( 14 ) in response to a compensation signal U ₂ (t) ( 28 ) is changeable, characterized in that the actuators have different masses or material properties and the compensation signal ( 28 ) with the exception of a constant offset U ₀ substantially proportional to the control signal ( 16 ) is (U ₂ (t) = U ₀ + αU ₁ (t)), which is due to the expansion changes of the first actuator ( 12 ) and the second actuator ( 22 ) on the carrier element ( 14 ) exerted forces at least partially cancel and wherein the proportionality constant α according to

where c _{i is} the coefficient of change in length and m ~ _{i is} the effective mass of the actuators ( 12 . 22 ) and wherein the proportionality constant α is positive when the two actuators ( 12 . 22 ) on opposite surfaces of the support element ( 14 ) are arranged. Positioning device according to claim 1, characterized in that to the carrier element ( 14 ) facing away from the actuators ( 12 . 22 ) of these moving masses ( 10 . 20 ) are arranged. Positioning device according to one of the preceding claims, characterized in that the actuators ( 12 . 22 ) Piezoactuators are. Positioning device according to one of the preceding claims, characterized in that the two actuators ( 12 . 22 ) on the same surface of the carrier element ( 14 ) are arranged. Positioning device according to one of the preceding claims, characterized in that the two actuators ( 12 . 22 ) on opposite surfaces of the support element ( 14 ) are arranged. Positioning device according to one of the preceding claims, characterized in that it comprises a control loop for controlling the proportionality constant α, wherein the control loop a on the support element ( 14 ) arranged position sensor ( 30 ), a multiplication stage ( 32 ) for multiplying a position sensor ( 30 ) supplied with the control signal ( 16 ) as well as a filter ( 34 ) for averaging one of the multiplication stage ( 32 ) supplied signal. Method for compensating acceleration forces in a positioning device ( 100 ), which is a first actuator ( 12 ), which on a support element ( 14 ) is arranged and its extension in a direction perpendicular to the surface of the support element ( 14 ) by a control signal U ₁ (t) ( 16 ), characterized in that on the carrier element ( 14 ) at least one second actuator ( 22 ) whose extent is in a direction perpendicular to the surface of the carrier element ( 14 ) by a compensation signal U ₂ (t) ( 28 ) is controlled so that by the expansion changes of the first actuator ( 12 ) and the second actuator ( 22 ) on the carrier element ( 14 ) at least partially cancel the forces exerted, wherein the actuators have different masses or material properties, wherein the compensation signal ( 28 ) with the exception of a constant offset U ₀ substantially proportional to the control signal ( 16 ) is (U ₂ (t) = U ₀ + αU ₁ (t)), where the proportionality constant α in accordance with

where c _{i is} the coefficient of change in length and m _{i is} the effective mass of the actuators ( 12 . 22 ) and wherein the proportionality constant α is positive when the two actuators ( 12 . 22 ) on opposite surfaces of the support element ( 14 ) are arranged. A method according to claim 7, characterized in that the proportionality constant α is controlled by the following additional method steps: - Measurement of the position X (t) of the carrier element ( 14 ); - formation of the product X (t) U ₁ (t); Averaging of the product X (t) U ₁ (t) in a suitable time window; Correction of the proportionality constant α as a function of the averaged product X (t) U ₁ (t).

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