DE4108688A1 - Accurate object positioner using proportional EM actuator - has push=pull stages with laser measurement of displacement to supply data to control stages operating in MM range - Google Patents

Abstract

A micropositioner, with a bandwidth of around 100 Hz, has rotationally symmetric armature (3) within a core (1). An airgap exists between the core and armature. Together with the windings (2,7) a pair of e.m. actuators is produced. At one end of the armature a mirror (10) is installed. The range of motion is in the millimetre range. A laser (12) is reflected off the mirror to provide measurement of the displacement and this provides feedback to regulating circuits (16,17) that adjust the excitation current to the coils. A digital processor (20) provides a reference value for the displacement. USE/ADVANTAGE - Provides high dynamic force over extremely small displacement range. Can dynamically correct position deviations caused by shaking of astronomical telescope.

Description

The present invention relates to a device for Position an object according to the generic term of Claim 1.

Find how to perform such positioning tasks Actuators Use with linear characteristic between Force and control quantity have good dynamics, d. H. the fast adjustment movements with bandwidths of up to several Enable 100 Hz.

It is known to use linear motors for such actuators use. These use the force to move the object between a permanent magnet and a through-current fin coil is generated. Such linear motors are known for example from EP-A-02 21 735. Linear motors allow almost any given size Adjustment paths, but they have the disadvantage that they themselves when using expensive permanent magnets from rare earths require a relatively large volume and a high loss Have performance.

The so-called piezo drives are also known, in which the change in length of special ceramic material in the electric field is used to generate a driving force. Such drives are capable of high driving forces small deflections and high dynamics. you are available on the market as finished components, for example as model P-840 from Physik Instrumente. Piezo drives have the disadvantage, however, that they have adjustment paths below are limited by 0.1 mm that they have a considerable overall length (approx. 1400 stroke) and hardly any in design are changeable. The adjustment paths that can be reached are for many applications too small.

It is the object of the present invention, a Device for positioning an object within a to create an adjustment path in the millimeter range, the high driving forces with good volume with low volume Generates dynamics and their design in a simple manner intended application is customizable.

This task is accomplished by a device according to the characterizing features of claim 1 solved.

The device according to the invention is based on the principle of the electromagnet that has long been in relays and Solenoid is used. With this use only the two end positions, d. H. Anchor tightened / anchor used decayed. The one between these end positions So far, it has not been possible to use the route covered by the Electromagnets generate forces regardless of the direction of the excitation current always try to pull the armature and thereby shortening the field lines, d. H. act unipolar and since the characteristic curves force / excitation current and force / displacement are are linear.

The invention enables a linear, bidirectional Manufacture drive according to the principle of the electromagnet, that can be used for high-precision positioning tasks where the adjustment ranges are in the millimeter range.

According to a characteristic feature of claim 1 the excitation of the electromagnet is regulated so that it by force exerted on the anchor regardless of the size of the Air gap between armature and core linear from the rudder size depends. From this, for example as a voltage The control variable placed in the control loop is the excitation current of the Electromagnet formed.  

The device according to the invention is characterized by low mass, large achievable forces and therefore good Dynamics with low manufacturing costs. The one certain volume of the new device can be generated force larger than a linear motor with the corresponding volume. It is readily understood that the device by appropriate training of the electromagnet in simple Way is adaptable to the respective application.

Further advantageous embodiments of the device according to the Invention are described in subclaims 2 to 11. The sub-claims 2 and 3 relate to special, advantageous embodiments. Subclaims 4 to 7 refer to the measurement of the used to regulate the pathogen current serving, proportional to the size of the air gap Signal. On the formation of the assigned control loop refer to sub-claims 8 and 9. The sub-claims 6 and 10 relate to an embodiment in which Linearization of the force-displacement characteristic of the magnetic flux is used. Subclaim 11 describes a preferred one Embodiment of the electromagnet. Other embodiments of the electromagnet are possible, the each used form based on the intended application.

The invention will in the following with reference to the execution examples representing FIGS. 1 to 6 of the accompanying drawings in detail. In detail show:

Figure 1 shows a first embodiment of the new device in the application for linear adjustment of an optical element, the arrangement for regulating the excitation current flowing through the solenoid coils is shown schematically.

Figure 2 shows the basic structure of a control loop for the excitation current.

Fig. 3 shows a second embodiment of the new device in a schematic representation;

Fig. 4 shows the basic structure of a control circuit used in connection with the device of Fig. 3;

FIG. 5 shows a further embodiment in the application to the linear displacement of an imaging system;

Fig. 6 shows another embodiment of the device.

In Fig. 1 with ( 1 ) the pot core of a first electric magnet is referred to, which carries the excitation coil ( 2 ). An armature ( 3 ) closes the iron core of the magnet via an air gap ( 4 ). The armature ( 3 ) is rotationally symmetrical and its axis ( 5 ) is mounted in the core so as to be longitudinally displaceable. The armature ( 3 ) also forms the armature of a second electromagnet, the pot core with ( 6 ) and the coil with ( 7 ). In the core ( 6 ), the axis ( 8 ) of the armature ( 3 ) is mounted for longitudinal displacement. The armature ( 3 ) closes the iron circuit of the second electric magnet via the air gap ( 9 ). With the axis ( 8 ) a mirror ( 10 ) is firmly connected to the ver, which can be moved by appropriate excitation of the electromagnets ( 1 , 2 ) and ( 6 , 7 ) in the direction of the double arrow ( 11 ) in different positions. This shift is in the millimeter range.

In order to measure the position of the mirror (10) exactly true in the illustrated example, a laser beam (12) onto the mirror (10) and falls after reflection by the mirror onto a sensor (13) which is formed for example as a diode row (13) is. The signal generated by the sensor ( 13 ) is therefore proportional to the actual position of the mirror ( 10 ).

With ( 16 ) and ( 17 ) two schematically illustrated control circuits are referred to, which conduct the excitation currents to the coils ( 7 ) and ( 2 ) via the lines ( 18 ) and ( 19 ). The target value of the air gap ( 4 ) or ( 9 ) is specified via the schematically represented computer ( 20 ). The control loops ( 16 ) and ( 17 ) generate excitation currents that are directly and linearly proportional to the force on the armature ( 3 ) regardless of the size of the air gap ( 4 , 9 ). This makes it possible to achieve the preselected value of the air gap ( 4 , 9 ) very precisely, very quickly and without disturbing transient processes.

The sensor ( 13 ) delivers a signal which is proportional to the actual position of the mirror ( 10 ) and which is fed to the control loops ( 16 ) and ( 17 ). In the event of deviations from the specified target value, these generate a correction signal which adjusts the mirror position via the two electromagnets.

The two electromagnets ( 1 , 2 ) and ( 6 , 7 ) work mirror images against each other, so that they exert an adjusting and restoring force on the armature ( 3 ). They are coordinated via the control loops ( 16 ) and ( 17 ) on the same course of the force-displacement characteristics.

In principle, it is possible to use only one of the two electromagnets, for example the magnet ( 1 , 2 ) and to generate a force by a spring which acts on the armature ( 3 ), which counteracts the effect of the armature ( 3 ) Magnets ( 1 , 2 ) preloaded.

In the exemplary embodiment in FIG. 1, the sensor ( 13 ) measures the position of the mirror ( 10 ) moved over the armature ( 3 ). This position is directly proportional to the size of the air gap ( 4 ), which is referred to below as l.

It is also possible to measure the air gap distance l directly. For this purpose, coils ( 2 , 7 ) auxiliary windings can be attached to or in the exciter, for example. The signal generated by these auxiliary windings is directly proportional to the magnetic flux and this is determined by the excitation current and the air gap distance l. Since the excitation current is known, a signal proportional to the air gap distance l is calculated in the control loops ( 16 ) and ( 17 ) from the signals of the auxiliary windings, which are supplied via the lines ( 14 ) and ( 15 ) shown in broken lines instead of the signal from the sensor ( 13 ) is used.

So-called differential field plates, which are integrated in the electromagnets ( 1 , 2 ) and ( 6 , 7 ), offer a further simple possibility for directly measuring the air gap distance l. Such differential field plates are offered for example under the name FP 212-100 from Siemens; they measure the air gap distance l with a linearity error <1%. The signal from these differential field plates is fed to the control circuits ( 16 , 17 ) via lines ( 14 , 19 ).

The measurement of the air gap distance l can also be done with the help done by optical devices. Such devices are widely known; on their representation here waived.

It is of course possible to effect a different movement of other elements with the device according to FIG. 1. If, for example, the mirror ( 10 ) is rotatably mounted and the arm ( 8 ) is connected to such a mirror in an articulated manner, the angular position of the mirror can be adjusted.

With the device of Fig. 1, it is also possible in the event of external disturbances such as. B. shocks or vibrations always keep the air gap ( 4 , 9 ) constant. For this purpose, the value proportional to the mirror spacing is specified via the computer ( 20 ). A vibration causes a change in the air gap distance l. Its size is then automatically and quickly adjusted to the predetermined target value.

The device of FIG. 1 can also be formed non-rotationally symmetrically, with U-shaped cores being used instead of the pot cores ( 1 and 6 ).

FIG. 2 shows a simplified exemplary embodiment for one of the control loops ( 16 , 17 ) in FIG. 1. The computer ( 20 ) of FIG. 1 supplies point ( 21 ) with a signal which is proportional to the target value of the air gap distance 1 and thus, for example, to the target position of the mirror ( 10 ) in FIG. 1. This signal is available as voltage value U ₁ . The signal U _{1 is} amplified by a PI controller ( 22 ) known per se and is present as signal U ₂ at point ( 23 ). In a subsequent link ( 24 ), which is formed, for example, from the ICL-8013 module from INTERSIL, the square root is formed from the value U ₂ . This root value is fed to a multiplier ( 25 ) which, for example, also consists of the ICL-8013 module and which is supplied with a signal proportional to the air gap distance l by the sensor on the electromagnet ( 1 , 2 ) shown schematically. The multiplier ( 25 ) thus forms the value √ · l. This is fed to a power amplifier ( 26 ), which converts the supplied voltage signal into a proportional current I, which is supplied as the excitation current to the coil ( 2 ) of the electromagnet ( 1 , 2 ).

For the following consideration it is assumed that U _{2 is} directly proportional to the control variable U₁, so that:

U₂ = c₂U₁ (c₂ = constant)

The voltage is at the output of the multiplier ( 25 )

at. The power amplifier ( 26 ) converts it into the excitation current I, which is directly proportional to the voltage · l, for which the following therefore applies:

or

The following applies to the force F exerted by the coil ( 2 ) of the electromagnet on the armature ( 3 ):

F = c₄ · I² / l² (basic equation)

If the value for the excitation current I is set according to the formula

one, so you get

This means that the force F exerted on the armature ( 3 ) is proportional to the control variable U 1 and is independent of the air gap distance l.

The force F is due to the parameters in every application of the system. Forming the reason given above equation, we get:

The air gap distance l then depends linearly on the current I through the excitation coil of the electromagnet at a constant F. By selecting the control signal U ₁ , which is proportional to this current, any air gap distance within the adjustment range can be set quickly and precisely by specifying a corresponding scatter signal U ₁ . For example, a small signal U ₁ and consequently a small excitation current I can be used to set a small air gap and vice versa.

The control loop shown in Fig. 2 consists of an inner (subordinate) control loop for the speed of the control process and the outer control loop for the regulation of the desired position of the air gap distance. The inner control circuit contains a differentiator ( 27 ), at whose output the signal U ₃ coming from the sensor of the electromagnet ( 1 , 2 ), which is proportional to the air gap distance l, is present as signal dU ₃ / dt. This signal is present at point ( 23 ) to which the output signal U _{2 of} the PI controller ( 22 ) is supplied. This signal forms the reference variable for the speed controller.

The signal U ₃ coming from the electromagnet ( 1 , 2 ), which is proportional to the air gap distance l, is present at point ( 1 ), to which the control signal U _{1 is also} supplied. At ( 21 ), the difference U ₁ -U _{3 is} formed, which is fed to the control loop as a manipulated variable via the PI controller. This regulates U ₁ -U ₃ to the value zero, ie it sets the excitation current I so that the air gap l reaches the preselected setpoint.

Via the subordinate speed control loop achieved that the setting to the target value l quickly he follows. With less dynamic requirements, the Speed control loop, d. H. the inner control loop gone be left.

The control loop shown in Fig. 2 is constructed with analog working elements. Of course, it is also possible to digitize the signal U ₃ coming from the electromagnet ( 1 , 2 ) and to build up the control loop from digital elements.

The air gap distance l is in the device according to the Invention at a maximum of 5 mm, preferably less than 1 mm. Depending on The application F can have different values. A for example, the value is 200 N, which is ent speaking training of the excitation coil with an exciter current in the order of 10 A can be reached. The before direction according to the invention has good dynamics, the Allows adjustment movements with a bandwidth of approx. 300 Hz.  

If the air gap distance l or that associated with it Position of the actuator connected to the magnet armature measured directly, this is also a linearization of the force Path characteristic to zero frequency and a static This actuator can be positioned. The minimum Air gap should be around 0.1 mm.

FIGS. 3 and 4 show another embodiment, wherein the path characteristic power, a control loop for the magnetic flux Φ is used for linearization of the.

Fig. 3 shows schematically an electromagnet consisting of a U-shaped or cup-shaped core ( 45 ), an armature ( 47 ) and the excitation winding ( 46 ). The distance l between the core ( 45 ) and anchor ( 47 ) should be regulated. The core ( 45 ) carries, in addition to the excitation winding ( 46 ), a schematically illustrated measuring winding ( 48 ) which supplies a voltage which is proportional to the change in the magnetic flux over time, ie the value dΦ / dt. The winding ( 48 ) is attached in the immediate vicinity of the air gap.

The basic structure of a control loop for linearizing the force-displacement characteristic is shown in FIG. 4. The computer ( 20 ) of FIG. 1 supplies the first link ( 50 ) with a signal which is proportional to the desired value of the air gap distance 1 and which is present as a voltage value U ₁ . The link ( 50 ) forms the value from this. This value is fed as a field current I to the field winding ( 46 ) of the electromagnet ( 45 , 46 , 47 ) via a P controller ( 51 ). The Meßwick development ( 48 ) generates a signal proportional to the value d proportion / dt, which is fed to an integrator ( 52 ). There is therefore a signal at point ( 53 ) proportional to the actual value of the magnetic flux Φ. The following applies to this signal

The proportional controller ( 51 ) forms the excitation current I according to the following equation from the signals present at point ( 53 ) and c₆ · I / l

If the control gain is sufficiently large, the value k goes against infinite, so that applies

If you put this value in the one already mentioned above Basic equation

one, so you get

The force F exerted on the armature ( 47 ) is therefore also proportional to the control variable U _1, regardless of the air gap distance l.

Because of the fundamental integration error caused by the integrator ( 52 ), the device according to FIGS. 3 and 4 cannot be used up to the frequency zero, ie the static case, without further additions. It is preferably used in the frequency range <10 Hz. A supplement that enables use down to zero frequency can be, for. B. look so that a predetermined position is approached at certain time intervals and the integrator is set to an associated voltage value.

Fig. 5 shows an embodiment in which an armature ( 30 ) is assigned to two electromagnets ( 31 , 32 ) and ( 33 , 34 ) working in opposite directions. The control loops are not shown here since they correspond to the arrangement according to FIG. 1. The anchor ( 30 ) is firmly connected to a carrier ( 35 ). Armature ( 30 ) and carrier ( 35 ) are fastened to a schematically illustrated housing ( 36 ) which contains an imaging optical system, for example a microscope objective. The focusing movement of this objective is effected by moving the armature ( 30 ) in the field of the electromagnets ( 31 , 32 ) and ( 33 , 34 ).

In principle, the device according to FIG. 3 can also contain only one electromagnet, for example the electromagnet ( 31 , 32 ). In this case, gravity exerts a restoring force on the armature ( 30 ).

To avoid eddy current losses, the core of the Laminated magnets, the sheet thickness for example Is 0.35 mm. The slats are made of one material that enables a high flux density (approx. 2 T) and its Hysteresis losses are negligibly small. Such one Material is for example under the name VACUFLUX of the vacuum melt Hanau commercially available.

In the described formation of the core of the electrical system laminated sheet magnets and the choice described of the core material it is not necessary to eddy current or Hysteresis losses to be taken into account, since in any case the Influence of the air gap l dominates.  

The design of the device according to the invention can be adapted to the installation conditions specified by the construction. For example, if only a small installation height is available, the embodiment according to FIG. 6 can be used. This consists of the flat electromagnet ( 37 , 38 ) to which the armature ( 39 ) is assigned. On the armature ( 39 ), two tension springs ( 41 , 42 ) connected to a base plate ( 40 ) engage here, which exert a force that is opposite to the force of the electromagnet ( 37 , 38 ).

The device according to the invention finds many Applications for positioning tasks with an adjustment range of a few millimeters. One of the possible uses is the dynamic correction of position deviations due to of vibrations on an astronomical telescope.

Claims (11)

1. Device for positioning an object within an adjustment path lying in the millimeter range, characterized in that the object ( 10 ) is connected to an armature ( 3 ) which is movably mounted via the adjustment path and which is part of an electromagnet ( 1 , 2 ). Closes the iron core of this magnet via an air gap ( 4 ) and that the electromagnet ( 1 , 2 ) is excited via a control circuit ( 17 ) so that the force exerted on the armature ( 3 ) is independent of the size of the air gap ( 4 ) depends linearly on the control variable (u ₁ ) fed to the control loop ( 17 ). 2. Device according to claim 1, characterized in that the armature ( 3 ) also forms the armature of a second, the first counteracting electromagnet ( 6 , 7 ). 3. Apparatus according to claim 1, characterized in that on the armature ( 39 ) of the electromagnet ( 37 , 38 ) engages a spring ( 41 , 42 ) serving to generate a restoring force. 4. Device according to one of claims 1 to 3, characterized in that an arrangement is provided which generates a, the size of the air gap between the armature ( 3 ) and electromagnet ( 1 , 2 ) proportional signal. 5. The device according to claim 4, characterized in that the arrangement for measuring the air gap ( 4 ) is designed as a differential field plate. 6. Device according to one of claims 1 to 3, characterized in that the electromagnet ( 45 , 46 ) carries an additional auxiliary winding ( 48 ) which generates a signal proportional to the temporal change in the magnetic flux Φ. 7. Device according to claims 4 and 6, characterized records that the additional auxiliary winding for extraction a signal is used that the air gap width l is proportional. 8. The device according to claim 1 and one or more of claims 2 to 5, characterized in that the control circuit ( 17 ) has a member ( 24 ) for forming the root from the supplied control signal U ₁ and a member ( 25 ) for multiplication contains this root value with the signal proportional to the air gap size l, and that the value obtained in this way determines the excitation current I of the electromagnet ( 1 , 2 ). 9. The device according to claim 8, characterized in that the control circuit ( 17 ) additionally contains a member ( 27 ) for differentiating the signal proportional to the air gap size l and for regulating the adjustment speed of the armature ( 3 ). 10. The device according to claim 1 to 3 and claim 6, characterized in that the control circuit a member ( 50 ) for forming the root from the supplied control signal U ₁ , one of the auxiliary winding ( 48 ) driven integer ( 52 ) to form a contains the actual value of the magnetic flux Φ proportional signal and a proportional amplifier ( 51 ), which forms the excitation current I from the quantities and Φ, and whose control gain k is infinite against the value. 11. The device according to one or more of claims 1 to 3, characterized in that the electromagnet consists of a U-shaped core ( 31 ) made of laminated iron sheet which carries the coil ( 32 ) through which the excitation current I flows.