KR101847357B1 - Stage of specimen holder for electron microscope and controlling method thereof - Google Patents

Abstract

According to an embodiment, a method for removing stress on a sample holder stage including a sample holder and a plurality of link assemblies connected to the sample holder and performing one degree of freedom movement, respectively, may include: step (a) of receiving the reference position of one link assembly of the plurality of link assemblies; step (b) of applying a current to a motor coupled to the link assembly such that the link assembly is driven towards the reference position; step (c) of determining the magnitude and direction of a load applied to the link assembly based on the applied current value; and step (d) of changing the position of the link assembly toward a correction position obtained by adding a set offset value to the reference position in a direction of reducing a load. It is possible to predict and eliminate the alignment error of the sample holder stage.

Description

TECHNICAL FIELD [0001] The present invention relates to a sample holder stage for an electron microscope, and a control method thereof. BACKGROUND ART [0002]

The present invention relates to a sample holder stage for an electron microscope and a control method thereof.

Electron microscopy scans and transmits electrons with shorter wavelengths compared to photons, and the electrons interacted with the sample are measured with a detector or an enlarged image of the sample is made through the transmitted image. The electron microscope has a slightly different operating principle depending on the type of electron microscope. The electron beam passes through the sample or focuses at one point on the surface of the sample, which is then scanned and collected by a detector to acquire an image.

Since the stage for the electron microscope is required to tilt or translate the sample in order to observe several surfaces or several places of the sample during observation with the electron microscope, the sample in the stage And a driver for driving a sample holder for supporting the sample holder. The actuator that drives the sample holder supporting the sample should be designed to realize various degrees of freedom in order to tilt and translate the sample. Ideally, it should be implemented outside the access space so as not to interfere with the insertion and withdrawal of the sample .

To implement the aforementioned multi-degrees-of-freedom motion, a device that implements a 6-degree of freedom, such as the well-known Stewart Platform, may be considered, Although it is a useful tool, its volume is too large to be mounted inside an electron microscope, and it is impossible to use it because it has a problem that it can occupy a moving path for entering and exiting the sample. In addition, there is a problem that the manufacturing cost is excessively high.

Another problem with existing sample holders is that conventional holders use a method of directly connecting a sample holder to a rotating motor shaft and moving it along a circular path in order to translate the sample, It is not a translational movement of a straight line, and a positional error occurs by a distance between a straight line and an arc. This causes a problem that the sample can not be moved to the precise position desired by the observer.

In order to simplify the design of the driving mechanism, another problem may be considered that a high-complexity drive mechanism part is installed in a vacuum electron-microscope barrel, and a vacuum type actuator is used to move the sample However, there is a problem that it is a virtual disadvantage of the producer and it is difficult to guarantee the completeness or precision of the drive.

Therefore, it is an urgent matter to study a simpler type of actuator that drives the sample holder to have a high degree of freedom. Such a driver is required to have an external space in which the mechanics and sensors do not occupy the space for entry and exit of the sample, A driver for a sample holder that can be implemented in a space outside the column supporting the sample holder is needed. In addition, such a driver must be capable of sufficient movement and rotation in a narrow space inside the electron microscope barrel, worrying about manufacturing costs, and avoiding too much complexity of the manufacturing process.

In particular, in the case of an electron microscope, it is difficult to compensate for stress due to alignment errors due to difficulty in accessing from the outside, since the sample setting space must be maintained in a vacuum.

An object according to an embodiment is to provide a method of operating a sample holder which can (i) drive a holder for supporting a sample with high freedom in order to observe various aspects of the sample smoothly, (ii) occupy the access space (Iii) it is possible to drive the sample holder efficiently in a narrow space while being outside the access space, and (iii) it is possible to predict and eliminate the alignment error of the sample holder stage for the electron microscope And to provide a control method.

According to an embodiment, there is provided a stress removing method of a sample holder stage including a sample holder and a plurality of link assemblies each connected to the sample holder and performing one degree of freedom movement, the method comprising: (a) Receiving a reference position of one link assembly; (b) applying a current to a motor coupled to the link assembly such that the link assembly is driven towards the reference position; (c) determining a magnitude and direction of a load applied to the link assembly based on the applied current value; And (d) changing the position of the link assembly toward a correction position obtained by adding the set offset value to the reference position in a direction of reducing the load.

If the current value applied to the motor in the step (b) is maintained below the set precision value, it is determined that the link assembly reaches the reference position and there is no load applied to the motor, .

In the step (b), the current applied to the motor may be a sinusoidal file having a set amplitude.

Wherein a maximum value of an expected driving range of the link assembly to be driven by a current applied to the motor is greater than a maximum value of an actual driving range of the link assembly, (A) to (d) while gradually decreasing the set amplitude when the minimum value of the estimated drive range of the link assembly is smaller than the minimum value of the actual drive range of the link assembly.

When the minimum value and the maximum value of the predicted drive range of the link assembly to be driven by the current applied to the motor are respectively less than a predetermined limit value based on the minimum value and the minimum value of the actual drive range of the link assembly , It is possible to determine the predicted drive range of the link assembly in that state as a range without stress and output it to the user.

The step (c) includes the steps of: (c-1) calculating a predicted drive range of the link assembly driven according to the input sinusoidal wave, assuming that the load does not act; (c-2) measuring an actual driving range of the link assembly driven according to the input sinusoidal wave; And (c-2) calculating a difference between the predicted drive range and the actual drive range, and determining a size and a direction of the load based on the difference.

The step (c-3) may include determining the magnitude of the load based on a deviation of a median value of the predicted drive range and a median value of the actual drive range.

The step (c-3) may include determining a direction of the load based on a relative position of a median value of the actual drive range with respect to a median value of the predicted drive range.

(E) resetting the correction position determined in step (d) to a new reference position in step (a), and repeating steps (a) to (d) As shown in FIG.

The set amplitude of step (b) may be set to gradually decrease until the expected drive range calculated in step (c-1) matches the actual drive range measured in step (c-2) .

The set offset value may be proportional to the difference between the predicted drive range and the actual drive range.

The sample holder stage includes a first drive module, a second drive module, and a third drive module, which are radially connected to the sample holder and have a translational degree of freedom in three directions and a rotational degree of freedom in at least two directions Wherein the first driving module, the second driving module, and the third driving module each include a connecting bar ball-jointed to three different portions of the sample holder, respectively; And an upper link assembly and a lower link assembly hinged to the upper and lower sides of the connection bar, respectively, for tilting the connection bar in a vertical direction.

The steps (a) to (d) may be performed on at least one of the upper link assembly and the lower link assembly.

Wherein one of the link assemblies of the upper link assembly and the lower link assembly is composed of two split links hinged to each other and the other link assembly of the upper link assembly and the lower link assembly includes three hinge- May be configured as segmented links.

The five segmented links can all move on the same two-dimensional plane.

Wherein the sample stage further includes a chamber surrounding the sample holder, the upper link assembly including: an upper sliding link slidable relative to the chamber; And a lower link assembly hinged to one side of the connecting bar and hinged to the upper sliding link, the lower link assembly comprising: a lower sliding link slidably movable relative to the chamber; A lower connecting link having one side hinged to the lower side of the connecting bar; And an intermediate link in which one side is hinged to the lower connecting link and the other side is hinged to the lower sliding link.

The rotation axis between the upper connection link and the connection bar may be orthogonal to the rotation axis between the upper connection link and the upper slide link.

The rotation axis between the lower connection link and the connection bar may be orthogonal to the rotation axis between the lower connection link and the intermediate link and may be perpendicular to the rotation axis between the intermediate link and the lower sliding link.

Wherein the driver of the electron microscope sample holder is connected to the sample holder for driving a sample holder for supporting the sample, wherein a plurality of pairs of link assemblies are provided so that the synchronized movement of the pair of link assemblies or the pair And the sample holder can be driven through relative movement between the link assemblies.

The plurality of link assemblies may be radially coupled to the sample holder.

The link assembly is composed of six pieces, and two pairs can be formed.

The position of the sample holder can be adjusted through the synchronized movement of the link assembly.

The driver of the sample holder can adjust the posture of the sample holder through the relative movement of the pair of link assemblies.

Wherein the pair of link assemblies are constituted by four-link links sequentially connected to enable relative rotation, and the driver of the sample holder is rotatable on any one of two links connected in the middle of the four- And a connection bar to which the other end is pivotally connected to the sample holder.

The connecting bar may be connected to the sample holder by a ball joint.

The driver may implement at least three degrees of translational motion and two degrees of freedom of rotational motion.

According to one embodiment, in a sample holder stage for an electron microscope in the form of a plurality of linear actuators, such as a Stuart platform, a link position range in which stress in the link due to alignment error of links through motor current feedback exists And the stage can be controlled based on the predicted stress to solve it.

According to one embodiment, there is an advantage that it is possible to predict and eliminate the stress of the sample holder stage for the electron microscope only by the motor current and the encoder signal which are necessary for the control without the additional force sensor.

According to one embodiment, in particular, it is difficult to access from the outside during operation of the electron microscope due to the characteristics of an electron microscope, which is required to keep the sample placing space in a vacuum. In the operation of the electron microscope, .

According to one embodiment, it can be utilized as a means for predicting the degree of machining assembly in an actual driving state of a sample holder stage for an electron microscope.

The effects of the present invention are not limited to those mentioned above, and other effects not mentioned may be clearly understood by those skilled in the art from the following description.

1 is a perspective view showing a stage for an electron microscope according to an embodiment.
2 is a perspective view illustrating a driver according to an exemplary embodiment of the present invention.
3 is a conceptual diagram for explaining the principle of position realization according to one embodiment.
4 is a conceptual diagram for explaining the principle of attitude implementation according to an embodiment.
5 is a perspective view showing a driving module according to an embodiment.
6 is a view schematically illustrating configurations for performing a method of controlling a sample holder stage for an electron microscope according to an embodiment.
7 is a block diagram of a sample holder stage for an electron microscope according to an embodiment.
Figs. 8 and 9 are block diagrams separately showing portions of Fig. 7. Fig.
10 is a diagram showing an algorithm of a method performed by a stress predicting unit of a stage for an electron microscope according to an embodiment.
11 is a diagram illustrating an algorithm of a method performed in stress relieving of a stage for an electron microscope according to an embodiment.
12 is a flowchart showing a control method of a stage for an electron microscope according to an embodiment.
13 is a flowchart showing an embodiment of step 930 of FIG.
14 is a flowchart showing a control method of a stage for an electron microscope according to an embodiment.
FIGS. 15 to 18 are graphs showing the feasibility and performance of simulation based on the control method of the stage for an electron microscope according to an embodiment.

Hereinafter, embodiments will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference numerals whenever possible, even if they are shown in different drawings. In the following description of the embodiments, detailed description of known functions and configurations incorporated herein will be omitted when it may make the best of an understanding clear.

In describing the components of the embodiment, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected or connected to the other component, Quot; may be "connected," "coupled," or "connected. &Quot;

The components included in any one embodiment and the components including common functions will be described using the same names in other embodiments. Unless otherwise stated, the description of any one embodiment may be applied to other embodiments, and a detailed description thereof will be omitted in the overlapping scope.

1 is a perspective view showing a stage for an electron microscope according to an embodiment.

Referring to FIG. 1, a stage 10 according to the present invention drives a sample holder 400 (see FIG. 2) located within a chamber 200 at a DOF of 5 degrees of freedom, Movement 2 freedom road, which will be described in detail later. According to the stage 10 according to the embodiment, tilting motions can be performed in all directions with respect to the observation point of the sample, and five degrees of freedom can be realized even in a space having a small vertical height. For example, even in a state where the two pole pieces are installed in a space of less than 15 mm, it is possible to tilt in all directions around the observation point on the desired sample. Therefore, the conventional single tilt- Compared with a double-tilt holder, it is possible to eliminate the problem that the observation point deviates from the beam axis when the sample is tilted.

The chamber 200 has a sample holder 400 therein, and three driving modules radially connected thereto drive the sample holder 400. The three drive modules include three connection bars 301, 302 and 303 and six link assemblies 310, 320, 330, 340, 350 and 360. One end of the link assembly is connected to the chamber 200, And is connected to the sample holder 400 through a connection bar, and the other end is connected to a motor for reciprocating the link.

The link assemblies 310, 320, 330, 340, 350, 360 may be provided with position sensors capable of measuring these movements. The sensors, links, motors, etc., So that the sample does not interfere with the entry and exit of the sample.

Figure 2 is presented to illustrate the driver. 2 is a perspective view illustrating a driver according to an exemplary embodiment of the present invention. The sample holder 400 may be connected to three connection bars 301, 302 and 303 and six link assemblies 310, 320, 330, 340, 350 and 360 connected thereto .

One end of each of the connecting bars 301, 302, and 303 may be pivotally moved relative to the sample holder 400. One end of each of the connecting bars 301, 302 and 303 may be connected to the sample holder 400 in a ball joint manner and tilted in at least two directions with respect to the sample holder 400, for example.

The other ends of the connecting bars 301, 302, and 303 may be connected in a hinge manner so as to be rotatable in the left-right direction with respect to the two link assemblies connected to the upper side and the lower side of the connecting bar. Here, the link assembly connected to the upper side of the pair of link assemblies connected to the upper side and the lower side of each link bar is referred to as an upper link assembly 310, 330, 350, and the link assembly connected to the lower side is referred to as a lower link Assemblies 320, 340, and 360, respectively.

As described above, the six link assemblies 310, 320, 330, 340, 350, and 360 may be connected to the motor to implement translational motion of the link assembly. In addition, the connection bars connected to one pair of link assemblies can be pivoted up and down according to the relative movement of the pair of link assemblies, which are paired up and down.

The six link assemblies 310, 320, 330, 340, 350 and 360 of the actuator 300 support the sample holder 400 through the chamber 200 to realize five degrees of freedom for controlling the position and attitude This is explained as follows.

3 and 4 for a more detailed description of the motion of the driver 300. [ FIG. 3 is a conceptual diagram for explaining a principle of positional realization according to an embodiment, and FIG. 4 is a conceptual diagram for explaining a principle of posture implementation according to an embodiment.

3, the position of the sample holder 400 connected to the six link assemblies 310, 320, 330, 340, 350, 360 can be changed while performing the translational motion . For example, the first and second link assemblies 310 and 320, the third and fourth link assemblies 330 and 340, the fifth and sixth link assemblies 350 and 360, respectively, The sample holder 400 can be moved in a plane and positioned at a desired position. In other words, as the pair of link assemblies move synchronously, translational movement due to the positional difference therebetween occurs, and the position of the sample holder 400 can be changed.

4, when a pair of link assemblies 310-320 moves while generating a relative position difference, a connection bar 301 connected to the link pair 310-320 is moved to a position May cause a motion to be raised or lowered. Similarly, when this movement is generated in each of the link pairs 330-340 and 350-360, movement of the connection bars 302 and 303 connected to the sample holder 400 occurs to determine the posture of the sample holder 400 . At this time, the connecting bars 301, 302, and 303 are connected to the sample holder 400 through ball joints.

For example, one of the link assemblies 310 of the upper link assembly 310 and the lower link assembly 320 is composed of two segment links 311 and 315, and the other link assembly 320 is composed of , And three segmented links 321, 323, and 325, respectively. The five segmented links 311, 315, 321, 323, and 325 can all move on the same two-dimensional plane (the plane shown in FIG. 4).

More specifically, the upper link assembly 310 includes an upper sliding link 315 slidable relative to the chamber 200, and a lower sliding link 315 hinged at one side to the connecting bar 301 and the other at an upper sliding link 315. [ And an upper connecting link 311 hinged to the upper link link 311. The lower link assembly 320 includes a lower sliding link 325 slidable with respect to the chamber 200 and a lower connecting link 321 hinged to the lower side of the connecting bar 301, And an intermediate link 323 hinged to the link 321 and hinged to the lower sliding link 325 on the other side. The rotation axis between the upper connection link 311 and the connection bar 301 may be orthogonal to the rotation axis between the upper connection link 311 and the upper slide link 315. The rotating shaft between the lower connecting link 321 and the connecting bar 301 is orthogonal to the rotating shaft between the lower connecting link 321 and the intermediate link 323 and the rotating shaft between the lower link 321 and the lower sliding link 325, And can be perpendicular to each other. According to the structure as described above, the five segmented links 311, 315, 321, 323, and 325 can all move on the same two-dimensional plane (the plane shown in FIG. 4) The position and orientation of the sample holder 400 can be adjusted according to the inverse kinematic analysis as described above.

On the other hand, the upper connecting link 311 and the lower connecting link 321 may be regarded as one link since substantially no relative movement occurs. In view of this, it may be understood that the paired link assemblies 310-320 consist of four-link links 315, 311-321, 323, and 325 that are sequentially connected to allow relative rotation. In this case, one end of the connection bar 301 is connected to one of the two links 311-321 and 323 connected in the middle among the four-link links 315, 311-321, 323 and 325 And the other end may be understood as being pivotally connected to the sample holder 400.

5 is a perspective view showing a driving module according to another embodiment.

5, the driving module according to another embodiment may include a connection bar 301 and two link assemblies 310 and 320 connected to the upper and lower sides of the connection bar 301, respectively.

The upper link assembly 310 includes an upper connecting link 311 and an upper sliding link 315. The lower link assembly 320 includes a lower connecting link 321, an intermediate link 323, 325).

The upper connecting link 311 may include a first separating link 3111 and a second separating link 3112 which are coupled to the upper side sliding link 315 on the left and right sides. The upper connecting link 311 is provided with a first separating link 3111 and a second separating link 3112 so that a space separated from each other is formed between at least a part of the first separating link 3111 and at least a part of the second separating link 3112, And a first support portion 311a disposed between the first and second separation links 3112. [ For example, as shown in FIG. 5, the first supporting portion 311a may be a protruding portion protruding from the first separating link 3111 toward the second separating link 3112. The first supporting portion 311a may be formed on the second separating link 3112 or may be provided as a separate component from the first separating link 3111 and the second separating link 3112. [ The upper connection link 311 includes a first hole 311b which penetrates the two separation links 3111 and 3112 and does not penetrate the first support portion 311a and a second hole 311b that penetrates the two separation links 3111 and 3112 And a second hole 311c passing through the first support portion 311a. The first hole 311b and the second hole 311c may be fastened with screws. The screw fastened to the second hole 311c can prevent the two separation links 3111 and 3112 from being separated from each other. The screw fastened to the first hole 311b adjusts the spacing space between the two separation links 3111 and 3112 and consequently the fastening force between the upper connecting link 311 and the upper sliding link 315 Can be adjusted.

The intermediate link 323 may include a third detachment link 3231 and a fourth detachment link 3232 which are coupled to the left and right around the lower connecting link 321 and the lower sliding link 325. The intermediate link 323 is connected to the third separating link 3231 and the fourth separating link 3231 so that a spaced space is formed between at least a part of the third separating link 3231 and at least a part of the fourth separating link 3232, And a second support portion 323a disposed between the separation links 3232. For example, as shown in FIG. 5, the second support portion 323a may be a protrusion formed to protrude from the third separation link 3231 toward the fourth separation link 3232. The second supporting portion 323a may be formed on the fourth separating link 3232 or may be provided as a separate component from the third separating link 3231 and the fourth separating link 3232. [ The intermediate link 323 includes a third hole 323b passing through the two separation links 3231 and 3232 and disposed behind the second support portion 323a and a third hole 323b extending through the two separation links 3231 and 3232 A fourth hole 323c disposed in front of the second support portion 323a and a fifth hole 323d passing through the second support portion 323a while passing through the two separation links 3231 and 3232 have. The third hole 323b, the fourth hole 323c, and the fifth hole 323d, respectively. The screw fastened to the third hole 323b can adjust the fastening force between the intermediate link 323 and the lower sliding link 315 by adjusting the spaced space behind the support portion 323a. Similarly, the screw fastened to the fourth hole 323c can adjust the fastening force between the intermediate link 323 and the lower connecting link 321 by adjusting the spaced space in front of the supporting portion 323a .

As shown in FIG. 5, the portions of the links adjacent to each other in the lengthwise direction may have arc-shaped convex portions or concave portions. According to the above-described shape, even if the adjacent links rotate relatively, It can be smoothly rotated.

The actuator according to the above-described embodiments is capable of generating the posture when the position and posture of the sample holder are determined, for example, as analyzed through an inverse kinematic analysis model described in Korean Patent No. 1742920 It is possible to obtain a relational expression indicating the position of a pair of the upper sliding link and the lower sliding link. A detailed description thereof will be omitted. Korean Patent No. 1742920 should be construed as being included in the present invention.

In the case of a manipulator structure such as the structure described above, the precision of machining assembly of the link and the joint is very important for precise control. On the other hand, if the length of the link and / or the position of the joint is different from the actual design specification, or if the link can not be accurately positioned at the calculated position, there is an error. These errors serve to increase not only the position and attitude error of the end-effector controlling the final sample holder 400 but also the internal stress. Such an error may cause a positional error of the sample holder 400 and seriously cause breakage.

Although the processing accuracy of each part constituting the stage 10 can be evaluated, there is a problem that it is difficult to evaluate the operation of the entire stage 10 assembled in a state where the entire stage 10 is assembled .

When the stage 10 is assembled into an electron microscope and a vacuum state is formed once, the stage 10 can be freely moved from the outside to the chamber 10 in order to repair the stage 10, because of the characteristics of the electron microscope, It becomes very difficult to access the inside of the portable terminal 200.

In consideration of the above problems, a stage control method capable of predicting the stress generated in the stage 10 and eliminating it through control will be described below. According to the following control method, the internal stress of the stage 10 can be predicted to evaluate how smooth the drive is, and the driving performance of the stage 10 can be improved through stress relief. Further, the load can be measured while the stage 10 is assembled and driven. Furthermore, without additional force sensors, stress can be predicted and solved based solely on the essential elements for control.

6 is a view schematically illustrating configurations for performing a method of controlling a sample holder stage for an electron microscope according to an embodiment. FIG. 7 is a block diagram of a sample holder stage for an electron microscope according to an embodiment, and FIG. 8 and FIG. 9 are block diagrams separately showing portions of FIG.

10 is a diagram showing an algorithm of a method performed by a stress predicting unit of a stage for an electron microscope according to an embodiment, and Fig. 11 is a flowchart illustrating an algorithm of a method performed in stress elimination of a stage for an electron microscope according to an embodiment Fig.

6 to 9, a sample holder stage 10 for an electron microscope according to an embodiment includes a sample holder 400 (see FIG. 2) and a sample holder 400 connected to the sample holder 400, A driver 300 for adjusting a position and an attitude, an input unit 500, and a processor 600.

The actuator 300 may include a plurality of link assemblies 310, 320, 330, 340, 350, 360 (see FIG. 2) each connected to the sample holder 400 and performing one degree of freedom motion. A motor is connected to each of the plurality of link assemblies, and each motor can linearly move each link assembly.

The input unit 500 may receive a drive command from a user, input a measured value from various sensors or updated information through the processor 600, and transmit the received information to the processor 600.

The processor 600 may perform a predetermined calculation operation based on the information input from the input unit 500 to adjust a control signal to be applied to the driver 300. [ The processor 600 may include a stress range predicting unit 610, a stress sensing unit 620, a stress simulation unit 630, a position control unit 640, and a stress relieving unit 650.

Based on the stress range accuracy (Det_Accuracy), the filtered motor control signal (Control_Sig_Filt), the wave basic waveform (Swing_Wave), the wave gain (Wave_Gain), and the gain variation step (Wave_C_Step), the stress range predicting unit (610) (Swing) and the wave gain (Wave_Gain) amplified by the first and second amplifiers can be determined.

The algorithm performed in the stress range predicting unit 610 may be performed, for example, as shown in FIG. Specifically, when the magnitude of the filtered motor control signal (Control_Sig_Filt) is out of the set stress range accuracy (Det_Accuracy), the wave gain (Wave_Gain) is reduced every time it is repeated every predetermined gain change step (Wave_C_Step) The gain (Wave_Gain) can be updated and stored. Through this process, the swing width of the link assembly can be reduced to the extent that the load does not exist.

The stress remover 650 calculates the stress of the reference position Ref_Position, the size of the step to move the reference position in the direction in which the stress is minimized (Sliding_Gain_Constant), the filtered motor control signal (Control_Sig_Filt) It is possible to determine a correction position (Ref_Mod) shifted to the center where stress is minimized and a setting offset value (Ref_offset) calculated according to an inverse kinematic analysis based on the amount of reference position (Ref_offset, hereinafter referred to as "setting offset value").

The algorithm performed in the stress remover 650 may be performed, for example, as shown in FIG. Specifically, as shown in FIG. 11, the reference offset can be corrected on the basis of the stored value in the next calculation by updating and storing the set offset value Ref_offset every time it is repeated.

The stress sensing unit 620 determines whether or not the current stress is lower than a predetermined threshold based on a range (S_Free_range), an actual current position (M_position), and a reference position (ref_traj) (Contact_flag) can be detected.

The stress simulation unit 630 may be configured such that the stress simulation unit 630 is to be provided to the driver 300 if the measured value of the stress sensing unit 620 is true, You can control the force. For example, the stress simulation unit 630 outputs the same value as the torque u of the motor as the output value y, and subtracts the output value y from the torque u of the motor, 0 to stop the motor.

On the contrary, when the value measured by the stress sensing unit 620 is false, that is, when stress does not occur, the output value y of the stress simulation unit 630 becomes 0, u) can be used to rotate the motor as it is without changing. On the other hand, the corrected position (Ref_Mod) and the excitation wave waveform (Swing) amplified by the gain can be added together to generate a corrected reference position. The torque u of the motor for controlling the motor to move the link assembly to the corrected reference position is calculated by the position controller 640, the torque coeff (K), and the inertia (1 / J) Lt; / RTI >

Meanwhile, in the case of the position controller 640, the control is performed through, for example, the PID control method. However, it is noted that the control can be performed through another control method.

Operations of the blocks 610, 620, 630, 640, and 650 shown in FIG. 7 will now be described. Even if proceeding from the top in order, it matches with the whole system operation sequence without any problem.

[stress Removal (650, Stress canceller )]

1. The position of each of the links (each of six) capable of determining the position and attitude of a desired sample by inverse kinematics is given to the stress eliminator 650 as a reference position Ref_Position.

2. An output value that is low-pass-filtered by the low pass filter, which is output from the position control unit 640, is given to the stress relieving unit 650 as a motor control signal (Control_Sig_Filt). The set offset value Ref_offset is corrected in the direction in which the low pass-filtered output value converges to zero. Here, the output value of the position control unit 640 is 0, which means that the load on the motor control is 0 and the motor reaches the desired reference position (Ref_Position). Consequently, the motor control signal (Control_Sig_Filt) will converge to near 0, which will go towards the middle if the load is least or there is a load in both directions of motor rotation.

3. A setting change gain (Ref_sliding_Gain) is given to the stress eliminator 650.

4. An initial value of the stored setting offset value (Ref_offset) is given to the stress eliminator 650.

5. If the value of the input motor control signal (Control_Sig_Filt) is greater than 0 in the stress remover 650, the setting change gain (Ref_sliding_Gain) and the motor control signal (Control_Sig_Filt) are subtracted from the input set offset value Ref_offset ) And then updates and stores the updated offset value (Ref_offset).

6. In the stress remover 650, if the value of the input motor control signal (Control_Sig_Filt) is less than 0, the setting change gain Ref_sliding_Gain and the motor control signal Control_Sig_Filt ), And then stores the sum in the offset value (Ref_offset).

7. The modified offset value Ref_offset through steps 5 and 6 is updated and stored in the memory through the output, and can be used in the next calculation. Further, the modified correction offset position Ref_offset value is added to the reference position Ref_Position to output the corrected correction position Ref_Mod in the direction of reducing the stress. As a result, the value of the correction position Ref_Mod is slightly shifted toward the point where the load is minimized at the reference position, resulting in a corrected position value.

[Stress range Prediction unit (610, Stress range estimator)

8. Receive the stress range precision (Det_Accuracy) as an input. The value of the stress range accuracy (Det_Accuracy) is a value that sets how accurately the sinusoidal wave for the excitation will converge to the range where the load does not exist.

9. An output value that is low-pass-filtered by the low pass filter and outputted from the position control unit 640 is input to the stress range predicting unit 610 as a motor control signal (Control_Sig_Filt) do.

10. The waveform is input to the stress range predicting unit 610 as a wave basic waveform (Swing_Wave) having waveform information of a sinusoidal wave as a basic form of the excitation.

11. An initial value (for example, 1) of a wave gain (Wave_Gain) to be used for adjusting the amplitude of a sinusoidal wave having an output by multiplying the excitation wave basic waveform (Swing_Wave) is given as an input to the stress range predicting unit 610 .

12. A gain change step (Wave_C_Step) corresponding to the change amount of the wave gain (Wave_Gain) is given as an input to the stress range predicting unit 610. [

13. In a stress range predicting unit 610, a motor control signal (Control_Sig_Filt) given as an input is compared with a stress range accuracy (Det_Accuracy) to determine whether the maximum value of the stress range accuracy (Det_Accuracy) If it is smaller than the minimum value, the wave gain (Wave_Gain) is reduced by the gain change step (Wave_C_Step) for each iteration. The modified wave gain Wave_Gain is updated and stored in the memory through the Wave_Gain output, and can be used in the next calculation stage.

14. In the stress range predicting unit 610, if the wave gain (Wave_Gain) becomes smaller than the gain change step (Wave_C_Step) value, the gain range changing step (Wave_C_Step) is maintained to maintain the minimum value.

15. In the stress range predicting unit 610, by changing the magnitude of the gain change step (Wave_C_Step) according to the system or the load state, the speed at which the amplitude of the sinusoidal waveform used at the excitation decreases and the accuracy of the region prediction where the load exists .

16. In the stress range predicting unit 610, a sine wave is output by multiplying the wave basic waveform (Swing_Wave) received as an input by the wave gain (Wave_Gain) obtained repeatedly in steps 13 and 14.

[Later Steps]

17. In a situation where there is a load, the output correction position Ref_Mod in the stress remover 650 and (ii) the sinusoidal wave adjusted in accordance with the range of the region where the load exists in the stress range predicting unit 610 Add swing to each other. Here, the sine wave output (Swing) can be obtained by multiplying the wave basic waveform (Swing_Wave) by the wave gain (Wave_Gain). By adding the two values (i) and (ii), a corrected reference position in the form of a sinusoidal wave having a center in a load range with a set amplitude and a load range as a center is obtained .

18. The position control unit 640 swings the actual system (link) to the corrected reference position (Refernce Position) obtained in the step 17 to the target position.

19. Step 18 is a step of obtaining a corrected reference position in the form of a sinusoidal wave centered on the range in which the final load is present as the amplitude and the center of the load range as zero through the preceding steps 1 to 17 It works together during the expiration process.

20. Finally, after a certain period of time, the position of the actual link swings along the corrected reference position in the form of a sine wave centered at the center of the load range with the amplitude at which the load is present, At this time, the amplitude of the sine wave corresponds to the range where the load does not exist, and the center position of the sinusoidal wave is a position where we should align the link.

For example, when the motor control signal (Control_Sig_Filt) is given as a current value, if the current value applied to the motor is kept below a predetermined threshold value, the link assembly reaches the reference position and there is no load applied to the motor And control can be terminated.

FIG. 12 is a flowchart showing a control method of a stage for an electron microscope according to an embodiment, and FIG. 13 is a flowchart showing an embodiment of step 930 of FIG.

A method of controlling a stage for an electron microscope according to an exemplary embodiment includes receiving (910) a reference position of a link assembly of a plurality of link assemblies from a user, and controlling the link assembly Determining a magnitude and direction of a load applied to the link assembly based on the value of the applied current, determining (930) a set offset in a reference position in a direction to reduce the load, A step 940 of determining whether the reference position is equal to the correction position, a step 960 of resetting the determined correction position to the reference position, And relocating the link assembly to a reference position (910, 920).

In step 920, the current applied to the motor may be a sine wave with a set amplitude.

On the other hand, the stress acting between the parts constituting the stage 10 exists in the link, but is also transmitted to the driver 300 that drives the links. The stress transmitted to the driver 300 acts as a load when operating the driver 300. This load affects the required power of the motor connected to each link of the driver 300. [ Therefore, the size and direction of the load applied to the driver 300 can be predicted based on the current value applied to the motor connected to the driver 300, and it can be resolved through position control of the driver 300. Thus, step 930 of determining the size and orientation of the load may be performed in the following steps.

For example, the step 930 may include calculating (931) a predicted drive range of the link assembly driven according to the input sinusoidal wave, assuming that no load is applied, and calculating a predicted drive range of the link assembly driven by the input sinusoid Measuring an actual drive range 932; calculating 933 the difference between the expected drive range and the actual drive range; and determining 933 the magnitude and direction of the load based on the difference.

Here, step 932 may include determining the magnitude of the load based on, for example, the deviation of the median value of the expected drive range and the median value of the actual drive range.

Step 933 may also include determining the direction of the load based, for example, on the relative position of the median value of the actual drive range to the median value of the expected drive range. On the other hand, the determination of the magnitude and direction of the load using the deviation of the median value is merely an example, and it is also possible to determine the magnitude and direction of the load by using the deviation of the maximum value or the minimum value as another example.

Meanwhile, in the course of repeating steps 910 to 960, the set amplitude at step 920 may be set to gradually decrease until the estimated drive range calculated at step 931 matches the actual drive range measured at step 932 have. According to this method, it is possible to prevent an excessive force from being applied to the driver 300 by preventing a sudden change in current.

Further, in step 940, the setting offset value may be set to a value proportional to a difference between the predicted driving range determined in step 931 and the actual driving range measured in step 932. [

14 is a flowchart showing a control method of a stage for an electron microscope according to an embodiment.

14, a stage for an electron microscope according to an embodiment includes a reference position following command step 910, a step 920 of applying a sinusoidal current of a set amplitude to the motor, a step of determining the size and direction of the load (940), determining whether the reference position is equal to the correction position (950), resetting the determined correction position to the reference position (960), repeating steps 910 to 950 A step 9710 of determining whether the step to perform, the expected drive range and the actual drive range are consistent, the step of decreasing the set amplitude 980, and the step of determining the stress range 990.

The description overlapping with the contents described above with reference to FIG. 12 and FIG. 13 will be omitted. Initially, the predicted drive range of the driver 300 may be set wide enough to exceed the actual drive range. If the predicted drive range exceeds the actual drive range in step 970, it can be performed (step 980) by stepping down the set amplitude until the expected drive range matches the actual drive range. If the predicted drive range coincides with the actual drive range, a range where the stress does not occur can be determined based on the current value of the motor applied in that state (990). Then, by transmitting the information identified in step 990 to the user, it is possible to provide the user with information on how much the sample holder 400 can freely operate in the current situation.

FIGS. 15 to 18 are graphs showing feasibility and performance of a control method for an electron microscope according to an exemplary embodiment.

Fig. 15 shows a waveform output when a sinusoidal wave is input so that swing can be performed by -1.5 to +1.5 based on a value of 0, assuming that an obstacle exists in -1 and +1. As can be seen from Fig. 15, it can be seen that, when compared with the theoretical motion of the actuator predicted based on the input waveform, the actual actuator exhibits limited motion due to stress.

16 shows a case where only the stress elimination algorithm is applied in the control method according to the embodiment. As the reference position is reset, the central position of the stress sensed by the driver of the stage for the electron microscope becomes the center of the ideal swing position This is a control process.

FIG. 17 shows a case where the stress elimination algorithm and the stress range predicting algorithm are applied at the same time in the control method according to one embodiment. As the reference position and the set amplitude are reset, the reference position of the driver of the stage for the electron microscope and the swing Width can be changed at the same time. As shown in FIG. 17, according to the embodiment of the present invention, it can be confirmed that the alignment can be made to be the center of the stress range within a range where the stress disappears over time.

18 shows the change in the amount of control current applied to the motor for driving the actuator when the stress elimination algorithm and the stress range predicting algorithm are simultaneously applied, as shown in FIG. 17, in the control method according to the embodiment. As shown in FIG. 18, the direction of the current is the same as the direction of the stress, and the magnitude of the current is reduced in proportion to the magnitude of the stress.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments, or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. For example, it is contemplated that the techniques described may be performed in a different order than the described methods, and / or that components of the described structures, devices, and the like may be combined or combined in other ways than the described methods, Appropriate results can be achieved even if they are replaced or replaced.

Claims (14)

1. A stress removing method of a sample holder stage including a sample holder and a plurality of link assemblies connected to the sample holder and performing one degree of freedom movement,
(a) receiving a reference position of one of the plurality of link assemblies;
(b) applying a current to a motor coupled to the link assembly such that the link assembly is driven towards the reference position;
(c) determining a magnitude and direction of a load applied to the link assembly based on the applied current value; And
(d) changing the position of the link assembly toward a correction position that is a sum of a set offset value at the reference position in a direction to reduce the load.
The method according to claim 1,
If the current value applied to the motor in the step (b) is maintained below a preset limit value, it is determined that the link assembly reaches the reference position and there is no load applied to the motor, And the stress of the sample holder stage is removed.
The method according to claim 1,
Wherein in step (b), the current applied to the motor is a sinusoidal wave having a predetermined amplitude.
The method of claim 3,
The maximum value of the predicted drive range of the link assembly to be driven by the current applied to the motor is larger than the maximum value of the actual drive range of the link assembly,
When the minimum value of the predicted drive range of the link assembly to be driven by the current applied to the motor is smaller than the minimum value of the actual drive range of the link assembly,
Wherein the steps (a) to (d) are performed while gradually decreasing the set amplitude.
5. The method of claim 4,
When the minimum value and the maximum value of the predicted drive range of the link assembly to be driven by the current applied to the motor are respectively less than a predetermined limit value based on the minimum value and the minimum value of the actual drive range of the link assembly ,
Determining a predicted drive range of the link assembly in a corresponding state to a range without stress and outputting the determined range to a user.
The method of claim 3,
The step (c)
(c-1) calculating a predicted drive range of the link assembly driven according to the input sinusoidal wave, assuming that the load does not act;
(c-2) measuring an actual driving range of the link assembly driven according to the input sinusoidal wave; And
(c-3) calculating a difference between the predicted drive range and the actual drive range,
And the size and direction of the load are determined based on the difference.
The method according to claim 6,
The step (c-3)
Determining a magnitude of the load based on a deviation of a median of the predicted drive range and a median of the actual drive range.
The method according to claim 6,
The step (c-3)
Determining a direction of the load based on a relative position of a median value of the actual drive range to a median value of the predicted drive range.
The method according to claim 6,
(e) resetting the correction position determined in step (d) to a new reference position in step (a), and repeatedly performing steps (a) to (d) Removal method.
10. The method of claim 9,
Wherein the set amplitude of the step (b) is set so as to gradually decrease until the predicted drive range calculated in the step (c-1) matches the actual drive range measured in the step (c-2) A method for removing stress on a stage.
The method according to claim 6,
Wherein the set offset value is proportional to the difference between the predicted drive range and the actual drive range.
The method according to claim 1,
The sample holder stage includes:
A first driving module, a second driving module, and a third driving module radially connected to the sample holder, the sample holder having a translational freedom in three directions and a rotational degree of rotation in at least two directions,
The first drive module, the second drive module, and the third drive module,
A connecting bar ball jointed to three different parts of the sample holder; And
And an upper link assembly and a lower link assembly hinged to the upper and lower sides of the connection bar, respectively, for tilting the connection bar in a vertical direction,
Wherein the steps (a) to (d) are performed on at least one of the upper link assembly and the lower link assembly.
13. The method of claim 12,
Wherein one of the upper link assembly and the lower link assembly is composed of two split links hinged to each other,
Wherein the other link assembly of the upper link assembly and the lower link assembly is composed of three split links hinged to each other.
A computer-readable medium having stored thereon a program for executing a method for removing stress on a sample holder stage according to any one of claims 1 to 13.

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