JPH10104131A - Cutting apparatus for frozen sample - Google Patents

Abstract

PROBLEM TO BE SOLVED: To considerably correctly set a cut thickness and enable cutting even to a sub-micron thickness. SOLUTION: A sample 5 being cooled by a freezing unit 4 is supported by a sample state 6. The sample stage 6 is minutely and sequentially let out in a wide range by a fine positioning control system including a piezoelectric actuator 7 and a rough positioning control system including a servo motor 13 and a ball screw 11. A front end face 5A of the sample 5 appearing sequentially is directly detected by a position detector 15, e.g. laser displacement sensor or the like, correctly positioned by the fine positioning control system, and accordingly can be cut to a sub-micron thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for accurately slicing the tip of a frozen sample.

[0002]

2. Description of the Related Art For observation or analysis of a sample, several μm
It is necessary to repeat cutting at a thickness of several tens of μm from
Conventionally, in this type of apparatus, a sample stage supporting a sample is controlled by a normal semi-closed or full-closed servo mechanism, and the sample is fed by a predetermined amount, and the tip of the fed sample is cut by a cutter or the like. I was

[0003]

However, when the sample is frozen and reaches −80 ° C., even if the position of the sample stage is controlled by a fully closed servo mechanism, the sample itself and the sample stage are affected by the temperature. Therefore, it is difficult to accurately position the tip surface of the sample, and the cut thickness cannot be accurately determined.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a cutting apparatus for a frozen sample which can determine a cutting thickness very accurately and can cut a submicron thickness.

[0005]

According to the present invention, there is provided a frozen sample cutting apparatus for cutting the tip of a frozen sample to a predetermined thickness. A sample stage movably provided in a direction perpendicular to the cut surface of the sample stage, a refrigeration unit that surrounds and cools the sample except for at least the distal end portion of the sample held on the sample stage, and the sample stage. A piezoelectric actuator for minute movement in the vertical direction, a movable body for holding the piezoelectric actuator and moving the sample stage in the same vertical direction via the piezoelectric actuator, and a sample tip surface sequentially appearing by cutting. The position detector in the vertical direction and the output of the position detector are fed back to the piezoelectric actuator, and the sample front surface that appears sequentially is cut before cutting. A fine positioning control system for positioning at the set position, and a control unit comprising a coarse positioning control system for controlling the position of the movable body by a servomotor in relation to the operation of the piezoelectric actuator by the fine positioning control system. It is a thing.

[0006] With this configuration, the sample tip surface can be accurately positioned by the fine positioning control system using the piezoelectric actuator without being affected by temperature or the like, and the cutting thickness can be accurately determined. Cutting with a micron thickness is also possible, and the cutting range of the sample can be made sufficiently wide by the coarse positioning control system.

Preferably, a heat insulating member is interposed between the refrigeration unit and the piezoelectric actuator.
The sample stage itself may be formed of a heat insulating material. Preferably, the position detector is a laser displacement meter,
Furthermore, the fine positioning control system interrupts the feedback from the position detector to the piezoelectric actuator during the sample cutting operation, and substitutes a substitute signal for a predetermined position at the start of cutting the sample tip surface. It is preferable that the control unit has a detection unit that detects a predetermined operation limit area of the piezoelectric actuator, and the piezoelectric actuator controls the position of the sample tip surface until the operation limit area is reached. The movable body may be configured to be moved by a predetermined amount corresponding to the operation limit area when the control is performed and the detector detects that the operation limit area has been reached.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. A cylindrical column 2 is erected on a base 1, and an annular refrigeration unit 4 is attached to the upper end side of the hollow hole via an annular heat insulating material 3 having a rectangular or circular cross section. The refrigerating unit 4 fits a frozen sample 5 into the hollow hole, and keeps the frozen state of the sample 5.

The rear end face (the lower face in FIG. 1) of the sample 5 fitted into the freezing unit 4 is supported by a sample table 6. Sample table 6 is made of alumina, bakelite, nylon 5
5 or a heat insulating material such as Teflon, and is mounted on the piezoelectric actuator 7. The piezoelectric actuator 7 is arranged so as to expand and contract in the vertical direction in FIG. 1, and the piezoelectric actuator 7 is mounted on the movable body 8.

The movable body 8 is movably mounted on a linear guide 9 mounted vertically along the inner surface of the hollow hole of the column 2. A ball screw nut 10 is attached to the movable body 8.
A ball screw 11 extending up and down is engaged with 0. The ball screw 11 is connected to a servomotor 13 via a coupling 12, and is rotated by the servomotor 13. 14 is a servo motor 13
The encoder is attached to.

Above the sample 5, the tip surface of the sample 5 (FIG. 1)
A laser displacement meter 15 as a position detector for detecting the height position is disposed to face the upper surface 5A.

Reference numeral 16 denotes a cutter, which is moved by an operating mechanism (not shown) and moves along a cut surface 5B shown by a two-dot chain line.
Is to be cut.

As shown in FIG. 2, the piezoelectric actuator 7
Command value (voltage) is always given a constant voltage of 0 (zero) volt (V) or a voltage close thereto (hereinafter referred to as zero volt). Laser displacement meter 15
Is supplied to a comparator 23 with a command value via a sensor amplifier 21 and a disconnection compensation gate 22 to be described later, and a difference voltage is applied to a first preamplifier & compensator 24 so that the difference voltage becomes zero. Voltage is applied to the piezoelectric actuator 7 from the first preamplifier & compensator 24 via the first power amplifier 25, and the disconnection compensation gate 2
A fine positioning control system for controlling the output of the laser displacement meter 15 to be zero volts when the reference numeral 2 is open, that is, the tip surface 5A of the sample 5 is always kept at a predetermined constant height position. ing.

The cutting-time compensating gate 22 receives a signal indicating that cutting is being performed by the cutter 16 during a cutting operation. In response to the cutting operation, the cutting operation is performed when the cutter 16 interrupts the laser displacement meter 15. The output voltage of the laser displacement meter 15 immediately before the start of the operation is given as a feedback value instead of the output voltage from the laser displacement meter 15, and the voltage applied to the piezoelectric actuator 7 is fixed. A feedback loop by the displacement meter 15 is configured.

When the cutting operation is started, the positioning of the sample tip surface 5A has already been completed, and the output voltage of the laser displacement meter 15 becomes almost zero volt. Therefore, in this embodiment shown in FIG. Instead of the output voltage of the laser displacement meter 15 immediately before entering, zero volt equal to the command value is provided as a feedback value.

The output voltage of the first preamplifier & compensator 24 is also applied to first and second comparators 26 and 27, respectively. The first comparator 26 is for detecting a predetermined operation limit area (hereinafter simply referred to as an operation limit area) within an actual operation limit area of the piezoelectric actuator 7, and detects an output voltage of the first preamplifier & compensator 24 as an operation limit. Voltage Vma indicating the area
x, when the output voltage of the first preamplifier & compensator 24 reaches the voltage Vmax indicating the operation limit range,
The hold gate 28 is set. The second comparator 27 is for detecting that the output voltage of the first preamplifier & compensator 24 has returned to zero volt, and resets the hold gate 28 by this detection.

The hold gate 28 supplies an ON signal to the AND gate 29 when it is in the set state. The AND gate 29 controls the supply and cutoff of the servo motor drive pulse. When the hold gate 28 is in the set state,
The drive pulse is supplied to the servomotor 13 from the time when the output voltage of the preamplifier & compensator 24 reaches the voltage Vmax indicating the operation limit range until it returns to zero volt.

The driving pulse of the servo motor that has passed through the AND gate 29 is added to a counter 30 and subtracted by a feedback pulse from the encoder 14. A signal corresponding to the difference pulse number is converted to a DA converter 31 and a speed comparator. 32, the second preamplifier & compensator 33 and the second power amplifier 34 via the servo motor 13
Until the hold gate 28 is reset, that is, until the output voltage of the first preamplifier & compensator becomes zero volts and the expansion of the piezoelectric actuator 7 becomes zero. Is composed. Reference numeral 35 denotes a differentiating circuit for feeding back the speed component of the output of the encoder 14 to the speed comparator 32.

Next, the operation of the present apparatus will be described. First, as a preparation stage, the sample stage 6 is placed at the lower limit position, and the frozen sample 5 is fitted into the freezing unit 4 such that the lower surface, that is, the rear end surface is supported by the sample stage 6. Next, the servomotor 13 is operated by a drive system (not shown) different from the coarse positioning control system to raise the tip surface 5A of the sample 5 to a position higher than the cut surface 5B by the cutter 16 by a predetermined amount. Cut off the tip of At the end of this preparation stage, the control unit shown in FIG. 2 is operated.

The tip end face 5A of the sample 5 newly appeared after being cut by the cutter 16 is initially at the position of the cut face 5B shown in FIG. 1, and the laser displacement gauge 15 is moved to the tip end face shown in FIG. A voltage corresponding to a difference from the position of 5A (a predetermined positioning position of the distal end surface 5A) is output. This position detection output is supplied to the comparator 23 through the disconnection compensation gate 22. Since the command value is zero volt, the first preamplifier & compensator 24 sets the difference voltage to zero.
, The voltage applied to the piezoelectric actuator 7 via the first power amplifier 25 is increased, the piezoelectric actuator 7 is extended, the sample stage 6 is raised, and the sample 5 is extended upward, as indicated by the symbol A in FIG. . At this time, the servo motor 13 remains stopped.

The positioning of the sample tip surface 5A by the laser displacement meter 15 or the piezoelectric actuator 7 is performed by directly detecting the position of the sample tip surface 5A by the laser displacement meter 15, so that not only the sample 5 but also the sample table 6 and the movable It is accurately performed with an accuracy of submicron or less without being affected by a dimensional change due to a temperature change or the like on the body 8 side.

After the sample 5 has been fed out by a predetermined amount, it is cut by the cutter 16. At the time of cutting, the compensation gate 22 for cutting is closed in conjunction with the cutting operation, and zero volts are sent to the comparator 23 instead of the detection output from the laser displacement meter 15 immediately before the start of the cutting operation, which has almost reached zero volts. Given. Therefore, even if the height of the sample tip surface 5A changes due to the passage of the cutter 16, the piezoelectric actuator 7 does not expand and contract, and the sample 5 is held at a position immediately before the start of cutting.

When the cutting is completed and the cutter 16 returns to the initial position shown in FIG. 1, the cutting compensation gate 22 is opened again. At this time, since the distal end surface 5A side of the sample 5 is removed by cutting, the cut surface 5B shown in FIG. 1 appears as the distal end surface. Therefore, the laser displacement meter 15 generates a detection output corresponding to the difference between the heights of the two surfaces 5A and 5B shown in FIG. 1, and this detection output is sent to the comparator 23 via the disconnection compensation gate 22. . Then, the piezoelectric actuator 7 is again extended as shown by the symbol B in FIG. 3, the sample stage 6 is raised, and the sample 5 is extended upward, and the cut surface 5 in FIG.
B is pushed up to the position of the distal end face 5A in FIG. 1 and cut.

When the feeding and cutting of the sample 5 are repeated, the driving voltage for the piezoelectric actuator 7 output from the first preamplifier & compensator 24 increases similarly to the amount of extension of the piezoelectric actuator 7 shown by a dotted line in FIG. Go. Then, when the drive voltage reaches the voltage Vmax indicating the operation limit area of the piezoelectric actuator 7, the first comparator 26 sets the hold gate 28 to the set state and outputs an ON signal to the AND gate 29.

As a result, the servo motor driving pulse is supplied to the counter 30 through the AND gate 29, and the servo motor 13 is driven as shown by reference numeral C in FIG. The driving of the servo motor 13 is performed at a predetermined speed in response to feedback from the encoder 14.

As the movable body 8 rises, the sample 5 is fed out via the piezoelectric actuator 7 and the sample stage 6, and the tip surface 5A rises. The rise of the tip surface 5A is detected by the laser displacement meter 15, and the piezoelectric actuator 7 is moved to the position shown in FIG.
To suppress the rise of the tip end surface 5A. Since the response of the operation of the piezoelectric actuator 7 is sufficiently higher than the response of the servomotor 13,
A is kept at substantially the same height.

That is, the rise by the servo motor 13
The lowering by the piezoelectric actuator 7 is performed almost synchronously as shown in FIG. When the servo motor 13 raises the drive voltage to the piezoelectric actuator 7 until it reaches zero volt, the second comparator 27
Resets the hold gate 28 and the AND gate 29
Interrupts the supply of the servo motor drive pulse from.

The elevation of the sample tip surface 5A by the servomotor 13 is controlled by the supply amount of the servomotor drive pulse based on the operation of the hold gate 28 and the semi-closed servo mechanism by the feedback from the encoder 14. 13 sample front surface 5A
In the final positioning, there is an error due to the effects of the ball screw 9, the ball screw nut 10, the movable body 8, and the like.
This is corrected by the fine positioning control system using the piezoelectric actuator 7, and the position of the sample tip surface 5A is accurately positioned again at the predetermined position. Hereinafter, feeding and cutting of the sample 5 are repeatedly performed in the same manner as described above.

In the above-described embodiment, the refrigeration unit 4
Is fixed and comes into contact with only the side surface around the sample 5, and the sample 5
Although the example in which the rear end surface (the lower surface in FIG. 1) is received by the sample stage 6 is shown, the refrigeration unit 4 is mounted on the sample stage 6, and the rear end surface of the sample 5 is also cooled by the refrigeration unit 4. Is also good. In this case, the sample stage 6 does not need to be formed of a heat insulating material unless it is necessary to consider the influence of the device due to the temperature. The formed heat insulating member may be provided above or below the sample table 6.

Further, in the above-described embodiment, until the piezoelectric actuator 7 reaches a predetermined operation limit area,
The position of the sample tip surface 5A is controlled only by the piezoelectric actuator 7, and when the operation limit is reached, the servo motor 13 is operated to contract the piezoelectric actuator 7 so that the drive voltage to the piezoelectric actuator 7 becomes zero volt. However, the present invention is not limited to this, and it goes without saying that the present invention can be implemented with various modifications such as control of a system that operates the servo motor 13 and the piezoelectric actuator 7 simultaneously and in parallel.

[0031]

As described above, according to the present invention, a frozen sample can be cut to an extremely accurate thickness, and a submicron thickness can be cut.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an outline of a mechanical component of the present invention.

FIG. 2 is a block diagram in which the configuration of a control unit is added to the mechanical components shown in FIG. 1;

FIG. 3 is a diagram showing an example of a driving relationship between a piezoelectric actuator and a servomotor according to the present invention.

[Explanation of symbols]

 Reference Signs List 4 Refrigeration unit 5 Sample 5A Sample tip surface 5B Cut surface 6 Sample table 7 Piezoelectric actuator 8 Moving body 9 Linear guide 10 Ball screw nut 11 Ball screw 13 Servo motor 14 Encoder 15 Laser displacement meter 16 Cutter 21 Sensor amplifier 22 Compensation gate at cutting 23 Comparison Device 24 first preamplifier & compensator 25 first power amplifier 26 first comparator 27 second comparator 28 hold gate 29 AND gate 30 counter 31 DA converter 32 speed comparator 33 second preamplifier & compensator 34 second power amplifier 35 differentiating circuit

Claims (6)

[Claims] 1. A frozen sample cutting apparatus for cutting a tip of a frozen sample to a predetermined thickness, wherein the sample supports the sample and is provided to be movable in a direction perpendicular to a cut surface of the sample. A refrigeration unit that surrounds and cools the sample except at least the tip portion of the sample held on the sample stage; a piezoelectric actuator for minutely moving the sample stage in the vertical direction; A movable body for holding the actuator and moving the sample stage in the vertical direction via the piezoelectric actuator, a position detector in the vertical direction of the sample tip surface which appears sequentially by cutting, and A fine positioning control system that feeds back an output to the piezoelectric actuator and positions the sequentially appearing sample tip surface at a predetermined position prior to cutting. And a control unit comprising a coarse positioning control system for controlling the position of the movable body by a servomotor in relation to the operation of the piezoelectric actuator by the fine positioning control system. . 2. The apparatus for cutting a frozen sample according to claim 1, wherein a heat insulating member is interposed between the refrigeration unit and the piezoelectric actuator. 3. The frozen sample cutting apparatus according to claim 1, wherein the sample stage is formed of a heat insulating material. 4. The apparatus for cutting a frozen sample according to claim 1, wherein the position detector is a laser displacement meter. 5. A fine positioning control system according to claim 1, wherein the fine positioning control system interrupts feedback from the position detector to the piezoelectric actuator during the cutting operation of the sample, and substitutes a substitute signal for a predetermined signal at the start of cutting of the front end surface of the sample. The apparatus for cutting a frozen sample according to claim 1, wherein the apparatus is held at a set position. 6. The control section has a detection section for detecting a predetermined operation limit area of the piezoelectric actuator, and controls the position of the tip end surface of the sample by the piezoelectric actuator until the operation limit area is reached. 6. The apparatus according to claim 1, wherein the movable body is moved by a predetermined amount corresponding to the operation limit area when the operation limit area is detected by the heater. A cutting device for a frozen sample according to item 1.