JPH03117858A - Cryogenic refrigerator - Google Patents

Abstract

PURPOSE:To stabilize the drive of a driving motor by providing driving current correcting means for detecting variation in a driving current to be detected by current detecting means and outputting a correction signal to an inverter in response to the variation in the current. CONSTITUTION:A power source is connected to a compressor 21 and an electric motor 13 through a power source line 24 and an inverter 25, and a current sensor 26 for detecting the amplitude of current is provided in the power supply line between the compressor 21 and the motor 13. The current detected by the sensor 26 is sent to a stepout detector 27, the variation in the current is detected based on the current value to determine whether a stepout occurs or not, and a determination result is output to the inverter 25. If the stepout occurs, the current flowing to the motor 13 is detected by the sensor 26, the abnormal variation in the current is detected by the detector 27, and a speed drop signal is applied to the inverter 25. Thus, the drive of the motor 13 can be stabilized to protect the motor 13.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a cryogenic refrigerator, and is used in cryopumps and the like used in semiconductor manufacturing equipment and vapor deposition equipment such as optical lenses.

(Prior art) Various technologies have been proposed to control the rotational speed of the drive motor of the expansion section with the aim of shortening the startup time (cooling down time) and increasing the output of cryogenic refrigerators. Some of these are disclosed in Japanese Patent Application Laid-Open No. 61-4874 and Japanese Patent Application Laid-Open No. 60-171359.

In the former, the timing at which the rotation speed of the drive motor is changed is controlled according to the temperature of the low temperature section, and in the latter, the timing at which the rotation speed of the drive motor is changed according to the compression section attribute force is controlled.

(Problem to be solved by the invention) Generally, the drive power to the drive motor is 50Hz or 6Hz.
A 0 Hz alternating current power source is used, and it rotates at a rotational speed synchronized with that frequency, but it is known that cooling time can be shortened by rotating at a higher rotational speed. On the other hand, it is well known that when the rotation speed of the drive motor increases, the drive current changes due to the influence of the drive motor's coil and the drive torque decreases, but when the expansion part reaches an extremely low temperature close to the final temperature, The mass flow rate of the working gas supplied to the expansion section increases, and the load on the drive motor increases, causing rotational failure, a so-called tax adjustment phenomenon. The step-out phenomenon refers to a state in which when the drive torque decreases to below the load, the excitation phase is switched before the stator has fully rotated, and the stator is pulled back in the opposite direction and can no longer rotate.

However, in the above-mentioned conventional cryogenic refrigerator, the movement of the drive motor cannot be detected, so if a rotation failure (step-out phenomenon) occurs due to a decrease in the torque of the drive motor during high-speed rotation as described above, However, there is no way to avoid this, and on the contrary, the rotation speed tends to increase in principle, which leads to the problem of damage to the drive motor.

Therefore, the technical object of the present invention is to detect the above-mentioned step-out phenomenon in the cryogenic refrigerator, avoid it, and stabilize the drive of the drive motor.

[Structure of the Invention] (Means for Solving the Problem) The means taken to solve the above-mentioned technical problem is to detect the drive current to the drive motor of the expansion section in the cryogenic refrigerator. a detection means, an impark for controlling the rotational speed of the expansion section, and a drive current correction for detecting fluctuations in the drive current detected by the current detection means and outputting a correction signal to the inverter according to the fluctuations in the drive current. This means that the means have been established.

(Operations and Effects of the Invention) According to the present invention, the current flowing through the drive motor is detected by the current detection means to detect the step-out phenomenon that occurs when the rotational speed of the drive motor increases, and the drive current correction means detects abnormal fluctuations in the current. This can be avoided by detecting this problem by detecting the problem, and the drive current correction means can provide a rotational speed drop signal to the inverter, thereby making it possible to stabilize the drive of the drive motor.

Further, according to the present invention, since a sensor or the like is not required on the side of the expansion part where the step-out phenomenon occurs, it can be constructed inexpensively and compactly.

(Example) Hereinafter, an embodiment 11 of a cryogenic refrigerator according to the present invention will be described based on the drawings.

The figure shows a Gifford-McMuffon-cycle cryogenic refrigerator 10 employing the present invention, and the cryogenic refrigerator 10 includes a stepped expansion cylinder 11.
A stepped expansion piston 12 is fitted inside the piston 12 so that it can be reciprocated by an electric motor 13 via a crank mechanism 14 . A first expansion space 15. A second expansion space 16 is formed, and each expansion space is communicated via a regenerator 17. Further, the lower surface of the other end of the large diameter portion of the stepped piston 12 communicates with the first expansion space 15 via the regenerator 18, and also has an inlet valve (not shown), an inlet port 192, a discharge valve (not shown), and a discharge port 20 (not shown). A compression space (not shown) that can communicate with the suction port and discharge port of the compressor 21 via the compressor 21 is formed. Note that an inlet valve and a discharge valve (not shown) are opened and closed at predetermined timings during the reciprocating movement of the expansion piston 12.

The large diameter end of the expansion cylinder 12 is heated to an extremely low temperature (30 to 70
A first stage cold head 22 is formed which generates a temperature of 10 to 20 K), and a second stage which generates a cryogenic temperature (10 to 20 K) lower than that of the first stage cold head 22 is formed at the small diameter end of the expansion cylinder 12. A cold head 23 is arranged.

An appropriate power source is connected to the compressor 21 and the electric motor 13 via a power line 24 and an inverter 25, and a current is connected to the power line between the compressor 21 and the electric motor 13 to detect the magnitude of the current flowing therethrough. A sensor 26 is provided.

The current detected by the current sensor 26 is sent to the step-out detection circuit 27, which detects fluctuations in the current based on the current value, determines whether step-out has occurred, and outputs the determination result (rotation speed drop signal).
is output to the inverter 25.

In this embodiment having the above configuration, when the expansion piston 12 (not shown) descends, the inlet valve (not shown) is closed and the discharge valve (not shown) is opened at a predetermined timing, so that the working gas is sucked into the compressor 21, and the working gas is sucked into the compressor 21. 1 expansion space 1
5 and the second expansion space 16 increase, and freezing occurs in the re-expansion space.

When the expansion piston 12 rises, an inlet valve (not shown) opens and a discharge valve (not shown) closes at a predetermined timing, so that the working gas flows into each expansion space 15.1.
6 and a compression space (not shown). At this time, the working gas exchanges heat with the cold air stored in the regenerator 18 before entering the first expansion space 15, and is further stored there in the regenerator 17 before entering the second expansion space 16. It exchanges heat with the cold air that is being cooled.

During the above operation, the electric motor is used at a frequency of 50 Hz to 60 Hz, and rotates at a rotational speed synchronized with the frequency, but it is known that cooling time is shortened when the electric motor is rotated at a higher rotational speed. On the other hand, as is well known, when the rotation speed of the electric motor 13 is increased, the current decreases due to the influence of the coil of the electric motor 13, and the driving torque decreases.
When the expansion space reaches an extremely low temperature near the final temperature, the mass flow rate of the working gas increases, and the load on the electric motor 13 increases.
Rotation failure (step-out phenomenon) occurs.

When a step-out phenomenon occurs, the step-out phenomenon causes the electric motor 13
The current flowing through is detected by the current sensor 26, and abnormal fluctuations in the current (current waveform or current value) are detected by the step-out detection circuit 27.
The out-of-step detection circuit 27 provides a rotational speed drop signal to the inverter 25, thereby avoiding the step-out detection circuit 27. Thereby, the drive of the electric motor 13 can be stabilized, and the electric motor 13 can be protected.

This makes it possible to stabilize the driving of the drive motor.

[Brief explanation of the drawing]

The figure is a block diagram of a cryogenic refrigerator according to the present invention. 10... Cryogenic refrigerator, 11... Expansion cylinder, 1
2... Expansion piston, 13... Electric motor, 21.
...Compressor, 24...Power line, 25...Inverter, 26...Current sensor, 27...Step-out detection circuit.

Claims (1)

[Claims] A cryogenic refrigerator in which a compression section and an expansion section are connected in a closed circuit, comprising: current detection means for detecting a drive current to a drive motor of the expansion section; and an inverter for controlling the rotation speed of the expansion section; A cryogenic refrigerator comprising drive current correction means for detecting fluctuations in the drive current detected by the current detection means and outputting a correction signal to the inverter in accordance with the fluctuations in the drive current.