JPH10145958A - Safety device for static discharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable and sensitive safety device for static dischargers that does not depend on the circuit conditions of the secondary side of a step-up transformer. SOLUTION: An abnormal current detecting means 51 is placed in the earth wire of a coaxial cable 11 between the secondary winding-side end of a step-up transformer 3 and earth. In the breakdown mode arising from a short circuit between the conductor of the coaxial cable and the earth wire, a large short-circuit current is passed due to the secondary-side voltage of the step-up transformer, and breakdown is warned of. Since the primary-side current is also increased due to breakdown on the secondary side, that is monitored and a circuit breaker 40 is actuated. In the abnormal discharge mode resulting from increase in capacitance due to a short circuit between a plurality of discharge electrodes 14 and earth, a short-circuit current due to the secondary-side voltage of the step-up transformer is passed through the detecting means 51 through the synthesized capacitance of the discharge electrodes, and abnormal discharge is warned of. In case of an abnormal discharge due to the proximity of a conductor having a ground potential to the discharge electrodes, the abnormal discharge to ground is alarmed by the charges stored in the capacitor of the coaxial cable being passed through the detecting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for a static eliminator for eliminating static electricity from an object.

[0002]

2. Description of the Related Art Since semiconductor devices are easily damaged by static electricity, it is necessary to remove the static electricity during storage and manufacturing processes. For this reason, conventionally, a static eliminator based on the principle as shown in FIG. 4 has been used in the semiconductor device manufacturing process and the like.

In FIG. 4, reference numeral 1 denotes a commercial AC power supply (100
V), 2 is a power switch, 3 is a step-up transformer, and 4 is a high-voltage cable. Reference numeral 5 denotes a neutralizing electrode composed of a ground electrode 6 and a discharge electrode 7. The discharge electrode 7 is connected to one end of the step-up transformer 3 via a conductor of the high-voltage cable 4. The ground electrode 6 is connected to the other end of the step-up transformer 3 via the ground wire of the high-voltage cable 4 and is grounded.
Reference numeral 8 denotes a charged object such as a semiconductor device which is opposed to the charge removing electrode 5 in a non-contact state.

In the above configuration, when the power switch 2 is turned on, the output voltage from the power source 1 (AC 1
00V) is boosted through the boosting transformer 3, and a positive or negative high voltage (for example, 7 kV) is alternately applied to the discharge electrode 7. Then, a corona discharge is generated between the discharge electrode 7 and the ground electrode 6, and the air around the charge removing electrode 5 is alternately ionized into positive and negative ions. And the charged object 8
Depending on the polarity of the charged charge, ions of any polarity are attracted to the charged object 8 and recombine with the charged charge of the charged object 8 to neutralize the charged charge.

[0005]

Since the above-described static eliminator utilizes a discharge phenomenon, an abnormal discharge may occur due to an abnormality of the apparatus or a state of the surrounding atmosphere.
When the discharge becomes abnormal, not only the static electricity of the charged object is not effectively removed, but also the charged object, that is, the semiconductor device may be damaged. As a countermeasure against this,
Conventionally, the following methods have been proposed. A high resistance or a capacitor is connected between the secondary side of the step-up transformer 3 and the charge eliminating electrode 5 to suppress the level of current caused by abnormal discharge. The high voltage cable 4 and the discharge electrode 7 are capacitively coupled. A leakage transformer is used as the step-up transformer 3. Since the leakage transformer has a large leakage reactance, the voltage on the secondary side decreases when the current flowing on the load side, that is, on the static elimination electrode 5 increases. Monitors the current flowing through the secondary side circuit.
Shut off the secondary circuit (see Japanese Utility Model Application Publication No. 62-64135).

The above methods (1) to (4) do not shut off the primary circuit, that is, the power supply when an abnormal discharge occurs, and cannot be said to be sufficient as a safety device. Further, the above method turns off the power supply when abnormal discharge occurs, but has the following disadvantages. For example, when the booster transformer and the static elimination electrode are connected with a coaxial cable that does not cause electric shock, the current level flowing through the secondary circuit increases during normal operation, and an increase in current due to abnormal discharge is detected with high sensitivity. It becomes difficult. If an excessive current or surge voltage is applied to the safety device due to a short circuit of the primary circuit of the step-up transformer, power supply abnormality, or the like, the safety device itself may be destroyed. The present invention has been made in view of the above-described circumstances, and has as its object to provide a stable and highly sensitive safety device for a static eliminator that does not depend on circuit conditions on the secondary side of a step-up transformer.

[0007]

According to a first aspect of the present invention, there is provided a step-up transformer having a primary side connected to an AC power supply, and a coaxial cable connected to one end of a secondary side of the step-up transformer. A safety device for a static eliminator, comprising: a discharge electrode coupled to the step-up transformer; and a ground electrode disposed to face the discharge electrode and connected to the other end of the booster transformer on the secondary side. Detecting means for detecting a current flowing between one end of the grounding wire of the coaxial cable on the side of the step-up transformer and ground, and a determining unit for alarming dielectric breakdown or abnormal discharge when an output of the detecting means is a predetermined value or more. It is characterized by doing.

According to a second aspect of the present invention, in the first aspect of the present invention, the primary circuit of the step-up transformer is shut off by detecting a current of a predetermined value or more by the detecting means. And a short-circuit interrupting means. According to a third aspect of the present invention, in the first or second aspect, the detection means is a pulse transformer.

According to the first aspect of the present invention, the current flowing between one end of the grounding wire of the coaxial cable on the boosting transformer side and the ground is detected by the detecting means. (A) The conductor of the coaxial cable and the grounding wire In the dielectric breakdown mode due to the short circuit, a large short-circuit current due to the secondary voltage of the step-up transformer flows through the detecting means, and the dielectric breakdown is warned. Furthermore, since the primary side current also increases due to the insulation breakdown on the secondary side, this increase is monitored and the primary side circuit is shut off. (B) In an abnormal discharge mode between a discharge electrode and a ground line caused by an increase in capacity (energy storage increase) due to a short circuit of a plurality of discharge electrodes, a short-circuit current due to a secondary voltage of the step-up transformer passes through a combined capacity of the discharge electrodes. The abnormal discharge is warned by flowing through the detecting means. (C) An abnormal discharge to the ground due to the approach of the conductor (grounding body) having the ground potential to the discharge electrode is caused by the electric charge accumulated in the capacitance of the coaxial cable flowing through the detection means, and the abnormal discharge to the ground is warned. Is done.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a static eliminator according to an embodiment of the present invention. The same reference numerals are given to portions common to the respective portions in FIG. 4, and description thereof will be omitted. In FIG. 1, reference numeral 10 denotes a power supply device, 12 denotes a neutralizing electrode, and both are connected by a coaxial cable 11. Here, the reason for using the coaxial cable 11 as the high-voltage cable is as follows.
This is to avoid the risk of electric shock to the human body in a clean room or the like.

Next, the configuration of the charge removing electrode 12 will be described with reference to FIG. 3 showing a specific structure thereof. 3, (A) is a front view, and (B) is a cross-sectional view in the XX ′ direction of the front view (A).

As shown in FIGS.
A predetermined length at the end of the central conductor portion is used as the high-voltage electrode 13. Next, reference numeral 17 in FIG. 3 denotes a coupling ring formed in a hollow cylindrical shape by an insulating material, and its surface is covered with a conductor such as brass. A needle-like discharge electrode 14 protrudes from the conductor.

A plurality of the coupling rings 17 are provided at predetermined intervals, and a high-voltage electrode 13 whose hollow portion is covered with an insulating coating 16 penetrates. That is, the high-voltage electrode 13 and each discharge electrode 14 are capacitively coupled via the above-described insulating portion. Reference numeral 18 denotes a mold portion that covers each coupling ring 17 from which the high-voltage electrode 13 and the discharge electrode 14 protrude. Reference numeral 19 denotes another mold portion provided so as to cover the mold portion 18. The ground electrode 15 is fixed in the form shown in FIG.
It plays the role of integrating and protecting the two.

Next, a description will be given of the safety shut-off circuit 20 provided on the primary side of the step-up transformer in the power supply device 10 shown in FIG. In the circuit 20, reference numeral 21 denotes a photocoupler, and light emitting diodes 22 and 23 and a phototransistor 24 coupled in parallel so as to have opposite polarities.
It is composed of When the abnormal operation current id flows in any direction through the line L1 shown in FIG.
Either 2 or 23 emits light at an emission intensity corresponding to the magnitude of the current, and a photocurrent flows through the phototransistor 24.
As shown in FIG. 1, a transistor 25 is connected to the phototransistor 24 in a Darlington connection, and a collector terminal 25C of the transistor 25 is connected to a positive electrode of a DC power supply 26.

Reference numerals 30 and 40 denote circuit breakers (circuit breakers for wiring), respectively. Circuit breaker 3
The operating coil 31 at 0 has one end connected to the negative electrode of the DC power supply 26 and the other end connected to the emitter terminal 25E of the transistor 25. Working coil 31
Is the current flowing through itself, that is, the photocoupler 21
And, an electromagnetic force based on the magnitude of the current amplified by the transistor 25 is generated, and when the current exceeds a predetermined level, the main contact 32 of the circuit breaker 30 switches from the on state to the off state. As a result, the primary circuit of the step-up transformer 3 is shut off.

In the circuit breaker 40, when a predetermined amount or more of current flows through the operating coil 41, the contact 42 is switched from the on state to the off state. Here, 1 of the step-up transformer 3 in the normal operation
Assuming that the primary current is i3_1 and the primary current when the secondary circuit is short-circuited is i3_1s, the predetermined amount of current, that is, the trip current i40 of the circuit breaker 40 is i3_1 <i40 <i3_1s (1) It is set to be. That is, when the secondary circuit of the step-up transformer 3 is short-circuited due to insulation breakdown of the coaxial cable, the contact 42 is turned off, and the step-up transformer 3 is turned off.
Is shut off.

Further, the circuit breakers 30 and 40
When both circuit breakers are in the ON state, the circuit breaker 40 is turned off when the circuit breaker 30 is turned off, and the circuit breaker 30 is turned off when the circuit breaker 40 is turned off. The breaker contacts are mechanically connected. That is, if at least one of the occurrence of the abnormal operation current id and the short circuit on the secondary side is detected,
The primary circuit is shut off.

In the above configuration, it is assumed that an object to be neutralized (hereinafter referred to as a charged object EO) is placed below the neutralizing electrode 12 in a non-contact state with the neutralizing electrode 12, and the power switch 2 is turned on. Thus, a low-frequency high voltage whose output voltage is boosted to, for example, 7 kV via the boosting transformer 3 is applied to the high-voltage electrode 13 via the coaxial cable 11. Then, corona discharge occurs between the discharge electrode 14 and the ground electrode 15 that are capacitively coupled to the high-voltage electrode 13, and the air around the charge removing electrode 12 is alternately ionized into positive ions and negative ions. Due to this corona discharge, a discharge current i1 circulating in the secondary circuit of the step-up transformer 3 is generated.
The discharge current i1 also includes the leakage current of the coaxial cable 11.

Here, assuming that the charged object EO opposed to the charge removing electrode 12 has a positive charge, the negative ions generated by the corona discharge are attracted to the charged object EO, and the charged charge of the charged object EO becomes medium. Be summed up. In the neutralization process, the positive ions become excessive around the neutralizing electrode 12, and the excess positive ions are attracted to the ground electrode 15. As a result, a static elimination current i2 is generated in the secondary circuit of the step-up transformer.

Next, the abnormality alarm circuit 50 provided in the secondary circuit will be described. 51 is a pulse transformer,
The primary winding is connected between one end of the ground wire of the coaxial cable 11 on the side of the step-up transformer and the ground, and the current flowing therethrough is
To monitor.

The current generated on the secondary side of the pulse transformer 51 is converted into a DC voltage Es by a rectifying / smoothing circuit comprising a parallel circuit of a diode 52, a capacitor 53 and a resistor 54. 55 is an amplifier for amplifying Es by a constant factor,
The output Eo is guided to the insulation breakdown determination unit 56 and the abnormal discharge determination unit 57.

The dielectric breakdown judging section 56 determines the level of the amplifier output Eo and the set value Eo obtained when the dielectric breakdown occurs.
1 to generate an insulation breakdown alarm output AL1 and supply an operation current id to the photocoupler 21 to operate the circuit breakers 30 and 40. That is, with respect to the dielectric breakdown, the circuit has a double safety configuration with the circuit breaker 40 that operates by monitoring the increase in the primary current.

The abnormal discharge judging section 57 determines the level of the amplifier output Eo and the set value Eo obtained when abnormal discharge occurs.
Then, an abnormal discharge break alarm output AL2 is generated, and an operation current id is supplied to the photocoupler 21 to operate the circuit breakers 30, 40.

Next, a method for detecting an abnormal current in each abnormal pattern will be described with reference to FIGS. 2 (A), 2 (B) and 2 (C). FIG. 2A shows the high voltage electrode 13 and the ground electrode 15.
Is a pattern of dielectric breakdown causing a short circuit.
The short-circuit pulse current i3 due to the secondary voltage flows through the pulse transformer 51.

FIG. 2B shows that the plurality of discharge electrodes 14 (three in the figure) are short-circuited and the capacity between the discharge electrodes 14 and the high-voltage electrode is increased (3).
ca), which is an abnormal discharge pattern that discharges through this impedance, and the short-circuit pulse current i4 due to the secondary voltage of the step-up transformer 3 flows through the pulse transformer 51 through the combined capacitor. In the normal case, the discharge of the ground electrode picture occurs at random from each discharge electrode, and the apparent impedance is extremely large, so the discharge current is extremely small.
It is easy to distinguish from an abnormal current.

FIG. 2C shows a conductor 60 having a ground potential.
Is a pattern generated when approaching the discharge electrode 14, and the pulse current i 5 due to the electric charge accumulated in the capacitance (Cc) of the coaxial cable 11 flows through the pulse transformer 51.

As described above, according to the above-described embodiment, since the abnormal pulse current generated between the ground line of the coaxial cable and the ground potential is monitored, the current (discharge) flowing through the secondary circuit of the step-up transformer is monitored. Abnormal discharge of any pattern can be detected with higher sensitivity as compared with the case of monitoring the current i1 + discharge current i2). Also, for similar reasons,
It is possible to obtain a safety device in which the safety shut-off circuit is not affected by the characteristics of the secondary circuit, for example, leakage current of the coaxial cable 11 and is not affected by changes in the power supply voltage or the frequency. Further, by using a pulse transformer as the current detecting element, a safety device in which the primary side circuit and the secondary side circuit of the step-up transformer are insulated can be obtained, and the reliability of the device is high. Also, since a circuit breaker is used as a means for interrupting the primary circuit of the step-up transformer, it is more resistant to overcurrent and overvoltage than a safety device using a relay, a thyristor, or the like as an interrupting device, and has high reliability as a safety device. .

[0028]

As described above, according to the present invention, the primary side circuit of the step-up transformer is cut off by detecting the charge elimination current. It is possible to obtain a stable and highly sensitive safety device for the static eliminator without depending on it. Therefore, abnormal discharge can be reliably stopped at an early stage, and the charged object can be protected from destruction or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a static eliminator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a method for detecting an abnormal current of each abnormal pattern in FIG. 1;

FIG. 3 is a diagram showing a specific structure of a charge removing electrode 12 in FIG.

FIG. 4 is a block diagram illustrating a configuration of a conventional static eliminator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 3 Step-up transformer 14 Discharge electrode 15 Ground electrode 21 Photocoupler (detection means) 30 Circuit breaker (interruption means at abnormal discharge) 40 Circuit breaker (interruption means at short circuit) 50 Abnormal alarm circuit 51 Current transformer 56 Short circuit break alarm circuit 57 Abnormal discharge alarm circuit

Claims (3)

[Claims] 1. A step-up transformer having a primary side connected to an AC power supply, a discharge electrode coupled to one end of a secondary side of the step-up transformer via a coaxial cable, and disposed so as to face the discharge electrode. A safety device for a static eliminator, comprising: a ground electrode connected to the other end on the secondary side of the boost transformer; and a current flowing between one end of the ground wire of the coaxial cable on the boost transformer side and ground. A safety device for a static eliminator, comprising: a detection unit for detecting a discharge; 2. A filter according to claim 1, further comprising a short-circuit cut-off means for cutting off a primary circuit of said step-up transformer when a current equal to or more than a predetermined value is detected by said detection means. Electrical safety device. 3. The safety device for a static eliminator according to claim 1, wherein said detecting means is a pulse transformer.