JPH021906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermal processing, and more particularly to a method and apparatus for controlling chemical-thermal processing of articles in a glow discharge.

The method and device of the invention can be applied in conjunction with controlling the processing of workpieces in ion nitration devices, which are used, for example, in machine building and the aerospace industry to obtain high workpiece strength. be done.

Chemical-thermal treatment of a workpiece by glow discharge, especially ion nitration treatment, usually involves two steps: cleaning the surface of the workpiece by cathodic sputtering, and applying diffusion saturation to the workpiece. It comprises two stages: maintaining the workpiece at a predetermined temperature. In order to rapidly remove various contaminants from the surface of the workpiece, as well as to harden a layer uniformly distributed over the entire surface, which is important in the processing of complex alloy steels, the cathodic sputtering method is required. It is considered good practice to use a voltage significantly higher than the current voltage. However, this method does not give good results at high voltages, since in this case glow discharges often transition to arc discharges, and the higher the voltage, the more frequently this transition occurs, especially at the beginning of the treatment stage. It gets expensive.
Under these circumstances, damage to the surface of the workpiece being treated may occur if the arcing frequency exceeds an acceptable limit. Therefore, when increasing the cathode sputtering voltage, it is necessary to prevent the frequency of arc occurrence from exceeding this permissible limit.

It must be noted that during cleaning the workpiece is heated. Therefore, the temperature of the workpiece and its rate of development must be kept within certain limits, otherwise deformation of the workpiece will occur and the properties of the nitration layer will deteriorate.

The chemical-thermal treatment method of a workpiece by glow discharge includes the steps of measuring the temperature of the workpiece and its rate of change, and comparing the measured quantity with a predetermined value. Processing methods are known which include the steps of generating an error signal by means of this comparison and forming a signal for controlling the glow discharge voltage. (FRG acceptance application No. 2606396, cl.
(See HO5B7/16).

A disadvantage of this method is that the heating rate of the workpiece or its temperature is often controlled by varying the glow discharge voltage, which does not allow for strong cathodic sputtering. The predetermined values of these adjustable quantities are obtained at lower voltages than strong cathodic sputtering is achieved, thereby reducing the quality of the process. Another disadvantage of this method is that the arcing frequency is not kept at a predetermined level during the chemical-thermal treatment, and the only control measures available are to suppress the rise in glow discharge voltage that would accompany the arcing. This is something that cannot be done. Finally, with this method, it is not possible to simultaneously maintain the workpiece temperature change rate and the arc occurrence frequency, or the workpiece temperature and the arc occurrence frequency, at specified levels. This is because it only has a controlling effect on the glow discharge voltage, which results in a longer chemical-thermal treatment time.

As an apparatus for carrying out the above method, there is an apparatus in which a power source is connected to a lead of a voltage chamber that accommodates a workpiece. In this device, a temperature sensor and a temperature change rate sensor are connected via respective comparison elements to a control unit, which is connected to a power supply. The output of the temperature comparison element is connected to a setting input of the temperature change rate comparison element, and the output of the temperature change rate comparison element is connected to a first input of the control unit. This is a large integral constant proportional-integral regulator whose second input is connected to a sensor that confirms arcing.

In the known device, this proportional-integral regulator is used to control the workpiece temperature and its rate of change, and its power supply supplies a continuously variable voltage, so that the process parameters can be adjusted correctly. Can not do it.

The basic object of the present invention is to maintain work piece temperature and arcing frequency at desired levels while simultaneously improving the control characteristics of these quantities in controlling the chemical-thermal treatment of glow discharges. The object of the present invention is to realize a method and apparatus that can shorten processing time and improve processing quality by performing strong cathode sputtering.

The purpose of this is to include a step of measuring the temperature of the workpiece and the rate of change of said temperature in the control of the chemical-thermal treatment of the workpiece in a glow discharge, and to set these measured quantities to their respective predetermined values. This is accomplished by a method comprising the steps of comparing, generating an error signal from the comparison, and generating a control signal for controlling the glow discharge voltage from the error signal. The method according to the present invention includes the step of measuring the arc occurrence frequency in the glow discharge simultaneously with the measuring step;
a step of comparing the measurement frequency with a predetermined value, a step of generating an error signal based on the comparison, a step of generating another control signal from the error signal, and a step of using the another control signal. controlling the frequency of arcing.

In addition, in the method of the present invention, a pulsed voltage having an adjustable amplitude value and an average value is used as the glow discharge voltage from the start of processing the workpiece to the end of cathode sputtering, and the average value of the pulsed voltage is Preferably, the value is used to control the temperature and its rate of change, and the amplitude value of the pulse voltage is used to control the frequency of arcing, thereby enabling intense cathode sputtering.

The present invention also compares a signal based on arc occurrence frequency suitable for controlling glow discharge voltage with a control signal based on temperature or a control signal based on temperature change rate, Preferably, a signal corresponding to the voltage is used to control the glow discharge voltage, thus increasing the quality of the simultaneous control of at least two processing characteristics.

In the method of the present invention, it is also preferable to reduce the predetermined value of the arc occurrence frequency when the temperature of the workpiece increases.

This object is achieved in an apparatus for carrying out the method of the present invention, which is equipped with a power source connected to a lead of a discharge chamber containing a workpiece, and a temperature control device for the workpiece. A sensor, a temperature change rate sensor, an element that compares the measured temperature and its rate of change with predetermined values, and a regulator unit, and the output of the sensor is transmitted through each comparison element. is connected to the regulator unit, and the regulator unit is connected to the power source. In this case, the device according to the invention additionally includes an arcing frequency sensor and a predetermined arcing frequency sensor. and a control unit and a glow discharge voltage transmitter. death,
The arcing frequency sensor is connected to the arcing frequency regulator via a corresponding comparison element, and the output of the arcing frequency regulator is connected to a corresponding one of the inputs of the control unit. The other two inputs are connected to the outputs of the temperature regulator and temperature rate of change regulator, one input of which is connected to the output of the temperature comparison element, and the remaining input is connected to the output of the lead via a glow discharge voltage transmitter. It is connected to its corresponding lead, and its output is connected to the power supply.

The control unit of the apparatus of the present invention preferably includes two switches, a zero detector, a minimum signal extractor, and a cathode sputtering completion confirmation circuit, where the output of the zero detector is a first input of a first of said two switches, an output of said switch being connected to a first input of a second switch, and a second input of said second switch being connected to a first input of said second switch; connected to an output of a cathode sputtering completion confirmation circuit, a first output of the second switch being connected to a first input of a minimum signal extractor, and a respective input of the first switch;
The input of the zero detector, the second input of the minimum signal extractor, and the input of the cathode sputtering completion confirmation circuit are respectively used as inputs of the control unit, and the second output of the second switch and the minimum signal The extractors are each used as an output of a control unit.

The cathode sputtering completion confirmation circuit of the apparatus of the present invention preferably includes a comparator, a reference power source, and a time counter, wherein the first input and output of the comparator are the reference power source and the time counter, respectively. The second input of the comparator and the output of the time counter are used as the input and output of the cathode sputtering completion confirmation circuit, respectively.

The present invention will be described in detail below with reference to the drawings.

In the following description of the invention, reference is made to the drawings which disclose an apparatus for carrying out the method of the invention.

In FIG. 1, the apparatus of the invention comprises a power supply 1, the output of which is connected to a lead 2 of a discharge chamber 3 in which a workpiece 4 is subjected to a chemical-thermal treatment. be exposed. The workpiece 4 in the discharge chamber 3 is suspended from a suspension member 5. The wall of the discharge chamber 3 functions as one of the leads 2. The apparatus of the invention includes a temperature sensor 6, the input of which is connected to the workpiece 4. A thermocouple with an amplifier can be used as the temperature sensor 6, and the output of the temperature sensor 6 is the input of the temperature change rate sensor 7,
The first input of the temperature comparison element 8 is connected to the first input of the temperature comparison element 8 . The output of the temperature sensor 7 is the first output of the temperature change rate comparison element 9.
connected to the input of Arc occurrence frequency sensor 10
The input of is connected to the output of the glow discharge current transmitter 11 and the glow discharge voltage transmitter 12. The output of the arcing frequency sensor 10 is connected to a first input of the arcing frequency comparison element 13. comparison element 8,
A second input at 9,13 is used to receive signals corresponding to predetermined values of the workpiece temperature, its rate of change, and the arcing frequency. The outputs of comparison elements 8, 9, 13 are connected to regulator unit 1.
The regulator unit 17 is connected to the input of each regulator 14, 15, 16 of 7.
is designed to generate control signals regarding the workpiece temperature, its rate of change, and arc occurrence frequency based on error signals supplied to the outputs of comparison elements 8, 9, and 13. Regulator 14, 15, 16
and the output of the comparison element 8 are respectively connected to inputs 18, 19, 20, 21 of the control unit 22, whose input 23 is connected to the output of the glow discharge voltage transmitter 12. The outputs 24, 25 of the control unit 22 are connected to the inputs of the power supply 1.

The control unit 22 is designed to control the amplitude and average value of the supply voltage.

Referring now to FIG. 2, control unit 22
comprises a switch 26, the output of which is connected to a first input of switch 27. The second input of the switch 27 is connected to the output 28 of the cathode sputtering completion confirmation circuit 29, and the first output of the switch 27 is connected to the first output of the minimum signal extractor 30.
connected to the input of A first input of switch 26 is connected to the output of zero detector 31. The other two inputs of the switch 26, the input of the zero detector 31, the second input of the minimum signal extractor 31, and the output of the cathode sputtering completion confirmation circuit 29 are inputs 18, 19, and 21 of the control unit 22, respectively. ，
Used as 20, 23. The output of the minimum signal extractor 30 and the second output of the switch 27 are used as outputs 25, 24 of the control unit 22, respectively. Switch 26 is used to connect the output of one of the regulators 14 or 15 of FIG. 1 to the corresponding input of switch 27 (FIG. 2) and switch 27 is used to connect the output of one of the regulators 14 or 15 of FIG. The minimum signal extractor 30 receives the output of (FIG. 1) depending on the presence or absence of the signal at the output 28 of the cathode sputtering completion confirmation circuit 29.
or directly to the input 25 of the control unit 22.
The minimum signal extractor 30 has the function of comparing the signals supplied to its two inputs and selecting the signal with the smaller amplitude.

Figure 3 shows the cathode sputtering completion confirmation circuit 29.
3, which includes a comparator 32 whose output is connected to a time counter 3.
Connected to input 3. A first input of comparator 32 is connected to reference power supply 34 and a second input is used as input 23 of control unit 22. The output of the time counter 33 is used as the output 28 of the cathode sputtering completion confirmation circuit 29. Comparator 3
2 has a function of comparing the power supply voltage with the reference voltage from the reference power supply 34 according to a predetermined value of the glow discharge voltage. Comparator 32 also generates an operating signal for time counter 33. A time counter 33 counts the time during which cathode sputtering is carried out in the presence of the signal at the output of comparator 32 and generates a signal that is applied to the output of switch 27 (FIG. 2) at the end of cathode sputtering.

FIG. 4 to FIG. 7 are graphs showing the history of the operation of the control device that controls the ion nitration reactor.

Figure 4 shows the temperature T (solid line) of the work piece 4 in Figure 1.
It shows how the arc occurrence frequency f (broken line) changes over time. The horizontal axis is the current value at time t, and the vertical axis is the values of T, f, and T _p . The vertical axis T _p is the predetermined temperature of the work piece 4 (FIG. 1).

FIG. 5 shows the arc occurrence frequency regulator 16.
1 shows how the control signal U ₁ at the output of FIG. 1 changes over time.

FIG. 6 shows how the control signal U ₂ (solid line) at the output of the temperature change rate regulator 15 and the control signal U ₃ (dashed line) at the output of the temperature regulator 14 change over time. be.

FIG. 7 shows how the power supply voltage _Up changes over time. In FIG. 7, the solid line shows the envelope waveform of the voltage, and the broken line shows the voltage averaged over the corresponding time. vertical axis
U ₄ is the supply voltage at which strong cathode sputtering occurs.

t ₁ , t ₂ , t ₃ , t ₄ , and t ₅ on the horizontal axis indicate the following values.

_t1 is the time for the heating temperature to reach a predetermined value.

_t2 is the time when the amplitude value of the power supply voltage reaches _U4 .

t ₃ is the start time of the interval between two consecutive pulses.

_t4 is the end time of cathode sputtering.

_t5 is the start time of the next arc discharge occurrence.

In FIG. 7, τ _p , τ ₁ , and τ _p represent the pulse interval, pulse width, and pulse period, respectively.

The method of the present invention is carried out using the apparatus shown in FIGS. 1, 2, and 3 as follows.

At the start time t=0 (from Fig. 4 to Fig. 7), the voltage of the power supply 1 is
(Fig. 7), whose value corresponds to the initial _value of the control signal at the input of power supply 1 (Fig. 7).
It is. At the beginning of the process, the glow discharge generally often changes to an arc discharge. The extinction of glow discharge is as follows. The supply voltage immediately drops to zero and is reapplied after sufficient time has elapsed for the discharge gap to achieve a deionized state.
For this purpose, the control signal at the input of the power supply 1 connected to the output 24 of the control unit 22 goes to zero and rises after a certain delay time. Due to the occurrence of arc discharge, the discharge current increases and the discharge voltage decreases.
Thus, the signal generated by current transmitter 11 (FIG. 1) and the signal generated by voltage transmitter 12 indicate the occurrence of an arc discharge. A signal proportional to the rate at which arc discharge occurs (arc occurrence frequency) is generated as the output of the arc occurrence frequency sensor 10.
This signal is fed to the input of an arcing frequency comparison element 13, where it is compared with a signal proportional to a predetermined arcing frequency. In this way, a signal is formed at the output of the arc frequency comparison element 13 that is proportional to the difference between the predetermined value and the measured value of the arc frequency.

This signal is fed to the input of an arcing frequency regulator 16, whose output contains the amplitude value U _a (7 U _{1 (FIG. 5) is used to modify the U 1} (FIG. 5) form. A proportional-integral regulator can be used as the regulator 16 (FIG. 1). The signal produced by regulator 16 is applied to an input 20 of control unit 22, which input can be used as one of the inputs of minimum signal extractor 30 (FIG. 2).
The other input of the minimum signal extractor 30 is the switch 27.
In addition to its basic functions, this switch 27 also functions as a reference power source. This signal has a constant value that significantly exceeds the value of the signal at input 20 of control unit 22. The minimum signal extractor has the function of comparing the signals at its two inputs, and the smaller of the compared signals appears at the output. This smaller signal is here obtained from the output of the arcing frequency regulator 16. This signal is applied to the input 24 of the power supply 1 and varies the value of U ₂ (voltage amplitude, FIG. 7) to maintain the arcing frequency at a predetermined level. In this case, U _a increases.

During this process, the workpiece 4 (FIG. 1) is heated. Therefore, at the outputs of the temperature sensor 6 and the temperature change rate sensor 7, signals appear that are proportional to the actual values of the workpiece temperature and its rate of change. Comparison elements 8, 9
has the function of comparing these signals with a signal proportional to a predetermined value of said quantity. The outputs of the comparison elements 8, 9 then form an error signal regarding the workpiece temperature and its rate of change.

According to these error signals and the selected regulation law, the regulators 14, 15 output signals U ₂ and U ₃ (6th
form). As the regulators 14 and 15, proportional-integral regulators can be used.
The generated control signal is input to input 1 of control unit 22.
8, 19 (Fig. 1), and the switch 26
(Fig. 2).
When the switch 26 is activated, before time t ₁ only the control signal U ₂ based on the rate of change of temperature is activated by the switch 26.
7 input. This signal is supplied from the output of regulator 15 via switch 27 to input 25 of power supply 1. Thus, the average value of the supply voltage
U ₅ changes. Accordingly, the average value of the discharge voltage changes, and the heating rate is maintained at a predetermined level. To change the average value U ₅ , for example, the pulse interval τ _p may be changed while keeping the pulse width τ ₁ and the pulse period τ _p constant.

At time t ₁ (FIG. 4), the workpiece temperature T reaches a predetermined value T _p . As a result, the output of the zero detector 31 (FIG. 2)
A signal appears which causes the control signal U ₃ generated by the temperature regulator 14 to appear at its output.

It is desirable that the transition from control signal U ₂ to control signal U ₃ occurs smoothly. This means that the initial value of U ₃ is equal to the value of U ₂ at the time of transition. Therefore, at time t ₁ a condition exists in which the control signal U ₃ (FIG. 6) from the temperature regulator 14 is applied to the input 25 of the power supply 1.
As a result, the average value of the discharge voltage changes, and the temperature of the work piece is maintained at a predetermined value T _p .

At time t ₂ (Fig. 7), the amplitude value U _a of the power supply voltage
reaches U ₄ , which causes the input 23 of the strong cathode sputtering completion confirmation circuit 29, that is, the comparator 3
The signal at one input of 2 (FIG. 3) will be equal to the signal sent to the other input of the comparator, and thus the comparator forms the signal that drives the time counter 33. At time t ₃ (Fig. 7), comparator 3
2 (FIG. 3) disappears, and the time counter 33 stops counting. Thus time counter 3
3 counts the time that the discharge voltage is maintained at U ₄ (Figure 7).

At time t ₄ , time counter 33 (Fig. 3)
The time counted by reaches a predetermined value, and a signal is generated at the output 28 of the cathode sputtering completion confirmation circuit 29 to switch the switch 27 (FIG. 2). This switches the signal at the output of switch 27. Thus, the input 25 (FIG. 1) of the power supply 1 receives a constant signal such that the discharge voltage is virtually continuous, and the first input of the minimum signal extractor 30 receives the signal formed by the temperature regulator 14. The signal produced by the arcing frequency regulator 16 is always received by the second input of the minimum signal extractor 30, at the output of which the smaller of the two input signals appears. When no arcing occurs, this smaller signal becomes the temperature-based control temperature _U3 . By changing the continuous wave power supply voltage (FIG. 7), the temperature of the work piece is maintained at a predetermined level T _p (FIG. 4).

When arcing occurs again at time t ₅ (FIGS. 4, 5, and 7), the output signal U ₁ (FIG. 5) of arcing frequency regulator 16 (FIG. 1) decreases. When this signal becomes smaller than the signal U ₃ (FIG. 6) produced by temperature regulator 14, the supply voltage decreases and the frequency of arcing decreases.

It is customary to reduce the frequency of arcing during heating, since the negative effects of arcing become stronger as the temperature increases. In this case, it is necessary to connect a predetermined input of the arc occurrence frequency comparison element 13 to the input of the temperature sensor 6. (This connection is not shown in FIGS. 1, 2, and 3).

In the method and apparatus of the present invention, by using two types of control parameters simultaneously, it is possible to control the entire required process before the end of cathode sputtering, and the two types of control parameters are the arc occurrence frequency and the These are the workpiece temperature, or the arc occurrence frequency and the rate of change in workpiece temperature, and in this case, the amplitude value and average value of the power supply voltage are the objects of control. This allows powerful cathodic sputtering to be carried out at high voltages, resulting in shorter processing times and improved workpiece quality.

The apparatus of the invention uses separate regulators for each control parameter, which provides improved control action and improved workpiece processing quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus for chemical-thermal treatment of a workpiece by glow discharge according to the invention, and FIG. 2 is a block diagram of a control unit of the apparatus according to the invention. FIG. 3 is a diagram showing one embodiment of the cathode sputtering completion confirmation circuit of the apparatus of the present invention, and FIG. 4 is a diagram showing the relationship between time and work piece temperature and time and arc occurrence frequency according to the present invention. FIG. 5 is a diagram showing the relationship between the control signal based on time and arc occurrence frequency according to the present invention, and FIG. 6 is a diagram showing the relationship between the control signal based on time and temperature and the time and temperature change rate according to the present invention. FIG. 7 is a diagram showing the relationship between time and power supply voltage according to the present invention. 1...Power supply, 2...Lead of discharge chamber 3, 3...
Discharge chamber, 4...Workpiece, 6...Temperature sensor, 7
... Temperature change rate sensor, 8 ... Temperature comparison element, 9
... Temperature change rate comparison element, 10 ... Arc occurrence frequency sensor, 12 ... Glow discharge voltage transmitter, 13
... Arc occurrence frequency comparison element, 14 ... Temperature regulator, 15 ... Temperature change rate regulator, 1
6...Arc occurrence frequency regulator, 18,1
9, 20, 21...Input of control unit 22, 2
2...control unit, 23...control unit 22
24, 25... Output of control unit 22, 26... First switch, 27... Second switch, 28... Output of cathode sputtering completion confirmation circuit 29, 29... Cathode sputtering completion confirmation circuit , 30...minimum signal extractor, 31...
Zero detector, 32... Comparator, 33... Time counter, 34... Reference power supply.

Claims (1)

[Claims] 1. Chemical treatment of a work piece carried out in a glow discharge
In the method of controlling thermal treatment, the temperature of the workpiece 4, the rate of change of said temperature, and the frequency with which arcs occur during glow discharge are measured, and these measured quantities are converted to their predetermined values. and from these error signals obtain a control signal for controlling the glow discharge voltage with respect to said temperature, its rate of change and said arcing frequency, and control based on the arcing frequency. A method characterized in that the generation of an arc during a glow discharge is controlled using a signal. 2. In the method for chemically and thermally treating a work piece as set forth in claim 1, in which the work piece held during glow discharge is simultaneously subjected to heating and cathode sputtering, the work piece 4 from the start of the process to the end of the cathode sputtering, using a pulsed voltage with adjustable amplitude and average value as the glow discharge voltage, and controlling the temperature and its rate of change using the average value of the pulsed voltage, A method characterized in that the frequency of arc occurrence is controlled using the amplitude value of the pulse voltage. 3 Compare a control signal based on arcing frequency to a temperature-based control signal for controlling the glow discharge voltage, and use the control signal corresponding to the smaller glow discharge voltage among these compared control signals to control the glow discharge voltage. The method according to claims 1 and 2, wherein the discharge voltage is controlled. 4. Comparing a control signal based on the arcing frequency for controlling the glow discharge voltage with a control signal based on the rate of change of temperature, and controlling the one of these compared control signals that corresponds to a smaller glow discharge voltage. 3. A method as claimed in claims 1 and 2, in which a signal is used to control the glow discharge voltage. 5. The method according to claim 1, wherein the value of the arc occurrence frequency is increased as the temperature of the work piece 4 becomes higher. 6 A power supply 1 connected to the lead 2 of the discharge chamber 3 housing the workpiece 4 and a temperature sensor 6 for the workpiece
, a sensor 7 for the rate of change of temperature, a sensor 10 for the frequency of arcing, and an element for comparing the measured quantities representing the temperature, its rate of change and the frequency of arcing, respectively, with their predetermined values. 8,9,
13, regulators 14, 15, and 16 that adjust the temperature, its rate of change, and the frequency of arc occurrence, respectively;
Control unit 22 and glow discharge voltage transmitter 12
The outputs of the sensors 6, 7, 10 are connected to the respective regulators 14, 15, 16 via the corresponding comparison elements 8, 9, 13, and the output of the regulator 16 is connected to the control unit 22.
input 20 of the control unit and input 1 of the control unit.
8, 19 are connected to the outputs of the regulators 14, 15, the input 21 of the control unit is connected to the output of the comparison element 8, the input 23 of the control unit is connected via the transmitter 12 to each of the leads 2, A device characterized in that the outputs 24, 25 of the control unit are connected to the power source 1. 7 The control unit 22 includes switches 26 and 27.
, zero detector 31, and minimum signal extractor 30
and a cathode sputtering completion confirmation circuit 29, the output of the zero detector 31 is connected to the first input of the switch 26, the output of the switch is connected to the first input of the switch 27, and the output of the zero detector 31 is connected to the first input of the switch 27. The second input of the switch 27 is connected to the output 28 of the cathode sputtering completion confirmation circuit 29, and the first output of the switch 27 is connected to the minimum signal extractor 30.
Each input of the switch 26, the input of the zero detector 31, the second input of the minimum signal extractor 30, and the input of the cathode sputtering completion confirmation circuit 29 are connected to the first input of the control unit 22, respectively. Claim 6, wherein the second output of the switch 27 and the output of the minimum signal extractor 30 are used as the outputs 25, 24 of the control unit 22, respectively. The device described in. 8 The above cathode sputtering completion confirmation circuit 29
comprises a comparator 32, a reference power supply 34, and a time counter 33, a first input and an output of the comparator 32 are connected to the power supply 34 and an input of the time counter 33, respectively, 8. The apparatus according to claim 7, wherein the two inputs and the output of the time counter 33 are used as the input and output 28 of the cathode sputtering completion confirmation circuit 29, respectively.