Methods and apparatus for controlling power in vapor jet vacuum pumps

Abstract

Methods and apparatus for controlling power supplied to vapor jet vacuum pumps are provided. A vapor jet vacuum pumping system includes a vapor jet pump having an inlet port, an exhaust port, a jet assembly and an boiler, the boiler including a heater, and a power controller for automatically controlling power supplied to the heater in response to at least one control parameter. The power may be controlled in response to a programmed sequence, to a sensed pressure in a process chamber, to control signals from a process control system, or to combinations of these control parameters.

Description

FIELD OF THE INVENTION

[0001] This invention relates to vapor jet vacuum pumps and, more particularly, to methods and apparatus for reducing power consumption by vapor jet vacuum pumps without significantly degrading pump performance.

BACKGROUND OF THE INVENTION

[0002] Vapor jet pumps, also known as diffusion pumps, are widely used for vacuum pumping of enclosed chambers to high vacuum. The basic components of a vapor jet pump include a generally cylindrical housing having an inlet at one end and a foreline. The foreline is typically coupled to a roughing pump and functions as an exhaust port. A boiler assembly is sealed within the other end of the housing. The boiler includes a reservoir for a liquid, such as oil, and a heater for vaporizing the liquid. A jet assembly mounted within the housing directs one or more vapor jets toward the housing wall, where the vapor is condensed. The condensed vapor returns to the liquid reservoir, and the cycle is repeated. The vapor jet drags the gas molecules from the enclosed chamber to which the pump is attached, thereby vacuum pumping the chamber. The vacuum chamber and the vapor jet pump may be part of a process control system.

[0003] Limiting power consumption is frequently an important issue in the operation of process control systems and other equipment where vapor jet pumps are used. Most modern vapor jet pumps function at power input as low as about one-third of the nominal specified power to the heater. The performance parameters usually change as follows. The maximum throughput capacity and the maximum permissible discharge pressure reduce with a linear relationship to power. The maximum compression ratios reduce significantly more than that.

[0004] With regard to work done to compress the pumped gas, vapor jet pumps are very inefficient. At maximum throughput operation, the efficiency may be only 1 or 2%. Most energy is going into re-heating and re-evaporating the condensed oil vapor. Typically the pump will maintain high vacuum in a vacuum chamber at power as low as about 25%, when the boiling process continues and the liquid is kept at the boiling temperature. In many applications where the compression ratios for light gases are not important and required pumping throughputs are low, power can be saved through operation at lower power.

[0005] A simple way of conserving power is to shut off the pump overnight or over a weekend.

[0006] This requires a loss of about an hour to restore the normal operation and at least a partial loss of vacuum level in the vacuum chamber.

[0007] Another way of conserving power is to switch some or all of the heater to a lower power. A product called Deltawatt included an electrical switching box for pumps with multiple heaters. The switching box was manually controlled.

[0008] Some users attempt to control the operation of the vapor jet pump by switching the power on and off while observing the temperature of the liquid in the boiler. This can work with good instrumentation and careful synchronization of peak throughput demand in the process period with peak vapor production. The temperature change is very small, typically 1° C. This method is difficult because the timing must be varied for each application and because distinguishing temperature differences of 1° C. may be difficult.

[0009] Accordingly, there is a need for methods and apparatus for controlling power in vapor jet vacuum pumping systems without significantly degrading performance.

SUMMARY OF THE INVENTION

[0010] According to a first aspect of the invention, a vapor jet vacuum pumping system is provided. The vapor jet vacuum pumping system comprises a vapor jet pump having an inlet port, an exhaust port, a jet assembly and a boiler, the boiler including a heater, and a power controller for automatically controlling power supplied to the heater in response to at least one control parameter.

[0011] In some embodiments, the control parameter comprises a programmed sequence of power levels. In other embodiments, the power controller is configured for controlling power supplied to the heater in response to a sensed pressure in a process chamber being pumped by the vapor jet pump. In further embodiments, the power controller is configured for controlling power supplied to the heater in response to control signals from a process control system. In additional embodiments, the power controller is configured for controlling power supplied to the heater in response to a combination of control parameters.

[0012] In some embodiments, the power controller may be configured for controlling power supplied to the heater at one of two or more discrete power levels. In other embodiments, the power controller may be configured for controlling power supplied to the heater over a continuous range of power levels. The heater may include two or more heater sections, and the power controller may be configured for selectively energizing one or more of the heater sections.

[0013] The power controller may be configured for synchronizing increased power input to the heater with increased load on the vapor jet pump. Preferably, the control parameter is representative of load on the vapor jet pump.

[0014] According to another aspect of the invention, a method is provided for vacuum pumping of a process chamber. The method comprises the steps of vacuum pumping a process chamber with a vapor jet pump having a boiler including a heater, and automatically controlling power supplied to the heater in response to at least one control parameter that is representative of load on the vapor jet pump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

[0016] FIG. 1 is a cross-sectional view of a prior art vapor jet vacuum pump;

[0017] FIG. 2 is a block diagram of a process control system incorporating a vapor jet vacuum pumping system in accordance with an embodiment of the invention;

[0018] FIG. 3A is a block diagram of an embodiment of a power controller that responds to a programmed sequence of power levels;

[0019] FIG. 3B is a timing diagram that illustrates an example of a programmed sequence of power levels;

[0020] FIG. 4A is a block diagram of an embodiment of a power controller that responds to a sensed pressure;

[0021] FIG. 4B is a graph of a first example of a control function that defines pump power as a function of sensed pressure;

[0022] FIG. 4C is a graph of a second example of a control function that defines pump power as a function of sensed pressure; and

[0023] FIG. 5 is a block diagram of an embodiment of a power controller that responds to one or more control signals from a process control system.

DETAILED DESCRIPTION OF THE INVENTION

[0024] A cross-sectional diagram of an example of a prior art vaporjet vacuum pump is shown in FIG. 1. Major components of the vapor jet pump include a housing 10, a boiler 12 and a jet assembly 14. The housing 10 includes a generally cylindrical shell 20 which defines an interior region 22, and a foreline conduit 24, which defines a foreline 28. An inlet 26 to interior region 22 is formed at one end of shell 20. A cold cap 27 mounted in inlet 26 suppresses overdivergent flow, as known in the art. The boiler 12 is sealed to the opposite of end of shell 20. The housing 10 further includes cooling fins 30, which are spaced apart from each other and which have a generally annular shape, and an inlet flange 32 for attachment of the pump to a vacuum chamber. A foreline conduit 24 includes a foreline flange 34 for attachment to a suitable conduit. Foreline conduit 24 is typically attached to a roughing pump. A baffle 36 located in foreline conduit 24 improves condensation and inhibits loss of oil vapor passing through foreline 28.

[0025] The boiler 12 includes a boiler housing 40 having an end plate 42 sealed to the end of shell 20 and a fin structure 44 that extends upwardly from end plate 42 into interior region 22. The fin structure defines a cylindrical compartment for mounting a heater 50. The boiler housing 40 is positioned within a cylindrical wall 52 of jet assembly 14. A liquid reservoir 54 is located between boiler housing 40 and the cylindrical wall 52 of jet assembly 14. A cylindrical shell 56 surrounds fin structure 44 and helps to control the temperature of fin structure 44 during operation. The boiler 12 may be surrounded by insulation 58 external to shell 20.

[0026] The jet assembly 14 has a generally cylindrical configuration which defines a central passage 60 that carries vapor from boiler 12 to a first annular pumping stage 62 and to a second annular pumping stage 64. An ejector stage is formed by a nozzle 66 that passes through a wall of jet assembly 14 and is aligned with foreline 28.

[0027] In operation, a liquid, such as oil, in reservoir 54 is vaporized by heater 50. The vapor passes upwardly through passage 60 to pumping stages 62 and 64. Each of the pumping stages 62 and 64 has an annular opening which directs the vapor outwardly and downwardly in a generally conical vapor jet. The vapor in each vapor jet is condensed by the relatively cool cylindrical outer shell 20, and the condensed vapor returns to liquid reservoir 54. The vapor jets drag the gas molecules from the vacuum chamber to which the pump is attached, thereby vacuum pumping the chamber. The pumped gas molecules are exhausted through foreline 28. The upper portion of cylindrical shell 20 is typically cooled by a cooling fan (not shown), which may be part of the vapor jet pump or may be part of the equipment in which the vapor jet pump is utilized. Water cooling is normally used for larger pumps.

[0028] A thermal switch 70, mounted on a block 72 that is integrally formed with shell 20, maybe used indicate when the liquid is vaporized and the pump is ready for operation. A second thermal switch (not shown) mounted on block 72 adjacent to thermal switch 70 may be used to indicate an abnormal temperature condition.

[0029] A block diagram of a process control system incorporating a vapor jet pumping system in accordance with an embodiment of the invention is shown in FIG. 2. A process chamber 110 is vacuum pumped by a vapor jet pump 112. The foreline of the vapor jet pump 112 is connected to a roughing pump 114. A process controller 116 controls a process in process chamber 110. A power controller 118 automatically controls the power supplied to vapor jet pump 112 as described in detail below.

[0030] As shown in FIG. 2, power controller 118 supplies controlled pump power to vapor jet pump 112. More particularly, power controller 118 supplies controlled pump power to heater 50 (FIG. 1) of vapor jet pump 112. The power controller 118 may receive control inputs from an external source, such as an operator or a host computer, from process controller 116, from a pressure sensor 120 in process chamber 110, or from a combination of these sources to control the power supplied to vapor jet pump 112. Power controller 118 controls the heater power for vapor jet pump 112 in response to at least one control parameter. Preferably, the control parameter is representative of the gas load on the vapor jet pump 112. The control parameter permits the power to be increased when the load is relatively high and permits the power to be decreased when the load is relatively low. The control is automatic in response to the control parameter or parameters. Embodiments of the power controller 118 with different control parameters are described with reference to FIGS. 3A, 3B, 4A, 4B, 4C and 5.

[0031] Referring to FIG. 3A, power controller 118 receives a programmed sequence of power levels as a function of time. The programmed sequence can be provided by process controller 116 (FIG. 2) or by an external source and can be stored in power controller 118. The programmed sequence is based on knowledge of the probable load on vapor jet pump 112 as a function of time during a specified process. It will be understood that the values of the programmed sequence, such as power levels and times, can be adjusted, or a new program sequence can be input to power controller 118. Furthermore, power controller 118 may store two or more programmed sequences of power levels, which correspond to different process conditions. Power controller 118 also receives a start signal to initiate the programmed sequence.

[0032] An example of a simple programmed sequence is shown in FIG. 3B, where pump power is plotted as a function of time. The sequence is initiated at time To, and pump power changes are programmed to occur at times T1, T2 and T3. The example of FIG. 3B utilizes a number of discrete pump power levels. This embodiment may be useful where the heater in the vapor jet pump 112 has several sections, one or more of which may be energized. It will be understood that the number of power levels and the times at which the power levels change may be varied to suit a particular application.

[0033] Referring to FIGS. 4A and 4B, power controller 118 controls power supplied to vapor jet pump 112 in response to a sensed pressure. As shown in FIG. 2, a pressure sensor 120 located in process chamber 110 provides a pressure signal to power controller 118 that is representative of the pressure in process chamber 110.

[0034] As illustrated in FIG. 4B, the power level supplied to the heater of vapor jet pump 112 may be increased as the sensed pressure in process chamber 110 increases. The increased pressure is indicative of an increased gas load on vaporjet pump 112. FIG. 4B illustrates an embodiment where the power level supplied to the heater in vapor jet pump 112 is a continuous function of the control parameter (sensed pressure) over a range of values. A time delay typically occurs between a sensed pressure increase and an increase in pumping capacity as a result of the increased power input. Accordingly, this approach, when utilized alone, is most useful for applications that are not sensitive to temporary pressure increases.

[0035] An embodiment of the power controller 118 wherein the pump power level is a discrete function of sensed pressure is illustrated in FIG. 4C. When the sensed pressure exceeds a pressure P0, the pump power increases to a first level, and when the sensed pressure exceeds a pressure P1, the pump power increases to a second level higher than the first level. In the embodiment of FIG. 4C, the power level increases in steps at specified pressure levels.

[0036] Referring to FIG. 5, power controller 118 controls the power supplied to vapor jet pump 112 in response to one or more control signals from process controller 116 (FIG. 2). The control signals from process controller 116 may supply specific pump power levels to power controller 118 or may command an increase or decrease in pump power level. The control signals are based on knowledge by process controller 116 of the load likely to be imposed on vapor jet pump 112 during a particular process or a step of a process.

[0037] In other embodiments, the power controller 118 may be configured for controlling the power supplied to vapor jet pump 112 in response to more than one control parameter. In one embodiment, the power controller 118 may control pump power in response to a programmed sequence of power levels and a sensed pressure level. Thus, for example, the power controller 118 may proceed according to the programmed sequence unless the sensed pressure exceeds a predetermined value. In this case, the sensed pressure overrides the programmed sequence and causes a pump power increase to reduce the pressure in process chamber 110 to a desired level. In another embodiment, the power controller 118 may control pump power in response to a programmed sequence and control signals from process controller 116. In this case, the power controller operates in accordance with the programmed sequence until a control signal is received from process controller 116. The control signal may indicate, for example, that the power supplied to vapor jet pump 112 may be reduced due to a delay in the process. It will be understood that many different control parameters and many different combinations of control parameters may be utilized within the scope of the invention. In general, the goal is to reduce the power consumption by vapor jet pump 112 without significantly degrading performance.

[0038] The power controller 118 may include control circuitry for implementing a desired control function in response to the control parameter and may further include power components for controlling AC power supplied to the heater of the vapor jet pump according to the control function. For example, the power controller 118 may include a programmed microprocessor and triac power control devices, which are controlled by the microprocessor. The microprocessor is programmed to implement a desired control function as a function of the control parameter, as shown by way of example in FIGS. 3B, 4A and 4B. In the case of a programmed sequence, the microprocessor stores the programmed sequence and controls the pump power in accordance with the sequence. In the case of an input control signal or sensed pressure, the microprocessor controls the pump power in accordance with a programmed control function.

[0039] Having described this invention in detail, those skilled in the art will appreciate that numerous modifications may be made of this invention without departing from its spirit. Therefore, it is not intended that the breadth of the invention be limited to the specific embodiment illustrated and described. Rather, the breadth of the invention should be determined by the appended claims and their equivalents.

Claims

1. A vapor jet vacuum pumping system comprising:

a vapor jet pump having an inlet port, an exhaust port, a jet assembly and boiler, said boiler including a heater; and

a power controller for automatically controlling power supplied to said heater in response to at least one control parameter.

2. The vapor jet vacuum pumping system as defined in claim 1, wherein the control parameter comprises a programmed sequence of power levels.

3. The vapor jet vacuum pumping system as defined in claim 2, wherein the programmed sequence of power levels is adjustable.

4. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for controlling power supplied to said heater in response to a sensed pressure in a process chamber being pumped by said vapor jet pump.

5. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for controlling power supplied to said heater in response to control signals from a process control system.

6. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for controlling power supplied to said heater in response to a combination of two or more control parameters.

7. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for controlling power supplied to said heater at one of two or more discrete power levels.

8. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for controlling power supplied to said heater over a continuous range of power levels.

9. The vapor jet vacuum pumping system as defined in claim 1, wherein said heater includes two or more heater sections and wherein said power controller is configured for selectively energizing one or more of said heater sections.

10. The vapor jet vacuum pumping system as defined in claim 1, wherein said power controller is configured for synchronizing increased power input to said heater with increased load on said vapor jet pump.

11. The vapor jet vacuum pumping system as defined in claim 1, wherein said control parameter is representative of load on said vapor jet pump.

12. A method for a vacuum pumping of a process chamber, comprising the steps of:

vacuum pumping a process chamber with a vapor jet pump having a boiler including a heater; and

automatically controlling power supplied to said heater in response to at least one control parameter that is representative of load on the vapor jet pump.

13. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater in accordance with a programmed sequence of power levels.

14. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater in response to sensed pressure in the process chamber.

15. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater in response to control signals from a process control system.

16. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater in response to a combination of two or more control parameters.

17. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater at one of two or more discrete power levels.

18. The method as defined in claim 12, wherein the step of controlling power comprises controlling power supplied to said heater over a continuous range of power levels.

19. The method as defined in claim 12, wherein said heater includes two or more heater sections and wherein the step of controlling power comprises energizing one or more of said heater sections.

20. A method for controlling a vapor jet pump having an inlet port, an exhaust port, a jet assembly, and a boiler, said boiler including a heater, the method comprising:

automatically controlling power supplied to the heater in accordance with a control algorithm.