Automatic temperature and humidity regulation – Motors – Electric
Reexamination Certificate
2003-05-16
2004-08-31
Norman, Marc (Department: 3744)
Automatic temperature and humidity regulation
Motors
Electric
C236S09100C, C236S012120, C700S042000
Reexamination Certificate
active
06783080
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems and methods for controlling process equipment temperatures, and more particularly to operator and automatically controllable digital systems for versatile modular based temperature control units.
BACKGROUND OF THE INVENTION
Digital control systems for process equipment and tools that are used for complex manufacturing procedures are known and in use in a wide variety of practical applications. Often, such systems are used to maintain one or a number of operating parameters at chosen static or variable setpoints during an operation or process. Control algorithms are used to interrelate sensed variables to target conditions, and to bring a controlled parameter to a chosen setpoint.
An important example of this use of control systems is in the operation of temperature control units (TCU) which heat or cool, in selectable fashion, one or more particular subunits of cluster tools employed in semiconductor fabrication. For some semiconductor fabrication process tools, TCU's may have to refrigerate or heat at different levels, changing levels when needed for the process. Usually, the temperature control is accomplished by circulating a thermal transfer fluid through the tool at temperatures and flow rates suitable for each given operating setpoint. Because cluster tool capital equipment and operating costs are very high, the temperature control units and their associated digital control systems must operate with maximum reliability and minimum down time. Moreover, steady state operation at a given temperature level is often required to be very precise while transition or ramp times between different steady state levels are desirably as short as possible.
Operation of such systems in practice, however, entails much more than operating stability and minimization of transition intervals. Initial installation, system setup, system monitoring and adjustment, trouble-shooting and field service are all factors which affect the economics and eases of use. In addition, TCU types and capabilities can vary substantially for a given cluster tool installation. For example, a new multi-TCU system has been introduced which is based on a modular approach in which different but interchangeable TCU modules are used. The modules each have at least two and up to four functional capabilities including both heating and cooling, and can have substantially different thermal capacities. Such TCU modules can control different subunits in a cluster tool, while meeting operational needs economically and in a space efficient manner. This approach also minimizes field service problems because troublesome and defective modules may quickly be replaced and either serviced on site or shipped to a common service facility. Generally, the different modular TCU's each have both heating and cooling capability, which can be exercised at the same time or independently.
A control system and method for operating different modules concurrently in different modes must present the options in such a way that the operator can be guided through the setup sequence and make needed choices without extensive pre-education or specialization. After setup, the operation should also be assisted with information at to real time operating conditions, significant changes in conditions, warning of problems and guidance as to how they can be resolved. Changes in the modular setup should be accommodated, and the control system should also be responsive to remote commands from a host system.
The digital control systems used for process control applications, being the process variable to a chosen operating setpoint and thereafter maintain the target setpoint with a closed loop servo approach. For improved response the servo loop follows a control algorithm, such as the PID (proportional, integral and derivative terms) algorithm to bring a process variable to a target level. A typical modern system using an algorithm of this type is designated model S7-200 and is a product of the Siemens Company. This digital control system includes programmed logic circuits, memory and software, together with various sensed inputs, for exercising the PID control algorithm. It operates in scanning sequences and includes expansion modules so that more than one process variable can be controlled concurrently. This control systems is not, by itself, capable of meeting more demanding requirements, such as those imposed on TCU's employed for control of semiconductor fabrication tool processes. For semiconductor fabrication processes, it is essential that steady state temperatures be very precisely maintained, but that transitions between different temperature levels be rapid. The heating and cooling capabilities must be used in making these changes, with maximum power efficiency. In addition, environmental and other variables which can arise must be compensated for. Because of the high capital and operating costs involved in semiconductor fabrication facilities, the system should also be capable of communicating information as to status and operating conditions, non-standard conditions, setup, warnings and alarms. Preferably, it should also automatically terminate operations when necessary.
SUMMARY OF THE INVENTION
A control and display system in accordance with the invention for a reconfigurable and complex control system having multiple control units accepts a variety of real time inputs and setpoints and generates commands for commanding individual units to regulate process variables. The commands are variable with time and based upon adaptive control algorithms which are responsive to changing operative and environmental conditions. The control system is particularly adapted for use with multi-module TCUs for cluster tools used in semiconductor fabrication, but is of applicability to other process and equipment meeting similar complex requirements.
It employs a scalable digital control system having a programmable logic controller, together with control and display software for setup, monitoring operator assistance and alarms. Using a touch screen and display unit, the system provides instinctively selectable, organized and unambiguous visual displays that facilitate selection and monitoring of operations. The operator, through observation of historical performance or by using known starting values, can provide initial setpoints for proportional, integral and derivative terms from which the dual adaptive control algorithm undertakes concurrent interrelated control of heating and cooling capabilities. While receiving data as to rate changes and historical changes in the process variables, ambient and cooling medium temperatures the system responds to temperature oscillations by making adjustments in the integral terms in both the dual algorithms. Also, bias values are changed in the heating algorithm in accordance with cooling medium changes.
The dual control algorithms are defined by data stored in the programmable logic controller associated with the data processor, an external section of the controller being changeable so that new programming can be used. Because use of the two oppositely directed thermal exchange capabilities (heating and cooling) is integrated, the heating algorithm is reset and no heating energy is supplied during cooling and non-transitional periods when the actual temperature is less than 0.2° C. below the setpoint. However, above that threshold the heating algorithm is reinstated, and a small bias value is added to assist the cooling function on maintaining the target level. Thus at the steady state temperature the heating capability and cooling capability are used concurrently in such fashion as to maintain the thermal transfer fluid at ±0.1° C. relative to the target level. The system control thus operates with high energy efficiency even though heating and cooling may be used concurrently in steady state. The ramp up or down from one temperature level to another is accomplished rapidly, with minimal undershoot and overshoot. Once temperature setpoint is reache
Antoniou Matthew
Christofferson Bryan
Advanced Thermal Sciences Corp.
Jones Tullar & Cooper PC
Norman Marc
LandOfFree
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