Data processing: generic control systems or specific application – Specific application – apparatus or process – Mechanical control system
Reexamination Certificate
1998-12-07
2001-05-01
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Mechanical control system
C454S052000
Reexamination Certificate
active
06226568
ABSTRACT:
TECHNICAL FIELD
This invention relates to the technology for balancing air flows and pressure drops throughout a series of interconnected painting cells of a conveyorized paint shop or booth, and more particularly to a two-part balancing technique which first sets the exhaust flow parameters, and secondly sets the supply flow parameters to produce desired downdrafts and cross-flows within the shop or booth.
DISCUSSION OF THE PRIOR ART
A typical automotive paint spray booth contains a series of adjacent treating cells each having its own requirements for air flows therethrough. The large number of flow control elements (i.e. fans, dampers, exhaust venturi adjustment) which may be in series or in parallel, are used to create multiple down drafts and cross-flows which vary among the cells. To achieve balanced air flows through the entire paint booth, the prior art has essentially used a sequential technique wherein existing supply, exhaust and cross-flows volumes are measured and one or more parts of the control system is adjusted sequentially. After such one part is adjusted, the flows are then remeasured, and other parts of the control system are adjusted. These steps are repeated as often as necessary to approach a balanced condition. However, the system can never achieve absolute balance by this technique because adjustment of one part of the system always unbalances another part of the system. This then becomes a hunting approach which is not optimum in efficiency and results.
For example, in choosing a part of the system to first adjust, adjustment of the fan speed is often first attempted; linear fan speed assumptions are made (using the manufacturer's fan speed curves) which assumptions fail to take into consideration environmental and associativity effects on fan speed as a result of the system in which it is placed. If the supply or exhaust fan speed values are too high or to low, as a result of the first try, other guesses are made as to how the fan speed should be changed, which subsequent guesses lead to numerous try and fail adjustments, never attaining the optimum set of balanced air flows through the several cells.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a method for rapidly balancing air flows in a complex paint spray booth, by use of perturbation data that will allow an operator to quickly set an accurate exhaust fan speed and venturi gap at each cell outlet, and thence to quickly set an accurate supply fan speed along with accurate damper positions to achieve a balanced cross-flow condition.
In a first aspect, the invention is a method of rapidly balancing air flows in a complex paint spray booth having a series of cells supplied by a common air flow that is pushed by an adjustable speed supply fan and then divided into downdrafts for each of the cells accompanied by cross-flows between the cells, the downdrafts and cross-flows converging into an exhaust flow drawn by an adjustable speed exhaust fan, the system having control elements for changing the downdrafts and/or cross-flows, and having means for passing the exhaust flow through a waste paint water scrubber having an adjustable venturi gap width, the method comprising;
(a) setting an exhaust fan speed and venturi gap by correlating perturbed exhaust air flow rate data with a desired exhaust air flow rate at-a desired exhaust pressure drop across the venturi gap to establish a target fan curve as a function of pressure drop and exhaust flow rate, the setting for the fan speed and venturi gap width being derived from such curve; and
(b) setting a supply fan speed in positions for each cross-flow damper by solving an objective optimization function for the sum of the cross-flows by using perturbed supply fan speed values and cross-flow rate values that establishes, distinct optimum cross-flow velocities at a specific common air supply velocity from which supply fan speed and cross-flow damper positions can be derived.
In a second aspect, the invention is a method for more rapidly balancing air flows in a paint booth system having a series of cells supplied by an air flow that is pushed by an adjustable speed supply fan and then divided into downdrafts for each of the cells including cross-flows between cells, the downdrafts and cross-flows converging into an exhaust flow drawn by an adjustable speed exhaust fan, the system having control elements for changing the downdraft and/or cross-flows, and having means for passing the exhaust flow through a waste paint water scrubber having an adjustable venturi gap width, the method comprising; (a) changing the exhaust flow rate by (i) collecting exhaust flow data by choosing and calculating a target exhaust air flow rate, and then measuring the actual initial operating exhaust air flow rate, as well as measuring the initial operating pressure operating drop of the exhaust flow across the venturi gap width, (ii) finding an adjusted speed for the exhaust fan and an adjusted width for the venturi gap that meets the target exhaust volume air flow rate by correlating measured perturbed exhaust flow and perturbed venturi pressure drop data to the target and initial operating data for the exhaust flow and venturi, and (iii) setting the exhaust fan speed according to such findings, (b) changing the down drafts and cross-flows by (i) choosing and calculating data for target downdraft and cross-flow rates, as well as booth pressurization values, (ii) measuring actual downdraft and cross-flow rates and booth pressurization values, by perturbing one or more control elements to generate downdraft and cross-flow rate data, as well as booth pressurization data, (iii) calculating an optimized combination of control elements effecting downdrafts and cross-flows at a target booth pressurization, the calculations using an objective function to simultaneously satisfy all of the target downdrafts and cross-flow rates, and (iv) adjusting the control elements according to the optimized calculation to obtain a balanced system.
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Filev Dimitar
Liu Yu-Ning
Tong Ernest Henry
Grant William
Hartman Jr. Ronald D
Porcari Damian
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