Handling: hand and hoist-line implements – Utilizing fluid pressure – Venturi effect
Reexamination Certificate
2002-02-25
2003-11-11
Lillis, Eileen D. (Department: 3652)
Handling: hand and hoist-line implements
Utilizing fluid pressure
Venturi effect
C294S064300
Reexamination Certificate
active
06644703
ABSTRACT:
FIELD OF INVENTION
The present invention is related to vacuum support systems. More particularly it relates to a self adaptive vacuum support system, employing aerodynamic forces.
BACKGROUND OF THE INVENTION
Vacuum support systems are widely used in many industrial areas. A vacuum support system may serve either to fix an object in place or to hold an object while it is being conveyed from one location to another. Vacuum support systems are widely in used in the Hi-Tech Industries. Holding a wafer during its fabrication process or during deicing in the Semiconductors (SC) industry, holding a Printed Circuit Board (PCR) or a flat-screen during Automatic Optical Inspection (the AOI industry), or holding an aluminum printing-plate to a rotating drum in the Printing or Art-Graphic industries, make just a short list of examples where vacuum support systems are being utilized.
Vacuum support systems employ the pressure difference between a higher ambient pressure that acts on the object upper surface, and the vacuum imposed on the object lower surface. The pressure difference, multiplied by the effective area, makes up the force that holds the object (hereafter referred to as “vacuum-force”). In Conventional systems, the vacuum-force is linearly dependent on both the pressure difference and the effective area.
Conventional vacuum-support systems comprise a vacuum pump fluidically connected by vacuum-pipes to a plurality of drilled cylindrical holes arranged on the system contact surface. In most cases, the contact surface is flat or a cylinder. In many practical cases such simple solution is not acceptable. A common vacuum support system failure occurs when a plurality of vacuum-conduits (i.e. the holes) are present but a significant number of them are not covered because the object to be held is smaller than the vacuum-frame. Another common problem in such systems may occur, when the object is not fully attached to the contact surface, or when the surface of the object has cavities and/or grooves, allowing air to escape through and failing to obtain a substantial vacuum force. In addition, situations where some of the initially closed vacuum-conduits become exposed during the process (such as the dicing process), are very common in the SC industry.
When all the vacuum-conduits are blocked, the parasite mass flow rate (hereafter referred to as MFR), of the air through the conduits is accountable and acceptable, but when a significant number of vacuum-conduits are opened, the parasite MFR severely increases, the vacuum level may critically degrade, and the vacuum-force may be lost. Many improvised solutions had been suggested to reduce the occurrence of parasite MFR: covering the exposed vacuum-conduits before operation, or activating only sectors of the vacuum-frame to introduce the vacuum only to the “active” section of the vacuum-frame, are some of such solutions. However these are only partial semi-effective solutions.
The problem of parasite MFR must be solved in order to achieve reliable vacuum support system. One common way, is to use a powerful vacuum pump to provide the required vacuum level to account for the presence of parasite MFR. Such a solution is expensive (the cost of powerful pump and auxiliary equipment and the wasted energy when the system operates), and occupies unnecessary volume and weight. It may also be a powerful source for significant noise and mechanical vibrations. In particular, the use of a simple vacuum-conduit may result in an unacceptable noise. Simple vacuum-conduits can not sustain internal pressure drops, and, therefore, when the vacuum-conduits are open and subjected to external pressure gap, the mechanism of external pressure relaxation (at the vacuum-conduits exit), may involve noisy jets. In cases where the external pressure gap is sufficiently large, super-sonic (extremely noisy) jets may develop. In such noisy situations the use of vacuum support systems may be questionable, when “quiet room” conditions are required.
Other solutions exist where small diameter vacuum-conduits are used, ending with enlarged effective area, thus MFR is reduced and the required vacuum-force is obtained. Such brute-force solutions severely increase the risk of mechanical blockage by contaminants, being particles or liquid. However, such mechanical blockage results in a loss of the vacuum-force, and it may dramatically increase maintenance expenses. In addition, small diameter vacuum-conduits are characterized by poor time response, including the response to control commands.
Solutions to control the MFR based on using an individual valve-like control device for each of the vacuum-conduit, are not practical, especially when a large number of vacuum-conduits are used. Valves are more expensive, and may involve mechanical or electromechanical means, thus the maintenance task becomes unfeasible. Controlling the parasite MFR must be solved in a favorable way, to meet the practical requirements for a well-functioning vacuum support system.
The Self Adaptive Vacuum Support Apparatus disclosed in the present Invention is based on the SASO concept, as described in detail in our Israeli Patent Application titled SELF ADAPTIVE SEGMENTED ORIFICE (SASO) DEVICE AND METHOD, simultaneously filed with the present application.
The only related prior art references having some relevance to the present invention deal with irrigation emitters only where the fluid passing through it is water which is practically incompressible (as opposed to air or other gases).
U.S. Pat. No. 3,896,999 (Barragan) disclosed an anti-clogging drip irrigation valve, comprising a wide conduit equipped with a plurality of partition means, integrally formed with the conduit wall, forming labyrinth conduits, in order to reduce the water pressure prior to its exit through the labyrinth conduits outlet.
U.S. Pat. No. 4,573,640 (Mehoudar) disclosed an irrigation emitter unit providing a labyrinth conduit similarly to the valve in U.S. Pat. No. 3,896,999. Examples of other devices providing labyrinth conduits for the purpose of providing a pressure drop along the conduit can be found in U.S. Pat. No. 4,060,200 (Mehoudar), U.S. Pat. No. 4,413,787 (Gilead et al.). U.S. Pat. No. 3,870,236 (Sahagun-Barragan), U.S. Pat. No. 4,880,167 (Langa), U.S. Pat. No. 5,620,143 (Delmer et al.), U.S. Pat. No. 4,430,020 (Robbins), U.S. Pat. No. 4,209,133 (Mehoudar), U.S. Pat. No. 4,718,608 (Mehoudar), U.S. Pat. No. 5,207,386 (Mehoudar).
In a labyrinth conduit the aerodynamic resistance is substantially large due to the viscous friction exerted by the walls of the conduit (acting opposite to the direction of the flow), and as the passage becomes tortuous and lengthier (that's the essential feature of a labyrinth) more wall contact surface is acting on the flow, increasing the viscous friction. In some cases cavities are provided for intercepting contaminants and for freeing the flow passage. None of these patents, which basically deal with two dimensional geometry (the third being either very small or degenerated), mention or make use of a vortical aerodynamic blockage mechanism, that is an essential feature of the present invention.
It is emphasized that while the above mentioned patents deal with the delivery of water through the conduit, the present invention seeks to provide and exploit aerodynamically induced vacuum grip force, with the fluid—air in most cases—merely serving as the means for generating this force, and on the other hand reducing the parasite mass flow rate through the conduit when the vacuum grip at the conduit's inlet is lost.
In an article titled “A FLOW VISUALIZATION STUDY OF THE FLOW IN A 2D ARRAY OF FINS” (S. Brokman, D Levin, Experiments in Fluids 14, 241-245 (1993)) a study of the flow field in a 2D arrangement of fins was carried out by means of flow visualization in a vertical flow tunnel. The study was related to an earlier studies that examined the fin arrangement as a conceptual heat sink. The above mentioned study went further to examine the complex flow field structure in order to obtai
Levin Daniel
Yassour Yuval
Chin Paul T.
Core Flow Ltd.
Dippert William H.
Lillis Eileen D.
Reed Smith LLP
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