Motors: expansible chamber type – Working member position responsive motive fluid control – Exhaust control
Reexamination Certificate
1999-05-10
2001-01-30
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position responsive motive fluid control
Exhaust control
C092S08500R, C060S414000
Reexamination Certificate
active
06178868
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a decelerating pneumatic circuit for air cylinders used in automated processes.
BACKGROUND OF THE INVENTION
In most applications, air cylinders are used to achieve the sliding, turning or upward and downward motions of some machine component or external load to be processed. In certain lumber making operations cylinder stroking at high speed and frequency is called for where the inertial resistance of the displaced load may be high in relation to the cylinder size.
One concrete example is the case of a lumber trimming saw assembly which, in the modern context of production, must be lowered and lifted by a pneumatic cylinder a number of times per second, through a vertical distance of several inches. Up to very few years ago, the maximum cycling frequency of such an assembly was of the order of 90 cuts per minute, whereas present day applications reach up to twice that number. It can be estimated that, in a high speed lumber trimming application, an industrial class pneumatic cylinder equipped with standard built-in cushions would not last more than a few work shifts before requiring parts replacements. The production losses and the extra maintenance caused by cylinder break-down in the lumber trimming phase is compounded by the number of saw units involved (up to seventeen) in a mill producing 6′ to 16′ lumber with the option of selective trimming in odd or even foot lengths. Since every sawmill must have a trimming operation of sufficient capacity and versatility for the total production and all market requirements, it follows that in order to meet operating conditions, an efficient and reliable means of cushioning the saw cylinder at the end of each stroke becomes a matter of necessity.
Other cylinder cushioning options, such as resilient inserts to prevent metal-to-metal contact of the piston with the cylinder heads, have not proven satisfactory in high cycling operations as the repetitive hammering within the cylinder causes a rapid break-down of the inserts which finally disintegrate and foul-up the valve circuit.
Another cushioning method consists of increasing the compression volume within the cylinder itself, by extending the barrel length beyond the actual piston travel requirements. This can be effective in some applications but not whenever exact positioning of the load at stroke end is necessary, such as in the field of application mentioned above.
OBJECTS AND STATEMENT OF THE INVENTION
It is therefore an object of the present invention to provide an efficient and reliable means of cushioning an air cylinder at each stroke by preventing any impact of the piston with either end of the cylinder.
It is also an object of the present invention to provide a cushioning system as a valuable tool in meeting the requirements of the lumber industry, among others, for high speed and high cycling displacement of inertial loads by means of pneumatic cylinders.
This is achieved by providing a pneumatic valve arrangement controlled by external electrical signals, combined in some applications with additional signals from load position sensors, and comprising pressure surge tanks connected by the valves in such a way as to compress the exhaust flow from the cylinder into said surge tanks and thus cause a deceleration of the cylinder load either throughout the stroke or at the end of it, thus preventing piston impact and cylinder damage. The valve arrangement also causes final exhausting to the atmosphere of the pressure built up at each stroke in the corresponding surge tank so that there is no heat or pressure accumulation at any cycling frequency. The load position sensors may be incorporated in the system to allow valve sequencing causing piston deceleration at any point of its travel, in cases where it would not be efficient to initiate such deceleration from the external signal at the beginning of the stroke.
The present invention therefore defines a system for producing a deceleration at either or both ends of the piston stroke, in a fast actuating, double acting air cylinder, the system broadly comprising:
a) an air pressure supply line to the pressure/exhaust ports of the cylinder;
b) control valve means in the supply line causing piston travel and stroke reversal on receipt of an electrical signal; and
c) an exhaust circuit for each cylinder port including a pressure surge tank; admission and venting valve means connected to the surge tank; the admission and venting valve means causing back pressure to be applied against the piston travel or vented to the atmosphere on receipt of an electrical signal;
the control valve means and the admission and venting valve means causing start and reversal of the piston travel and a controlled deceleration thereof.
In some form of the invention, the system may further comprise signal means consisting of positionally adjustable load position sensors to independently cause the closing of the venting valve means on either pressure surge tank to thereby initiate deceleration at any selected point of the piston travel rather than at the start of this travel.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
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Gagnon Andr{acute over (e)}
Harvey Gilles
Denis Comact Chicoutimi Inc.
Farkas & Manelli PLLC
Look Edward K.
Rodriguez Hermes
Taltavull W. Warren
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