Motors: expansible chamber type – With motive fluid valve – For double-acting motor
Reexamination Certificate
2001-08-30
2003-09-30
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
For double-acting motor
C091S466000
Reexamination Certificate
active
06626082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a table feed system for moving and positioning a feed table of a machine tool.
2. Description of the Related Art
Concerning a table feed system for moving and positioning a feed table of a machine tool, a motor-driven type table feed system, in which a servo motor and a ball screw are combined with each other so as to conduct numerical control (NC control), is commonly used at present. In the case where high accuracy, high output and high rigidity are required for cutting and grinding in the operation of a machine tool, it is necessary to use a large-scale, complicated and expensive table feed system. When mirror face work is conducted in the field of precision work, feed marks, which are caused by the feed command, are transferred onto the work face. Therefore, quality of the mirror face is impaired.
On the other hand, concerning the hydraulic type table feed system, although the hydraulic type table feed system is small-scale and the output is high, its structure can be made simple. However, the energy transmission medium used in this system is a liquid such as a hydraulic fluid. Since liquid has compressibility and relatively high viscosity, it is not appropriate as an energy transmission medium to be used in numerical control in which a high response property is generally required. Therefore, at present, the hydraulic type table feed system is not often applied to a system in which highly accurate table feed is required. Especially, the hydraulic type table feed system is seldom used in the table feed system of a machine tool, the operation speed of which is high, in which high accuracy, of the micron order, is required.
However, as one of the few examples in which a hydraulic cylinder is applied to the table feed system of a machine tool for precision work, Japanese Unexamined Patent Publication No. 8-150527 discloses a technique for a hydraulic type table feed system. In this example, as a means for preventing feed marks from being transferred onto a work face in the process of mirror face work, a static pressure bearing for supporting a piston rod is combined with a hydraulic cylinder, and a static pressure coupling is interposed between the piston rod and the feed table. Due to the above structure, the feed table can be smoothly moved, so that the generation of feed marks, which are caused by pulsation of the hydraulic pressure and fluctuation of the piston shaft, can be prevented. However, the piston feed control system is the conventional flow rate control conducted by a proportional valve and others. Therefore, it is possible to realize a smooth feeding motion by this prior art, however, it is impossible to obtain a high positioning accuracy. The prior art has the above problems of controllability.
As the prior art, and to enhance controllability, Japanese Unexamined Patent Publication No. 58-82643 discloses a table feed system in which pneumatic pressure is utilized. According to this technique, a feed table is pulse-driven by ON-OFF valves, which can be easily controlled by a computer, so that a highly accurate feed motion can be accomplished. According to this table feed system, it is possible to enhance the positioning accuracy, however, feed marks appear on a work face because the feeding waveform is step-like.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above problems of the prior art by a new means. The first object of the present invention is to provide a table feed system for a machine tool, at low cost, which is capable of smoothly moving a table so that a mirror face can be made by realizing a highly accurate feed motion conducted by a pulse drive of high controllability by using a computer.
Specifically, the second object of the present invention is to extend control ranges of the feed speed and of the resolution by making a flow rate of hydraulic fluid to a hydraulic cylinder, for operating a table feed system, very small.
In the table feed system of the present invention, a pair of hydraulic chambers, one being arranged on the right and the other being arranged on the left, are formed in at least one hydraulic cylinder corresponding to the moving direction, to right and left, of the table feed of a machine tool, and a pressure adjusting mechanism is arranged, by which pressure of hydraulic fluid in each hydraulic chamber can be independently adjusted. The characteristic of this table feed system is described as follows. Pressure in the hydraulic chambers, one being arranged on the right and the other being arranged on the left, is independently increased and decreased by the pressure adjusting mechanism. When the piston is moved to the right and the left by the pressure difference between the hydraulic chambers, a time difference occurs between periods in which the pressure adjusting mechanism conducts an adjustment of pressure on the respective hydraulic chambers.
When a time difference occurs between periods in which the pressure adjusting mechanism conducts an adjustment of pressure on the respective hydraulic chambers as described above, when pressure in one hydraulic chamber is increased, pressure in the other hydraulic chamber is not simultaneously decreased. Therefore, at first, the piston is moved to a position at which pressure in both hydraulic chambers becomes an equilibrium condition. After that, when pressure in the other hydraulic chamber is decreased, the piston is moved to a position at which the decreased pressure in the other hydraulic chamber and pressure in one hydraulic chamber become an equilibrium condition. According to the increase and decrease in pressure in the right and the left hydraulic chamber, which are made with a time difference, the piston is smoothly moved little by little. Accordingly, even when a pressure adjusting mechanism such as a common electromagnetic valve, the minimum opening and closing period of which is long, is used, it is possible to obtain the same effect as that of a case in which the valve is opened for a period of time shorter than the minimum valve opening period. Therefore, it is possible to obtain a high controllability by an inexpensive system of a simple structure. Further, it is possible to finely adjust a flow rate of hydraulic fluid to the hydraulic cylinder by a pressure adjusting mechanism such a common electromagnetic valve. Therefore, highly accurate positioning can be done by a simple structure. Accordingly, ranges of controlling the feed speed and the resolution can be extended.
This table feed system utilizes hydraulic pressure, which has seldom been used in recent years. However, this table feed system can be formed into a digital system when valves composing the pressure adjusting mechanism are subjected to duty control by a stream of pulse signals. Therefore, controllability by the computer is high, and it is possible to provide the same effect as that of a case in which a valve, the minimum valve-opening period of which is very short, is used. Accordingly, a highly accurate feed can be easily realized at low cost. This table feed system utilizes hydraulic pressure and is different from the conventional motor-driven digital system. Therefore, due to a slight compressibility of hydraulic fluid, step portions of displacement are chamfered, so that a smooth motion can be made. Accordingly, in the process of machining or drilling, it is possible to reduce a sudden change in a load given to a cutting tool. Further, the hydraulic system is advantageous in that the damping property is high. Therefore, the hydraulic system can provide an effect that the occurrence of chatter marks is prevented.
This table feed system is characterized in that a time difference is provided between the time at which pressure adjustment is conducted on the right hydraulic chamber and the time at which pressure adjustment is conducted on the left hydraulic chamber. As an embodiment, it is possible to provide a phase difference between the duty control of the hydraulic fluid inflow valve
Kojima Hisatoshi
Morita Hiromichi
Muto Takayoshi
Ohashi Goshin
Tsuchiya Sojiro
Denso Corporation
Lazo Thomas E.
Posz & Bethards, PLC
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