Motors: expansible chamber type – Moving cylinder
Reexamination Certificate
2002-09-12
2004-09-14
Lazo, Thomas E. (Department: 3745)
Motors: expansible chamber type
Moving cylinder
C091S36300A
Reexamination Certificate
active
06789457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas pressure actuator, particularly to an air pressure actuator and a method for controlling the air pressure actuator.
2. Description of the Related Art
As an air pressure actuator, there has been one which was suggested by the inventors of the present invention and is shown in FIG.
1
. Referring to
FIG. 1
, such an air pressure actuator comprises a guide shaft
14
extending in one axial direction with both ends thereof fixed on a pair of support members
18
, and a slider
13
movable along the guide shaft
14
. In fact, the slider
13
is a cylindrical hollow body which is so formed that it can cover up part of the guide shaft
13
. In this way, a cylinder space is formed between the inner surface of the slider
13
and the outer periphery surface of the guide shaft
14
. Practically, such a cylinder space is used as a pressure chamber. In more detail, the cylinder space has been divided (in its axial direction) into two pressure chambers
16
A and
16
B by virtue of a pressure receiving plate (partition wall)
17
fixed on the internal wall of the slider
13
. Accordingly, both the pressure receiving plate
17
and the slider
13
are slidable along the guide shaft
14
.
On both sides of the guide shaft
14
are provided a plurality of static pressure air bearings
12
arranged to be separated from one another at a predetermined interval in the circumferential direction. Practically, these static pressure air bearings
12
are connected with an air pressure source
10
through a regulator
11
A. For this purpose, a plurality of air passages are formed in the guide shaft
14
and communicated with the static pressure air bearings
12
. However, since each of the static pressure air bearings is a well-known bearing in the art, a detailed explanation as to the structure thereof will be omitted in this specification.
On both sides of the guide shaft
14
and with the two pressure chambers
16
A,
16
B are connected intake/exhaust systems for introducing a compressed air into the pressure chambers or for discharging the same therefrom. To ensure such an air instruction and discharge, a plurality of air passages, which are independent from the above air passages for use with the static pressure air bearings, are formed in the guide shaft
14
, extending from both ends of the guide shaft to the pressure chambers
16
A and
16
B The intake/exhaust systems are respectively equipped with servo valves
22
A and
22
B so as to form a desired servo control. These servo valves
22
A and
22
B are all connected to the air pressure source
10
through a regulator
11
B.
In this way, an air which is supplied from the air pressure source
10
and whose pressure has been properly regulated by the regulator
11
A can be supplied to the static pressure air bearings
12
. By virtue of the compressed air blown out of the static pressure air bearings
12
, the slider
13
will float from the guide shaft
14
, enabling the slider
13
to move with respect to the guide shaft
14
without touching it. For this reason, there would be no sliding resistance during the movement of the slider
13
. Further, a position sensor
15
based on a linear scale or the like is used to detect the position of the slider
13
, and to produce an electric signal representing the slider's position. The detected position signal fed from the position sensor
15
is then fed to a controlling and computing device
20
.
The controlling and computing device
20
performs control and computation based on the inputted position information and outputs position instruction signals to servo amplifiers
21
A and
21
B. At this time, the instruction values to be fed to the servo amplifiers
21
A and
21
B are those having the same absolute values but opposite signs.
The servo valves
22
A and
22
B receive the supply of a compressed air which has been regulated by the regulator
11
B to an appropriate pressure, while the flow rate of an air flowing through each of these valves can be changed depending on the position of a spool within each of the servo valves
22
A and
22
B. Air flows which have passed through the servo valves
22
A and
22
B are supplied to the pressure chambers
16
A and
16
B formed within slider
13
. As a result, a pressure difference occurs between the pressure chamber
16
A and the pressure chamber
16
B, and such a pressure difference acts on the pressure receiving plate
17
provided on the internal wall of the slider
13
, causing the slider
13
to move in one of the two directions.
Since the air pressure actuator described above can control a large amount of output with a compact structure, it has been expected to be used as an actuator for performing a positioning between any two points. However, when performing a continuous positioning, such an air pressure actuator has been found to be difficult in performing a stabilized control, because a dynamic characteristic change and the like based on the position of the pressure receiving plate are non-linear. Consequently, it is difficult to obtain an effective long stroke with respect to a mechanical stroke of the slider. This is because whenever the position of the pressure receiving plate is changed within the pressure chambers, the pressures within the pressure chambers will also change, hence bringing about an undesired influence to a stabilized control.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved gas pressure actuator based on a gas pressure actuator whose slider is driven by a gas pressure using two servo valves, which is characterized in that its dynamic characteristic change depending on the position of the slider can be compensated, so as to effect a stabilized control of the slider within the stroke thereof. Further, it is another object of the invention to provide an improved method for controlling the gas pressure actuator described above.
A control method according to the present invention can be suitably applied to a gas pressure actuator described hereunder. The gas pressure actuator includes a guide shaft and a slider movable along the guide shaft, and a pressure receiving plate provided on one of the guide shaft and the slider to form a cylinder chamber between the outer surface of the guide shaft and the internal surface of the slider and to define the cylinder chamber into two pressure chambers arranged side by side in the slider moving direction. The gas pressure actuator is constructed in a manner such that a compressed gas is introduced into or discharged from the two respective pressure chambers by way of servo valves, so as to use a pressure difference between the two pressure chambers to drive the slider. Further, the gas pressure actuator includes a position sensor for detecting the position of the slider, two servo amplifiers for controlling the servo valves, and a controlling and computing device for receiving a position detection signal fed from the position sensor and for producing position instruction values to the two servo amplifiers.
According to an aspect of the present invention, the method comprises the steps of: performing a computation on each of the position instruction values to be fed to the two servo amplifiers, so as to compensate for a pressure change which has occurred in each of the pressure chambers due to a change in the position of the pressure receiving plate in the cylinder chamber; and producing position instruction values to the two servo amplifiers.
A gas pressure actuator according to the present invention is characterized by incorporating an improved controlling and computing device which performs the following steps. Namely, the controlling and computing device performs the steps of: differentiating a slider position represented by a detected position signal, and calculating the velocity of the slider, meanwhile differentiating the calculated velocity so as to calculate an acceleration; using a slider target position, said slider position, said v
Makino Fuminori
Sakaki Kazutoshi
Arent & Fox PLLC
Lazo Thomas E.
Sumitomo Heavy Industries
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