The present disclosure relates to pneumatic actuators.
The pneumatic actuator has a simple structure compared to other actuators and has the advantages of being inexpensive and lightweight. In addition, the pneumatic actuator can easily generate a large force. Furthermore, the air used by the pneumatic system is inexhaustible and clean. For these reasons, pneumatic systems using pneumatic actuators are used in assembly devices and transport devices in various factories such as automobiles, semiconductors, and foods. Further, unlike an electric actuator, a pneumatic actuator does not generate a magnetic field or an electric field and is therefore suitable for applications that avoid a magnetic field or an electric field.
On the other hand, the pneumatic actuator has a disadvantage of low energy efficiency because it is necessary to release compressed air to the atmosphere as it is. Because of this shortcoming, the movement to replace pneumatic actuators with electric actuators has begun in recent years.
The present disclosure has been made in such circumstances.
One embodiment of the present disclosure relates to a pneumatic cylinder. The pneumatic cylinder includes a first cylinder, a second cylinder and a control valve. The first cylinder includes a first cylinder tube and a first piston that divides the space in the first cylinder tube into two air chambers. The second cylinder includes a second cylinder tube, a second piston that divides the space in the second cylinder tube into two air chambers. The second piston is coupled to the first piston so that the first piston and the second piston have the same displacement. Among two pressure receiving surfaces of the first piston and two pressure receiving surfaces of the second piston, the cross-section area of one of the two pressure receiving surface of the first piston is the smallest, and the cross-section area of one of the two pressure receiving surface of the second piston is the third smallest. The two air chambers of the first cylinder and the two air chambers of the second cylinder are referred to as a first chamber, a second chamber, a third chamber, and a fourth chamber in ascending order in cross-section area, respectively. The control valve is structured to connect an air pressure source to the first air chamber, to connect the second air chamber to the third air chamber, and to open the fourth air chamber to the atmosphere in forward stroke
One embodiment of the preset disclosure also relates to a pneumatic cylinder. The pneumatic cylinder includes a plurality of N (N≥2) cylinders and a control valve. Each of the N cylinders includes a cylinder tube and a piston that divides the space inside the cylinder tube into two air chambers. The pistons of each of the N cylinders are connected so that the displacements are equal, that is, the displacements are interlocked. Among the all pressure receiving surfaces of the pistons of each of the N cylinders, a cross-section area of one pressure receiving surface of the i-th (1≤i≤N) pistons is the (2i−1)th smallest. The two air chambers of each of the N cylinders are referred to as a first air chamber, a second air chamber, . . . , a (2N−1)th air chamber, and a (2N)th air chamber in ascending order in cross-section area, respectively. The control valve is structured (i) to connect the air pressure source to the first air chamber, to open the (2N)th air chamber to the atmosphere, and to connect adjacent pair among the second air chamber through the (2N−1)th air chamber in the forward stroke.
It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth is effective as and encompassed by the present embodiments. Moreover, this summary does not necessarily describe all necessary features so that the disclosure may also be a sub-combination of these described features.
Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
An overview of some exemplary embodiments of the present disclosure will be given. This overview simplifies and describes some concepts of one or more embodiments for the purpose of basic understanding of embodiments, as a prelude to the detailed description described below, and is an invention or disclosure. It does not limit the size. Also, this overview is not a comprehensive overview of all possible embodiments and does not limit the essential components of the embodiment. For convenience, “one embodiment” may be used to refer to one or more embodiments disclosed herein.
The pneumatic cylinder according to one embodiment includes a first cylinder, a second cylinder and a control valve. The first cylinder includes a first cylinder tube and a first piston that divides the space in the first cylinder tube into two air chambers. The second cylinder includes a second cylinder tube and a second piston that divides the space in the second cylinder tube into two air chambers. The second piston is connected to the first piston so that the first piston and the second piston have the same displacement. Among the two pressure receiving surfaces of the first piston and the two pressure receiving surfaces of the second piston, one of the two pressure receiving surfaces of the first piston has the smallest cross-section area, and one of the two pressure receiving surfaces of the second piston has the third smallest cross-section area. The two air chambers of the first cylinder and the two air chambers of the second cylinder are referred to as, in ascending order in the cross-section area, a first air chamber, a second air chamber, a third air chamber, and a fourth air chamber respectively. In the forward stroke, the control valve connects an air pressure source to the first air chamber, connects the second air chamber to the third air chamber, and opens the fourth air chamber to the atmosphere.
In this configuration, the second air chamber and the third air chamber behave as a differential circuit. Therefore, when compressed air remains in the second air chamber and the third air chamber immediately before the forward stroke, the energy of the compressed air is effectively used by expanding them and using them as the driving force of the piston, and the efficiency of the pneumatic cylinder can be increased. Further, the resultant force of the total output of the two cylinders at this time is larger than that of the single cylinder.
In one embodiment, the control valve may connect the first air chamber and the second air chamber to the air pressure source and connect the third air chamber to the fourth air chamber in the return stroke. In this embodiment, the pneumatic cylinder functions as a double acting cylinder. In the return stroke, the pair of the first air chamber and the second air chamber and the pair of the third air chamber and the fourth air chamber act as a differential circuit, and while effectively utilizing the energy of the remaining compressed air, the output in the return direction can be obtained. Further, the resultant force of the total output of the two cylinders at this time is larger than that of the single cylinder.
In one embodiment, in the return stroke the control valve may connect the first air chamber to the second air chamber in a state of being separated from the air pressure source and connect the third air chamber to the fourth air chamber. In this embodiment, the pneumatic cylinder functions as a single-acting cylinder that does not consume compressed air in the return stroke. In the return stroke, the pair of the first air chamber and the second air chamber and the pair of the third air chamber and the fourth air chamber act as a differential circuit, and while effectively utilizing the energy of the remaining compressed air, the output in the return direction can be obtained.
In one embodiment, the first cylinder and the second cylinder may be arranged non-coaxially. In this case, the axial dimension of the pneumatic cylinder can be reduced.
In one embodiment, the first air chamber and the second air chamber may be formed in the same cylinder, and the third air chamber and the fourth air chamber may be formed in the same cylinder.
In one embodiment, the first cylinder and the second cylinder may be single rod cylinders. This can reduce the cost.
In one embodiment, the first cylinder and the second cylinder may be arranged coaxially.
In one embodiment, the first air chamber, the second air chamber, the third air chamber, and the fourth air chamber may be arranged in order in the axial direction.
In one embodiment, the third air chamber, the fourth air chamber, the first air chamber, and the second air chamber may be arranged in order in the axial direction.
In one embodiment, the first air chamber, the fourth air chamber, the third air chamber, and the second air chamber may be arranged in order in the axial direction.
In one embodiment, the third air chamber, the second air chamber, the first air chamber, and the fourth air chamber may be arranged in order in the axial direction.
In one embodiment, the control valve may include a 4-port first control valve and a 4-port second control valve. In the first position, the first port communicates with the second port, and the third port and the fourth port are closed. In the second position, the first port and the second port are closed, and the fourth port communicates with the third port. The first port and the third port of the first control valve are connected to the second air chamber, the second port of the first control valve is connected to the third air chamber and the fourth port of the second control valve. The fourth port of the first control valve is connected to the first air chamber and the air pressure source, the first port and the third port of the second control valve are connected to the fourth air chamber, and the second port of the second control valve is connected to the atmosphere. Regarding the double-acting cylinder, the first control valve and the second control valve can be configured by using commercially available products (four-port directional control valve or two two-port directional control valves), respectively.
Description will be made below regarding the present disclosure based on preferred embodiments with reference to the drawings. The same or similar components, members, and processes are denoted by the same reference numerals, and redundant description thereof will be omitted as appropriate. The embodiments have been described for exemplary purposes only and are by no means intended to restrict the present disclosure. Also, it is not necessarily essential for the present disclosure that all the features or a combination thereof be provided as described in the embodiments.
In addition, the dimensions (thickness, length, width, etc.) of each member shown in the drawings may be appropriately enlarged or reduced for ease of understanding. Furthermore, the dimensions of the plurality of members do not necessarily represent the magnitude relationship between them, and even if one member A is drawn thicker than another member B on the drawing, the member A is the member B. It can be thinner than.
1. 1. Efficiency of Conventional Pneumatic Actuators
First, consider the efficiency of conventional pneumatic actuators.
The compressed air used for the pneumatic system is usually 0.7 MPa (gauge) [=0.8 MPa (abs)], which is created by compressing the air in the atmospheric pressure (0.1 MPa (abs)) state with a compressor.
dE=−PdV (1)
On the other hand, the change in the state of air is expressed by the equation (2), where T is the temperature and R is the gas constant.
PV=RT (2)
The actual state change is not an isothermal change, but an adiabatic change or a polytropic change, but for ease of understanding or simplification of the explanation, an isothermal change is assumed. This assumption is useful in obtaining approximate values, as the final air temperature converges to the ambient temperature if the event is viewed on a somewhat long time scale. Assuming an isothermal change, since dPV+pdV=dT=0, the equation (1) becomes the equation (3). When it is integrated, Eq. (4) is obtained.
Therefore, the energy E0 required to compress the air at atmospheric pressure Pa=0.1 [MPa (abs)] to the air having a volume V at the pressure Ps=0.8 [MPa (abs)] is expressed by the equation (5) when the state change is an isothermal change.
Next, the efficiency of the pneumatic actuator will be described using a pneumatic cylinder as an example.
As shown in
Next, in the return stroke shown in
E=PSV (6)
Therefore, the energy efficiency η can be obtained from the equations (5) and (6) as in the equation (7) when the compressed air is discarded in the return stroke.
In other words, the efficiency is about 0.5 at the maximum according to the simple calculation. The reason why the efficiency is low is that the high-pressure air in the left chamber 14 is discharged to the outside as it is during the return stroke.
2. Differential Circuit
In the pneumatic cylinder according to the embodiment described below, the energy efficiency is greatly increased by using the expansion process of the high pressure air for driving the cylinder without discarding the high pressure air as it is at high pressure. However, as the air expands, the pressure decreases and it cannot be used as a sufficient driving force. Therefore, some ingenuity is required to use the air in the expansion process for driving.
2.1 Differential Circuit in the Hydraulic System
In order to understand the pneumatic cylinder according to the embodiment, it is indispensable to understand the differential circuit often used in the hydraulic circuit. Therefore, this section describes the differential circuit.
In the forward stroke shown in
On the other hand, in the return stroke shown in
That is, since the pressure receiving area of the oil chamber 36 on the right side is large, the force toward the left becomes large, and the piston rod 38 moves to the left. At this time, the oil coming out of the left oil chamber 34 and the oil from the pump 22 are combined and flow into the right oil chamber 36, so that the cylinder moves at high speed. As described above, the feature of the differential circuit 20 is that the return stroke can be moved at high speed, and the smaller the area difference |A2-A1| on both sides of the cylinder, the faster the movement. Assuming that the cylinder speed is v, the following equation holds.
A1v+Q=A2v (8)
Therefore, the cylinder speed v is expressed by the equation (9). Since the oil from the pump 22 is used only to fill the volume of the piston rod 38, the thinner the rod, the faster the cylinder speed v.
On the other hand, the output is as shown in equation (10), and the thinner the piston rod 38 (the smaller the AR), the smaller the output.
F=A2p−A1p=(A2−A1)p=ARp (10)
In order to take advantage of such characteristics, the differential circuit 20 has been used for the return stroke when a large output is not required when the return is to be quick.
2.2 Application of Differential Circuit to Pneumatic System
Next, the application of the differential circuit to the pneumatic system will be described.
Specifically, when the differential circuit 40 is used in the pneumatic system, as shown in
Let L be the cylinder length and x be the length of the right chamber 16 of the piston 12. The volume V of the air chamber in the cylinder is expressed by the following equation, and the volume V increases as the piston 12 moves to the left, that is, as the length x increases.
Assuming an isothermal change as a state change, PV=constant, so when the volume V increases with the movement of the piston 12, the pressure P gradually decreases. If the air pressure source 42 is connected as shown by the broken line in the figure, compressed air is supplied from the air pressure source 42, so that the pressure P does not decrease even if the piston 12 moves.
The above is the behavior of the differential circuit in the pneumatic system.
3. Pneumatic Actuator According to the Embodiment
Hereinafter, the pneumatic actuator according to the embodiment will be described in detail. This pneumatic cylinder utilizes the concept of the differential circuit described above in three stages. Thereby, the efficiency is improved by effectively utilizing all (or most of) the output of compressed air “while expanding from supply pressure to atmospheric pressure”.
3.1 Basic Configuration
The pneumatic actuator according to the present embodiment is used by directly connecting two pneumatic cylinders having different pressure receiving areas on both sides of the piston and is also referred to as a double cylinder actuator below. The double cylinder actuator 100 has four pressure receiving surfaces, and the pressure receiving areas thereof are A1 and A2 on both sides of the first cylinder and A3 and A4 on both sides of the second cylinder. These areas are increased in order such that A1<A2<A3<A4.
The first cylinder 110 includes a first cylinder tube 112 and a first piston 114. The first piston 114 is displaceable in the first cylinder tube 112, and the space in the first cylinder tube 112 is partitioned by the first piston 114 into the left air chamber 116 and the right air chamber 118.
The pressure receiving area A1 on the first surface (left air chamber 116 side) of the first piston 114 is smaller than the pressure receiving area A2 on the second surface (right air chamber 118 side).
A1<A2
In the present embodiment, the first cylinder 110 is double-ended rod cylinders, the left rod 120 is installed on the left air chamber 116 side of the first piston 114, and the right rod 122 is installed on the right air chamber 118 side. When the cross-sectional area of the first cylinder tube 112 is AC1, the cross-sectional area of the left rod 120 is AR1_L, and the cross-sectional area of the right rod 122 is AR1_R, the following relational expression holds.
A1=AC1−AR1_L
A2=AC1−AR1_R
where,AR1_L>AR1_R
The second cylinder 130 includes a second cylinder tube 132 and a second piston 134. The second piston 134 is displaceable in the second cylinder tube 132, and the space in the second cylinder tube 132 is partitioned by the second piston 134 into the left air chamber 136 and the right air chamber 138.
The first cylinder 110 and the second cylinder 130 are arranged so that the first piston 114 and the second piston 134 are parallel to each other. Further, the second piston 134 is connected so that the displacement is the same as that of the first piston 114. In
The pressure receiving area A3 on the first surface (left air chamber 136 side) of the second piston 134 is smaller than the pressure receiving area A4 on the second surface (right air chamber 138 side).
A3<A4
In the present embodiment, the second cylinder 130 is also a double-ended rod cylinder, the left rod 140 is installed on the left air chamber 136 side of the second piston 134, and the right rod 142 is installed on the right air chamber 138 side. When the cross-sectional area of the second cylinder tube 132 is AC2, the cross-sectional area of the left rod 140 is AR2_L, and the cross-sectional area of the right rod 142 is AR2_R, the following relational expression holds.
A3=AC2−AR2_L
A4=AC2−AR2_R
where,AR2_L>AR2_R
Further, in the present embodiment, the relationship of A2<A3 is satisfied. That is,
A1<A2<A3<A4
The two air chambers 116, 118 of the first cylinder 110 and the two air chambers 136, 138 of the second cylinder 130 are referred to as a first air chamber, a second air chamber, a third air chamber, and a fourth air chamber in order from the one having the smallest pressure receiving area, and the reference numerals 161, 162, 163, and 164 will be newly added to these chambers. In this example, they are associated as follows:
A part or all of the rods of the first cylinder 110 and the second cylinder 130 are used as a design parameter of the pressure receiving area, and also serve as a coupling means for connecting the first piston 114 and the second piston 134.
In this example, the control valve 150 is shown as a 6-port 2-position valve. The first port (1) to the sixth port (6) are connected to the air pressure source 102, the atmosphere 104, and the first air chamber 161 to the fourth air chamber 164, respectively. The control valve 150 may be at least as long as the first position and the second position described below can be switched, and the number of positions is not limited to two. For example, when it is assumed that the piston stops at a position in the middle of the forward stroke, a directional control valve having a closed center function may be used. In this case, a 3-position valve may be used. Further, the method of holding and operating the control valve is not particularly limited, and a single solenoid type (spring return type), a double solenoid type, or another type of valve can be used.
In general, pneumatic cylinders include a “double-acting cylinder” that outputs both during the forward stroke and the return stroke, and a “single-acting cylinder” that outputs during the forward stroke but does not require output during the return stroke and returns by a spring or its own weight. Therefore, the double-cylinder actuator 100 according to the embodiment may also have a double-acting cylinder and a single-acting cylinder. The configuration of the control valve 150 differs depending on whether the double cylinder actuator 100 is a single-acting cylinder or a double-acting cylinder. Therefore, in the following, a double-acting cylinder and a single-acting cylinder will be described in this order.
(1) Double-Acting Cylinder
(1-1) Forward Stroke
In the forward stroke (movement of rightward output), compressed air is supplied to the first air chamber 161 to obtain rightward output. Further, the second air chamber 162 and the third air chamber 163 are connected, but since A2<A3, a rightward output can be obtained by the same principle as the differential circuit. The resultant force F of these two rightward outputs is larger than that of a single cylinder 110 alone.
(1-2) Return Stroke
In the return stroke (movement of the leftward output), compressed air is supplied to the second air chamber 162, and at the same time, the second air chamber 162 of the first cylinder 110 and the first air chamber 161 are connected. Since A1<A2, a leftward output can be obtained by the same principle as the differential circuit.
Further, the third air chamber 163 and the fourth air chamber 164 of the second cylinder 130 are connected, since A3<A4, a leftward output can be obtained by the same principle as the differential circuit. The resultant force FR of these two leftward outputs is larger than that of a single cylinder 110 alone.
As described above, in the double-acting cylinder, the outputs F and FR of the double-acting cylinder are larger than those of the single cylinder 110 at both the forward stroke and the return stroke. This is because the force of the expansion process of compressed air is also used.
For example, the pressure receiving area ratio of the double cylinder actuator 100 is assumed to be A1:A2:A3:A4=1:2:4:8. If the state change is an isothermal change, the pressure in each chamber is inversely proportional to the volume, and the supply pressure of the compressed air is usually 0.8 [MPa (abs)], so that the pressure in each air chamber changes as follows in each of the forward stroke and the return stroke.
Forward Stroke
Return stroke
In the final fourth air chamber 164, the pressure drops to about 0.2 MPa, and it can be seen that the force of the expansion process of the compressed air can be fully utilized up to near the atmospheric pressure as compared with the conventional actuator. Further, for example, if the output of the double cylinder actuator 100 is twice that of the case of only a single cylinder 110, the entire pressure receiving area of the double cylinder actuator 100 can be halved in order to obtain the same output. As a result, the amount of air consumed will be halved, and the efficiency approaches 100% from the current 50%.
When using only a single cylinder, sound is generated when compressed air is discharged into atmospheric pressure. In order to reduce this sound, a silencer is often inserted. When the double cylinder actuator 100 is used, the air whose pressure has dropped to the vicinity of the atmospheric pressure is exhausted, so that it is possible to omit the silencer, thereby reducing the cost.
(2) Single-Acting Cylinder
(2-1) Forward Stroke
The forward stroke of the single-acting cylinder is the same as the forward stroke of the double-acting cylinder, and is as described with reference to
(2-2) Return Stroke
In the single-acting cylinder, the output is not always required in the return stroke (movement of the leftward output), so the compressed air from the pneumatic source 102 is not supplied to the second air chamber 162. Therefore, compressed air is not consumed during the return stroke. However, since the pair of the first air chamber 161 and the second air chamber 162 and the pair of the third air chamber 163 and the fourth air chamber 164 each form a differential circuit, a certain amount of output can be obtained even during the return stroke.
In the single-acting cylinder, the pressure receiving area ratio of the double cylinder actuator 100 is assumed to be set to A1:A2:A3:A4=1:2:4:8, and the supply pressure of the compressed air is assumed to be set to 0.8 [MPa (abs)]. At that time, the pressure in each air chamber changes as follows in each of the forward stroke and the return stroke.
Forward Stroke
Return stroke
In the final fourth air chamber 164, the pressure dropped to 0.1 MPa, which is an atmospheric pressure, and it can be seen that the energy can be used more effectively than the double-acting cylinder.
4. Output Characteristics of Double Cylinder Actuator 100
Next, the output characteristics of the double cylinder actuator 100 will be described for each of the double-acting cylinder and the single-acting cylinder.
(1) Double Acting Cylinder
(1-1) Output During the Forward Stroke
The pressures of the first air chamber 161, the second air chamber 162, the third air chamber 163, and the fourth air chamber 164 are referred to as P1, P2, P3, and P4.
In
In the initial state x=L, P2=Ps, which is the final state of the immediately preceding return stroke. Afterwards, pressure changes from P2=P3=Ps toward P2=P3=(A2/A3)Ps. Further, since P1=Ps and P4=Pa (atmospheric pressure) remain, the output in the initial state is represented by the equation (12), and the output in the final state is represented by the equation (13).
(1-2) Output During the Return Stroke
In
In this case, the pair of the first air chamber 161 and the second air chamber 162, the pair of the third air chamber 163 and the fourth air chamber 164 are connected to each other. Further, compressed air from air pressure source 102 is supplied to the second air chamber 162. In the initial state x=0, pressure of the third chamber is P3=(A2/A3) Ps, which is the final state of the immediately preceding stroke. Then, as x→L, it changes from P3=(A2/A3) Ps to P3=P4=(A2/A3)Ps×(A3/A4)=(A2/A4)Ps. The pressures of first air chamber 161 and the second air chamber 162 remain P1=P2=Ps. Therefore, the output in the initial state is expressed by the equation (15), and the output in the final state is expressed by the equation (16).
Here, as an example, let's find the F and FR of the double acting cylinder in the case of A2/A1=A3/A2=A4/A3=2. This is the case of A4=2A3=4A2=8A1. The supply pressure of the compressed air is Ps=0.8 MPa (abs). That is, Ps=8 Pa.
The output F in the initial state and the final state at the time of the forward stroke is as follows.
Also, the output FR in the initial state and the final state at the time of the return stroke is as follows.
In each case, the output at the start of movement is considerably larger than twice the output of A1Ps, which is the output of the single cylinder 110, but the output at the end of movement is less than twice. This is often fine, as it is important for the cylinder to start moving. Rather, the smaller output F, FR in the final state can be regarded as a pseudo cushion at the forward stroke end, which is preferable in some applications.
If the decrease in output in the final state becomes a problem, it is necessary to smooth the output in the initial state and the output in the final state. This method will be described later.
(2) Single-Acting Cylinder
What is explained here is the output of the single-acting double cylinder actuator 100b. A single-acting cylinder outputs a force during the forward stroke but is not required to output a force during the returning stroke and returns by a spring or its own weight.
(2-1) Output During the Forward Stroke
In
In this case, in the initial state x=L, pressure of the second chamber is P2=(A1/A2) Ps, which is the final state of the immediately preceding return stroke. Then, as x→0, it changes from P2=P3=(A1/A2)Ps to P2=P3=(A1/A2)Ps×(A2/A3)=(A1/A3) Ps. Further, since the pressures of first air chamber and the fourth air chamber remain P1=Ps and P4=Pa (atmospheric pressure), the output F in each of the initial state and the final state is expressed by the equations (17) and (18).
(2-2) Output During the Return Stroke
In
In this case, the pair of the first air chamber 161 and the second air chamber 162 and the pair of the third air chamber 163 and the fourth air chamber 164 are connected, respectively. In the initial state x=0, P3=P4=(A1/A3) Ps, which is the final state of the immediately preceding stroke, and P1=P2=Ps. As x→L, it changes from P1=P2=Ps to P1=P2=(A1/A2) Ps, and from P3=P4=(A1/A3) Ps to P3=P4=(A1/A3)Ps×(A3/A4)=(A1/A4)Ps. Therefore, the output FR in each of the initial state and the final state in the return stroke is expressed by the equations (19) and (20).
Here, as an example, let's find the F and FR of the single-acting cylinder in the case of A2/A1=A3/A2=A4/A3=2. This is the case of A4=2A3=4A2=8A1. The supply pressure of the compressed air is Ps=0.8 MPa (abs). That is, Ps=8 Pa.
The output F in each of the initial state and the final state in the forward stroke is as follows.
In a single-acting cylinder, only the output F in the forward stroke is important. The output in the initial state of the forward stroke is larger than the output of a single cylinder, but it is not doubled, and in the final state, it is not much different from that of a single cylinder. This is because compressed air is not supplied during the return stroke.
5. Optimization of Cylinder Pressure Receiving Area
(1) Explanation of Design Parameters
Here, we will consider the pressure receiving area ratio of the cylinder. Therefore, the pressure receiving area ratio is set as follows.
A2/A1=α
A3/A2=β
A4/A3=γ
As it is, there are 3 parameters, so it is difficult to consider. Therefore, here, we will proceed with the study with α=γ as a constraint condition. This is because α and γ have an area ratio on both sides of the same cylinder. Therefore, it becomes as follows.
A2/A1=α
A3/A2=β
A4/A3=α
Further, since the supply pressure of the compressed air is Ps=0.8 MPa (abs) and Ps=8 Pa, the product of the area ratio is set to 8 in order to utilize all the force generated when compressed air expands to the atmospheric pressure. That is, the constraint below is added.
α2·β=8
(2) Relationship Between the Output of the Double-Acting Cylinder and the Pressure Receiving Area Ratio
The output F in the forward stroke is obtained by substituting the above design parameters into the equations (12) and (13) and is expressed as follows.
The output FR in the return stroke is obtained by substituting the above design parameters into the equations (15) and (16) and is expressed as follows.
The average of both outputs during that period is larger than 2 in the vicinity indicated by the thick arrow in the figure.
F(AVE)=(2.04)A1PS,FR(AVE)=(2.04)A1PSfor α=2.06,β=1.89
In this case, the average value of the outputs F and FR is about twice that of the output A1PS of a single cylinder during both the forward stroke and the return stroke.
(3) Relationship Between the Output of the Single-Acting Cylinder and the Pressure Receiving Area Ratio
The output F in the forward stroke is obtained by substituting the above design parameters into the equations (17) and (18) and is expressed as follows.
The output FR in the return stroke is obtained by substituting the above design parameters into the equations (19) and (20) and is expressed as follows.
The average output during the forward stroke is larger than 2, and the latter half of the operation is also relatively large in the vicinity indicated by the thick arrow in the figure.
F(AVE)=(2.0)A1PS,FRR(max)=(0.45)A1PSfor α=1.51,β=3.51.
In this case, the average value F(AVE) of the output F in the forward stroke is more than twice the output A1PS of a single cylinder. On the other hand, although the output during the return stroke is not required, it is possible to obtain an output close to half of the output of a single cylinder.
6. Smoothing the Output of the Double Cylinder Actuator 100
As described above, in the double cylinder actuator 100, when the displacement of the cylinder becomes large, the pressure inside the cylinder decreases, so that the output becomes small. In applications where this is not desirable, “negative spring properties” may be introduced to smooth the output.
The means for introducing the negative spring characteristic is not limited to the one using a magnet, and for example, a method such as attaching a two-position stable spring to the piston can be considered.
In the case of a single-acting cylinder, the magnet 170 is not required and only the magnet 172 may be used.
The present disclosure has been described above based on the embodiment. This embodiment is an example, and various modifications can be made to the combination of each component and each process. It is also understood by vendors that such modifications are also within the scope of this disclosure. Hereinafter, such a modification will be described.
In the basic form, the first cylinder 110 and the second cylinder 130 were double-ended rod cylinders, but the present invention is not limited thereto. In the first modification of shown in
In the second modification shown in
Modified example 4 shown in
The following techniques can be grasped from
In the modified example 5 shown in
In the modified example 6 shown in
In the modified example 8 shown in
Although the control valve 150a for the double-acting cylinder is shown in
Generally, a single rod cylinder is cheaper than a double-ended rod cylinder.
The first port (1) and the third port (3) of the first control valve 152 are connected to the second air chamber 162. The second port (2) of the first control valve 152 is connected to the third air chamber 163 and the fourth port (4) of the second control valve 154. The fourth port (4) of the first control valve 152 is connected to the first air chamber 161 and the air pressure source 102. The first port (1) and the third port (3) of the second control valve 154 are connected to the fourth air chamber 164. The second port (2) of the second control valve 154 is connected to the atmosphere 104.
In the first state (first position), the first control valve 155 conducts from the first port (1) toward the second port (2), and from the fourth port (4) toward the third port (3). In the second state (second position), the first control valve 155 conducts from the third port (3) to the first port (1), and the second port and the fourth port are closed.
In
Following the modification of
In addition to what is shown here, there are various modifications in the configurations of the control valves 150a and 150b, and such modifications are also included in the scope of the present disclosure.
In the embodiment, the double cylinder actuator 100 is composed of a combination of cylinders with two rods, but the present invention is not limited to this.
For example, the double cylinder actuator 100 may be configured by combining two guided cylinders.
Alternatively, the double cylinder actuator 100 can be configured by combining two rodless cylinders. There are two types of rodless cylinders: slit type and magnet type. When the slit type is used, the cushion pipe extending from the center of the cylinder head can be used. That is, the cushion pipe may be extended to the piston, and the pressure receiving area may be changed like a rod according to the cross-sectional area of the cushion pipe. Furthermore, even when the magnet type is adopted, the pressure receiving area can be adjusted according to the cross-sectional area of the rod by adding a rod inside.
As described above, the configuration of the cylinders constituting the double cylinder actuator 100 is not particularly limited. It can be configured by combining various cylinders having different pressure receiving areas on both sides of the piston that divides the air chamber into two.
In the embodiment, the double cylinder actuator 100 including two cylinders has been described, but the number of cylinders may be increased to three, four, . . . This will be generalized and referred to as a multi-cylinder actuator. The multi-cylinder actuator has the following features.
The multi cylinder actuator includes a plurality of N cylinders (N 2) and a control valve. Each of the N cylinders includes a cylinder tube and a piston that divides the space inside the cylinder tube into two air chambers. The pistons of each of the N cylinders are connected so that the displacements are equal. The pressure receiving area of one of the i-th (1≤i≤N) pistons is the (2i−1)th smallest. The two air chambers of N cylinders (2N air chambers in total) are called the first air chamber, second air chamber, . . . , (2N−1)th air chamber, and (2N)th air chamber in order from the one with the smallest pressure receiving area to the one with the largest pressure receiving area. In the forward stroke, the control valve (i) connects the air pressure source to the first air chamber, opens the (2N)th air chamber to the atmosphere, and connects the other two adjacent pairs of air chambers.
In the return stroke, in the case of a double-acting multi-cylinder actuator, the control valve (ii) connects the first air chamber and the second air chamber to the air pressure source. Further, for the third air chamber to the (2N)th air chamber, a pair of two adjacent air chambers is connected.
In the return stroke, in the case of single-acting multi cylinder actuator, the control valve (iii) connects a pair of two adjacent air chambers from the first air chamber to the (2N)th air chamber.
Although the present disclosure has been described using specific terms based on the embodiments, the embodiments merely indicate the principles and applications of the present disclosure. In the embodiments, many modifications and arrangement changes are permitted without departing from the ideas of the present invention defined in the claims.
Number | Date | Country | Kind |
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2019-239641 | Dec 2019 | JP | national |
This application is a continuation under 35 U.S.C. § 120 of PCT/JP2020/048748 filed Dec. 25, 2020, which is incorporated herein by reference, and which claimed priority to Japanese Application No. 2019-239641 filed on Dec. 27, 2019. The present application likewise claims priority under 35 U.S.C. § 119 to Japanese Application No. 2019-239641, filed on Dec. 27, 2019, the entire content of which is also incorporated herein by reference.
Number | Name | Date | Kind |
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2699651 | Douglas | Jan 1955 | A |
3171331 | Walter | Mar 1965 | A |
6029450 | Wittich | Feb 2000 | A |
6227112 | Becker | May 2001 | B1 |
20210139134 | Atkins | May 2021 | A1 |
Number | Date | Country |
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102006034645 | Jan 2008 | DE |
102014007439 | Nov 2015 | DE |
H08226401 | Sep 1996 | JP |
2013199869 | Oct 2013 | JP |
Entry |
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DE102014007439A1_t machine translation thereof (Year: 2015). |
International Search Report for International Application No. PCT/JP2020/048748; dated Mar. 2, 2021. |
PCT International Preliminary Report on Patentability with Written Opinion of the International Searching Authority for International Application No. PCT/JP2020/048748; dated Mar. 2, 2021. |
Number | Date | Country | |
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20220333621 A1 | Oct 2022 | US |
Number | Date | Country | |
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Parent | PCT/JP2020/048748 | Dec 2020 | US |
Child | 17849944 | US |