1. Field of the Invention
The present invention relates to a pneumatic actuator, and more particularly, to a pneumatic actuator system and method.
2. Statement of the Problem
An actuator is a device that performs some mechanical action. One actuator is a piston, wherein a plunger of the piston moves in a reciprocating manner. The plunger can therefore be connected to some manner of work piece or other mechanical system.
In some actuator applications, it is desirable to have more than one actuation speed and/or more than one actuation force over the range of motion of the actuator. For example, in a spot welder machine, a pair of welding jaws must be brought together onto a work piece during a welding operation. The jaws must clamp onto the work piece with a desired force. Therefore, at the end of a clamping motion range, a relatively high actuation force must be provided to the welding jaws.
However, an actuator that provides a high level of force typically provides a relatively small range of actuation travel. This can be a problem where the jaws of the spot welder machine must open wide in order to be positioned on the work piece. Therefore, a jaw actuator of the spot welder machine needs to move relatively rapidly during a first actuation span and a large force is not required. During the second actuation span, the jaws need to move only a small distance, but must be able to provide a large clamping force.
An actuator for a machine typically requires precise control, with a minimum of slop. The need may be greater for a two-phase actuator having a first actuation phase followed by a second actuation phase, wherein the first actuation phase covers a greater actuation span at a greater speed but offers less force. The subsequent second actuation phase has a small actuation span and a lesser speed but offers a greater actuation force.
However, there are many other machines or devices that employ pneumatic actuators. Consequently, there is a need to flexibly control an actuation speed, force, and/or distance. There may additionally be a need to implement a custom actuation profile.
In addition, in a machine that includes an actuator, the machine will inevitably wear and degrade over time. This will lead to increased resistance in the machine. Therefore, there is a need for an actuator that can compensate for wear or other changes in operational conditions.
A pneumatic actuator system is provided according to an embodiment of the invention. The pneumatic actuator system comprises a pneumatic actuator including an actuator component, with the pneumatic actuator being configured to include a first actuation phase and a second actuation phase. The pneumatic actuator system further comprises one or more feedback sensors configured to provide one or more actuation feedback values, an actuator valve coupled to and providing a first pneumatic pressure and a second pneumatic pressure to the pneumatic actuator, and a controller coupled to the one or more feedback sensors and the actuator valve. The controller is configured to receive the one or more actuation feedback values from the one or more feedback sensors and control the actuator valve in order to actuate the actuator component according to an actuation profile and according to the one or more actuation feedback values.
An actuation method for a pneumatic actuator system comprising a pneumatic actuator including an actuator component is provided according to an embodiment of the invention. The method comprises receiving one or more actuation feedback values related to movement of the actuator component and actuating the actuator component according to an actuation profile and according to the one or more actuation feedback values.
An actuation method for a pneumatic actuator system comprising a pneumatic actuator including an actuator component is provided according to an embodiment of the invention. The method comprises receiving a displacement signal corresponding to a displacement of an actuator component of the pneumatic actuator. The method further comprises calculating a calculated actuation force value from a first pressure signal and a second pressure signal. The first pressure signal corresponds to a first pneumatic pressure in a pneumatic portion of the piston assembly and the second pressure signal corresponds to a second pneumatic pressure in a hydraulic force-multiplier portion. The method further comprises receiving a measured actuation force value from a force sensor. The measured actuation force value comprises a measurement of an actuation force generated by the piston assembly. The method further comprises actuating the actuator component according to an actuation profile and according to the displacement signal, the calculated actuation force value, and the measured actuation force value.
An actuation method for a pneumatic actuator system comprising a pneumatic actuator including an actuator component is provided according to an embodiment of the invention. The method comprises receiving a displacement signal corresponding to a displacement of an actuator component of the pneumatic actuator. The method further comprises calculating a calculated actuation force value from a first pressure signal and a second pressure signal. The first pressure signal corresponds to a first pneumatic pressure in a pneumatic portion of the piston assembly and the second pressure signal corresponds to a second pneumatic pressure in a hydraulic force-multiplier portion. The method further comprises receiving a measured actuation force value from a force sensor. The measured actuation force value comprises a measurement of an actuation force generated by the piston assembly. The method further comprises actuating the actuator component according to an actuation profile and according to the displacement signal, the calculated actuation force value, and the measured actuation force value. The method further comprises modifying an actuation profile in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value.
In one aspect of the system, the one or more feedback sensors comprises a displacement sensor configured to generate a displacement signal corresponding to a displacement of the actuator component, with the controller actuating the actuator component according to the actuation profile and according to the displacement signal.
In another aspect of the system, the one or more feedback sensors comprises a force sensor configured to generate a measured actuation force value, with the controller actuating the actuator component according to the actuation profile and according to the measured actuation force value.
In yet another aspect of the system, the one or more feedback sensors comprises a first pressure sensor configured to generate a first pressure signal corresponding to a first pneumatic pressure in a pneumatic portion of the pneumatic actuator, with the first pneumatic pressure moving the actuator component according to the first actuation phase, and a second pressure sensor configured to generate a second pressure signal corresponding to a second pneumatic pressure in a hydraulic force-multiplier portion of the pneumatic actuator, with the second pneumatic pressure moving the actuator component according to the second actuation phase and wherein a calculated actuation force value is derived from the first pressure signal and the second pressure signal and with the controller actuating the actuator component according to the actuation profile and according to the calculated actuation force value.
In yet another aspect of the system, the one or more feedback sensors comprises a displacement sensor configured to generate a displacement signal corresponding to a displacement of the actuator component, a force sensor configured to generate a measured actuation force value comprising a measurement of an actuation force generated by the actuator component, a first pressure sensor configured to generate a first pressure signal corresponding to a first pneumatic pressure in a pneumatic portion of the pneumatic actuator, with the first pneumatic pressure moving the actuator component according to the first actuation phase, and a second pressure sensor configured to generate a second pressure signal corresponding to a second pneumatic pressure in a hydraulic force-multiplier portion of the pneumatic actuator, with the second pneumatic pressure moving the actuator component according to the second actuation phase, wherein a calculated actuation force value is derived from the first pressure signal and the second pressure signal and with the controller actuating the actuator component according to the actuation profile and according to the measured actuation force value, the calculated actuation force value, and the displacement signal.
In yet another aspect of the system, the controller is further configured to modify the actuation profile in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value.
In yet another aspect of the system, the controller is further configured to modify the actuation profile in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value over an operational life of the pneumatic actuator system.
In yet another aspect of the system, a second stroke span of the second actuation phase is substantially smaller in length than a first stroke span of the first actuation phase.
In yet another aspect of the system, the first stroke span is traversed by the piston rod using a first actuation force and the second stroke span is traversed by the piston rod using a second actuation force that is substantially greater than the first actuation force.
In yet another aspect of the system, the second stroke span occurs at any point along the actuation span.
In yet another aspect of the system, the second stroke span is generated by a hydraulic force-multiplier portion of the actuator.
In one aspect of the method, the one or more actuation feedback values comprise a displacement signal received from a displacement sensor and corresponding to a displacement of the actuator component.
In another aspect of the method, the one or more actuation feedback values comprises a measured actuation force value received from a force sensor, with the measured actuation force value comprising a measurement of an actuation force generated by the actuator component.
In yet another aspect of the method, the one or more actuation feedback values comprises a calculated actuation force value generated from a first pressure signal and a second pressure signal, with the first pressure signal corresponding to a first pneumatic pressure in a pneumatic portion of the pneumatic actuator and with the second pressure signal corresponding to a second pneumatic pressure in a hydraulic force-multiplier portion.
In yet another aspect of the method, the one or more actuation feedback values comprises a displacement signal received from a displacement sensor and corresponding to a displacement of the actuator component, a measured actuation force value received from a force sensor, with the measured actuation force value comprising a measurement of an actuation force generated by the pneumatic actuator, and a calculated actuation force value generated from a first pressure signal and a second pressure signal, with the first pressure signal corresponding to a first pneumatic pressure in a pneumatic portion of the pneumatic actuator and with the second pressure signal corresponding to a second pneumatic pressure in a hydraulic force-multiplier portion.
In yet another aspect of the method, the method further comprises modifying an actuation profile in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value.
In yet another aspect of the method, the method further comprises modifying an actuation profile in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value over an operational life of the pneumatic actuator system.
The same reference number represents the same element on all drawings. It should be understood that the drawings are not necessarily to scale.
The actuator cylinder 102 receives a first pneumatic air supply from the actuator valve 213 via the first conduit 207 and receives a second pneumatic air supply from the actuator valve 213 via the second conduit 208. The internal components of the actuator cylinder 102 are discussed in detail below in conjunction with
The actuator valve 213 can comprise a valve system including one or more valves that is connected to some manner of pneumatic air supply. The actuator valve 213 selectively supplies pressurized pneumatic air to the first, second, and third conduits 207, 208, and 210. The actuator valve 213 can selectively supply pressurized pneumatic air to the first and/or second conduits 207 and 208 in order to actuate the actuator cylinder 102 and extend the actuator component 108. The actuator valve 213 can supply pressurized pneumatic air to the first conduit 207 in order to accomplish a first actuation phase. The actuator valve 213 can supply pressurized pneumatic air to the second conduit 208 in order to accomplish a second actuation phase. The actuator valve 213 can supply pressurized pneumatic air to the third conduit 210 in order to retract the actuator component 108.
The first actuation phase comprises an actuation accomplished through pneumatic air supplied to the first conduit 207 and the second actuation phase comprises an actuation accomplished through pneumatic air supplied to the second conduit 208. The first and second actuation phases can be performed singly or in combination. The first and second actuation phases can be performed at any time and in any order, including substantially simultaneously. When both the first and second actuation phases are performed simultaneously, the actuation component 108 can be moved according to a third phase. In addition, other actuation phases can be achieved, such as by varying the pressure of air supplied to the first and second conduits 207 and 208. An actuation profile 242, discussed below, can be used to specify any desired number of actuation occurrences, any desired actuation length, and any desired actuation speed and force.
The controller 240 regulates the actuation of the pneumatic actuator system 200. The controller 240 is coupled to the one or more feedback sensors 220 and to the actuator valve 213. The controller 240 controls the operation of the actuator valve 213 in order to control the operation of the actuator cylinder 102. In some embodiments the controller 240 can receive valve feedback information from the actuator valve 213.
The controller 240 receives one or more actuation feedback values from the one or more feedback sensors 220. The one or more feedback sensors 220 can comprise any manner of feedback sensors related to motion of the actuator component 108 (see
The controller 240 can perform and regulate actuations according to an actuation profile 242 (see
The first pneumatic air supply in some embodiments is used for a relatively low-force, relatively high actuation speed first actuation phase of the pneumatic actuator system 200. The second pneumatic air supply in some embodiments is used for a relatively high-force, relatively low actuation speed second actuation phase. The two actuation phases can occur at any time and in any order. The actuator cylinder 102 receives a third pneumatic air supply from the actuator valve 213 via the third conduit 210. The third pneumatic air supply in some embodiments is used to retract the actuator component 108.
One improvement over the prior art is in a required pneumatic pressure. Advantageously, the first and second pneumatic air supplies can supply a relatively low pressure to the pneumatic actuator system 200. In addition, the first and second pneumatic air supplies can supply a relatively low air volume.
A two-stage actuator of the prior art requires 10-12 bars of pneumatic pressure to perform the actuation of an actuator component. In contrast, the pneumatic actuator system 200 of the present invention requires only about 6 bars of pneumatic pressure. It should be understood that more pressure can be supplied, as needed. However, generating higher pressures and higher volumes of pneumatic air requires more energy and therefore a higher cost. The pneumatic actuator system 200 therefore provides a lower operational cost.
Another improvement over the prior art is in size. The pneumatic actuator system 200 achieves this low pressure, low volume performance while reducing a cross-sectional size of the pneumatic actuator system 200. For example, a prior art pneumatic actuator using 10-12 bars of pneumatic pressure typically has a cross-sectional dimension of about 160-200 millimeters (mm). In contrast, the pneumatic actuator system 200 can achieve such low pressure, low volume actuation with a cross-sectional size of about 63 mm. The pneumatic actuator system 200 therefore can provide an equivalent actuator having a smaller size and lower material and manufacturing costs.
However it to be understood that this is just one actuation profile example and others are contemplated. In addition, it should be understood that the actuation profile can be designed for a particular application. The actuation profile in this example may be designed for the jaws or tongs of a spot welding machine, for example.
The displacement signal received by the controller 240 indicates a displacement (i.e., a relative position) of the actuator component 108. The controller 240 can therefore use the displacement signal to control the position and speed of the actuator component 108 as the actuator component 108 moves in and out of the actuator cylinder 102.
The measured actuation force value received by the controller 240 indicates an actuation force being generated by the actuator component 108. The force sensor 223 is an optional component and may or may not be present in the pneumatic actuator system 200. The controller 240 can use the measured actuation force value to determine an actual force applied to a work piece or work device acted on by the actuator component 108.
The first and second pressure sensors 225 and 226 can be located in the first and second conduits 207 and 208. Alternatively the first and second pressure sensors 225 and 226 can be located in appropriate regions of the actuator valve 213 or the actuator cylinder 102. The first and second pressure sensors 225 and 226 measure a first pneumatic pressure and a second pneumatic pressure employed to actuate the actuator component 108. The first pressure sensor 225 measures a first pneumatic pressure of pressurized air supplied to a purely pneumatic piston in the actuator cylinder 102 and generates a first pressure signal. The second pressure sensor 226 measure a second pneumatic pressure of pressurized air supplied to a hydraulic force-multiplier portion in the actuator cylinder 102 and generates a resulting second pressure signal. Hydraulic is defined herein to include any operation or movement of a component through a force of a supplied liquid. The liquid can comprise a substantially non-compressible liquid.
The force generated by the actuator component 108 due to the first pneumatic pressure can be calculated as the first pneumatic pressure multiplied by the active area of the purely pneumatic piston to produce a calculated actuation force value. The force generated by the actuator component 108 can be calculated as the second pneumatic pressure multiplied by the active area of the hydraulic force-multiplier portion to produce the calculated actuation force value. If both the first pneumatic pressure and the second pneumatic pressure are being supplied at the same time, then the calculated actuation force value comprises the sum of the force generated by the first pneumatic pressure plus the force generated by the second pneumatic pressure.
It should be understood that the actuation force value thus derived from the first pressure signal supplied from the first pressure sensor 225 and the second pressure signal supplied from the second pressure sensor 226 will closely track the actual force generated by the actuator component 108. Therefore, the calculated actuation force value may render the force sensor 223 unnecessary.
However, at times the calculated actuation force value may deviate from the measured actuation force value generated by the force sensor 223. This may be due to the size, weight, and/or geometry of a working piece or working mechanism that is actuated by the actuator component 108 (i.e., some of the force supplied by the pneumatic air pressure is absorbed by either the pneumatic actuator 100 or by a working mechanism). The difference in force values may be caused by frictional forces and wear in various components of the pneumatic actuator system 200, for example. As a result, over time, the calculated actuation force value may drift away from the measured actuation force value, as measured by the force sensor 223. However, the controller 240 can track any such deviation and can use any deviation to determine whether and when the controller 240 may adjust operation of the actuator valve 213 in order to compensate. As a result, the controller 240 can adjust a first pneumatic pressure supplied to the actuator cylinder 102 in order to maintain a desired actuator component force. Therefore, the controller 240 can be configured to modify an actuation profile 242 in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value. Further, the controller 240 can be configured to modify an actuation profile 242 in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value over an operational life of the pneumatic actuator system 200.
In step 402, the pneumatic actuator can be actuated according to an actuation profile and according to the one or more actuation feedback values. The feedback values combined with the actuation profile can be used to determine the control actions taken with regard to the pneumatic actuator.
In step 502, a calculated actuation force value is calculated from a first pressure signal and a second pressure signal. The first pressure signal corresponds to a first pneumatic pressure in a pneumatic portion of the pneumatic actuator. The second pressure signal corresponds to a second pneumatic pressure in a hydraulic force-multiplier portion of the pneumatic actuator.
In step 503, a measured actuation force value is received. The measured actuation force value can be received from a force sensor, for example. In some embodiments, the measured actuation force value can be measured as a force exerted by the actuator component, for example.
In step 504, the pneumatic actuator can be actuated according to an actuation profile and according to the displacement signal, the calculated actuation force value, and the measured actuation force value. The displacement signal, the calculated actuation force value, and the measured actuation force value, combined with the actuation profile, can be used to determine the control actions taken with regard to the pneumatic actuator.
In step 602, a calculated actuation force value is calculated, as previously discussed.
In step 603, a measured actuation force value is received, as previously discussed.
In step 604, as previously discussed, the pneumatic actuator can be actuated according to an actuation profile and according to the displacement signal, the calculated actuation force value, and the measured actuation force value.
In step 605, the actuation profile can be modified. The actuation profile can be modified in order to ensure a continuing accuracy of the calculated actuation force value. The modification can be triggered if the difference between the calculated actuation force value and the measured actuation force value exceeds a predetermined tolerance. The actuation profile can be modified in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value. The actuation profile can be modified in order to keep the calculated actuation force value within a predetermined tolerance of the measured actuation force value over an operational life of the pneumatic actuator system.
Port 1 of the valve 301 receives the pneumatic pressurized air from the air supply. Port 1 can be selectively connected to either port 2 or port 4 of the valve 301. The valve 301 therefore selectively provides pneumatic air to the valve 302 and the valve 303. The valve 303 selectively provides pneumatic air to the valve 304.
When the pneumatic air from the air supply is connected to port 4 of the valve 301, as shown in the figure, and if the valve 302 is actuated, then pressurized air is supplied to both the third conduit 210 and the fourth conduit 211. As a result, the pressurized air from the fourth conduit 211 will move the ram 160 to the right in the figure and will retract the ram 160 while the pressurized air from the third conduit 210 will move the piston 120 to the right in the figure and will retract the piston 120 (see
Conversely, when the pneumatic air from the air supply is connected to port 2 of the valve 301, and the valve 303 is actuated, then pressurized air is supplied to both the first conduit 207 and to the second conduit 208. The first conduit 207 is coupled to a pneumatic portion of the pneumatic actuator 100, while the second conduit 208 is coupled to a hydraulic force-multiplier portion. Pressurized air supplied to the first conduit 207 will move the piston 120 to the left in the figure and will extend the piston 120. However, the second conduit 208 is further controlled by the valve 304. In some embodiments, when the piston 120 is substantially fully extended by the pneumatic portion via the first conduit 207, then the valve 304 can be actuated and pressurized air is supplied to the second conduit 208. The pressurized air supplied by the second conduit 208 actuates the hydraulic force-multiplier portion and the ram 160 is moved to the left in the figure. When the valve 304 is not actuated, then the valve 304 exhausts air to the right of the ram 160, allowing the ram 160 to be retracted.
The first pressure sensor 225 is in communication with port 2 of the valve 301 and generates the first pressure signal. The second pressure sensor 226 is in communication with port 4 of the valve 301 and generates the second pressure signal. Both the first pressure sensor 225 and the second pressure sensor 226 are electrically coupled to the controller (μC) 240.
In the embodiment shown, a third pressure sensor 309 can be included. The third pressure sensor measures a hydraulic fluid pressure of the hydraulic force-multiplier portion. The third pressure sensor is also electrically coupled to the controller (μC) 240.
This embodiment further includes the displacement sensor 221 and the force sensor 223. Both the displacement sensor 221 and the force sensor 223 are electrically coupled to the controller (μC) 240.
The first stroke span can be traversed at a first actuation speed and the second stroke span can be traversed at a second actuation speed. In one embodiment, the second actuation speed is substantially slower than the first actuation speed.
The first stroke span can be traversed using a first actuation force and the second stroke span can be traversed using a second actuation force. In one embodiment, the second actuation force is substantially greater than the first actuation force.
The actuator 100 in one embodiment includes a force amplifier. In one embodiment, the actuator 100 includes a hydro-pneumatic force amplifier. The force amplifier can provide a force greater than a force generated by a supplied pneumatic pressure alone. The actuator 100 in one embodiment can provide a force amplifier at any point in the overall actuation span. The force amplifier can be actuated at a midpoint of the actuation span or can be actuated before or after the midpoint.
Referring again to
The actuator 100 further includes an inner shell 109, a lower inner plug 131, and an upper inner plug 135. The inner shell 109 forms the piston chamber 126. The lower inner plug 131 is located at a bottom region of the piston chamber 126 and the upper inner plug 135 is located at a top region of the piston chamber 126. In addition, the lower inner plug 131 and the upper inner plug 135 hold the inner shell 109 substantially in position within the outer shell 101. In one embodiment, the inner shell 109 is substantially coaxial with the outer shell 101. The upper inner plug 135 includes an upper inner plug seal(s) 136 that substantially seal the upper inner plug 135 to the outer shell 101. In addition, the upper inner plug 135 includes hydraulic fluid passages 137, a ram throat 138, and ram throat seals 139. The ram throat 138 receives a ram 160, with the ram throat seals 139 sealing the ram 138 to the upper inner plug 135. As a consequence, the ram 138 blocks the ram throat 138 and can move reciprocally up and down in the ram throat 138.
The actuator 100 further includes a piston ring 110. The piston ring 110 can include piston ring seals 112. The piston ring 110 can move with respect to the outer shell 101 and can move with respect to the piston rod 108. The piston ring 110 can move under influence of pressurized gas above and below the piston ring 110. The pressurized gas can be introduced and exhausted from above and below the piston ring 110 by port D and port E, respectively.
The actuator 100 further includes a movable ring 140 located in a ring chamber 147 formed between the inner shell 109 and the outer shell 102. The upper side of the movable ring 140 contacts a hydraulic fluid, which is also present in the piston chamber 126 above the piston 120. The movable ring 140 is configured to move reciprocally up and down between the outer shell 101 and the inner shell 109 in response to gas introduced and exhausted by port A. The movable ring 140 can include movable ring seals 144. The movable ring seals 144 substantially seal the movable ring 140 to the outer shell 101. In addition, the movable ring seals 144 substantially seal the movable ring 140 to the inner shell 109.
The actuator 100 further includes the ram 160. The ram 160 moves reciprocally up and down in a ram chamber 161. The ram 160 includes ram seals 163, a ram conduit(s) 163, and a ram filling cavity 166. The ram filling cavity 166 is fed pressurized gas by a pipe 170 that extends from the top plug 103 and that is connected to port B. The gas is transferred to a portion of the ram chamber 161 below the ram 160, with the gas traveling through the ram conduit(s) 163 to the portion of the ram chamber 161. In addition, the ram 160 is in communication with port C. As a result, the ram 160 can be moved down by introduction of pressurized gas into port C and can be moved up by introduction of pressurized gas into port B.
Upward movement of the movable ring 140 forces the piston 120 downward over a first stroke span due to movement of a first volume of the hydraulic fluid from the ring chamber 147 into the piston chamber 126. Downward movement of the ram 160 forces a second volume of the hydraulic fluid down into the piston chamber 126, wherein the downward movement of the ram 160 forces the piston 120 downward over a second stroke span.
The figure shows the actuator 100 in a fully retracted position, where the piston rod 108 is fully retracted within the actuator 100. Pressurized gas can be supplied into port D to move the piston 120 to (and hold the piston 120 in) the fully retracted position. Correspondingly, port A, port B, and port C are released in order to allow the piston 120 and the ram 160 to move to fully retracted upward positions. As the piston 120 is moved upwards, the hydraulic fluid above the piston 120 is moved out of the piston chamber 126 and is forced into the chamber between the outer shell 101 and the inner shell 109, pushing the movable ring 140 fully downward. As a result, gas is forced out of port A. In addition, port C is released and the gas between the ram 160 and the top plug 103 is not held. As a result, the upward movement of the piston 120 causes the ram 160 to move fully upward.
To actuate the force multiplier, port B is released, the pressure at port A is held, and pressurized gas is further supplied to port C. This moves the ram 160 downward in the ram chamber 161, moving the ram 160 fully into the ram throat 138. As a result, the ram 160 blocks off the hydraulic fluid passage(s) 137 and consequently seals the hydraulic fluid in the piston chamber 126. The volume of hydraulic fluid displaced by the ram 160 in the ram throat 138 causes the piston 120 to move additionally downward. The large cross-sectional area of the top of the ram 160, combined with the smaller cross-sectional area of the bottom of the ram 160, provides the force multiplier effect. The ram 160 presses the hydraulic fluid into the piston chamber 126. The force at the end of the ram 160 in one embodiment is about 6 times the force on the upper side of the ram 160. No additional hydraulic fluid needs to be provided to the actuator 100. The ram 160 therefore provides a large second actuation force over the second (small) stroke span.
It should be understood that the force multiplier can be actuated at any point in the first (large) stroke span. As a result, even if the piston rod 108 is only at a midpoint of the first stroke span, the ram 160 can be moved downward and the second (small) stroke span can be traversed by the piston rod 108, in addition to any portion of the first stroke span already traversed.
The retraction operation is essentially the opposite of the extension operation. For retraction, the pressurized gas at port A and port C is released. Subsequently, pressurized gas is supplied to port B, moving the ram 160 upward to a fully retracted position. The retraction of the ram 160 unblocks the hydraulic fluid passage(s) 137, allowing hydraulic fluid to move from the piston chamber 126 to the ring chamber 147. Then, pressurized gas is introduced to port E in order to force the piston ring 110 fully upward, thereby forcing the piston 120 partially upward (see
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP07/03291 | 4/13/2007 | WO | 00 | 10/5/2009 |