Patent Publication Number: US-2016222995-A1

Title: Piston limit sensing for fluid application

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/109,796, filed Jan. 30, 2015, the content of which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to liquid pumps, and more specifically, to a limit sensor system used to determine the position of a piston in a liquid delivery system. Position sensing can provide instantaneous analog or digital electronic position feedback information about the piston within a cylinder. 
     SUMMARY 
     A liquid delivery system is disclosed. The liquid delivery system includes a cylinder having an end, a piston within the cylinder, and a rod connected to the piston and extending at least to the end of the cylinder. The liquid delivery system can also include a limit sensor system having a magnet connected to the rod, outside the cylinder and on an opposite side of the end of the cylinder as the piston. The magnet can have a first position corresponding to the piston located at a first stroke limit position and a second position corresponding to the piston located at a second stroke limit position. Furthermore, the limit sensor system can have sensors such as reed switches located outside the cylinder and configured to sense when the magnet is at the first position and when the magnet is at the second position. 
     The above summary is not intended to describe each illustrated embodiment or every implementation of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings included in the present application are incorporated into, and form part of, the specification. They illustrate embodiments of the present disclosure and, along with the description, serve to explain the principles of the disclosure. The drawings are only illustrative of certain embodiments and do not limit the disclosure. 
         FIG. 1  depicts an exemplary painting system, consistent with embodiments of the present disclosure. 
         FIGS. 2A and 2B  depict an exemplary pump assembly, consistent with embodiments of the present disclosure. 
         FIG. 3  depicts an exemplary exploded view of a pump assembly, consistent with embodiments of the present disclosure. 
         FIG. 4A  depicts an exemplary cylinder in a first position with a limit sensor system, consistent with embodiments of the present disclosure. 
         FIG. 4B  depicts the exemplary cylinder in a second position with a limit sensor system, consistent with embodiments of the present disclosure. 
         FIG. 5A  depicts an exploded view of an exemplary planetary roller screw drive, consistent with embodiments of the present disclosure. 
         FIG. 5B  depicts an assembled view of the exemplary planetary roller screw drive, consistent with embodiments of the present disclosure. 
         FIG. 6A  depicts an exemplary planetary roller screw drive in a first position with a limit sensor system, consistent with embodiments of the present disclosure. 
         FIG. 6B  depicts the exemplary planetary roller screw drive in a second position with a limit sensor system, consistent with embodiments of the present disclosure. 
         FIG. 7  depicts an exemplary hydraulic circuit, consistent with embodiments of the present disclosure. 
     
    
    
     While embodiments of the present invention are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION 
     Aspects of the present disclosure relate to hydraulic powered liquid pumps, more particular aspects relate to a limit sensor system used to determine the position of a piston in a liquid delivery system. While the present disclosure is not necessarily limited to such applications, various aspects of the disclosure may be appreciated through a discussion of various examples using paint as context. 
     According to various embodiments, the liquid delivery system can include a hydraulic cylinder. The hydraulic cylinder can be a mechanical actuator that distributes a force on a liquid using reciprocating piston strokes. The piston is connected to a piston rod or other suitable structure and movement of the piston causes the reciprocal movement of the piston rod. The cylinder is closed on one end by a cylinder top (hereinafter referred to as the head) and on the other end by a cylinder bottom (hereinafter referred to as the base) where the piston rod comes out of the cylinder. In a hydraulic powered liquid delivery system, the hydraulic cylinder derives its power from a pressurized hydraulic fluid. In certain embodiments, an actuator (e.g., a solenoid valve) can direct the hydraulic fluid flow generated by a hydraulic pump through a first port (e.g., a port near the head hereinafter referred to as the head port) located on the cylinder. As the hydraulic fluid is directed by the actuator to the head port, pressure builds in the cylinder to force the piston to move from the head, through the cylinder, and to the base. 
     In various embodiments, a limit sensor system can be used to detect that the piston has reached the end of its stroke. The limit sensor system can include a magnet and reed switches. During each piston stroke, a portion of the piston rod remains outside the cylinder, regardless of the location of the piston inside the cylinder. In particular embodiments, the magnet is located on this portion of the piston rod (on the opposite side of the base of the cylinder as the piston), enabling the magnet to remain outside the cylinder as well. When the piston has completed a stroke, the magnetic field created by the magnet causes the reed switch to open or close. The reed switch can be connected to an electrical circuit that can feed logic gates that enable the actuator to direct the hydraulic fluid through the valve into a second port (e.g., a port near the base hereinafter referred to as the rod port) located on the cylinder. As the hydraulic fluid is directed by the actuator to the rod port, pressure builds in the cylinder to force the piston to move from the base, through the cylinder, and to the head. During this process, the hydraulic fluid is forced into the head port, back into the actuator, and returned to a hydraulic fluid reservoir. As the piston moves from the base to the head, the magnetic field applied to the reed switch decreases and the reed switch will change its state (open if application of the magnetic field forced it to close and close if application of the magnetic field forced it to open). As the piston draws near the head and approaches the second reed switch, its magnetic field causes the second reed switch to change its state. 
     In various embodiments, since the magnet is located on the portion of the piston rod that is outside of the cylinder, the magnet is not exposed to the pressurized hydraulic fluid inside the cylinder. This may protect the magnet from damage and corrosion that could occur from exposure to the hydraulic fluid if the magnet was located in the cylinder (e.g., on the piston). Moreover, if the magnet becomes damaged (e.g., cracked or has depleted magnetic properties), it may need to be repaired or replaced. However, because the magnet is located outside the cylinder, the hydraulic pump does not need to be disassembled to repair or replace the magnet. 
     According to particular embodiments, the reed switches may also be located outside the cylinder. As a result, in a paint delivery system, the reed switches, reed switch connectors, and an electrical circuit board may be exposed to paint. In particular embodiments, the reed switches and the reed switch connectors can be hermetically sealed and the electrical circuit board can be enclosed to protect them from damage, corrosion, and depletion of sensor properties that may be caused from exposure to the paint. 
     Embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures. However, there can be several embodiments of the present invention and the present invention is not limited to the embodiments set forth herein. The embodiments disclosed are provided so that this disclosure can fully convey the scope of the invention to those skilled in the art. Therefore, the following detailed description is not to be taken in a limiting sense. 
       FIG. 1  depicts an exemplary painting system  100  that includes an upper shroud  126 , a frame  128 , wheels  130 , a lower shroud  132 , a motor system  102 , a solenoid valve (not shown in  FIG. 1 ) under the lower shroud  132 , a pump assembly  106 , a hydraulic motor  136 , and a paint reservoir (not shown). The motor system  102  can be electrically powered, gas powered, etc. and can include a hydraulic pump (not shown in  FIG. 1 ) under the lower shroud  132  and a hydraulic fluid reservoir (not shown in  FIG. 1 ) also under the lower shroud  132 . The hydraulic pump delivers hydraulic fluid (e.g., oil) from the hydraulic fluid reservoir to the solenoid valve. The solenoid valve can be an electromechanical device that includes a solenoid, a head port on the valve body and a rod port on the valve body. The head port on the valve body and the rod port on the valve body can be controlled by an electric current through the solenoid. For the solenoid valve, the electric current can alternate the flow from the head port on the valve body and the rod port on the valve body. 
     According to various embodiments, the pump assembly  106  includes a hydraulic cylinder  114  and a paint pump  116 . The solenoid valve directs the hydraulic fluid, generated by the hydraulic pump, through the head port on the valve body to a head port  122  of the hydraulic cylinder  114 . As the hydraulic fluid is directed by the solenoid valve through the head port  122  of the hydraulic cylinder  114 , pressure builds in the cylinder and forces the hydraulic piston to move. As the hydraulic piston moves through the cylinder, the hydraulic fluid is forced through a rod port  124  of the hydraulic cylinder  114 , into the solenoid valve through the rod port on the valve body, and returned to the hydraulic fluid reservoir. In addition, a hydraulic piston rod (not shown in FIG.  1 ), connected to the hydraulic piston, can also be connected to a paint piston rod (not shown in  FIG. 1 ). As a result, the hydraulic piston moves the paint piston rod through the paint pump  116  to pump paint from the paint reservoir to an outlet hose  134  connected to a paint applicator (not shown in  FIG. 1 ). 
     In particular embodiments, a magnet is connected to the hydraulic piston rod. Moreover, at least two sensors are located outside the cylinder that correspond to the two limit positions of the hydraulic piston at each end of its stroke, hereinafter referred to as a stroke limit position. In certain embodiments, the sensor can be a reed switch. A reed switch is an electrical switch operated by an applied magnetic field. It may consist of a pair of contacts on  1  reeds in a hermetically sealed airtight envelope constructed from a suitable material, such as glass or plastic. In certain embodiments, the contacts can be open, making no electrical contact. The switch can be closed by bringing the magnet near the switch. Once the magnet is pulled away, the reed switch will open again. In other embodiments, the contacts can be closed and the switch can be opened by bringing the magnet near the switch. Once the magnetic field is removed, the reed switch closes. 
     For example, as the hydraulic piston moves from the head, through the cylinder, a magnet located on the hydraulic piston rod moves closer to a first reed switch. When the hydraulic piston has reached a stroke limit position in the cylinder, the magnetic field closes the first reed switch and completes an electrical circuit (not shown in  FIG. 1 ). The electrical circuit can provide a voltage or other suitable indication that activates a set of metal oxide semiconductor field effect transistors (MOSFETs) or other suitable switching devices to change the state of the solenoid. In this example, the hydraulic fluid can now be released from the rod port on the valve body, into the cylinder through the rod port  124  of the hydraulic cylinder  114 . As the hydraulic piston moves through the cylinder in the opposite direction, the magnetic field strength, with respect to the first reed switch, decreases and the first reed switch opens. Moreover, the hydraulic fluid can be pushed back through the head port  122  of the hydraulic cylinder  114 , into the solenoid valve through the head port on the valve body, and returned to the hydraulic fluid reservoir. The paint piston rod can then move through the paint pump  116  and continue to pump paint from the paint reservoir. When the hydraulic piston has reached a stroke limit position, the magnetic field causes a second reed switch to close, thereby completing the electrical circuit, and reverse the hydraulic fluid flow from the solenoid valve. 
     In another embodiment, a hall-effect sensor system can be used to determine when the hydraulic piston has reached the end of a piston stroke. A hall-effect sensor system can include a magnet and a sensor. In various embodiments, the hall-effect sensor system can be hermetically sealed or enclosed. The sensor can be a transducer that varies its output voltage in response to an applied magnetic field produced by the magnet. When the hydraulic piston has reached a stroke limit position, the magnet is located at a position such that its magnetic field is perpendicular with respect to the sensor. The perpendicular magnetic field can induce the output voltage from the sensor that enables the solenoid valve to alternate the flow of the hydraulic fluid. 
     In another embodiment, a photoelectric sensor is used to determine that the hydraulic piston has reached a stroke limit position. A photoelectric sensor is a device used to detect the distance, absence, or presence of an object by using a light transmitter and a photoelectric receiver. In yet further embodiments, other sensors can be used that include, but are not limited to, mechanical sensors, base active transducer sensors, eddy-current sensors, inductive position sensors, photodiode array sensors, and proximity sensors. In particular embodiments, the sensor systems can be hermetically sealed or enclosed to protect them from exposure to the paint. 
       FIG. 2A  depicts an outside view of the exemplary pump assembly  106  and  FIG. 2B  depicts an inside view of the exemplary pump assembly  106 . As can be seen in  FIG. 2B , the pump assembly  106  includes head port  122  of the hydraulic cylinder  114 , rod port  124  of the hydraulic cylinder  114 , a hose outlet  206 , a paint piston rod  208 , a paint pump cavity  210 , a hydraulic piston rod  212 , a hydraulic piston  214 , a paint intake  216 , a hydraulic cylinder cavity  218 , a first reed switch  220 , a second reed switch  222 , and a magnet  224 . An actuator (e.g., solenoid valve) directs a hydraulic fluid into the hydraulic cylinder cavity  218  through head port  122  of hydraulic cylinder  114 . The hydraulic fluid forces hydraulic piston  214  to move down through the hydraulic cylinder cavity  218 . As the hydraulic piston  214  moves down through the hydraulic cylinder cavity  218 , the paint piston rod  208  moves down through the paint pump cavity  210  and pushes the paint out hose outlet  206 . In addition, hydraulic fluid is forced back through the rod port  124  of the hydraulic cylinder  114 , into the solenoid valve and returned to a hydraulic fluid reservoir. 
     When hydraulic piston  214  is at a stroke limit position, magnet  224  causes first reed switch  220  to close and complete an electrical circuit (not shown in  FIG. 2B ). The electrical circuit provides a voltage or other suitable indication that reverses the state of the solenoid valve and causes the hydraulic fluid to flow into the hydraulic cylinder cavity  218  through the rod port  124  of the hydraulic cylinder  114 , thereby reversing the direction of piston  214 . As piston  214  travels up, the hydraulic fluid is forced back through the head port  122  of the hydraulic cylinder  114 , into the solenoid valve and returned to the hydraulic fluid reservoir. The paint piston rod  208  also moves up through the paint pump cavity  210  and draws the paint through the paint intake  216 . When the hydraulic piston has reached its upper stroke limit position, the magnet  224  causes second reed switch  222  to close, thereby completing an electrical circuit and reversing the hydraulic fluid flow into the hydraulic cylinder cavity through the head port  122  of the hydraulic cylinder  114 . 
       FIG. 3  depicts an exploded view of the exemplary pump assembly  106 , consistent with embodiments of the present disclosure. The pump assembly  106  includes hydraulic cylinder  114 , paint pump  116 , and sensor cover assembly  304 . The sensor cover assembly  304  can prevent paint from entering the area where the paint piston rod (e.g., paint piston rod  208 , from  FIG. 2 ) and the hydraulic piston rod  212  are coupled together and can prevent paint from reaching magnet  224  and reed switches  220  and  222 . In addition, sensor cover assembly  304  can include first reed switch  220 , the second reed switch  222 , and a circuit board  330 . 
     As shown in  FIG. 3 , hydraulic cylinder  114  can include hydraulic cylinder fasteners  306 , cylinder  308 , piston head wear ring  310 , piston head seal  312 , hydraulic piston  214 , hydraulic piston rod  212 , magnet  224 , hydraulic piston coupler  318 , piston rod seal  324 , jam nut  332 , and a fluid section block  334 . Hydraulic cylinder fasteners  306  securely attaches the cylinder  308  to the fluid section block  334 . The cylinder  308  can include the hydraulic cylinder cavity  218 , from  FIG. 2 , the head port  122  of the hydraulic cylinder  114 , from  FIG. 2 , and the rod port  124  of the hydraulic cylinder  114 , from  FIG. 2 . The piston head wear ring  310  is a ring that fits into a groove on the outer diameter of hydraulic piston  214 . The piston head seal  312  can be a dynamic seal. It can be single acting or double acting and it can be made from nitrile rubber, polyurethane, fluorocarbon viton, etc. The jam nut  332  can lock the hydraulic piston coupler onto the piston rod  212  and the hydraulic piston coupler  318  can attach the hydraulic piston rod  212  to a paint piston rod (e.g., paint piston rod  208 , from  FIG. 2 ). 
       FIG. 4A  depicts an exemplary hydraulic cylinder  402  in a first position with a limit sensor system, consistent with embodiments of the present disclosure. The hydraulic cylinder  402  can include piston  404 , piston rod  406 , head  408 , base  410 , head partition  412 , base partition  414 , magnet  416 , first reed switch  420 , and second reed switch  418 . 
     According to various embodiments, as shown in  FIG. 4A , the piston  404  is initially located at a stroke limit position, near head  408  and magnet  416  causes first reed switch  420  to change state and complete an electrical circuit (not shown in  FIG. 4A ). The electrical circuit provides a voltage or other suitable signal to reverse the state of an actuator (e.g., a solenoid valve) and direct hydraulic fluid into the cylinder  402  through the head partition  412  (as shown by arrow  422 ). As the hydraulic fluid flows through the head partition  412 , piston  404  is forced away from head  408 . As the piston  404  moves through the cylinder  402 , first reed switch  420  changes state and the hydraulic fluid is forced back into the actuator through the base partition  414  (as shown by arrow  424 ). 
       FIG. 4B  depicts the exemplary hydraulic cylinder  400  in a second position with a limit sensor system, consistent with embodiments of the present disclosure. Magnet  416  is positioned on the piston rod  406  such that when the piston  404  moves through the cylinder  402  and approaches base  410 , magnet  416  approaches second reed switch  418  and causes second reed switch  418  to change state. This will complete an electrical circuit and provide a voltage or other suitable signal to reverse the state of the solenoid valve and thus, reverse the flow of the hydraulic fluid and move the piston  404  away from base  410 . 
       FIG. 5A  depicts an exploded view of an exemplary planetary roller screw drive  600  and  FIG. 5B  depicts an assembled view of the exemplary planetary roller screw drive  600 , consistent with embodiments of the present disclosure. The planetary roller screw drive  600  includes rod  602 , cog  604 , rollers  606 , roller retainer  608 , and tube  610 . According to various embodiments, the planetary roller screw drive  600  can be used in place of or in combination with a hydraulic cylinder (e.g., hydraulic cylinder  400 ). The planetary roller screw drive  600  is a mechanical device for converting rotational motion to linear motion. 
     According to various embodiments, the threaded rod  602  provides a helical raceway or thread  612  for multiple rollers  606  radially arrayed around the rod  602  and encapsulated by the threaded tube  610 . The lead for thread  612  is the axial travel for a single revolution. The pitch of thread  612  is defined as the axial distance between adjacent threads of the thread  612 . The thread  612  of the rod  602  typically has the same pitch or corresponding features to the internal thread of the tube  610 . The rollers  606  spin in contact with, and serve as transmission elements between the rod  602  and the tube  610 . The rollers  606  typically have a single-start thread where a single helical thread is along their length and the lead and pitch are equal. This can limit the friction as the rollers  606  contact the rod  602  and the tube  610 . The rollers  606  orbit the rod  602  as they spin and rotation of the tube  610  results in rod  602  travel, and rotation of the rod  602  results in tube  610  travel. 
       FIG. 6A  depicts an exemplary planetary roller screw drive  700  in a first position with a limit sensor system, consistent with embodiments of the present disclosure. The planetary roller screw drive  700  can include a rod  702 , rollers  704 , tube  706 , head  708 , base  710 , magnet  712 , first reed switch  714 , and second reed switch  716 . 
     According to various embodiments, as shown in  FIG. 6A , the rod  702  is initially located at a stroke limit position, near head  708  and magnet  712  causes first reed switch  714  to change state and complete an electrical circuit (not shown in  FIG. 6A ). The electrical circuit provides a voltage or other suitable signal to reverse the rotation of the rollers  704  and move the rod  702  away from head  708 . As the rod  702  moves through the tube  706 , first reed switch  714  changes state. 
       FIG. 6B  depicts the exemplary planetary roller screw drive  700  in a second position with a limit sensor system, consistent with embodiments of the present disclosure. Magnet  712  is positioned on the rod  702  such that when the rod  702  moves through the tube  706  and approaches base  710 , magnet  712  approaches second reed switch  716  and causes second reed switch  716  to change state. This will complete an electrical circuit and provide a voltage or other suitable signal to reverse the rotation of the rollers  704  and move the rod  702  away from base  710 . 
       FIG. 7  depicts an exemplary hydraulic circuit  500 , consistent with embodiments of the present disclosure. In various embodiments, the hydraulic circuit  500  can include a hydraulic reservoir  502 , a hydraulic pump  504 , a solenoid  506 , a head port  508 , a rod port  510 , a hydraulic cylinder  512 , a paint cylinder  514 , a paint reservoir  516 , and a spray gun  518 . In certain embodiments, the hydraulic pump  504  can pump hydraulic fluid from the hydraulic reservoir  502  to the solenoid  506 . In  FIG. 7 , the solenoid  506  is illustrated as a directional control valve. Directional control valves can allow fluid to flow into different paths from one or more sources. They can consist of a spool inside a cylinder and can be mechanically, electrically, and hydraulically controlled. Moreover, the movement of the spool can restrict or permit the flow of the hydraulic fluid from the hydraulic reservoir  502 . 
     In this embodiment, an electromechanical solenoid is used to operate a 4-way, 2 position valve since there are 2 spool positions and 4 valve ports. However, other position valves can be used. The 4-way, 2 position valve combined with the reed switch sensor (not shown in  FIG. 7 ) enables fast switching between the down stroke and the up stroke of the hydraulic cylinder  512 . This allows the hydraulic circuit  500  to achieve a consistent paint pressure. In this example, initially, the head port  508  is the pressure port which is connected to the hydraulic pump  504  and the rod port is connected to the hydraulic reservoir  502 . As the hydraulic fluid is directed into the head port  508  the pressure inside the hydraulic cylinder  512  forces the hydraulic piston to move down through the hydraulic cylinder  512  and the hydraulic fluid is pushed out the rod port  510  and back to the hydraulic reservoir  502 . Since hydraulic piston is attached to the paint piston, the paint piston also moves down through the paint cylinder  514  and paint, located in the paint cylinder, is pushed into the spray gun  518 . 
     When the hydraulic piston has reached a stroke limit position, the reed switch sensor can provide a voltage that activates a set of MOSFETs (not shown in  FIG. 7 ) and the solenoid  506  slides the spool to its second position. As a result, rod port  510  is the pressure port which is connected to the hydraulic pump  504  and the head port is connected to the hydraulic reservoir  502 . As the hydraulic fluid is directed into the rod port  510  the pressure inside the hydraulic cylinder  512  forces the hydraulic piston to move up through the hydraulic cylinder  512  and the hydraulic fluid is pushed out the head port and back to the hydraulic reservoir  502 . Moreover, the paint piston also moves up through the paint cylinder  514  and paint from the paint reservoir  516  can be drawn up into the paint cylinder  516 . 
     The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.