Patent Application
20140354269
The present disclosure relates to a method and apparatus for determining the condition of a control element. More specifically, the present invention relates to a method and apparatus for determining the condition of a control element comprising a ferrous armature movable within an electro-magnetic field of a solenoid.
Hydraulic, pneumatic or other motion control or fluid control systems may include a movable component such as a valve or other device. The movable component may include a control element, and the control element may be actuated, for example, by an electro-magnetic actuator, by a pilot actuator or other actuator in response to a command control signal. When the command control signal has been given to the actuator, it can be desirable to know that the control element has in fact reached the desired condition in response to the command control signal.
Prior art methods and apparatuses for determining the condition of a control element may include a sensing element such as a linear variable differential transformer (“LVDT”), a mechanical switch, or a potentiometer. While such devices provide satisfactory results, they require some connection to the control element and thus may require a “seal point” to prevent fluids or other contaminants from entering the connection point. Other prior art devices may include a Hall-effect sensor or a permanent magnet arranged to move with a fluid control element, the movement or position being transmitted magnetically to a sensor such as for example a reed switch. Such devices, however, may not operate properly when subjected to magnetic fields generated by electric solenoids. Still other prior art devices may include a displacement measurement device and associated method of the type disclosed in U.S. Pat. No. 7,969,146.
A device and method in accordance with the present disclosure enables status detection of a control element, such as an armature of a solenoid, without being detrimentally affected by magnetic fields or requiring a physical connection point. In this regard, dips and/or spikes in the current passing though the solenoid windings can be detected and used to determine when the armature has shifted from one position to another.
A signal indicative of the armature status can be based on pull-in current spike detection along with a solenoid energized condition to indicate both the presence of a command control signal and the presence of the condition desired by the command control signal. Further, by combining back EMF current spike detection with solenoid de-energized condition, the presence of an opposite command control signal and the presence of the condition desired by the opposite command control signal can be detected.
According to one aspect of the invention, a circuit is provided for determining a position of a control element arranged in proximity to an electro-magnetic field of a solenoid coil for movement in one direction toward one stopped position relative to the solenoid coil in response to increasing electrical current flow through the solenoid coil, and for movement away from the one stopped position relative to the solenoid coil in response to decreasing electrical current flow through the solenoid coil. The circuit includes: a first detector circuit configured to obtain first current fluctuations during increasing current flow through the solenoid coil, and provide an output indicative of the control element being at the one stopped position based on a comparison of the first current fluctuations and a first prescribed value; and a second detector circuit configured to obtain second current fluctuations during decreasing current flow through the solenoid coil, and provide an output indicative of the control element being away from the one stopped position based on a comparison of the second current fluctuations and a second prescribed value.
According to one aspect of the invention, the circuit further includes a switching device for selectively applying power to the solenoid coil, wherein the first detector circuit is arranged electrically in series with the switching device and the solenoid coil, and the second detector circuit is arranged in parallel with the solenoid coil.
According to one aspect of the invention, the first detector circuit comprises: a first sensor operative to measure a first current passing through the solenoid coil while the power switch is in a first position providing power to the solenoid coil and current flow through the solenoid coil is increasing; and a first comparator operative to compare fluctuations in the first measured current to the first prescribed value.
According to one aspect of the invention, the first sensor comprises a first resistor and a first voltage sensor connected in parallel with the first resistor, the first sensor providing a measured current based on a measured voltage drop across the first resistor.
According to one aspect of the invention, the circuit further includes a first integrator operatively coupled to the first sensor and the first comparator, the first integrator operative to provide to the first comparator an output corresponding to an integral of the first current.
According to one aspect of the invention, the second detector circuit comprises: a second sensor operative to detect a second current flowing through the solenoid coil while the power switch is in a second position isolating power from the solenoid coil and current flow through the solenoid coil is decreasing; and a second comparator operative to compare fluctuations in the second measured current to the second prescribed value.
According to one aspect of the invention, the second sensor comprises a second resistor and a second voltage sensor connected in parallel with the second resistor, the second sensor providing a measured current based on a measured voltage drop across the second resistor.
According to one aspect of the invention, the circuit further includes a second integrator operatively coupled to the second sensor and the second comparator, the second integrator operative to provide to the second comparator an output corresponding to an integral of the second current.
According to one aspect of the invention, the second detector circuit comprises a diode operative to prevent current flow through the second detector circuit while current flow through the solenoid coil is increasing.
According to one aspect of the invention, a cathode of the diode is electrically connected to the solenoid coil.
According to one aspect of the invention, the circuit further includes a signal generator circuit operatively coupled to the first detector circuit and the second detector circuit, the signal generator circuit operative to provide an output indicative of the control element being at the one stopped position based on the output from the first detector circuit or the control element not being at the one stopped position based on the output of the second detector circuit.
According to one aspect of the invention, the circuit further includes a power supply for providing power to the solenoid coil, wherein the first detector circuit is series connected with the solenoid coil and the power supply, and the second detector circuit is parallel connected with the solenoid coil.
According to one aspect of the invention, the circuit further includes the solenoid coil.
According to one aspect of the invention, the circuit further includes circuitry configured to detect application of power to the solenoid coil, wherein the first detector circuit is configured to determine the occurrence of a pull-in spike based on the comparison and the application of power to the solenoid coil.
According to one aspect of the invention, the circuit further includes circuitry configured to detect removal of power to the solenoid coil, wherein the second detector circuit is configured to determine the occurrence of another condition based on the comparison and the removal of power to the solenoid coil.
According to one aspect of the invention, a method is provided for determining the position of a control element. The method includes: placing the control element in proximity to an electro-magnetic field of a solenoid coil for movement in one direction toward one stopped position relative to the solenoid coil in response to increasing electrical current flow through the solenoid coil and for movement away from the one stopped position relative to the solenoid coil in response to decreasing electrical current flow through the solenoid coil; obtaining current fluctuations during increasing current flow through the solenoid coil and comparing the measured current fluctuations with a first prescribed limit to detect when a pull-in current flow condition is reached to identify when the control element reaches the one stopped position; and obtaining current fluctuations during decreasing current flow through the solenoid coil and comparing the measured current fluctuations with a second prescribed limit to detect when another condition is reached to identify when the control element moves away from its one stopped position.
According to one aspect of the invention, measuring current fluctuations during increasing current flow and comparing the measured current fluctuations with the first prescribed limit includes detecting the presence of a connected external voltage source across the solenoid coil.
According to one aspect of the invention, measuring current fluctuations during decreasing current flow and comparing the measured current fluctuations with second predetermined limits includes detecting the absence of a connected external voltage source across the solenoid coil.
According to one aspect of the invention, the other condition is back emf.
According to one aspect of the invention, the method includes generating an output indicating a location of the control element.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
Embodiments of this invention will now be described in further detail with reference to the accompanying drawings, in which:
In the case of control elements such as ferrous armatures associated with electrical solenoids, phenomena or events known as pull-in current, drop-out current, and back EMF occur. When an electrical current flows through an electrical solenoid and its associated armature bottoms out in its fully displaced position in the direction of the electro-magnetic force acting on the armature, a negative current spike (referred to as “pull-in” current spike) occurs. Similarly, when the electrical current is turned off and the armature moves in the opposite direction off its fully displaced position, a positive current spike (referred to as “drop-out” current spike) occurs. Also, when the electrical current is turned off and the armature moves in the described opposite direction off its fully displaced position, movement of the armature through the solenoid produces a back EMF across the solenoid. A method and apparatus in accordance with the present disclosure uses a combination of these events to detect and signal the condition of the control element.
Referring now to the drawings in greater detail,
The exemplary valve assembly 10 of
The exemplary valve assembly 10 includes a valve body 12 having a valve spool 14 for selectively coupling an input port 16 to an output port 18. More specifically, when the spool 14 is in a first position (e.g., to the left), the input port 16 is isolated from the output port 18 by the spool 14 and thus the flow of fluid is inhibited. When the spool 14 is in a second position (e.g., to the right) the input port 16 is in fluid communication with the output port 18 via port 14a in the spool 14 and thus fluid will flow through the respective ports.
The spool 14 is coupled to an actuator, such as an electro-mechanical solenoid 20. The solenoid 20 includes an electromagnetically inductive coil 22 wound around a movable steel or iron slug (termed the armature 24). An air gap 26 within the solenoid allows the magnetic flux to circulate with minimum resistance (reluctance), while a spring 28 provides a force that urges the spool 14 to the closed position.
To operate the valve 10, electrical power is applied to the solenoid coil 22 via electrical leads (not shown), thereby creating magnetic flux that produces magnetic poles in the armature 24. The armature 24 then will be urged along the lines force in such a direction so as to be drawn within the solenoid coil 22, thereby overcoming the spring force and moving the spool 14 to the open position. Upon removal of power from the solenoid coil 22, the flux will collapse and the force applied by the armature 24 will be reduced to zero. The spring 28 causes the spool 14 and armature 24 to move to the closed position thereby inhibiting fluid flow.
A signaling circuit 40 receives data from the pull-in spike detector circuit 36 and the back EMF spike detector circuit 38, and provides a signal indicative of the status of the valve (e.g., open or closed).
For example, a typical solenoid operating time may be in the range of hundredths of a second, but for illustrative purposes the operating time illustrated in
The horizontal axis in
As shown in
Referring now to
In operation, the power supply 32 creates a voltage potential across the solenoid coil 22 when the switch 34 is closed. Sensor 54 measures current flow and current fluctuations through solenoid 20 by measuring voltage drop across resistor 52 and calculating the current based on the measured voltage drop and the known resistance of resistor 52.
The graph of
As shown in
Specifically, the pull-in current spike confirms a condition at which the armature 24 bottoms out and reaches a first stopped position, and the back EMF current spike confirms a condition at which the armature 24 moves away from the first stopped position. As further described below, the preferred embodiment in accordance with the present disclosure generates a status signal by combining pull-in current spike detection with solenoid energized/powered condition to indicate both the presence of a command control signal and the presence of the condition desired by the command control signal. Further, the preferred embodiment in accordance with the present disclosure also generates the status signal by combining back EMF current spike detection with solenoid de-energized condition to indicate both the presence of an opposite command control signal and the presence of the condition desired by the opposite command control signal.
In operation, the power supply 32 creates a voltage potential across the solenoid 22 when switch 34 is closed (also referred to as a first switch position), thereby creating an increasing current through the solenoid coil 22 and moving armature 24 to the bottom out position, while diode 64 prevents current flow through resistor 62 under this condition. When switch 34 is opened (also referred to as a second switch position) the current through the solenoid coil 22 decreases toward zero amps. Further, the second sensor is isolated from the power supply 32 and diode 64 permits the back EMF generated by movement of the armature 24 away from the bottom out position to cause current to flow through resistor 62 due to EMF. The sensor 66 measures this back EMF by measuring voltage drop across resistor 62 and calculating the current based on the measured voltage drop and the known resistance of resistor 62.
Referring now to
The combination of the resistor 52 and sensor 54 are shown is forming a first current sensor and the combination of the resistor 62 and sensor 66 are shown as forming a second current sensor. It is noted, however, that other types of current sensors may be employed in the circuit 70 without departing from the scope of the invention.
Pull-in integrator 72, which may be an analog integrator or a digital integrator, receives the current measurement from the sensor 54 along with first prescribed limit 74 for detecting pull-in current. The specific values entered for the first prescribed limit 74 may be a factory preset value. Alternatively, the first prescribed limit 74 may be calculated and/or scaled based an auto calibration routine. It is noted that the sensing and/or integration functions can take many forms, including analog or digital circuitry, without departing from the scope of the invention.
Pull-in integrator 72 may be embodied as a combination of an integrator and a comparator. More specifically, the pull-in integrator 72 can operate by analyzing a change in current with respect to time. In this regard, an integrator function may be employed to the measured current. The integrated current may then be compared to the first prescribed limit 74, and if the integrated current exceeds the first prescribed limit the pull-in integrator will provide a “TRUE” (1) output. If the integrated current does not exceed the first prescribed limit, then the pull-in integrator 72 will provide a “FALSE” (0) output. The integrator and comparator functions may be embodied in a single integrated device, or separate integrator and comparator may be connected together to form the pull-in integrator 72.
The output of the pull-in integrator 72, which may be a binary signal corresponding to the presence or absence of pull-in current in the coil 22, is provided to one input of first AND gate 76. A second input of the first AND gate 76 is coupled to the second terminal of switch 34 and corresponds to the status of switch 34 (i.e., ON (TRUE or “1”) or OFF (FALSE or “0”)). Accordingly, the output of the first AND gate 76 is TRUE when the switch 34 is closed and the current fluctuation sensed through resistor 52 exceeds the preset pull-in limit.
EMF integrator 78 receives the current measurement from sensor 66, along with a second prescribed limit value 80 for detecting back EMF. Like the first limit value 74, the second limit value 80 may be factory preset or may be calculated/scaled after installation based on an auto calibration routine. EMF integrator 78 operates in a manner as described above with respect to the pull-in integrator 72 and therefore its operation will not be described here.
The output of the EMF integrator 78, which may be a binary signal corresponding to the presence or absence of EMF induced current in the coil 22, is provided to one input of second AND gate 80. A second input of the second AND gate 80 is coupled to an output of inverter 82, which has an input coupled to the second terminal of switch 34. Accordingly, the output of the second AND gate 80 is TRUE when the switch 34 is open and the current fluctuation sensed through resistor 62 exceeds the preset EMF limit. The output of first AND gate 76 and second AND gate 80 are provided to status indicator 84, which for example may be a multi-colored light (e.g., red and green).
The resistor 52, sensor 54, pull-in integrator 72, limit 74 and first AND gate 76 may be considered to be part of the pull-in spike detector circuit 36. Further, the resistor 62, diode 64, sensor 66, EMF integrator 78, limit 80, second AND gate 82 and inverter 84 may be considered to be part of the back EMF spike detector circuit 38.
In operation, the valve 10 is operated by closing switch 34, which applies power to solenoid coil 22 through resistor 52 thereby causing armature 24 to move. Diode 64 prevents current flow through resistor 62 while current flow through the solenoid coil is increasing and thus back EMF cannot be detected. Sensor 54 measures the current passing through resistor 52 and provides the measurement to pull-in integrator 72. Pull-in integrator 72 compares current fluctuations in the measured current to the first limit 74. Assuming the armature 24 has not yet reached its bottom out position (and thus a pull-in spike has not occurred), the fluctuations will be minimal and therefore the output of pull-in integrator 72 will be FALSE (0). Thus, output of the first AND gate 76 will also be false.
When the armature 24 reaches the bottom-out position, a pull-in spike will occur and this spike is provided to the pull-in integrator 72. Since the measured current spike will cause a current fluctuation that will exceed the first limit 74, the output of the pull-in integrator will be TRUE (1), which is provided to the input of first AND gate 76. Further, since the switch 34 is closed (indicating the solenoid is energized) the second input of the first AND gate 76 also will be TRUE (1), while the inverter 84 provides a FALSE input to second AND gate 82 thus maintaining its output at FALSE (0). Accordingly, the output of the first AND gate 76 will be TRUE, the output of the second AND gate 82 will be FALSE, and the light 86 will be commanded to illuminate a first color (e.g., green indicating the valve is open).
The valve 10 may be returned to its normal position by opening switch 34, thereby de-energizing the solenoid coil 22. The term “opened” and “de-energized” include conditions in which relatively small residual current flows through the solenoid coil 22 after application and removal of sufficient current to cause movement of the armature 24, such as might occur when the switch 34 is an electronic switching device. De-energizing the solenoid coil 22 provides a FALSE signal to the first AND gate 76 and a TRUE signal (by virtue of the inverter 84) to one input of the second AND gate 82. Assuming the armature 24 has not yet begun to move off the bottom out position (and thus an EMF spike has not occurred), the current fluctuations will be minimal (less than that of the predetermined limit 80) and therefore the output of EMF integrator 78 will be FALSE (0). Accordingly, the output of both the first AND gate 76 and the second AND gate 82 will be FALSE.
As the armature 24 shifts off the bottom-out position, back EMF in the solenoid coil 22 causes fluctuation in the current flowing through the resistor 62, which is measured by sensor 66 and provided to EMF integrator 78. Since the current fluctuation corresponding to the back EMF due to armature movement will be greater than the second limit 80, the output of the EMF integrator 78 will be TRUE (1) and thus the output of the second AND gate 82 will be TRUE. Thus, the output of the first AND gate 76 will be FALSE and the output of the second AND gate 82 will be TRUE, and the light 86 will be commanded to illuminate a second color (e.g., red indicating the valve closed position).
Accordingly, when it has been detected that the armature 24 has shifted in a direction corresponding to the valve being open, the output from first AND gate 76 can illuminate the green light. When it has been detected that the armature 24 has shifted in a direction corresponding to the valve being closed, the output from second AND gate 82 can illuminate the red light. In this manner, the status of the armature 24 (and thus the valve) can readily be determined.
Referring now to
If an energized command has been issued, then at block 106 a determination is made as to whether power is present at the coil 22. If power is not present, then a pull-in spike will not occur and the method moves back to block 102. However, if power is present, then fluctuations in the current are monitored and compared to a preset limit (a pull-in spike limit) as indicated at block 108. At block 110, if the fluctuations in the current are less than the pull-in limit then it can be concluded that a pull-in spike is not present. Thus, it also can be concluded that the armature 24 has not moved to the bottom-out position and the method moves back to block 102. However, if at block 110 the current fluctuations are greater than the preset limit, then it can be concluded that a pull-in spike has occurred (and thus the armature 24 has moved to the bottom-out position). At block 110 a signal is generated indicative of the armature 24 being at the bottom-out position (and that the valve 10 is in one of an open or closed state).
Moving back to block 104, if it is determined that a de-energize command is provided to the solenoid coil 22, then at block 114 it is determined if power is present at the coil 22. If power is present at the coil 22, then the method moves back to block 102 as there is no need to check for back EMF. However, if at block 114 power is not present at the coil 22, then at block 116 fluctuations in the monitored current are compared to the back EMF limit. If at block 118 the fluctuations are not greater than the back EMF limit, then the method moves back to block 102. However, if at block 118 the fluctuations are greater than the back EMF limit, it can be concluded that the armature 24 has moved off the bottom-out position and the method moves to block 120, where a signal is generated indicative of the armature 24 moving off the bottom-out position (and that the valve is in the other of the open or closed state).
Accordingly, the apparatus and method in accordance with the present disclosure enable a position of a control element to be determined, without requiring a physical connection of a sensor to the control element.
Although the invention has been shown and described with respect to a certain embodiment or embodiments, equivalent alterations and modifications may occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This application claims priority of U.S. Provisional Application No. 61/827,906 filed on May 28, 2013, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61827906 | May 2013 | US |
