Position sensing techniques

An apparatus includes a housing which defines a longitudinal axis; a positioning element which, relative to the housing, translates linearly along the longitudinal axis; and a rotational member which, relative to the housing, rotates about the longitudinal axis as the positioning element translates linearly along the longitudinal axis. The rotational member defines a helix to receive torque from the positioning element as the positioning element translates linearly along the longitudinal axis. The apparatus further includes a first sensor assembly to detect minor angular displacement of the rotational member (e.g., less than 360 degrees). The apparatus further includes a second sensor assembly to detect major angular displacement of the rotational member (e.g., a number of full 360 degree rotations). Such detection is capable of identifying a full angular displacement of the rotational member in response to linear translation of the positioning element from an initial position to a sensed position.

BACKGROUND

Some conventional actuators include an elongated housing, an elongated positioning element, and a motor. The elongated housing attaches to a fixed body, and the elongated positioning element attaches to an object. The motor moves the elongated positioning element along a central axis defined by the elongated housing to move the object relative to the fixed body.

To sense position, these actuators may further include a helix-shaped rotational member and a bearing element. The helix-shaped rotational member is disposed along the central axis defined by the elongated housing. Additionally, the bearing element provides support for the elongated positioning element, and enables the elongated positioning element to travel laterally along the helix-shaped rotational member and rotate the helix-shaped rotational member about the central axis in the process. As the helix-shaped rotational member rotates in response to lateral movement of the elongated positioning member, magnets mounted to the helix-shaped rotational member move past Hall sensors which detect rotation of the helix-shaped rotational member. As a result, linear movement of the elongated positioning element can be measured based on rotation of the helix-shaped rotational member.

SUMMARY

The above-described conventional actuators do not require memory to store current position information provided that the helix-shaped rotational member does not rotate more than 360 degrees. Rather, as long as the helix-shaped rotational member does not rotate more than 360 degrees, the current angular displacement of the helix-shaped rotational member correlates with the current linear displacement of the elongated positioning element. Accordingly, such actuators are capable of providing accurate position sensing even after power interruption.

Additionally, the above-described conventional actuators are capable of providing high position sensing resolution. That is, the geometries of the helix-shaped rotational member such as the rate of turn of the helix can be tailored to accurately convert sensed angular displacement of the helix-shaped rotational member with lateral movement of the elongated positioning element along the central axis. Additionally, as the length of the actuator decreases, the position sensing resolution proportionately increases.

Furthermore, the above-described conventional actuators are well-suited for certain situations such as short stroke applications. An example of such an application is the control of an aircraft flight control surface.

Similar position sensing assemblies and actuators are disclosed in U.S. Pat. No. 7,956,606. The teachings of U.S. Pat. No. 7,956,606 are hereby incorporated by reference in their entirety.

Improved techniques are directed to position sensing and actuator techniques which involve use of a helix-shaped rotational member and sensor assemblies which accurately detect rotation of the helix-shaped rotational member beyond 360 degrees. Such techniques are well suited for applications requiring relatively large linear displacement (e.g., long stroke actuators). Moreover, such techniques still do not require memory to store current position information thus enabling accurate position sensing even after power interruption, and can alleviate the need to sacrifice actuator length for higher resolution.

One embodiment is directed to a position sensing apparatus which includes a housing which defines a longitudinal axis; a positioning element which, relative to the housing, translates linearly along the longitudinal axis; and a rotational member which, relative to the housing, rotates about the longitudinal axis as the positioning element translates linearly along the longitudinal axis. The rotational member defines a helix to receive torque from the positioning element as the positioning element translates linearly along the longitudinal axis. The position sensing apparatus further includes a first sensor assembly having (i) a set of magnets coupled to the rotational member and (ii) a first set of sensors coupled to the housing, the first set of sensors being constructed and arranged to detect angular displacement of the set of magnets about the longitudinal axis. The position sensing apparatus further includes a second sensor assembly having (i) a linear displacement member, which relative to the housing, translates linearly along the longitudinal axis and (ii) a second set of sensors coupled to the housing, the second set of sensors being constructed and arranged to detect linear displacement of the linear displacement member along the longitudinal axis.

In some arrangements, the rotational member is capable of rotating more than 360 degrees about the longitudinal axis in response to linear translation of the positioning element from an initial position along the longitudinal axis to a sensed position along the longitudinal axis. In these arrangements, the initial position and the sensed position reside within a linear range of motion for the linear displacement member along the longitudinal axis. Additionally, the second set of sensors (e.g., a set of proximity sensors) is constructed and arranged to provide a signal indicating a number of full 360 degree rotations of the rotational member in response to linear translation of the positioning element from the initial position to the sensed position. Furthermore, the first set of sensors (e.g., a set of Hall sensors) is constructed and arranged to provide a signal indicating a partial rotation of the rotational member which is less than 360 degrees in response to linear translation of the positioning element from the initial position to the sensed position. The number of full 360 degree rotations and the partial rotation of the rotational member which is less than 360 degrees identifies a full angular displacement of the rotational member in response to linear translation of the positioning element from the initial position to the sensed position.

In some arrangements, the linear displacement member defines an outer surface which, based on depth sensing, is detected by the second set of sensors to identify a current position of the linear displacement member along the longitudinal axis. For example, the linear displacement member can have a constant outer diameter, and the second set of sensors includes multiple proximity sensing devices, each of the multiple proximity sensing devices being constructed and arranged to detect presence of the output surface of the linear displacement member at the same depth.

In some arrangements, the second set of sensors outputs a multi-bit signal in which a number of asserted bits of the multi-bit signal indicates a number of full revolutions performed by the rotational member in response linear translation of the positioning element from the initial position to the sensed position. In other arrangements, the second set of sensors outputs a multi-bit signal in which a particular order of a highest order asserted bit of the multi-bit signal indicates a number of full revolutions performed by the rotational member in response linear translation of the positioning element from the initial position to the sensed position. In yet other arrangements, the second set of sensors outputs a multi-bit signal in which a particular bit location of an asserted bit of the multi-bit signal indicates a number of full revolutions performed by the rotational member in response linear translation of the positioning element from the initial position to the sensed position.

In some arrangements, the linear displacement member has a stepped outer diameter. In these arrangements, the second set of sensors includes multiple proximity sensing devices, each of the multiple proximity sensing devices being constructed and arranged to detect presence of the output surface of the linear displacement member at the different depth. For example, the second set of sensors can output a multi-bit signal in which a particular bit pattern of the multi-bit signal indicates a number of full revolutions performed by the rotational member in response linear translation of the positioning element from the initial position to the sensed position.

In some arrangements, the linear displacement member physically contacts the rotational member at a sliding interface to enable the linear displacement member to translate linearly relative to the rotational member. For example, the linear displacement member can take the form of an axially moving nut having fine threads which engage the housing or an outer nut attached to the housing. Here, the rotational member has a drive key which interfaces with a key slot defined by the axially moving nut. Accordingly, as the rotational member rotates, the axially moving nut moves along the central axis by threading further into or out of the housing.

In some arrangements, the linear displacement member is physically coupled to the positioning element to enable the linear displacement member to translate linearly with linear translation of the positioning element. Here, the number of moving parts is minimized, but the number of rotations of the rotational member can still be determined by sensing of the surface of the linear displacement member.

In some arrangements, the position sensing apparatus further includes summation circuitry coupled to the first set of sensors and the second set of sensors. The summation circuitry has a first input, a second input and a terminal. The first input receives, as a first input signal, the signal indicating a partial rotation of the rotational member which is less than 360 degrees from the first set of sensors in response to linear translation of the positioning element from the initial position to the sensed position. The second input receives, as a second input signal, the signal indicating the number of full 360 degree rotations of the rotational member from the second set of sensors in response to linear translation of the positioning element from the initial position to the sensed position. The terminal provides a summation signal based on the first input signal and the second input signal, the summation signal indicating the total angular displacement of the rotational member in response to linear translation of the positioning element from the initial position to the sensed position.

In some arrangements, the position sensing apparatus further includes positioning circuitry coupled to the summation circuitry. The positioning circuitry has an input which receives the summation signal from the summation circuitry, and an output which provides a current position signal indicating a current position of the positioning element relative to the housing.

In some arrangements, the positioning element is constructed and arranged to connect to an external object (e.g., an aircraft's control surface such as an aileron, elevator, rudder, etc.). In these arrangements, the position sensing apparatus may further include an electric motor coupled to the housing, the electric motor being constructed and arranged to move the positioning element linearly along the longitudinal axis based on, as feedback, the current position signal to control positioning of the external object relative to the housing.

Other embodiments are directed to electronic systems and apparatus, processing circuits, computer program products, and so on. Some embodiments are directed to various actuation methods, actuators, electronic components and circuitry which are involved in position sensing and/or actuation.

DETAILED DESCRIPTION

Overview

An improved technique is directed to a position sensing assembly and an actuator which involve use of a helix-shaped rotational member and sensor assemblies to accurately detect rotation of the helix-shaped rotational member more than 360 degrees. Such a technique is well suited for position sensing applications requiring relatively large linear displacement (e.g., long stroke actuators). Additionally, such a technique does not require memory to store current position information thus enabling accurate position sensing even after power interruption. Furthermore, such a technique can alleviate the need to sacrifice actuator length for higher resolution.

The positioning element30is configured to be attached to the external control element24. For example, the positioning element30includes an attachment portion40, such as an eyelet which is configured to receive a fastener to secure the positioning element30to the external control element24. With such attachment, linear movement45of the positioning element30causes the external control element24(e.g., an aircraft's control surface) to change its position and/or orientation relative to the base23(e.g., an aircraft frame). Additionally, interaction between the attachment portion40and the external control element24also constrains rotation of the positioning element30about a longitudinal axis34during operation.

In one arrangement, the apparatus10further includes a protective sheath42disposed around the positioning element30. The protective sheath42, such as a bellows, extends between the attachment portion40and the housing26. The protective sheath42is configured to allow linear motion of the positioning element30relative to the longitudinal axis34defined by the housing26while minimizing the ability for dust or other contaminants to enter the housing26and damage internal components.

The motor32, such as a servo motor, is configured to control linear motion of the positioning element30relative to the longitudinal axis34. For example, in one arrangement, the motor32includes a ball nut38supported at least partially by a rotary bearing44disposed within the housing26. The ball nut38defines a set of threads46that mesh with corresponding threads48disposed on the positioning element30. During operation, in response receiving a command signal, the motor32rotates the ball nut38relative to the positioning element30. Based upon the interaction between the threads46of the ball nut38and the threads48of the positioning element30and because the external control element24rotationally constrains the positioning element30, such rotation causes the positioning element30to linearly translate (arrow45) along the longitudinal axis34and relative to the housing26. Such linear translation45of the positioning element30causes the external control element24to change its position relative to the base23.

Position Sensing Details

FIGS. 2 and 9show general details of the position sensing apparatus22. The position sensing apparatus22is configured to detect displacement of the positioning element30of the actuator28relative to the housing26(also seeFIG. 2). In particular, in response to operation of the motor32, the positioning element30moves within a predefined linear range of motion along the longitudinal axis34from an initial position (e.g., a starting or zero position) to a sensed position.

The position sensing apparatus22includes sensing subsystem60and a rotation assembly61. The rotation assembly61has a bearing element62carried by the positioning element30and a rotational member64. During operation, as the positioning element30translates linearly along the longitudinal axis34(FIG. 2), the positioning element30applies torque to the rotational member64to rotate the rotational member64about the longitudinal axis34.FIGS. 5 through 8show various views of the bearing element62which engages the rotational member64.FIGS. 3 and 4show various views of the rotational member64on which the bearing element62rides and to which the bearing element62provides rotation as the positioning element30translates linearly along the longitudinal axis34.

As shown inFIG. 9, the sensing subsystem60includes a partial rotation sensing assembly66and full rotation sensing assembly68. The partial rotation sensing assembly66is configured to identify angular displacement of the rotational member64inside 360 degrees (i.e., angular displacement between 0 and 360 degrees) due to movement of the positioning element30from the initial position to the sensed position along the longitudinal axis34. The full rotation sensing assembly68is configured to sense linear displacement of a linear displacement member200(e.g., an outer surface of a nut which is guided by the rotational member64, a portion of the positioning element30, etc.) along the longitudinal axis34to identify the number of full rotations (i.e., complete 360 degree revolutions) by the rotational member64due to movement of the positioning element30from the initial position to the sensed position along the longitudinal axis34.

In some arrangements, the partial rotation sensing assembly66and the full rotation sensing assembly68provide separate signals via a port50to an actuator controller52(FIG. 1). Accordingly, the actuator controller52can process these separate signals to accurately determine the full angular displacement of the rotational member64(i.e., a total of the partial angular displacement and the number of full rotations) and thus identify the precise linear displacement of the positioning element30relative to the housing26.

In other arrangements, the sensing subsystem60of the position sensing apparatus22includes additional logic which generates a summation signal which is provided via the port50to the actuator controller52(FIG. 1). The summation signal is indicative of the total angular displacement of the rotational member64resulting from travel of the positioning element30from the initial position to the sensed position along the longitudinal axis34thus alleviating the need for the actuator controller52to perform this operation.

As mentioned above, the partial rotation sensing assembly66identifies partial angular displacement of the rotational member64inside of 360 degrees when the positioning element30moves from an initial position to a sensed position. As shown inFIGS. 2 and 4, the partial rotation sensing assembly66includes a set of magnets70(i.e., one or more magnets70) attached to the rotational member64and a set of sensors72(i.e., one or more sensors72) attached to the housing26. In some arrangements, the partial rotation sensing assembly66is configured as a rotary sensor such as a Digital Rotary Magnetic Encoder. The set of magnets70, for example, includes a bipolar magnet having a north pole N and a south pole S. The set of sensors72is configured to detect flux or variations in the magnetic field of the set of magnets70as the set of magnets70rotates relative to the set of sensors72. For example, in one arrangement, the set of sensors72is configured as a set of Hall sensors (or a set of magnetic field sensors). While the Hall sensors can have a variety of configurations, in one arrangement, the Hall sensors are included as part of an integrated circuit (ICs) mounted on a printed circuit board (PCB)74. In use, the set of sensors72, located next to the set of magnets70, senses the rotation of the north N and south S poles and provides a corresponding output signal (1024 or 4096 counts or signals per revolution) to the port50and/or additional logic of the sensing assembly60(FIG. 15). When the output signal is provided to the port50, the actuator controller52can combine the information from the partial rotation sensing assembly66with information from the full rotation sensing assembly68to determine the absolute position of the positioning element30, i.e., the sensed position. When the output signal is provided to the additional logic of the sensing assembly60, the additional logic uses the information with other information to internally generate an output signal which indicates the total positioning of the positioning element30. Accordingly, if the apparatus10were to lose and regain power, upon resumption of power, the actuator controller52can determine the current position of the positioning element30relative to the housing26based upon signals from the sensing assembly60after the resumption of power.

As will be described in further detail below, bearing element62and the rotational member64of the rotation assembly61are configured to convert the linear motion of the positioning element30into a rotary motion of the magnet portion70. When used in conjunction with the full rotation sensing assembly68, the rotation assembly61adapts the sensing subsystem60to allow the sensing subsystem60to read linear movement of the positioning element30in the actuator assembly20.

With respect to the bearing element62, in one arrangement and with particular reference toFIG. 2, the bearing element62is carried by the positioning element30. For example, the positioning element30defines a bore or chamber80that extends from a second end82of the positioning element30toward a first or connector end83of the positioning element30. As indicated, a base portion84of the bearing element62is disposed within the chamber80. Interaction, such as a friction fit, between the base portion84and the chamber80secures the bearing element62to the positioning element30.

While the rotational member64can be carried by the actuator assembly20in a variety of ways, in one arrangement, the rotational member64includes a first portion96carried by the bearing element62and a second portion98rotatably coupled to the housing26. With respect to the first portion of the rotational member64, and as indicated above, interaction between the bearing element62and the rotational member64is configured to convert the linear motion of the positioning element30into a rotary motion of the set of magnets70to cause the sensing subsystem60to generate a signal identifying an angular displacement inside 360 degrees. Accordingly, description of arrangements of the rotational member64and the bearing element is provided below.

While bearing element62can have a variety of configurations, in one arrangement and with particular reference toFIGS. 5-8, the bearing element62is configured as a roller bearing element. For example, the bearing element62includes a bearing support portion86that carries a set of roller bearings88. While the bearing support portion86can be configured with any number of roller bearings88, in the illustrated example, the bearing support portion86includes four roller bearings88. As illustrated, the bearing support portion86includes first and second roller bearings88-1,88-2rotatably mounted via an axel90to a first bearing support portion86-1and third and fourth bearings88-3,88-4rotatably mounted via an axle92and to a second bearing support portion86-2. Also as shown, the roller bearings88define a channel94configured to support the rotational member64, as described in detail below. For example, the first roller bearing includes a first flange95-1while the fourth roller bearing88-4defines a second flange95-2where the first and second flanges95-1,95-2are spaced apart by a distance l. Additionally, the first and second roller bearings88-1,88-2and the third and fourth bearings88-3,88-4are offset by a distance d. In one arrangement, distance d is less than the thickness of the rotational member64. Taken collectively, distance l between the first and second flanges95-1,95-2and the offset distance d define the channel94for support of the rotational member64.

In one arrangement, the bearing support members86-1,86-2are formed from a spring steel material, such as 17-7PH stainless steel define a second channel94-2. In such an arrangement, the support members86-1,86-2are configured as cantilevered beams or springs that maintain a substantially constant force, such as about three pounds force, on the rotational element64to minimize or eliminate backlash between the support members86-1,86-2and the rotational member64.

As indicated above, the rotational member64includes a first portion96carried by the bearing element62. In one arrangement and with reference toFIGS. 3 and 4, the first portion96of the rotational member64is configured as a helix or a spiral shape extending between a first end100of the rotational member64and a second end102of the rotational member64where the first end100opposes the second end102. While the rotational member64can be manufactured from a variety of materials, in one arrangement the rotational member64is manufactured from a flat strip of spring steel, twisted about a longitudinal axis65of the strip into a spiral shape.

The rotational member64includes a first edge portion104extending between the first end100and the second end102of the rotational member64and a second edge portion106extending between the first end100and the second end102of the rotational member64, the first edge portion104opposing the second edge portion106. As illustrated inFIGS. 10A and 10B, the first and second edge portions104,106are configured to be disposed in proximity to the first and second flanges95-1and95-2of the bearing element62. For example, in one arrangement the first edge portion104of the rotational member64is disposed in proximity to the first flange95-1and the second edge portion106of the rotational member64is disposed in proximity to the second flange95-2. Interaction between the edge portions104,106of the rotational member64and the first and second flanges95-1and95-2of the bearing element62constrains lateral motion of the rotational member64during operation.

Returning toFIG. 3, in one arrangement, the length of the edge portions104,106are configured such that, in use, as the bearing element62translates (arrow45inFIG. 2) within the housing26over a stroke length of about three inches, the bearing element62causes the rotational member64to rotate about its longitudinal axis65. Other dimensions are suitable for use as well.

In the aforementioned configuration, in order to reduce the overall size (i.e., length and height) of the actuator assembly20, in one arrangement the longitudinal axis65of the rotational member64and the longitudinal axis34of the positioning element30and the housing26are substantially collinear. For example, the first portion96of the rotational element64extends through an opening85defined by the bearing element62, as best illustrated inFIG. 8, and into the chamber80defined by the positioning element30, as illustrated inFIG. 2. With a portion84of the rotational member64being carried by the bearing element62and extending into the positioning element's chamber80, such an arrangement reduces the overall size of the actuator assembly20.

As indicated above, in one arrangement, the rotational member64also includes a second portion98rotatably coupled to the housing26. With reference toFIGS. 2, 3, and 4, the rotational member64carries the set of magnets70used as part of the sensor assembly60. For rotary sensors, such as the sensor assembly60, the stability of the set of magnets70is important to the accurate operation of the rotary sensor since exposure of the rotary sensor to external vibrations can cause the rotary sensor to generate erroneous output signals. Accordingly, in one arrangement and with reference toFIGS. 1, 3, and 4, the rotational member64includes a bearing110, such as a rotary bearing, disposed at the second end102of the rotational element64. As shown inFIG. 1, the bearing110secures the second portion98(i.e., the second end portion102) of the rotational member64to the housing26. The bearing110is configured to constrain both longitudinal motion45of the rotational element64relative to the housing26and lateral and longitudinal movement of the set of magnets70to isolate the magnet portion from undesired vibrations. Additionally, the bearing110is configured to allow rotational movement of the rotational member64and the set of magnets70about the longitudinal axes34,65for detection by the set of sensors72carried by the housing26.

While the bearing110can have a variety of configurations, in one arrangement, the bearing110includes a first bearing element110-1and a second bearing element110-2. The use of two bearing elements110-1,110-2as part of the rotation assembly61aids in minimizing backlash between the rotational element64and the housing26. Accordingly, by minimizing backlash in the rotation assembly61, the bearing elements110-1,110-2improve the accuracy of the position or output signals generated by the sensor assembly60during operation.

In the arrangement described above, during operation, the actuator assembly20operates both the external control element24and the position sensing apparatus22. For example, in response receiving a command signal, the motor32rotates the ball nut38relative to the positioning element30. Based upon the interaction between the threads46of the ball nut38and the threads48of the positioning element30and because the external control element24rotationally constrains the positioning element30, such rotation causes the positioning element30to linearly translate45relative to the longitudinal axis34of the actuator assembly20. Such translation drives both the external control element24and the position sensing apparatus22. In particular, as the positioning element30translates45along the longitudinal axis34of the housing26, the positioning element30causes the bearing element to translate relative to the longitudinal axes34,65of the rotational member64. Such linear translation causes the edge portions104,106to ride relative to the flanges95-1,95-2and rotate the rotational member64relative to the longitudinal axis65of the rotational member64. The rotational member64, in turn, rotates the set of magnets70of the sensor assembly60relative to the set of sensors72.

Furthermore, because the distance d is less than the thickness of rotational member64, when the rotational member64is disposed between the first and second roller bearings88-1,88-2and the third and fourth bearings88-3,88-4, the rotational member64causes the first and bearing support portions86-1,86-2to bend or spring open. With such bending, the first and bearing support portions86-1,86-2operate as cantilevered beam springs that maintain a substantially constant force on the rotational member64to minimize or eliminate backlash between the bearing support86and the rotational member64.

In conventional rotary sensor devices, the presence of hysteresis or backlash, such as can occur with the use of gears or other power transmission devices used to drive a portion of the rotary sensor devices, can degrade the accuracy of the rotary sensor output. In the present position sensing apparatus22, interaction of the bearing assembly62and the helically-shaped rotational member64reduces the presence of backlash within the position sensing apparatus22while converting the linear motion of the positioning element30into a rotary motion of the set of magnets70. Accordingly, the position sensing apparatus22provides relatively accurate position sensing of the external control element24. Additionally, the rotary sensor device used with the position sensing apparatus22does not require signal conditioning and signal processing equipment as does a conventional LVDT. Accordingly, installation and operation of the position sensing apparatus22is relatively less expensive compared to conventional position sensors.

As indicated above, the interaction of the bearing assembly62and the helically-shaped rotational assembly64reduces the presence of backlash within the position sensing apparatus22. In one arrangement, the uniformity of the helix-shape of the rotational member64is integral to the accuracy of the output signal generated by the sensor assembly60. In one arrangement, the helix-shape of the rotational member64is considered uniform when, with reference toFIG. 3, an angle115formed between a surface117of the rotational member64and a plane119perpendicular to the longitudinal axis65is substantially constant along the length of the rotational member64. Such consistency provides uniform correlation between linear displacement of the positioning element30along the longitudinal axis34and angular displacement of the set of magnets70relative to the set of sensors72.

Full Rotation Sensing (Number of Full 360 Degree Rotations)

The full rotation sensing assembly68, which identifies the number of full rotations of the rotational member64when the positioning element30moves from an initial position to a sensed position, includes a linear displacement member200and a set of sensors202(also seeFIG. 9). During operation, the linear displacement member200translates along the longitudinal axis34(FIG. 2) as the rotational member64rotates. The set of sensors202sense the position of the linear displacement member200along the longitudinal axis34to determine the number of times the rotational member64has fully rotated 360 degrees while the positioning element30moved from the initial position to the sensed position.

Accordingly, the partial angular displacement of the rotational member64as measured by the partial rotation sensing assembly66(explained earlier) and the number of fully 360 degree rotations of the rotational member64as measured by the full rotation sensing assembly68equals the total angular displacement of the rotational member64. Since each sensing assembly66,68is capable of providing accurate current position information even after a power loss, the sensing subsystem60is able to provide an accurate current position of the positioning element30without storing any current count information in memory. That is, the apparatus22is able to provide reliable position information even after a power interruption.

It should be understood that there are various configurations for the linear displacement member200and the set of sensors202to enable effective sensing of the number of full 360 degree revolutions of the rotational member64when the positioning element30linearly translates from the initial position to the sensed position. For example, herein below is described an axial proximity embodiment in which the linear displacement member200has a constant radius and moves past a series of proximity sensors202which sense the same depth (FIGS. 11 and 12). As another example, further below is described a radial proximity embodiment in which the linear displacement member200has a stepped radius (i.e., a stepped surface which varies in depth) and proximity sensors202which sense different depths (FIGS. 13 and 14).

Axial Proximity Embodiment Details

FIGS. 11 and 12show side views of a portion of the apparatus10at different times of operation in accordance with an axial proximity embodiment.FIG. 11shows a side view of the portion of the apparatus10when the positioning element30(seeFIG. 9) is at an initial position along the longitudinal axis34prior to rotating the rotational member64.FIG. 12shows a side view of the portion of the apparatus10when the positioning element30is at a current sensed position after rotating the rotational member64.

As shown inFIGS. 11 and 12, the linear displacement member200takes the form of a nut210which defines a constant radius. Additionally, the set of sensors202takes the form of a series of proximity sensors212each of which is configured to sense at the same depth. By way of example only, the series of proximity sensors212includes four proximity sensors212and the nut210has a length which is spans all four proximity sensors212.

In some arrangements, the nut210defines a fine pitch inner thread, and a non-helix-shaped portion (or extension) of the rotational member64defines a matching outer thread. In these arrangements, the nut210further defines a key, and the housing26(seeFIG. 9) defines a slot enabling the nut210to translate linearly along the longitudinal axis34without any rotation. It should be understood that if the rotational member64turns in the reverse direction due to movement of the positioning element30back toward the initial position, the nut210translates linearly along the longitudinal axis34in the reverse direction.

In other arrangements, the nut defines a fine pitch outer thread, and a portion of the housing26defines a matching inner thread. In these arrangements, the nut210further defines a key slot, and the rotational member63(shown only inFIG. 2for simplicity) defines a key enabling the nut210to translate linearly while rotating with the rotational member64. It should be understood that if the rotational member64turns in the reverse direction due to movement of the positioning element30back toward the initial position, the nut210translates linearly along the longitudinal axis34as well as rotates in the reverse direction.

In these configurations, each full 360 degree rotation of the rotating member64causes the nut210to uncover exactly one proximity sensor212. For example, one rotation exposes one proximity sensor212, two rotations exposes two proximity sensors, and so on. Furthermore, each proximity sensor212outputs a bit of information, e.g., a signal having a de-asserted level if the nut210is immediately blocking that proximity sensor212and an asserted level if the nut210is not blocking that proximity sensor212.

Accordingly, the outputs of the proximity sensors212form a bit pattern which identifies the number of full rotations performed by the rotational member64. For example, at the initial position shown inFIG. 11, the bit pattern is “0000”. However, at the sensed position shown inFIG. 12, the bit pattern is “1110”. Here, number of asserted bits in the bit pattern (e.g., three) indicates the number of full 360 degree rotation of the rotating member64.

It should be understood that a variety of alternatives are suitable for use as well. For example, the assertion levels and/or component geometries could be modified so that the number of de-asserted bits in the bit pattern indicates the number of full 360 degree rotation of the rotating member64.

As another example, the assertion levels and/or component geometries can be configured so that a particular order of a highest order asserted bit of the bit pattern indicates a number of full revolutions performed by the rotational member64. For example, with reference toFIGS. 11 and 12, suppose that the rightmost proximity sensor outputs the highest order bit, the next rightmost proximity sensor outputs the next highest order bit, and so on. In this example, there are no asserted bits inFIG. 11thus indicating that the rotational member64has not made any full revolutions. However, inFIG. 12, the third highest order asserted bit of the bit pattern is set thus indicating that the rotational member64has fully rotated three times from the initial position.

As yet another example, suppose that the nut length of the nut210along the longitudinal axis34is modified so that it blocks only one proximity sensor at a time. In such an arrangement, the particular asserted (or de-asserted) bit of the bit pattern indicates how many full revolutions the rotational member64has made in response to linear translation of the positioning element30from the initial position to the sensed position. Other arrangements are suitable for use as well.

Radial Proximity Embodiment Details

FIGS. 13 and 14show side views of a portion of the apparatus10at different times of operation in accordance with a radial proximity embodiment.FIG. 13shows a side view of the portion of the apparatus10when the positioning element30(seeFIG. 9) is at an initial position along the longitudinal axis34prior to rotating the rotational member64.FIG. 14shows a side view of the portion of the apparatus10when the positioning element30is at a current sensed position after rotating the rotational member64.

As shown inFIGS. 13 and 14, the linear displacement member200takes the form of a nut220which defines a stepped radius, i.e., a stepped outer surface. Additionally, the set of sensors202takes the form of radially-aligned proximity sensors222each of which is configured to sense at a different depth. For example, the set of radially-aligned proximity sensors222can include four proximity sensors each sensing at a different depth and each positioned within a plane which is perpendicular to the longitudinal axis34.

In some arrangements, the nut220defines a fine pitch outer thread, and a portion of the housing26defines a matching inner thread. In these arrangements, the nut220further defines a key slot230, and the rotational member64defines a key232enabling the nut220to translate linearly while rotating with the rotational member64. It should be understood that if the rotational member64turns in the reverse direction due to movement of the positioning element30back toward the initial position, the nut220translates linearly along the longitudinal axis34as well as rotates in the reverse direction.

In other arrangements (also seeFIGS. 11 and 12), the nut220defines a fine pitch inner thread, and a non-helix-shaped portion of the rotational member64defines a matching outer thread. In these arrangements, the nut220further defines a key, and the housing26(shown only inFIG. 2for simplicity) defines a slot enabling the nut220to translate linearly along the longitudinal axis34without any rotation. It should be understood that if the rotational member64turns in the reverse direction due to movement of the positioning element30back toward the initial position, the nut220translates linearly along the longitudinal axis34in the reverse direction.

In these configurations, each full 360 degree rotation of the rotating member64causes a particular step of the stepped outer surface of the nut220to align with the radially-aligned proximity sensors202. For example, one rotation aligns a first step having a first radius with the sensors202, two rotations exposes a second step having a second radius with the sensors202, and so on. Furthermore, each proximity sensor outputs a bit of information, e.g., a signal having an asserted level if the depth of the aligned step of the nut220matches the sensing depth of that sensor222, and a de-asserted level if the depth of the aligned step of the nut220does not match the sensing depth of that sensor222.

As a result, the outputs of the proximity sensors222form a bit pattern which identifies the number of full rotations performed by the rotational member64. For example, at the initial position shown inFIG. 11, the bit pattern of four sensors sensing at different depths can be “0010” indicating that the rotational member has rotated one full 360 degree revolution. Additionally, at the sensed position shown inFIG. 12, the bit pattern can be “1000” indicating that the rotational member has since rotated two more 360 degree revolutions for a total of three full 360 degree revolutions. Other arrangements are suitable for use as well.

Control Logic

FIG. 15shows a position identification circuit240which is suitable for combining the outputs of the set of sensors72of the partial rotation sensing assembly66(also seeFIGS. 2 and 4) and the set of sensors202of the full rotation sensing assembly68(also seeFIGS. 11 through 14). In particular, the output252of the set of sensors72indicates the partial angular displacement of the rotation member inside 360 degrees. Additionally, the output254of bit pattern circuitry256which combines bit signals of the set of sensors202indicates the number of full 360 degree rotations of the rotational member64.

As shown inFIG. 15, the position identification circuit240further includes summation circuitry260coupled to the sets of sensors72,202. The position identification circuitry further includes positioning circuitry262coupled to the summation circuitry260.

During operation, the summation circuitry260receives the outputs252,254from both assemblies66,68and provides a summation signal270. As mentioned earlier, the outputs provide accurate information without the need for any memory. Accordingly, the summation signal270is capable of providing a reliable indication of total rotation of the rotational member64in response to movement of the positioning element30from the initial position to the sensed position even following power interruption.

The positioning circuitry262receives the summation signal270from the summation circuitry260and outputs a signal272identifying the current position of the positioning element30relative to the housing26. That is, the positioning circuitry262identifies the current actuator position for further processing or analysis, e.g., for use by the actuator controller52(FIG. 1).

It should be understood that control logic involved in determining the current position of the position element30relative to the housing26may reside in the housing26of the apparatus10, or partly in the apparatus10and partly outside the housing26of the apparatus10. For example, such control logic may be discrete from the actuator controller52(FIG. 1). Alternatively, some of the control logic may be formed by the actuator controller52.

Since the position identification circuit240is able to withstand power interruption as well as track multiple revolutions of the rotational member64, the apparatus10is well suited for a variety of application such as applications requiring high fault tolerance, long stroke applications, etc.

Further Details

In one arrangement, as indicated inFIG. 16, the position sensing apparatus22includes a controller120of the positioning circuitry262configured to compensate or correct for inaccuracies in the summation signal270, such as caused by a non-uniform helical geometry of the rotational member64. For example, the controller120, such as a processor, is configured with a position signal table124that relates a set of output signals126to a set of actual position data elements128.

Prior to operation, a manufacturer empirically configures the position signal table124for a corresponding position sensing apparatus22. For example, in order to characterize the position sensing apparatus22, the manufacturer causes the rotational member64to translate by preset amounts, such as 0.010 inch increments, to rotate the set of magnets70. At each increment, the manufacturer measures the corresponding output signal generated by the sensor assembly60. The manufacturer then configures the position signal table124with the incremental position amounts as the set of actual position data elements128and the measured output signals as the corresponding set of output signals126. In such an arrangement, each current position signal272provided by the sensor assembly60corresponds to an exact position of both the rotational member64and a corresponding external control element24, for example, as recorded in the position signal table124.

During operation of the position sensing apparatus22, as the controller120receives the summation signal270from the summation circuitry260, the controller120accesses the position signal table124to detect a correspondence between the received output signal130and entry in the set of output signals126. After detecting such a correspondence, the controller120detects an actual position data element in the set of actual position data elements128that corresponds to the entry in the set of output signals126. The controller120in turn, provides, as a reporting signal132to the actuator controller52, the detected actual position data element where the detected actual position data element relates to the actual position of an actuated element, such as an external control element24.

As described above, improved techniques are directed to position sensing and actuator techniques which involve use of a helix-shaped rotational member64and sensor assemblies66,68which accurately detect rotation of the rotational member64beyond 360 degrees. Such techniques are well suited for applications requiring relatively large linear displacement (e.g., long stroke actuators). Moreover, such techniques still do not require memory to store current position information thus enabling accurate position sensing even after power interruption, and can alleviate the need to sacrifice actuator length for higher resolution.

For example, as indicated above, the set of magnets70of the partial rotation sensing assembly60is configured as a bipolar magnet having a north pole N and a south pole S. Such description is by way of example only. In one arrangement, the set of magnets70is configured as a permanent multi-pole magnet. Alternately, the set of magnets70is configured as multiple magnets, each of the multiple magnets configured as a bipolar magnet.

As indicated above, the position sensing apparatus22operates as part of the actuator assembly20. Such indication is by way of example only. In one arrangement, the position sensing apparatus22is configured as a stand-alone device that is configured to attach to an actuated element, such as an external control element24.

Additionally, it should be understood that the proximity sensors212,222ofFIGS. 11 through 14were shown as detecting depth of the linear displacement member200. The linear displacement member200was described above as being disposed around a non-helix-shaped portion of the rotational member64. In other arrangements, the proximity sensors212,222sense depth of the positioning element30, or the depth of the linear displacement member200which attaches to the positioning element30. Such modifications and enhancements are intended to belong to various embodiments of the disclosure.