Patent Grant
8261625
(Not Applicable)
(Not Applicable)
1. Field of the Invention
The present invention relates generally to positioning control systems and more particularly to a stepper actuator having a braking element configured to apply a braking force to mitigate unwanted rotation of the stepper actuator.
2. Description of the Prior Art
A positioning control system may be used in applications requiring accurate and precise regulation over the position of a given element. For instance, it may be desirable to have precise and accurate regulation over a control valve in a flow line carrying fluid at high pressure. Exemplary of such high pressure flow lines include the flow of gas or oil from a well, or the flow of high pressure steam to and from a turbine within a power plant. In an exemplary application, the control valve may be used to maintain the downstream pressure of the fluid in the flow line at safe and manageable levels.
Although precise regulation over a control valve in a high pressure fluid flow line may be desirable, it is often difficult to achieve. For instance, in certain applications, it is difficult to generate a sufficient amount of force to overcome the high pressure in the flow line to move the control valve at prescribed, accurate increments between its open and closed positions. In this regard, precise and accurate control over the fluid in the flow line may require small, incremental movements of the control valve, which is typically more difficult at high pressure.
To address this particular need, it is know in the prior art to employ the use of a hydraulic or pneumatic stepper actuator to achieve more precise and accurate positioning control over a fluid control valve. Known stepper actuators typically include a drive shaft which is adapted to be rotated in small increments. The rotation of the drive shaft corresponds to the incremental opening or closing of the control valve. In the prior art stepper actuators, the drive shaft is usually rotated by pneumatic or hydraulic actuation members. In certain prior art stepper actuators, the actuation members are mechanically connected to the drive shaft via a gear. The gear may be incrementally rotated by the actuation members through repeated engagement and disengagement of the actuation members to the gear, as needed to achieve incremental opening or closing of the fluid control valve. In this manner, the fluid control valve may be incrementally opened or closed to achieve desired flow parameters.
Once the fluid control valve is in the desired position, the actuation members of the prior art actuators are often disengaged from the gear. In this regard, one of the primary drawbacks of known stepper actuators is that upon such disengagement, forces are able to act on the drive shaft in a manner resulting in undesirable rotation thereof. As will be recognized, such rotation of the drive shaft, even in a small amount, may cause the fluid control valve to move from its desired position. For instance, vibration of the fluid control system may cause the drive shaft to rotate. As indicated above, such unwanted rotation of the drive shaft may compromise the precise control over the flow of fluid through the flow line.
Thus, there exists a need in the art for a stepper actuator having a braking mechanism configured to mitigate or prevent unwanted rotation of the stepper actuator, and in particular the drive shaft extending therethrough, upon the disengagement of the actuation members from the internal drive shaft rotational assembly (e.g., a gear) of the stepper actuator. The present invention addresses this particular need and others, as will be discussed in more detail below.
The present invention specifically addresses and alleviates the above-referenced deficiencies associated with stepper actuators of the prior art. More particularly, the present invention comprises a stepper actuator which, in one embodiment, includes a brake drum and a central gear having a plurality of gear teeth. The central gear is mechanically connected to the brake drum. The brake drum and the central gear are concurrently rotatable in either first (clockwise) or second (counter-clockwise) rotational directions.
The stepper actuator also includes a first actuation member that is moveable through a first actuation cycle. The first actuation member initiates the first actuation cycle from a retracted position. The first actuation member initially engages the central gear teeth and subsequently disengages the central gear teeth as the first actuation member moves through the first actuation cycle and returns to the retracted position. The first actuation member is sized and configured to rotate the central gear at a first prescribed angular displacement in the first rotational direction during engagement with the central gear teeth. The stepper actuator also includes a second actuation member that is moveable through a second actuation cycle. The second actuation member initiates the second actuation cycle from a retracted position. The second actuation member initially engages the central gear teeth and subsequently disengages the central gear teeth as the second actuation member moves through the second actuation cycle and returns to the retracted position. The second actuation member is sized and configured to rotate the central gear at a second prescribed angular displacement in the second rotational direction during engagement with the central gear teeth.
A braking assembly is operatively connected to the first and second actuation members. The braking assembly engages the brake drum to mitigate or prevent rotation of the brake drum when the first and second actuation members are both in their respective retracted positions. The braking assembly disengages the brake drum when one of the first or second actuation members is moved from its retracted position and into its corresponding actuation cycle.
The brake drum defines a peripheral brake drum wall. The brake drum wall in turn defines an inner contact surface. The braking assembly is brought into abutting, frictional engagement to the inner contact surface of the brake drum wall when the first and second actuation members are both in their retracted positions. The braking assembly disengages from the inner contact surface of the brake drum wall when one of the first or second actuation members is moved from its respective retracted position into its actuation cycle. The braking assembly may define an arcuate braking surface that is frictionally engageable with the inner contact surface of the brake drum to mitigate rotation thereof.
The braking assembly may include a brake pad which is connected to an elongate brake link. The elongate brake link may define opposed first and second end portions. The first end portion may be pivotally connected to the first actuation member and the second end portion may be pivotally connected to the second actuation member. The brake link may be in a primary position when the first and second actuation members are both in their respective retracted positions. The brake pad may engage the brake drum to mitigate rotation of the brake drum when the brake link is in the primary position. The brake pad may disengage from the brake drum when the brake link is moved from the primary position, as occurs when either of the first and second actuation members is moved from its fully retracted position into its actuation cycle.
The stepper actuator may be configured to enable manual control or actuation of either of the first and second actuation members. The stepper actuator may include a manual actuation lever that may be mechanically connected to one of the first and second actuation members, and is pivotable about a corresponding axis. As a result, one of the first and second actuation members may be moveable through a respective one of the first and second actuation cycles by the manual actuation lever.
The stepper actuator of the present invention may be configured to apply a braking force to the brake drum to mitigate rotation of the central gear, and hence a drive shaft extending therethrough, when the first and second actuation members are each in their retracted positions. The stepper actuator may further be configured discontinue the application of such braking force when one of the first and second actuation members is engaged with the gear teeth of the central gear. In this manner, the actuation members do not have to overcome the frictional braking force applied by the brake pad to the brake drum wall of the brake drum as they rotate the central gear. In addition, as indicated above, the stepper actuator of the present invention may be configured to facilitate the manual actuation of either the first or second actuation members.
Further in accordance with the present invention, there is provided alternative embodiments of the stepper actuator which are outfitted with braking mechanisms differing from the above-described brake drum and corresponding braking assembly comprising the brake pad and brake link. More particularly, in one alternative embodiment of the present invention, the brake drum, brake pad and brake link are eliminated in favor of a rigid half collar that is frictionally engageable to an integral, cylindrical neck of the central gear when the first and second actuation members are each in the retracted position. In accordance with another alternative embodiment of the present invention, the aforementioned rigid half collar is substituted with a flexible belt that is operative to exert a frictional braking force on the neck of the central gear when the first and second actuators are each in the retracted position.
In accordance with a further alternative embodiment of the present invention, the brake drum, brake pad and brake link may be eliminated in favor of an elongate locking bar that is radially moveable relative to the axis of the central gear, and is operative to push against and apply a braking force to the neck thereof when moved to a braking position as a result of the movement of one of the first and second actuation members out of its retracted position. Finally, in accordance with yet another alternative embodiment of the present invention, the radially movable locking bar may be substitute with one that moves along a different path and is cooperatively engaged to the first and second actuators so as to be advanceable between adjacent teeth of the central gear when both the first and second actuation members reside in their fully retracted positions.
The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.
These as well as other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:
Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the present invention only, and not for purposes of limiting the same,
In the stepper actuator 10, the drive shaft 11 is advanced through and mechanically connected to a cylindrically configured central hub 12 of the stepper actuator 10. As seen in
In the stepper actuator 10, the central hub 12 is mechanically connected to a central gear 22. The mechanical connection between the central hub 12 and the central gear 22 is such that they rotate concurrently with each other. Thus, as the central gear 22 rotates, the central hub 12 and hence the drive shaft 11 also rotate. The central gear 22 defines a plurality of gear teeth 24 which are disposed about the periphery thereof. As will be recognized by those of ordinary skill in the art, the number of gear teeth 24 included on the central gear 12, as well as the size of such gear teeth 24, may be varied from that shown in
The central gear 22 of the stepper actuator 10 is selectively rotatable in either a first (clockwise) direction or a second (counter-clockwise) direction. The incremental rotation of the central gear 22 in either the first or second directions is facilitated by first and second actuation members 26, 28 of the stepper actuator 10. In this regard, the first and second actuation members 26, 28 are adapted to separately engage the central gear 22, and to incrementally rotate the central gear 22 in either the first or second directions. More particularly, the rotation of the central gear 22 in the first, clockwise direction is facilitated by the engagement of the first actuation member 26 with the central gear 22. Upon the engagement of the first actuation member 26 to the central gear 22, the second actuation member 28 is necessarily disengaged therefrom. Conversely, the rotation of the central gear 22 in the second, counter-clockwise direction is facilitated by the engagement of the second actuation member 28 to the central gear 22. When the second actuation member 28 is engaged to the central gear 22, the first actuation member 26 is necessarily disengaged therefrom. As will be discussed in more detail below, it is contemplated that the first and second actuation members 26, 28 may each be either hydraulically or pneumatically actuated.
In the stepper actuator 10, it is contemplated that the first and second actuation members 26, 28 will normally be operated under automatic control. In this regard, though not shown, the stepper actuator 10 may be used in conjunction with a complimentary control unit which is operative to automatically control the rotation of the central gear 22, and hence the drive shaft 11, by the selective actuation of the first and second actuation members 26, 28. Along these lines, a user may input a desired setting into the control unit, with the stepper actuator 10 then being operative to facilitate the rotation of the central gear 22 in either a clockwise or counter-clockwise direction until the desired setting is achieved. As will be recognized by those of ordinary skill in the art, the desired setting may correspond to desired flow parameters of fluid flowing within the flow line accommodating the flow control valve to which the drive shaft 11 is operatively coupled. The stepper actuator 10 may also be manually controlled, as will also be described in more detail below.
As indicated above, the central gear 22 of the stepper actuator 10 is incrementally rotated in either the first or second directions by the first and second actuation members 26, 28. In the stepper actuator 10, the first actuation member 26 is moveable relative to the central gear 22 through a first actuation cycle. Such first actuation cycle is initiated when the first actuation member 26 is in its retracted position, as shown in
In the stepper actuator 10, the first actuation member 26 is moved through the first actuation cycle and the second actuation member 28 through the second actuation cycle by respective ones of an identically configured pair of actuators 27. As best seen in
The first and second actuation members 26, 28 of the stepper actuator 10 are identically configured, and each comprise an actuation link 30 defining opposed end portions 29, 31. As best seen in
In addition to the actuation links 30, the first and second actuation members 26, 28 each include a pawl 42 which is pivotally connected to the end portion 31 of a respective one of the actuation links 30. The pivotal connection of each pawl 42 to a respective one of the actuation links 30 is preferably facilitated by the advancement of a pin 37 through coaxially aligned apertures within the pawl 42 and the actuation link 30. As best seen in
In the stepper actuator 10, each pawl 42 is adapted to be pivotally moveable between engaged and disengaged positions relative to a respective one of the actuation links 30. When either pawl 42 is in its engaged position, the contact pin 44 thereof is cooperatively engaged to the central gear 22 in the above-described manner. Conversely, when either pawl 42 is in its disengaged position, the contact pin 44 thereof is disengaged from the central gear 22. Each pawl 42 is pivotally moveable between its engaged and disengaged positions as the corresponding actuation member 26, 28 moves through its respective actuation cycle.
In the stepper actuator 10 of the present invention, it is contemplated that each pawl 42 will normally be biased towards its engaged position. Consequently, the stepper actuator 10 preferably includes a pair of actuation collars 36 which are configured to selectively pivot respective ones of the pawls 42 into the disengaged position. Only one of the actuation collars 36 is clearly shown in
As indicated above, each actuation collar 36 is adapted to mechanically engage a respective one of the pawls 42 as it moves through its corresponding actuation cycle, thus causing such pawl 42 to be pivoted into its disengaged position. With regard to the first actuation member 26, after the contact pin 44 of the pawl 42 thereof facilitates an incremental rotational movement of the central gear 22 in the first, clockwise direction, the engagement pin 38 of the corresponding actuation collar 36 is adapted to act against the engagement portion 46 of the pawl 42 of the first actuation member 26 as effectively overcomes the biasing force acting on such pawl 42 to pivot the same into its disengaged position, thus allowing the first actuation member 26 to be moved back to its retracted position without interfering with the central gear 22. In the same manner, after the second actuation member 28 has been moved in a manner causing the contact pin 44 of the pawl 42 thereof to facilitate an incremental rotational movement of the central gear 22 in the second, counter-clockwise direction, the engagement pin 38 of the corresponding actuation collar 36 is adapted to act against the engagement portion 46 of the pawl 42 of the second actuation member 28 in a manner overcoming the biasing force acting thereon, thus pivoting such pawl 42 into its disengaged position as is needed to allow the second actuation member 28 to return to its retracted position without the pawl 42 thereof interfering with the central gear 22.
In the stepper actuator 10, each actuation collar 36 may be biased to rotate in the same direction as that of the corresponding pawl 42. In other words, for that pawl 42 of the first actuation member 26 which is adapted to rotate the central gear 22 in the first, clockwise direction, the corresponding actuation collar 36 is preferably also biased in the first direction. Similarly, for the pawl 42 of the second actuation member 28 which is adapted to rotate the central gear 22 in the second, counter-clockwise direction, the corresponding actuation collar 36 is preferably biased in the second direction as well. Along these lines, each actuation collar 36 may include a contact portion which is engageable to a respective one of a pair of stoppers 40, such stoppers 40 being operative to restrict the rotation of the corresponding actuation collar 36 in a direction opposite its desired direction. In other words, each actuation collar 36 is biased to place the contact portion thereof into engagement with a corresponding one of the stoppers 40.
In the stepper actuator 10, the actuation collars 36 are cooperatively engaged to respective ones of a pair of bearing members 71. The bearing members 71 are each cooperatively engaged to the central hub 12 and are adapted to allow respective ones of the actuation collars 36 to rotate independently of the central hub 12, and hence the central gear 22. As indicated above, the central gear 22 is also cooperatively engaged to the central hub 12 and, more particularly, is rigidly attached thereto so as to be concurrently rotatable therewith. Each of the bearing members 71 comprises annular inner and outer housings 72, 74 which are concentrically oriented relative to each other and include a plurality of ball bearings 76 captured therebetween.
With the contact pin 44 of the pawl 42 of the first actuation member 26 being cooperatively engaged to the central gear 22, the actuation rod 32 of the actuator 27 interfaced to the first actuation member 26 continues its advancement from the corresponding housing 34, which in turn allows the pawl 42 of the first actuation member 26 to incrementally rotate the central gear 22 through a prescribed angular displacement. The rotation of the central gear 22 by the first actuation member 26 ceases when the actuation rod 32 of the corresponding actuator 27 reaches the full extent of its outward stroke. Once this full outward stroke is reached, the central gear 22 stops rotating, with the an inward stroke of the actuation rod 32 then being initiated to facilitate the return the first actuation member 26 to its retracted position. More particularly, the initiation of the inward stroke of the actuation rod 32 interfaced to the first actuation member 26 causes the pawl 42 of the first actuation member 26 to contact the engagement pin 38 of the corresponding actuation collar 36, which in turn causes such pawl 42 to pivot to its disengaged position, thus releasing the contact pin 44 thereof from between an adjacent pair of gear teeth 24 of the central gear 22. With the pawl 42 of the first actuation member 26 being disengaged from the central gear 22, the first actuation member 26 returns to its retracted position, which corresponds to the full inward stroke of the actuation rod 32 of the corresponding actuator 27.
As will be recognized by those of ordinary skill in the art, the above-mentioned cycle or sequence may be repeated as needed to rotate the central gear 22 in a clockwise direction in a prescribed manner. Additionally, though not shown in
The braking mechanism of the stepper actuator 10 of the present invention comprises a brake drum 14 which is also rigidly attached to the central hub 12, and thus rotatable concurrently with the central gear 22 as well as the drive shaft 11. As a result, the brake drum 14 is itself rotatable in either a first, clockwise direction or a second, counter-clockwise direction. In this regard, as the central gear 22 rotates in the first (clockwise) direction, the brake drum 14 also rotates in the first direction. Similarly, as the central gear 22 rotates in the second (counter-clockwise) direction, the brake drum 14 also rotates in the second direction.
The braking mechanism of the stepper actuator 10 further comprises a braking assembly 52 which is adapted to apply a frictional braking force to the brake drum 14. In this regard, the braking assembly 52 is frictionally engageable to the brake drum 14 as needed to mitigate or prevent any undesired rotation of the brake drum 14, and hence the central gear 22, central hub 12, and drive shaft It. In the stepper actuator 10, the braking mechanism is configured such that the braking assembly 52 frictionally engages the brake drum 14 when both the first and second actuation members 26, 28 are each in their retracted positions. Conversely, the braking assembly 52 disengages from the brake drum 14 when either the first or second actuation members 26, 28 is moved out of its fully retracted position, and into its corresponding actuation cycle. Thus, as either the first or second actuation members 26, 28 begins its respective actuation cycle, the braking force otherwise applied to the brake drum 14 by the braking assembly 52 to prevent any undesirable rotation of the central gear 22 and hence the drive shaft 11 is removed.
The brake drum 14 defines an annular, peripheral brake drum wall 16. The brake drum wall 16 has a wall thickness “T,” and a wall depth “D.” The wall thickness T and the wall depth D may be varied as desired by those of ordinary skill in the art. The brake drum wall 16 further defines an inner contact surface 20 of a prescribed curvature. The braking assembly 52 preferably defines an arcuate, convex braking surface 54 which is complimentary to and adapted to frictionally engage the inner contact surface 20 of the brake drum wall 16 to facilitate the application of the braking force to the brake drum 14. However, those of ordinary skill in the art will recognize that curvature of the braking surface 54 may differ from that of the inner contact surface 20 without departing from the spirit and scope of the present invention.
In the braking assembly 52 of the stepper actuator 10, the braking surface 54 is defined by a brake pad 66 of the braking assembly 52. The brake pad 66 is itself connected to the bottom end of a brake pad link 67. That end of the brake pad link 67 opposite the end having the brake pad 66 connected thereto is advanced through a complimentary opening in an elongate brake link 56. As best seen in
As best seen in
In the braking assembly 52 for the stepper actuator 10, when both the first and second actuation members 26, 28 are in their retracted positions, the brake link 56 is disposed in a primary, braking position. When the brake link 56 is in its primary position, the brake pad 66, and in particular the braking surface 54 defined thereby, is disposed in frictional engagement with the inner contact surface 20 defined by the peripheral brake drum wall 16 of the brake drum 14. As a result, a frictional braking force is applied by the brake pad 66 to the brake drum 14 when the brake link 56 is in its primary position, thus preventing any undesired rotation of the central gear 22. When either of the first and second actuation members 26, 28 begins to move through its corresponding actuation cycle by moving from its retracted position, the brake link 56 of the braking assembly 52 is moved from its primary position. As the brake link 56 is moved from its primary position, the brake pad 66, and in particular the braking surface 54 defined thereby, is moved out of frictional engagement with the inner contact surface 20 defined by the peripheral brake drum wall 16 of the brake drum 14. As a result, no braking force is applied by the brake pad 66 to the brake drum 14 when the brake link 56 is moved from its primary position. Thus, as will be recognized, the movement of either the first or second actuation members 26, 28 through its corresponding actuation cycle as occurs when either of the first and second actuation members 26, 28 engages and incrementally rotates the central gear 22 will eliminate the frictional, braking contact between the brake pad 66 and the brake drum 14 due to the resultant movement of the brake pad 66 out of contact with the brake drum 14. As a result, neither of the first and second actuation members 26, 28 has to overcome the braking force applied by the brake pad 66 to brake drum 14 when being used to incrementally rotate the central gear 22 in either the clockwise or counter-clockwise directions.
As indicated above, the first and second actuation members 26, 28 will only be actuated one at a time, and never concurrently. In this regard, as also explained above, the movement of only one of the first and second actuation members 26, 28 from its retracted position into its corresponding actuation cycle is all that is needed to facilitate the movement of the brake link 56 from its primary position, and thus the cessation of the braking force applied by the brake pad 66 to the brake drum 14. When both the first and second actuation members 26, 28 are in their fully retracted positions, the brake link 56 is moved back into its primary position, thus causing the brake pad 66 to once again frictionally engage the brake drum 14, thus applying the braking force to the brake drum 14 to prevent any unwanted rotation thereof, and hence the central gear 22, central hub 12 and drive shaft 11.
In the stepper actuator 10, the central hub 12, central gear 22 and brake drum 14 are each concurrently rotatable about a primary rotational axis A. It is contemplated that the diameter of the brake drum 14 may be increased as needed to facilitate a corresponding increase in the torque created by the braking force applied by the brake pad 66 to the brake drum 14, such torque being equal to the product of the radius of the brake drum 14 and the magnitude of the applied braking force. As a result, by increasing the diameter of the brake drum 14, the torque may also be increased. Consequently, it may be desirable to form the brake drum 14 to have a diameter that is greater than the maximum diameter of the central gear 22.
Although the stepper actuator 10 of the present invention is typically operated under automated control through the selective actuation of either of the above-described actuators 27, it is contemplated that either the first actuation member 26 or the second actuation member 28 may be manually actuated in the event the automated control fails (e.g., a loss of power). Therefore, in accordance with another aspect of the present invention, there is provided a manual actuation assembly which may be used to manually operate or actuate either of the first and second actuation members 26, 28. The manual actuation assembly comprises a pair of link members 70, each of which has an end portion pivotally connected to a respective one of the above-described pins 35. The end portion of each link member 70 opposite that pivotally connected to a respective pin 35 is itself pivotally connected to one end of a link member 68. Each of the link members 68 is in turn attached to one end of a shaft 69. The shafts 69 are each rotatably connected to a base plate 80 of the stepper actuator 10 via a bearing member, and each include a reduced diameter engagement portion 82 which protrudes from an exterior surface of the base plate 80. The engagement portion 82 of each shaft 69 defines a notch which is adapted to accommodate one end of an elongate, manual actuation lever 78. The actuation lever 78 is of a preferred length L.
In the stepper actuator 10, each shaft 69 is rotatable about an axis A′ defined thereby upon the cooperative engagement of the manual actuation lever 78 thereto. In this regard, the rotation of the shaft 69 cooperatively engaged to the first actuation member 26 by the corresponding link members 68, 70 may be used to facilitate the manual actuation of the first actuation member 26 through its actuation cycle. Similarly, the cooperative engagement of the actuation lever 78 to the engagement portion 82 of the control shaft 69 coupled to the second actuation member 28 by the corresponding link members 68, 70 and subsequent rotation of the actuation lever 78 may be used to facilitate the manual actuation of the second actuation member 28 through its actuation cycle. As will be recognized, the length L of the actuation lever 78 may be increased as needed to increase the level of torque which is applied to the engagement portions 82 of the shafts 69 to facilitate the manual actuation of either of the first and second actuation members 26, 28.
Referring now to
The primary distinction between the stepper actuators 10, 100 lies in the substitution of the braking mechanism of the stepper actuator 10 with an alternatively configured braking mechanism in the stepper actuator 100. More particularly, in the stepper actuator 100, the brake drum 14 and braking assembly 52 (comprising the brake link 56, brake pad 66 and brake pad link 67) of the stepper actuator 10 are completely eliminated and substituted with an alternative braking mechanism which is adapted to selectively exert a frictional braking force on the central hub 12. In the stepper actuator 100, the alternative braking mechanism comprises an identically configured pair of elongate brake struts 112, each of which has one end pivotally connected to the brake link 56 by a pivot pin 114. The opposite end of each brake strut 112 is pivotally connected by a pivot pin 116 to a locking collar 118. It should be noted that in
In the stepper actuator 10 of the first embodiment shown in
In the braking mechanism for the stepper actuator 100, when both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are each disposed in a primary, braking position. When the brake links 56, 56a are each in the primary position, a tensile force is exerted on the brake struts 112, which in turn causes the engagement surface 120 defined by the locking collar 118 to be disposed in frictional engagement with the central hub 12, thus resulting in a frictional braking force being applied by the locking collar 120 to the central hub 12 and hence the central gear 22. Conversely, when either of the first and second actuation members 26, 28 begins to move through its corresponding actuation cycle by moving from its retracted position, the brake links 56, 56a are moved from the primary position. As the brake links 56, 56a are moved from the primary position, the locking collar 118, and in particular the engagement surface 120 defined thereby, is moved out of frictional engagement with the central hub 12. More particularly, the pivotal movement of the brake links 56, 56a toward the central hub 12 pushes the brake struts 112 in a manner effectuating the separation of the engagement surface 120 of the locking collar 118 from the outer surface of the central hub 12. As a result, no braking force is applied to the central hub 12, thus allowing the central gear 22 attached to the central hub 12 to freely rotate. Thus, the movement of either the first or second actuation members 26, 28 through its corresponding actuation cycle as occurs when either of the first and second actuation members 26, 28 engages and incrementally rotates the central gear 22 will eliminate the frictional, braking contact between the locking collar 118 and the central hub 12. As a result, neither of the first and second actuation members 26, 28 has to overcome the braking force applied by the locking collar 118 to the central hub 12 when being used to incrementally rotate the central gear 22 in either a clockwise or counter-clockwise direction.
As indicated above in relation to the stepper actuator 10, the first and second actuation members 26, 28 of the stepper actuator 100 will only be actuated one at a time, and never concurrently. As a result, the movement of only one of the first and second actuation members 26, 28 from its retracted position into its corresponding actuation cycle is all that is needed to facilitate the movement of the brake links 56, 56a from the primary position, and thus the cessation of the braking force applied by the locking collar 118 to the central hub 12. When both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are moved back into the primary position, thus causing the engagement surface 120 of the locking collar 118 to once again frictionally engage the central hub 12, thus applying the braking force to the central hub 12 to mitigate any unwanted rotation thereof and hence the central gear 22 and drive shaft 11.
Referring now to
The primary distinction between the stepper actuators 100, 200 lies in the substitution of the braking mechanism of the stepper actuator 100 with an alternatively configured braking mechanism in the stepper actuator 200. More particularly, in the stepper actuator 200, the above-described brake struts 112 and locking collar 118 are eliminated, and substituted with an elongate, flexible brake belt 224. As seen in
In the braking mechanism for the stepper actuator 200, when both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are each disposed in a primary, braking position. When the brake links 56, 56a are each in the primary position, a tensile force is exerted on the brake belt 224, which in turn causes the brake belt 224 to be disposed in frictional engagement with the central hub 12, thus resulting in a frictional braking force being applied by the brake belt 224 to the central hub 112 and hence the central gear 22. Conversely, when either of the first and second actuation members 26, 28 begins to move through its corresponding actuation cycle by moving from its retracted position, the brake links 56, 56a are moved from the primary position. As the brake links 56, 56a are moved from the primary position, the brake belt 224 is moved out of frictional engagement with the central hub 12. As a result, no braking force is applied to the central hub 12, thus allowing the central gear 22 attached to the central hub 12 to freely rotate. Thus, the movement of either the first or second actuation members 26, 28 through its corresponding actuation cycle as occurs when either of the first and second actuation members 26, 28 engages and incrementally rotates the central gear 22 will eliminate the frictional, braking contact between the brake belt 224 and the central hub 12. As a result, neither of the first and second actuation members 26, 28 has to overcome the braking force applied by the brake belt 224 to the central hub 12 when being used to incrementally rotate the central gear 22 in either a clockwise or counter-clockwise direction.
As indicated above in relation to the stepper actuator 10, the first and second actuation members 26, 28 of the stepper actuator 100 will only be actuated one at a time, and never concurrently. As a result, the movement of only one of the first and second actuation members 26, 28 from its retracted position into its corresponding actuation cycle is all that is needed to facilitate the movement of the brake links 56, 56a from the primary position, and thus the cessation of the braking force applied by the brake belt 224 to the central hub 12. When both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are moved back into the primary position, thus causing the brake belt 224 to once again frictionally engage the central hub 12, thus applying the braking force to the central hub 12 to mitigate any unwanted rotation thereof and hence the central gear 22 and drive shaft 11.
Referring now to
In the stepper actuator 300, the brake belt 224 described above in relation to the stepper actuator 200 is eliminated, and substituted with a braking mechanism comprising a brake housing 328 which is attached to and protrudes upwardly from the interior surface of the base plate 80 of the stepper actuator 400. Pivotally connected to and partially residing within the brake housing 328 is an elongate brake arm 330. As best seen in
In the braking mechanism for the stepper actuator 300, when both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are each disposed in a primary, braking position. When the brake links 56, 56a are each in the primary position, the brake arm assumes the engaged position shown in
As indicated above in relation to the stepper actuator 10, the first and second actuation members 26, 28 of the stepper actuator 300 will only be actuated one at a time, and never concurrently. As a result, the movement of only one of the first and second actuation members 26, 28 from its retracted position into its corresponding actuation cycle is all that is needed to facilitate the movement of the brake links 56, 56a from the primary position, and thus the cessation of the braking force applied by the brake arm 330 to the central gear 22. When both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are moved back into the primary position, thus causing the brake arm 330 to once again engage the central gear 22 in the aforementioned manner, thus mitigating any unwanted rotation thereof.
Referring now to
In the stepper actuator 400, the brake housing 328 and the brake arm 330 described above in relation to the stepper actuator 300 are eliminated, and substituted with a braking mechanism comprising a support block 438 which is attached to and protrudes upwardly from the interior surface of the base plate 80 of the stepper actuator 400. Also attached to and protruding upwardly from the interior surface of the base plate 80 is a guide block 440. Pivotally connected to the support block 438 is a generally V-shaped actuation link 442. As best seen in
In the braking mechanism for the stepper actuator 400, when both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are each disposed in a primary, braking position. When the brake links 56, 56a are each in the primary position, the brake bar 446 assumes the position shown in
Conversely, when both of the first and second actuation members 26, 28 return to their fully retracted position, thereby returning the brake links 56, 56a to the primary position, the movement of the brake links 56, 56a toward the primary position facilitates the rotation of the actuation link 442 in a counter-clockwise direction when viewed from the perspective shown in
As indicated above in relation to the stepper actuator 10, the first and second actuation members 26, 28 of the stepper actuator 400 will only be actuated one at a time, and never concurrently. As a result, the movement of only one of the first and second actuation members 26, 28 from its retracted position into its corresponding actuation cycle is all that is needed to facilitate the movement of the brake links 56, 56a from the primary position, and thus the cessation of the braking force applied by the brake bar 446 to the central hub 12. When both the first and second actuation members 26, 28 are in their fully retracted positions, the brake links 56, 56a are moved back into their primary position, thus causing the brake bar 446 to once again engage the central hub 12 in the aforementioned manner, thus preventing any unwanted rotation of the central gear 22 as indicated above.
The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.
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| Number | Date | Country | |
|---|---|---|---|
| 20090282937 A1 | Nov 2009 | US |
