US20010025534A1 - Stabilizer for ball screw actuator - Google Patents
Stabilizer for ball screw actuator Download PDFInfo
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- US20010025534A1 US20010025534A1 US09/794,752 US79475201A US2001025534A1 US 20010025534 A1 US20010025534 A1 US 20010025534A1 US 79475201 A US79475201 A US 79475201A US 2001025534 A1 US2001025534 A1 US 2001025534A1
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- stabilizer
- housing
- spindle
- relative
- cylinder
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
- F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
- F16H25/20—Screw mechanisms
- F16H25/24—Elements essential to such mechanisms, e.g. screws, nuts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
- F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
- F16H25/20—Screw mechanisms
- F16H25/24—Elements essential to such mechanisms, e.g. screws, nuts
- F16H2025/2436—Intermediate screw supports for reducing unsupported length of screw shaft
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/18—Mechanical movements
- Y10T74/18568—Reciprocating or oscillating to or from alternating rotary
- Y10T74/18576—Reciprocating or oscillating to or from alternating rotary including screw and nut
- Y10T74/18656—Carriage surrounded, guided, and primarily supported by member other than screw [e.g., linear guide, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/18—Mechanical movements
- Y10T74/18568—Reciprocating or oscillating to or from alternating rotary
- Y10T74/18576—Reciprocating or oscillating to or from alternating rotary including screw and nut
- Y10T74/1868—Deflection related
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/18—Mechanical movements
- Y10T74/18568—Reciprocating or oscillating to or from alternating rotary
- Y10T74/18576—Reciprocating or oscillating to or from alternating rotary including screw and nut
- Y10T74/18688—Limit stop
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T74/00—Machine element or mechanism
- Y10T74/18—Mechanical movements
- Y10T74/18568—Reciprocating or oscillating to or from alternating rotary
- Y10T74/18576—Reciprocating or oscillating to or from alternating rotary including screw and nut
- Y10T74/18704—Means to selectively lock or retard screw or nut
Definitions
- the present invention relates generally to a linear positioning system and more specifically to a stabilizing means for a linear positioning system such as a ball screw actuator.
- a variety of systems are known in the prior art and utilized for linearly moving and positioning a workpiece relative to a housing.
- Some of such positioning systems use an elongated housing in the form of an elongated hollow cylinder with a slot therein and a piston or other motion transfer member moveable reciprocally along the cylinder.
- a carrier bracket is connected to the piston or other motion transfer member and extends through the slot for the purpose of transferring the linear movement of the piston or motion transfer member to a workpiece.
- movement of the piston or other motion transfer member results from the use of piston rods or pneumatic pressure selectively delivered to pneumatic pressure chambers within the cylinder on opposite sides of the piston.
- movement of the piston or other motion transfer member is in the form of a spindle nut having internal threads matching the external threads of an elongated, rotatably driven threaded spindle.
- the rotatably driven spindle extends substantially from one end of the cylinder to the other and the spindle nut which is rotationally fixed relative to the cylinder, advances or retracts linearly along the cylinder in response to rotational movement of the spindle.
- Linear positioning systems of this type are sometimes referred to as threaded actuators or ball screw actuators.
- the internally threaded spindle or drive nut, and thus the connected workpiece can be linearly positioned along the length of the cylinder or other supporting housing.
- actuators of this type efficiencies of cost and operation are achieved by decreasing the diameter of the threaded spindle and increasing the speed at which the spindle rotates, thereby increasing the speed at which the drive nut and thus the workpiece can be moved from one position to another.
- both of these tendencies place significant limitations on the actuator. Because the threaded spindle is supported only at its ends, the middle portion of the spindle will tend to sag, thereby creating an out-of-balance or eccentric condition when the spindle is rotated.
- the critical rotation speed at which the spindle begins to unacceptably vibrate or whip is a function of the spindle length and the spindle diameter.
- the critical speed can be increased by using larger spindle diameter for a particular spindle length, this leads to increased cost.
- the diameter, and thus the mass of inertia, of the spindle increases, larger and more expensive rotational drive motors are needed.
- the present invention relates to a stabilizing mechanism for a ball screw actuator or the like which dramatically increases the critical speed for a given actuator system of up to three times or more. More specifically, the stabilizing mechanism of the present invention includes one or more a support members which are moveable linearly along the rotating spindle to selected locations between the support points to provide support for the spindle. This reduces vibrations and whipping action and thus increases the critical speed of the spindle.
- the stabilizing mechanism of the present invention is designed for use with a ball screw actuator or the like having an elongated housing in the form of a hollow cylinder, a threaded spindle extending the length of the cylinder and a spindle or drive nut rotationally fixed relative to the housing for linear movement along the cylinder.
- the stabilizing mechanism generally includes one or more stabilizing units, each of which includes a stabilizer nut with internal threads substantially matching those of the spindle and means in the form of a stop for limiting the linear movement of the stabilizer nut relative to the spindle.
- a bearing member is provided to limit friction between such elements.
- Each stabilizing unit in accordance with the present invention further includes a first member or slider which is moveable linearly relative to the housing and which engages the stop positioned on the housing.
- a first member or slider which is moveable linearly relative to the housing and which engages the stop positioned on the housing.
- a bearing member which is adapted for engagement by the stabilizer nut.
- the slider is rotationally fixed, but linearly moveable, relative to the housing.
- the stabilizer unit in accordance with the present invention includes a pair of linearly spaced bearings mounted within the slider, with the stabilizer nut positioned therebetween.
- grease or other drag inducing means is provided between an external surface of the stabilizer nut and an internal surface of the slider to create a controlled drag between the slider and the stabilizer nut to advance the stabilizer nut in a controlled movement along the spindle.
- Another object of the present invention is to provide a stabilizer mechanism for a ball screw actuator or the like which effectively increases the critical speed at which a given actuator can operate.
- Another object of the present invention is to provide a stabilizing means for a linear positioning system of the type having a rotatable spindle which includes a stabilizer nut with internal threads substantially matching that of the spindle.
- a further object of the present invention is to provide a stabilizing mechanism for a ball screw actuator or the like which includes an outer slider and an inner stabilizing nut with controlled drag means disposed between such elements.
- a still further object of the present invention is to provide a stabilizing mechanism for a ball screw actuator or the like which provides a spindle damping mechanism moveable along the spindle and positioned between the points of spindle support.
- FIG. 1 is an isometric, exploded view with portions removed, of a ball screw actuator of the type with which the stabilizer of the present invention is designed for use.
- FIG. 2 is an isometric, exploded view of the stabilizer mechanism in accordance with the present invention.
- FIG. 3 is a view, partially in section of the stabilizer support nut as viewed along a plane extending along its longitudinal axis.
- FIG. 4 is a view, partially in section showing the assembled stabilizer of the present invention installed in a ball screw actuator cylinder.
- FIG. 5 is an isometric view of an alternate housing member for the stabilizer of the present invention.
- FIG. 6 is a view, partially in section, as viewed along the section line 6 - 6 of FIG. 4.
- FIG. 7 is a sectional view of the ball screw cylinder showing the relationship between the stabilizer stop members and the drive nut.
- FIG. 8 is an elevational plan view of a portion of the ball screw cylinder showing the stop members.
- FIG. 9 is a view of an actuator with two stabilizing mechanisms.
- FIG. 10 is a view, partially in section, as viewed along the section line 10 - 10 of FIG. 9.
- FIG. 11 is a view, partially in section as viewed along the section line 11 - 11 of FIG. 9.
- the stabilizing mechanism of the present invention is designed for use with a ball screw actuator or the like for the purpose of decreasing the vibrations and whipping action resulting from rotation of the lead screw, to thereby increase the critical speed for a given actuator system. It is contemplated that the stabilizer mechanism of the present invention can be used with any system having a rotating screw member, but particular application to systems which are commonly referred to as ball screw actuators or screw drives. The present invention is particularly applicable to ball screw actuators having lead screws of extended length. Although the stabilizer mechanism of the present invention has a variety of applications, the preferred embodiment of the present invention will be described with respect to a ball screw actuator of the type illustrated in FIG. 1.
- a ball screw actuator to which the stabilizing mechanism of the present invention has particular application includes an elongated tube or cylinder 10 having an internal bore 11 extending the length of the cylinder.
- One side of the cylinder 10 is provided with an elongated slot 12 opening into the bore 11 .
- the slot 12 extends the entire length of the cylinder 10 .
- An actuator head 15 is connected to each end of the cylinder 10 by cap screws 14 or the like.
- the bore 11 has a circular cross-section of constant diameter, however, various other shapes which are elongated in cross-sectional dimensions or have corners can be used as well.
- an elongated lead screw or spindle 16 extending through the entire length of the bore 11 and rotatably supported at each of its ends in the actuator heads 15 , 15 .
- a plurality of support elements including a bearing sleeve 18 and a contact bearing 19 are mounted in each of the actuator heads 15 to rotatably support the screw 16 .
- the bearing is retained by the retaining ring 20 .
- the axial position of the screw 16 relative to the cylinder 10 is retained by a lock washer 21 and lock nut 22 at each end.
- the lead screw 16 is provided with external threads along a substantial portion of its length.
- threads may be ACME, v-groove or any other form of thread used in connection with ball screw actuators or other screw drives.
- a motor mounting plate 24 and a motor 25 are mounted at one end of the cylinder assembly to one of the actuator heads 15 .
- the motor 25 includes an appropriate means for connection with an end of the lead screw 16 to rotate the same.
- the motor 25 can be of any type commonly used with ball screw actuators including motors which are electrically or hydraulically driven, among others.
- the drive nut bracket assembly includes a generally cylindrical body 28 having a generally cylindrical exterior configuration, an interior bore 29 and a motion transfer portion 30 extending from the main body portion 28 and through the elongated slot 12 in the cylinder 10 . As shown best in FIG. 6, the dimensions of the cylindrical configuration of the body 28 are less than the dimensions of the cylinder bore 11 . This allows the drive nut assembly 26 to move back and forth along the longitudinal axis of the bore 11 and to avoid engagement with the stop pins 61 (FIG. 6) as will be described in greater detail below.
- the motion transfer web 30 extends upwardly through the cylinder slot 12 for connection with a carrier bracket 31 or other work piece.
- the carrier 31 is connected with the transfer web 30 by a plurality of cap screws 32 extending through the carrier 31 and into threaded openings 34 in the outer edge of the transfer web 30 . Because the web 30 extends through the cylinder slot 12 , the assembly is rotationally fixed relative to drive nut 26 and the cylinder 10 . However, the drive nut assembly 26 is free to move reciprocally along the length of the slot 12 .
- the drive nut bore 29 is provided with internal threads which match the exterior threads of the lead screw 16 .
- the ball screw actuator shown in FIG. 1 also preferably includes various other elements including a plurality of bumpers 35 and spacers 36 .
- a dust band 38 and dust band clamps 39 , 39 may also be used, if desired, to keep dust and other contaminants from the internal cylinder bore 11 .
- Various other elements common to ball screw actuators or screw drives may also be utilized. Such other elements are well-known in the art. Examples of screw drives to which the present invention has particular application are screw drives such as those manufactured and sold by Tol-O-Matic, Inc. of Hamel, Minn.
- FIG. 1 Also shown in FIG. 1 is a stabilizing mechanism 40 in accordance with the present invention.
- This mechanism 40 is positioned within the cylinder bore 11 between the drive nut assembly 26 and an end of the cylinder 10 .
- the stabilizing mechanism 40 is designed to move through the cylinder bore 11 to one or more selected positions for the purpose of supporting the lead screw 16 at a point between the drive nut 26 and a corresponding end of the cylinder 10 . This support decreases the vibration and whipping action of the screw 16 , and the thus increases the critical speed for a particular actuator configuration.
- Means are also provided in the cylinder 10 for stopping or limiting linear movement of the mechanism 40 along the cylinder.
- such means in the preferred embodiment comprise pins 62 (FIG. 6) positioned in holes 63 (FIGS. 1, 6 and 7 ) in the cylinder wall.
- the stabilizing mechanism 40 includes an external support housing or slider 41 , a center support nut 42 , a pair of thrust bearings 44 and a pair of thrust washers 45 and 46 on opposite sides of each of the bearings 44 .
- the washers 45 and 46 are constructed of a relatively hard material and function to provide a race for the bearings 44 .
- the center support nut 42 , the bearings 44 and the washers 45 and 46 are retained within the housing 41 by a pair of retaining rings 48 .
- the support housing or slider 41 of the preferred embodiment is a generally cylindrical element having a generally cylindrical exterior surface 49 and a generally cylindrical internal bore 50 .
- the diametrical dimension of the cylindrical exterior surface 49 is slightly less than the diametrical dimension of the interior cylinder bore 11 . This enables the housing 41 to move longitudinally along the axis of the bore 11 while also minimizing and limiting radial movement of the housing 41 within the bore 11 .
- the difference between the exterior diametrical dimension of the surface 49 and the interior diametrical bore 11 will vary with the size of the bore, the level of dimensional tolerances and the degree to which stabilization is desired.
- this difference in diametrical dimensions ranges between about 0.10 and 0.200 inches, more preferably between about 0.025 and 0.125 inches, and most preferably between about 0.030 and 0.070 inches.
- a retaining ring groove 51 is provided near each end of the internal bore 50 for the purpose of receiving the retaining rings 48 .
- the exterior cylindrical surface 49 includes a guide member for preventing relative rotational movement between the housing 41 and the cylinder 10 , while still permitting linear movement of the housing 41 along the cylinder 10 in a direction generally parallel to the longitudinal axis of the bore 11 .
- this guide member is shown as a rib 52 integrally formed with the exterior surface 49 and extending outwardly therefrom.
- the rib 52 is designed to be located within the cylinder slot 12 (FIG. 1) and thus move along the slot as the housing 41 moves through the cylinder bore 11 .
- the rib 52 should extend outwardly from the surface 49 a sufficient distance to engage the cylinder slot 12 and should have a width less than the width of the slot 12 to permit the housing 41 to freely move along the slot in the longitudinal direction of the cylinder 10 .
- the housing 41 is preferably constructed of an aluminum or aluminum alloy material. However, various other materials may be used as well.
- the preferred embodiment shows the exterior configuration 49 to be generally cylindrical, it can also comprise other shapes as long as it is moveable longitudinally within the cylinder bore 11 .
- the configuration 49 should match that of the cylinder bore 11 configuration. Because the housing 41 does not rotate relative to the cylinder 10 , the bore 11 and the exterior configuration 49 do not need to be circular. However, regardless of the shape of the configuration 49 , the internal 50 should be circular or cylindrical to accommodate relative rotation of the support nut 42 .
- the center support nut 42 includes a generally cylindrical section 54 and a pair of end cylindrical sections 56 , 56 extending outwardly from opposite ends of the cylindrical section 54 .
- the cylindrical section 54 includes generally annular end sections 57 , a generally cylindrical outer surface 55 having a diametrical dimension slightly less than the interior diametrical dimension of the housing bore 50 . This permits the center nut 42 to be inserted into the interior bore 50 of the housing 41 and to rotate relative to it.
- the end cylindrical sections 56 , 56 have an exterior cylindrical surface with a diametrical dimension less than that of the surface 55 and of a dimension sufficient to support the bearings 44 and washers 45 and 46 . Accordingly, the outer cylindrical sections 56 , 56 extend outwardly from the ends 57 of the center section 54 a distance sufficient to support the bearing 44 and the washers 45 and 46 .
- the support nut 42 includes a central bore 58 extending through the entirety of the nut 42 in a direction parallel to the longitudinal axis of the nut 42 .
- the bore 58 is provided with internal threads which substantially match the external threads of the lead screw 16 (FIG. 1).
- the nut 42 can be constructed of a variety of materials. Preferably, however, the nut 42 is constructed of a low friction plastic material such as Delrin AF or the like. Other materials can, however, be used.
- the bearings 44 are conventional roller thrust bearings which have an exterior diameter slightly less than the exterior cylindrical surface 55 and an interior diameter slightly greater than the exterior dimension of the cylindrical end sections 56 to permit the bearings 44 to be rotatably mounted relative to the nut 42 as shown in FIG. 4. Similar to the bearings, the washers 45 and 46 have an exterior diameter slightly less than the diameter of the cylindrical surface 55 and an internal diameter slightly greater than the exterior diameter of the cylindrical portions 56 .
- the washers 45 and 46 are thrust washers and are preferably constructed of a hard material. The washers 45 and 46 are positioned on opposite sides of each bearing and function as a race for such bearings.
- a retaining ring 48 is positioned at each end and inserted into the retaining ring grooves 51 in the housing bore 50 to retain the nut 42 , the bearings 44 and the washers 45 and 46 within the housing 41 as shown in FIG. 4.
- a slight space 59 exists between the outer cylindrical surface 55 of the nut 42 and the inner cylindrical surface of the housing bore 50 .
- This space 59 results from the difference in diametrical dimensions between the two cylindrical surfaces 50 and 55 .
- the size of this space 59 is selected to provide the preferred amount of drag as the nut 42 rotates relative to the housing 41 .
- the difference in diametrical dimensions between the surface 55 and the bore 50 is preferably between about 0.001 and 0.100, more preferably between about 0.003 and 0.025 and most preferably between about 0.005 and 0.015 inches.
- a viscous material is introduced into the space 59 to increase the drag between the nut 42 and the housing 41 .
- This viscous material is preferably an oil or a grease which is sufficiently viscous to prevent it running out of or leaking from the space 59 , but not so viscous that it significantly impedes operation of the actuator.
- the viscous material is applied to the space 59 by coating the outside cylindrical surface 55 of the nut 42 before inserting the same into the housing bore 50 .
- FIGS. 4 and 6 also show the stabilizer mechanism 40 positioned within the cylinder bore 11 of the cylinder 10 .
- the exterior cylindrical surface 49 of the housing 41 conforms closely to the configuration of the bore 11 , but with dimensions slightly less. This provides sufficient support for the lead screw 16 , while also permitting linear movement of the housing 41 along the cylinder 10 .
- the rib member 52 of the housing 41 extends into the cylinder slot 12 to prevent relative rotation between the housing 41 and the cylinder 10 .
- FIG. 5 illustrates an alternate embodiment of the housing 41 .
- the guide member for guiding the housing and thus the stabilizing mechanism along the cylinder 10 is provided by a pin 60 which is press fit into a hole 61 in the exterior surface 49 of the housing 41 .
- the portion of the pin 60 extending outwardly from the surface 49 rides in the cylinder slot 12 to prevent relative rotational movement between the housing 41 and the cylinder 10 , while permitting longitudinal movement along the cylinder.
- Various other structures are also possible for preventing rotational movement between the stabilizer housing 41 and the cylinder 10 such as ribs or grooves formed on the surface 49 and complementary grooves or ribs formed on the inner surface of the bore 11 .
- the scope of the present invention is intended to cover all such mechanisms for preventing relative rotational movement between the housing 41 and the cylinder 10 while permitting linear movement along the length of the cylinder.
- a means for limiting the travel of the stabilizer mechanism 40 along the cylinder is positioned within the cylinder 10 and associated with the stabilizer mechanism 40 .
- a variety of means can be utilized to perform this function.
- One such means is illustrated in FIGS. 6, 7 and 8 comprising cross-sectional views of the cylinder 10 .
- the stop means includes a pair of pins 62 extending through holes 63 in the top of the cylinder 10 as shown in FIG. 8.
- the holes 63 extend downwardly from a side surface of the cylinder 10 to a point where they intersect at least a portion of the cylinder bore 11 .
- the holes 63 must be spaced apart a distance less than the diametrical dimension of the cylinder bore 11 .
- a portion of the pin extends inwardly from the internal surface of the cylinder bore 11 , thus forming a stop surface to prevent movement of the stabilizing mechanism beyond that point.
- Various other stop means can be used as well including other forms of stop surfaces positioned in the bore 11 or stop surfaces associated with the guide members 52 (FIG. 2) or 60 (FIG. 5).
- the stop member shown in FIGS. 6, 7 and 8 it is necessary for the diametrical dimension of the drive nut assembly 26 to be less than the distance between the pins 62 to permit the nut assembly 26 to pass the pin 62 during its movement along the cylinder 10 .
- the preferred embodiment of the present invention contemplates a single stabilizing mechanism 40 for a ball screw actuator; however, two or more such stabilizing mechanisms could, if desired, be utilized in a single ball screw actuator.
- additional mechanisms 40 might be desired is for a ball screw actuator or screw drive of extended length. In such a case, it would be desirable to use multiple stabilizer mechanisms which are stopped at various positions along the length of the cylinder to provide additional lead screw support.
- two or more stop members corresponding to the mechanisms 40 and 40 ′ must be used. Specifically, a stop member associated with each mechanism is utilized to stop that mechanism at a particular selected point along the length of the cylinder 10 . Further, such stop members must be designed so that they are independent of one another and accordingly, selectively stop or limit the movement of only the particular mechanism with which the stop member is associated.
- One way of providing stop members for more than one mechanism is to utilize stop members which are comprised of grooves in the internal portion of the bore, with corresponding ribs in the housings 41 of the mechanisms 40 and 40 ′. For example, in FIGS.
- the bore 11 includes a groove 65 which extends from the end 67 to the position of the mechanism 40 shown in FIG. 9 and a groove 66 which extends from the end 67 to the position of the mechanism 40 ′ of FIG. 9.
- the grooves 65 and 66 accommodate the ribs 68 , 69 of the mechanism 40
- the groove 65 also accommodates the rib 70 of the mechanism 40 ′.
- the operation can be understood as follows: during operation, the drive nut assembly 26 and the thus the carrier 31 and/or other load connected to the assembly 26 is caused to move along the length of the cylinder 10 from one end to the other as a result of rotation of the lead screw 16 .
- This movement along the cylinder results from the drive nut assembly having internal threads matching those of the lead screw 16 and being rotationally fixed relative to the cylinder.
- the stabilizer mechanism 40 will tend to follow the movement of the drive nut 26 until it reaches the stabilizer stop pins 62 , 62 (FIGS. 6 and 7). These pins 62 are preferably positioned approximately midway between the cylinder ends.
- the movement of the stabilizer mechanism 40 occurs because of the drag between the rotationally fixed housing 41 and the support nut 42 threadedly positioned on the lead screw 16 .
- a drag is preferably created by the viscous material between the nut 42 and the housing 41 .
- the support nut 42 rotates with the lead screw 16 and relative to the housing 41 within the bore 50 . Friction between the relatively rotating members 42 and 41 is decreased by the existence of the bearings 44 .
- the existence of the stabilizing mechanism at this point along the cylinder supports the lead screw 16 to prevent or minimize its sagging. This accordingly reduce vibrations and whipping action.
- the drive nut Upon reversing the rotation of the lead screw, the drive nut will return to the opposite or beginning end of the cylinder and the stabilizing mechanism, because of the internal drag between the nut 42 and the housing 41 , will also return to the beginning end of the cylinder.
- the present invention relates generally to a ball screw actuator or the like of the type having a housing, an externally threaded lead screw or spindle rotatably supported at first and second points relative to the housing and a spindle or a drive nut which is movable linearly along the lead screw between the first and second points.
- the stabilizer mechanism is comprised of a first member in the form of the housing 41 which is movable linearly relative to the housing between one of the first and second points and a support point defined by a stop member.
- the stabilizing mechanism includes a second member in the form of the support nut 42 which is rotatable relative to the first member and substantially linearly fixed relative to the first member.
- the second member includes internal threads substantially matching the external threads of the lead screw 16 and 15 threadedly mounted onto the lead screw.
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Abstract
Description
- 1. Field of the Invention
- The present invention relates generally to a linear positioning system and more specifically to a stabilizing means for a linear positioning system such as a ball screw actuator.
- 2. Description of the Prior Art
- A variety of systems are known in the prior art and utilized for linearly moving and positioning a workpiece relative to a housing. Some of such positioning systems use an elongated housing in the form of an elongated hollow cylinder with a slot therein and a piston or other motion transfer member moveable reciprocally along the cylinder. In these systems, a carrier bracket is connected to the piston or other motion transfer member and extends through the slot for the purpose of transferring the linear movement of the piston or motion transfer member to a workpiece. In some embodiments, movement of the piston or other motion transfer member results from the use of piston rods or pneumatic pressure selectively delivered to pneumatic pressure chambers within the cylinder on opposite sides of the piston.
- In other embodiments, movement of the piston or other motion transfer member is in the form of a spindle nut having internal threads matching the external threads of an elongated, rotatably driven threaded spindle. In these embodiments, the rotatably driven spindle extends substantially from one end of the cylinder to the other and the spindle nut which is rotationally fixed relative to the cylinder, advances or retracts linearly along the cylinder in response to rotational movement of the spindle. Linear positioning systems of this type are sometimes referred to as threaded actuators or ball screw actuators.
- By rotating the externally threaded spindle, the internally threaded spindle or drive nut, and thus the connected workpiece, can be linearly positioned along the length of the cylinder or other supporting housing. In actuators of this type, efficiencies of cost and operation are achieved by decreasing the diameter of the threaded spindle and increasing the speed at which the spindle rotates, thereby increasing the speed at which the drive nut and thus the workpiece can be moved from one position to another. Unfortunately, both of these tendencies place significant limitations on the actuator. Because the threaded spindle is supported only at its ends, the middle portion of the spindle will tend to sag, thereby creating an out-of-balance or eccentric condition when the spindle is rotated. This out-of-balance condition is accentuated with a decrease in the diameter of the spindle, an increase in the rotational speed of the spindle or an increase in the length of the spindle. Thus, for a given spindle diameter, an unacceptable increase in the rotational speed or spindle length will cause the spindle to wobble or whip in jump rope fashion along the axis of the cylinder. This not only places an upper limit on the acceptable linear speed and spindle length, but also leads to premature fatigue and wear of the spindle and drive nut and faulting of the rotary drive mechanism. Such vibrations and whipping action can also impair the accuracy of the positioning system.
- In ball screw actuators as described above, the critical rotation speed at which the spindle begins to unacceptably vibrate or whip is a function of the spindle length and the spindle diameter. Although the critical speed can be increased by using larger spindle diameter for a particular spindle length, this leads to increased cost. Further, as the diameter, and thus the mass of inertia, of the spindle increases, larger and more expensive rotational drive motors are needed.
- A variety of solutions have been proposed to dampen the vibrations or whipping action of the threaded spindle and thus effectively increase the critical speed at which a given spindle can be rotated. These solutions function primarily by providing a vibration damping member on the spindle between the support points. Such clamping members are generally moveable or displaceable along the spindle as the spindle nut advances and retracts along the length of the spindle. Some of these prior means are disclosed in U.S. Pat. No. 4,794,810 issued to Parsons, U.S. Pat. No. 4,821,456 issued to Nogaki, U.S. Pat. No. 4,878,390 issued to Hauser, U.S. Pat. No. 5,251,501 issued to Katahira, U.S. Pat. No. 5,425,607 issued to Hardesty and U.S. Pat. No. 5,531,557 issued to Springer.
- Although some of these function to increase the critical speed for a given actuator system to some extent, various drawbacks and limitations continue to exist. These include the complexity of the devices and the limit to which the critical speed can be increased, among others. Accordingly, there is a continuing need in the art for a stabilizer mechanism usable with a ball screw actuator or the like which limits the vibration or whipping action of the spindle and thus increases the critical speed at which a given spindle rotates.
- The present invention relates to a stabilizing mechanism for a ball screw actuator or the like which dramatically increases the critical speed for a given actuator system of up to three times or more. More specifically, the stabilizing mechanism of the present invention includes one or more a support members which are moveable linearly along the rotating spindle to selected locations between the support points to provide support for the spindle. This reduces vibrations and whipping action and thus increases the critical speed of the spindle.
- Still more specifically, the stabilizing mechanism of the present invention is designed for use with a ball screw actuator or the like having an elongated housing in the form of a hollow cylinder, a threaded spindle extending the length of the cylinder and a spindle or drive nut rotationally fixed relative to the housing for linear movement along the cylinder. The stabilizing mechanism generally includes one or more stabilizing units, each of which includes a stabilizer nut with internal threads substantially matching those of the spindle and means in the form of a stop for limiting the linear movement of the stabilizer nut relative to the spindle. In the preferred embodiment, a bearing member is provided to limit friction between such elements.
- Each stabilizing unit in accordance with the present invention further includes a first member or slider which is moveable linearly relative to the housing and which engages the stop positioned on the housing. Mounted within the slider is a bearing member which is adapted for engagement by the stabilizer nut. In the preferred embodiment, the slider is rotationally fixed, but linearly moveable, relative to the housing.
- In a most preferred embodiment, the stabilizer unit in accordance with the present invention includes a pair of linearly spaced bearings mounted within the slider, with the stabilizer nut positioned therebetween. In a still further preferred embodiment, grease or other drag inducing means is provided between an external surface of the stabilizer nut and an internal surface of the slider to create a controlled drag between the slider and the stabilizer nut to advance the stabilizer nut in a controlled movement along the spindle.
- Accordingly, it is an object of the present invention to provide an improved stabilizer mechanism for a ball screw actuator or the like.
- Another object of the present invention is to provide a stabilizer mechanism for a ball screw actuator or the like which effectively increases the critical speed at which a given actuator can operate.
- Another object of the present invention is to provide a stabilizing means for a linear positioning system of the type having a rotatable spindle which includes a stabilizer nut with internal threads substantially matching that of the spindle.
- A further object of the present invention is to provide a stabilizing mechanism for a ball screw actuator or the like which includes an outer slider and an inner stabilizing nut with controlled drag means disposed between such elements.
- A still further object of the present invention is to provide a stabilizing mechanism for a ball screw actuator or the like which provides a spindle damping mechanism moveable along the spindle and positioned between the points of spindle support.
- These and other objects of the present invention will become apparent with reference to the drawings, the description of the preferred embodiment and the appended claims.
- FIG. 1 is an isometric, exploded view with portions removed, of a ball screw actuator of the type with which the stabilizer of the present invention is designed for use.
- FIG. 2 is an isometric, exploded view of the stabilizer mechanism in accordance with the present invention.
- FIG. 3 is a view, partially in section of the stabilizer support nut as viewed along a plane extending along its longitudinal axis.
- FIG. 4 is a view, partially in section showing the assembled stabilizer of the present invention installed in a ball screw actuator cylinder.
- FIG. 5 is an isometric view of an alternate housing member for the stabilizer of the present invention.
- FIG. 6 is a view, partially in section, as viewed along the section line6-6 of FIG. 4.
- FIG. 7 is a sectional view of the ball screw cylinder showing the relationship between the stabilizer stop members and the drive nut.
- FIG. 8 is an elevational plan view of a portion of the ball screw cylinder showing the stop members.
- FIG. 9 is a view of an actuator with two stabilizing mechanisms.
- FIG. 10 is a view, partially in section, as viewed along the section line10-10 of FIG. 9.
- FIG. 11 is a view, partially in section as viewed along the section line11-11 of FIG. 9.
- The stabilizing mechanism of the present invention is designed for use with a ball screw actuator or the like for the purpose of decreasing the vibrations and whipping action resulting from rotation of the lead screw, to thereby increase the critical speed for a given actuator system. It is contemplated that the stabilizer mechanism of the present invention can be used with any system having a rotating screw member, but particular application to systems which are commonly referred to as ball screw actuators or screw drives. The present invention is particularly applicable to ball screw actuators having lead screws of extended length. Although the stabilizer mechanism of the present invention has a variety of applications, the preferred embodiment of the present invention will be described with respect to a ball screw actuator of the type illustrated in FIG. 1.
- With reference to FIG. 1, a ball screw actuator to which the stabilizing mechanism of the present invention has particular application includes an elongated tube or
cylinder 10 having an internal bore 11 extending the length of the cylinder. One side of thecylinder 10 is provided with anelongated slot 12 opening into the bore 11. Similar to the bore 11, theslot 12 extends the entire length of thecylinder 10. Anactuator head 15 is connected to each end of thecylinder 10 bycap screws 14 or the like. In the preferred embodiment, the bore 11 has a circular cross-section of constant diameter, however, various other shapes which are elongated in cross-sectional dimensions or have corners can be used as well. - Mounted within the bore11 of the
cylinder 10 is an elongated lead screw orspindle 16 extending through the entire length of the bore 11 and rotatably supported at each of its ends in the actuator heads 15, 15. A plurality of support elements including abearing sleeve 18 and acontact bearing 19 are mounted in each of the actuator heads 15 to rotatably support thescrew 16. The bearing is retained by the retainingring 20. The axial position of thescrew 16 relative to thecylinder 10 is retained by alock washer 21 andlock nut 22 at each end. As shown, thelead screw 16 is provided with external threads along a substantial portion of its length. These threads may be ACME, v-groove or any other form of thread used in connection with ball screw actuators or other screw drives. Amotor mounting plate 24 and amotor 25 are mounted at one end of the cylinder assembly to one of the actuator heads 15. Themotor 25 includes an appropriate means for connection with an end of thelead screw 16 to rotate the same. Themotor 25 can be of any type commonly used with ball screw actuators including motors which are electrically or hydraulically driven, among others. - Also positioned within the bore11 of the
cylinder 10 is a drivenut bracket assembly 26. The drive nut bracket assembly includes a generallycylindrical body 28 having a generally cylindrical exterior configuration, aninterior bore 29 and amotion transfer portion 30 extending from themain body portion 28 and through theelongated slot 12 in thecylinder 10. As shown best in FIG. 6, the dimensions of the cylindrical configuration of thebody 28 are less than the dimensions of the cylinder bore 11. This allows thedrive nut assembly 26 to move back and forth along the longitudinal axis of the bore 11 and to avoid engagement with the stop pins 61 (FIG. 6) as will be described in greater detail below. Themotion transfer web 30 extends upwardly through thecylinder slot 12 for connection with acarrier bracket 31 or other work piece. Thecarrier 31 is connected with thetransfer web 30 by a plurality ofcap screws 32 extending through thecarrier 31 and into threadedopenings 34 in the outer edge of thetransfer web 30. Because theweb 30 extends through thecylinder slot 12, the assembly is rotationally fixed relative to drivenut 26 and thecylinder 10. However, thedrive nut assembly 26 is free to move reciprocally along the length of theslot 12. - The drive nut bore29 is provided with internal threads which match the exterior threads of the
lead screw 16. As a result, rotation of thescrew 16, while thedrive nut 26 remains rotationally fixed within thecylinder 10, causes thenut 26 to move along the length of thecylinder 10 in a direction generally parallel to its longitudinal axis. This in turn results in a corresponding movement of thecarrier 31 and/or other connected work piece. - The ball screw actuator shown in FIG. 1 also preferably includes various other elements including a plurality of
bumpers 35 andspacers 36. Adust band 38 and dust band clamps 39, 39 may also be used, if desired, to keep dust and other contaminants from the internal cylinder bore 11. Various other elements common to ball screw actuators or screw drives may also be utilized. Such other elements are well-known in the art. Examples of screw drives to which the present invention has particular application are screw drives such as those manufactured and sold by Tol-O-Matic, Inc. of Hamel, Minn. - Also shown in FIG. 1 is a stabilizing
mechanism 40 in accordance with the present invention. Thismechanism 40 is positioned within the cylinder bore 11 between thedrive nut assembly 26 and an end of thecylinder 10. Although only one stabilizing mechanism is shown, more than one such mechanism can be used, particularly for lead screws of extended length. In general, the stabilizingmechanism 40 is designed to move through the cylinder bore 11 to one or more selected positions for the purpose of supporting thelead screw 16 at a point between thedrive nut 26 and a corresponding end of thecylinder 10. This support decreases the vibration and whipping action of thescrew 16, and the thus increases the critical speed for a particular actuator configuration. - Means are also provided in the
cylinder 10 for stopping or limiting linear movement of themechanism 40 along the cylinder. As will be described in greater detail below, such means in the preferred embodiment comprise pins 62 (FIG. 6) positioned in holes 63 (FIGS. 1, 6 and 7) in the cylinder wall. - Reference is next made to FIGS.2-5 illustrating the detailed structure of the stabilizing
mechanism 40 in accordance with the present invention. As shown best in FIG. 2, the stabilizingmechanism 40 includes an external support housing orslider 41, acenter support nut 42, a pair ofthrust bearings 44 and a pair ofthrust washers bearings 44. Thewashers bearings 44. As shown best in FIGS. 2 and 4, thecenter support nut 42, thebearings 44 and thewashers housing 41 by a pair of retaining rings 48. - More specifically, the support housing or
slider 41 of the preferred embodiment is a generally cylindrical element having a generally cylindricalexterior surface 49 and a generally cylindricalinternal bore 50. The diametrical dimension of thecylindrical exterior surface 49 is slightly less than the diametrical dimension of the interior cylinder bore 11. This enables thehousing 41 to move longitudinally along the axis of the bore 11 while also minimizing and limiting radial movement of thehousing 41 within the bore 11. The difference between the exterior diametrical dimension of thesurface 49 and the interior diametrical bore 11 will vary with the size of the bore, the level of dimensional tolerances and the degree to which stabilization is desired. Preferably, however, for a two inch bore, this difference in diametrical dimensions ranges between about 0.10 and 0.200 inches, more preferably between about 0.025 and 0.125 inches, and most preferably between about 0.030 and 0.070 inches. A retainingring groove 51 is provided near each end of theinternal bore 50 for the purpose of receiving the retaining rings 48. - The exterior
cylindrical surface 49 includes a guide member for preventing relative rotational movement between thehousing 41 and thecylinder 10, while still permitting linear movement of thehousing 41 along thecylinder 10 in a direction generally parallel to the longitudinal axis of the bore 11. In the embodiment of FIG. 2, this guide member is shown as arib 52 integrally formed with theexterior surface 49 and extending outwardly therefrom. Therib 52 is designed to be located within the cylinder slot 12 (FIG. 1) and thus move along the slot as thehousing 41 moves through the cylinder bore 11. To permit this movement, therib 52 should extend outwardly from the surface 49 a sufficient distance to engage thecylinder slot 12 and should have a width less than the width of theslot 12 to permit thehousing 41 to freely move along the slot in the longitudinal direction of thecylinder 10. Thehousing 41 is preferably constructed of an aluminum or aluminum alloy material. However, various other materials may be used as well. - Although the preferred embodiment shows the
exterior configuration 49 to be generally cylindrical, it can also comprise other shapes as long as it is moveable longitudinally within the cylinder bore 11. Preferably, theconfiguration 49 should match that of the cylinder bore 11 configuration. Because thehousing 41 does not rotate relative to thecylinder 10, the bore 11 and theexterior configuration 49 do not need to be circular. However, regardless of the shape of theconfiguration 49, the internal 50 should be circular or cylindrical to accommodate relative rotation of thesupport nut 42. - The
center support nut 42 includes a generallycylindrical section 54 and a pair of endcylindrical sections cylindrical section 54. Thecylindrical section 54 includes generallyannular end sections 57, a generally cylindricalouter surface 55 having a diametrical dimension slightly less than the interior diametrical dimension of the housing bore 50. This permits thecenter nut 42 to be inserted into the interior bore 50 of thehousing 41 and to rotate relative to it. The endcylindrical sections surface 55 and of a dimension sufficient to support thebearings 44 andwashers cylindrical sections ends 57 of the center section 54 a distance sufficient to support thebearing 44 and thewashers - As shown in FIG. 3, the
support nut 42 includes acentral bore 58 extending through the entirety of thenut 42 in a direction parallel to the longitudinal axis of thenut 42. Thebore 58 is provided with internal threads which substantially match the external threads of the lead screw 16 (FIG. 1). As a result, any force on thenut 42 tending to prevent rotation relative to thecylinder 10 will tend to move thenut 42 along thecylinder 10 in response to rotation to thelead screw 16. Thenut 42 can be constructed of a variety of materials. Preferably, however, thenut 42 is constructed of a low friction plastic material such as Delrin AF or the like. Other materials can, however, be used. - The
bearings 44 are conventional roller thrust bearings which have an exterior diameter slightly less than the exteriorcylindrical surface 55 and an interior diameter slightly greater than the exterior dimension of thecylindrical end sections 56 to permit thebearings 44 to be rotatably mounted relative to thenut 42 as shown in FIG. 4. Similar to the bearings, thewashers cylindrical surface 55 and an internal diameter slightly greater than the exterior diameter of thecylindrical portions 56. Thewashers washers ring 48 is positioned at each end and inserted into the retainingring grooves 51 in the housing bore 50 to retain thenut 42, thebearings 44 and thewashers housing 41 as shown in FIG. 4. - When the
stabilizer mechanism 40 is assembled as shown in FIG. 4, aslight space 59 exists between the outercylindrical surface 55 of thenut 42 and the inner cylindrical surface of the housing bore 50. Thisspace 59 results from the difference in diametrical dimensions between the twocylindrical surfaces space 59 is selected to provide the preferred amount of drag as thenut 42 rotates relative to thehousing 41. Preferably, for a two inch bore cylinder, the difference in diametrical dimensions between thesurface 55 and thebore 50 is preferably between about 0.001 and 0.100, more preferably between about 0.003 and 0.025 and most preferably between about 0.005 and 0.015 inches. In some cases, sufficient drag exists between the rotatable nut and the rotationally fixedhousing 41 to cause movement of thestabilizer mechanism 40 along thecylinder 10 in response to rotation of thelead screw 16; however, preferably, a viscous material is introduced into thespace 59 to increase the drag between thenut 42 and thehousing 41. This viscous material is preferably an oil or a grease which is sufficiently viscous to prevent it running out of or leaking from thespace 59, but not so viscous that it significantly impedes operation of the actuator. In general, the viscous material is applied to thespace 59 by coating the outsidecylindrical surface 55 of thenut 42 before inserting the same into the housing bore 50. - FIGS. 4 and 6 also show the
stabilizer mechanism 40 positioned within the cylinder bore 11 of thecylinder 10. When themechanism 40 is positioned within the cylinder bore 11, the exteriorcylindrical surface 49 of thehousing 41 conforms closely to the configuration of the bore 11, but with dimensions slightly less. This provides sufficient support for thelead screw 16, while also permitting linear movement of thehousing 41 along thecylinder 10. As shown, therib member 52 of thehousing 41 extends into thecylinder slot 12 to prevent relative rotation between thehousing 41 and thecylinder 10. - FIG. 5 illustrates an alternate embodiment of the
housing 41. In this embodiment, the guide member for guiding the housing and thus the stabilizing mechanism along thecylinder 10 is provided by apin 60 which is press fit into ahole 61 in theexterior surface 49 of thehousing 41. In this embodiment, the portion of thepin 60 extending outwardly from thesurface 49 rides in thecylinder slot 12 to prevent relative rotational movement between thehousing 41 and thecylinder 10, while permitting longitudinal movement along the cylinder. Various other structures are also possible for preventing rotational movement between thestabilizer housing 41 and thecylinder 10 such as ribs or grooves formed on thesurface 49 and complementary grooves or ribs formed on the inner surface of the bore 11. The scope of the present invention is intended to cover all such mechanisms for preventing relative rotational movement between thehousing 41 and thecylinder 10 while permitting linear movement along the length of the cylinder. - Also positioned within the
cylinder 10 and associated with thestabilizer mechanism 40 is a means for limiting the travel of thestabilizer mechanism 40 along the cylinder. A variety of means can be utilized to perform this function. One such means is illustrated in FIGS. 6, 7 and 8 comprising cross-sectional views of thecylinder 10. As shown, the stop means includes a pair ofpins 62 extending throughholes 63 in the top of thecylinder 10 as shown in FIG. 8. Specifically, theholes 63 extend downwardly from a side surface of thecylinder 10 to a point where they intersect at least a portion of the cylinder bore 11. Thus, theholes 63 must be spaced apart a distance less than the diametrical dimension of the cylinder bore 11. When apin 62 is inserted into thehole 63, a portion of the pin extends inwardly from the internal surface of the cylinder bore 11, thus forming a stop surface to prevent movement of the stabilizing mechanism beyond that point. Various other stop means can be used as well including other forms of stop surfaces positioned in the bore 11 or stop surfaces associated with the guide members 52 (FIG. 2) or 60 (FIG. 5). In the embodiment for the stop member shown in FIGS. 6, 7 and 8, it is necessary for the diametrical dimension of thedrive nut assembly 26 to be less than the distance between thepins 62 to permit thenut assembly 26 to pass thepin 62 during its movement along thecylinder 10. - The preferred embodiment of the present invention contemplates a single stabilizing
mechanism 40 for a ball screw actuator; however, two or more such stabilizing mechanisms could, if desired, be utilized in a single ball screw actuator. One example whereadditional mechanisms 40 might be desired is for a ball screw actuator or screw drive of extended length. In such a case, it would be desirable to use multiple stabilizer mechanisms which are stopped at various positions along the length of the cylinder to provide additional lead screw support. - When two or more stabilizing
mechanisms 40 are used in a single actuator as shown in FIG. 9, two or more stop members corresponding to themechanisms cylinder 10. Further, such stop members must be designed so that they are independent of one another and accordingly, selectively stop or limit the movement of only the particular mechanism with which the stop member is associated. One way of providing stop members for more than one mechanism is to utilize stop members which are comprised of grooves in the internal portion of the bore, with corresponding ribs in thehousings 41 of themechanisms groove 65 which extends from theend 67 to the position of themechanism 40 shown in FIG. 9 and agroove 66 which extends from theend 67 to the position of themechanism 40′ of FIG. 9. Thegrooves ribs 68, 69 of themechanism 40, while thegroove 65 also accommodates therib 70 of themechanism 40′. With this structure, themechanisms end 67 to their respective positions shown in FIG. 9. - Having described the preferred embodiment of the present invention, the operation can be understood as follows: during operation, the
drive nut assembly 26 and the thus thecarrier 31 and/or other load connected to theassembly 26 is caused to move along the length of thecylinder 10 from one end to the other as a result of rotation of thelead screw 16. This movement along the cylinder results from the drive nut assembly having internal threads matching those of thelead screw 16 and being rotationally fixed relative to the cylinder. As thenut 26 moves from one end of the cylinder to the other, thestabilizer mechanism 40 will tend to follow the movement of thedrive nut 26 until it reaches the stabilizer stop pins 62, 62 (FIGS. 6 and 7). Thesepins 62 are preferably positioned approximately midway between the cylinder ends. The movement of thestabilizer mechanism 40 occurs because of the drag between the rotationally fixedhousing 41 and thesupport nut 42 threadedly positioned on thelead screw 16. Such a drag is preferably created by the viscous material between thenut 42 and thehousing 41. When themechanism 40 reaches thestop members 62, further linear movement of themechanism 40 along the cylinder is prevented. At this point, thesupport nut 42 rotates with thelead screw 16 and relative to thehousing 41 within thebore 50. Friction between the relativelyrotating members bearings 44. The existence of the stabilizing mechanism at this point along the cylinder supports thelead screw 16 to prevent or minimize its sagging. This accordingly reduce vibrations and whipping action. Upon reversing the rotation of the lead screw, the drive nut will return to the opposite or beginning end of the cylinder and the stabilizing mechanism, because of the internal drag between thenut 42 and thehousing 41, will also return to the beginning end of the cylinder. - Accordingly, it can be seen that the present invention relates generally to a ball screw actuator or the like of the type having a housing, an externally threaded lead screw or spindle rotatably supported at first and second points relative to the housing and a spindle or a drive nut which is movable linearly along the lead screw between the first and second points. The stabilizer mechanism is comprised of a first member in the form of the
housing 41 which is movable linearly relative to the housing between one of the first and second points and a support point defined by a stop member. The stabilizing mechanism includes a second member in the form of thesupport nut 42 which is rotatable relative to the first member and substantially linearly fixed relative to the first member. The second member includes internal threads substantially matching the external threads of thelead screw - Although the description of the preferred embodiment has been quite specific, it is contemplated that various modifications could be made without deviating from the spirit of the present invention. Accordingly, it is intended that the scope of the present invention be dictated by the appended claims rather than by the description of preferred embodiment.
Claims (17)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US09/794,752 US6418807B2 (en) | 2000-03-06 | 2001-02-27 | Stabilizer for ball screw actuator |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US18731600P | 2000-03-06 | 2000-03-06 | |
US09/794,752 US6418807B2 (en) | 2000-03-06 | 2001-02-27 | Stabilizer for ball screw actuator |
Publications (2)
Publication Number | Publication Date |
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US20010025534A1 true US20010025534A1 (en) | 2001-10-04 |
US6418807B2 US6418807B2 (en) | 2002-07-16 |
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US09/794,752 Expired - Lifetime US6418807B2 (en) | 2000-03-06 | 2001-02-27 | Stabilizer for ball screw actuator |
Country Status (3)
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US (1) | US6418807B2 (en) |
AU (1) | AU2001241858A1 (en) |
WO (1) | WO2001066972A1 (en) |
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US8973453B2 (en) * | 2010-01-18 | 2015-03-10 | Smc Kabushiki Kaisha | Feed screw mechanism |
CN105840752A (en) * | 2015-01-12 | 2016-08-10 | 上银科技股份有限公司 | Limited travel ball screw |
KR102359366B1 (en) * | 2021-06-03 | 2022-02-08 | 이종기 | Ball nut for lead ball screw, Curved supporter and rectilinear movement apparatus comprising the same |
WO2022255726A1 (en) * | 2021-06-03 | 2022-12-08 | 이종기 | Curved holder and linear motion apparatus comprising same |
Also Published As
Publication number | Publication date |
---|---|
US6418807B2 (en) | 2002-07-16 |
WO2001066972A1 (en) | 2001-09-13 |
AU2001241858A1 (en) | 2001-09-17 |
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