|
|
| Line 1: |
Line 1: |
| [[File:Roller_Screw.gif|185px|right|Roller screw]]
| | While this mindset is certainly understandable, it simply isn't practical at that price point. Various means of transportation come second - from yachts or boats and cars to motorcycles. The trail then follows the side of the glacial Lake Pukaki through to Twizel, the town build in the 60s only to house workers from the Waitaki Hydroelectricity Scheme. If they aren't a know brand, don't panic, I'm certain they'll be fit for purpose, but bear in mind if they look really cheap then you may struggle with things such as adjustment of your gears. Two hunters may choose to use trailers if their distance from the truck is over four or five miles. <br><br> |
|
| |
|
| A '''roller screw''', also known as a '''planetary roller screw''' or '''satellite roller screw''', is a low-[[friction]] precision screw-type [[actuator]], a mechanical device for converting rotational motion to linear motion, or vice versa. Planetary roller screws are used as the actuating mechanism in many electro-mechanical [[linear actuator]]s. Due to its complexity the roller screw is a relatively expensive actuator (as much as an [[order of magnitude]] more expensive than [[ball screw]]s), but may be suitable for high-precision, high-speed, heavy-load, long-life and heavy-use applications.
| | There are also single speed mountain bikes that only have one set gear ratio. You want to be pedaling as hard as you can while other riders right next to you are doing the exact same thing. An alternative to Clipless pedals are Mountain Bike shoes with Shimano Pedaling Dynamics (SPD). Cost shouldn't be a factor as a good helmet can be acquired for around $25-$45. However, that being said, many cross country riders prefer hardtail ones because the lighter and stiffer rear ends are better for acceleration and sprinting. <br><br>The steeper the angles, the more beneficial it would be for stability and high speed pedaling. It is just much easier to be a participant in a team and enter the race as a whole unit. There are great coaches, who will train you to tweet like a bird in spring or Link in, befriend and get a fan page. If you can't ride from home, park on either side of Galvin Parkway Road at the first intersection north of Van Buren Street (a. If you happen to crash, then you will see that your hands are the first thing that will probably come into contact with the ground. <br><br>When discount sales are on, you need to be sure you understand the terms and conditions of your purchase, including warranty information. Then, the shorter and wider teeth as well as the ramps and pegs in a bike are used in sprocket technology to ease the transition of the gear. In the purest sense of the word, a mountain bikes sole mission is to travel "off-road" only. I should have had that Bicycle repair tool with me, becuase when I got home and lowered the seat. With Adventure Kerala ( you will enjoy adventure sports like mountaineering, rapelling, rock climbing, river crossing, and a whole lot of adventure activities. <br><br>Together, you will be responsible for forming a life, raising children, making a home. The circumstances will dictate which method to use. Mountain biking amongst the majestic backdrop of the great mountains of Kerala is an unforgettable and thrilling experience. To see more information in regards to [http://dencle.lonnieheart.gethompy.com/?document_srl=219948 Info size bike mountain bike sizing.] take a look at our own web-page. Calipers can be actuated with a side pull or center pull. The bike retailer staff will likely be more then glad to expand on and point out the advantages and disadvantages of each design. |
| | |
| Roller screw mechanisms are commonly incorporated into motion/positioning systems in a variety of industries such as manufacturing and aerospace.
| |
| | |
| ==Principle of operation==
| |
| [[File:Roller_Screw_Timing.gif|thumb|right|Standard roller screw timing]]
| |
| | |
| A roller screw is a [[Linear_actuator#Mechanical_actuators|mechanical actuator]] similar to a [[ball screw]] that uses rollers as the load transfer elements between nut and screw instead of balls. The rollers are typically threaded but may also be grooved depending on roller screw type. Providing more bearing points than ball screws within a given volume, roller screws can be more compact for a given load capacity while providing similar efficiency (75%-90%) at low to moderate speeds, and maintain relatively high efficiency at high speeds. Roller screws can surpass ball screws in regard to positioning precision, load rating, rigidity, speed, acceleration, and lifetime. Standard roller screw actuators can achieve dynamic load ratings above 130 tons of force (exceeded in single-unit actuator capacity only by [[hydraulic cylinder]]s).
| |
| | |
| The three main elements of a typical planetary roller screw are the screw shaft, nut and planetary roller. The screw, a shaft with a [[Pitch_(screw)#Lead.2C_pitch.2C_and_starts|multi-start]] V-shaped [[Screw_thread|thread]], provides a helical raceway for multiple rollers radially arrayed around the screw and encapsulated by a threaded nut. The thread of the screw is typically identical to the internal thread of the nut. The rollers spin in contact with, and serve as low-friction transmission elements between screw and nut. The rollers typically have a single-start thread with convex flanks that limit friction at the rollers' contacts with screw and nut. The rollers typically orbit the screw as they spin (in the manner of [[Gear#Sun_and_planet|planet gears to sun gear]]), and are thus known as planetary, or satellite, rollers. As with a lead screw or ball screw, rotation of the nut results in screw travel, and rotation of the screw results in nut travel. | |
| | |
| For a given screw diameter and quantity of thread starts more rollers corresponds to higher static load capacity, but not necessarily to a higher dynamic load capacity. Preloaded split nuts and double nuts are available to eliminate [[Backlash_(engineering)|backlash]].
| |
| | |
| ==Planetary roller screw types==
| |
| | |
| Carl Bruno Strandgren developed some of the earliest effective forms of roller screws and applied for a patent in Nice, France on February 1942. The French patent # 888.281 was granted in August1943 and published in December of the same year. The first commercial Roller Screw was designed and manufactured under his supervision in 1949 and was mounted on a narrow gauge locomotive which operated in a northern France coal mine. Subsequent units were produced and mounted on machine-tools and starting in 1955 on aircraft. At that time Carl Bruno Strandgren applied for a new patent incorporating detailed calculations and detailed manufacturing considerations for which he was awarded US patents for such a “Screw-Threaded Mechanism” in 1954,<ref name="cite patent|US|2683379">{{cite patent|US|2683379}}</ref> and “Nut and Screw Devices”<ref>{{cite patent|US|3173304}}</ref> and the "Roller Screw" in 1965.<ref name="cite patent|US|3182522">{{cite patent|US|3182522}}</ref>
| |
| | |
| Roller screw types are defined by the motion of the rollers relative to the nut and screw. The four commercially available types of roller screw are ''standard'', ''inverted'', ''recirculating'', and ''bearing ring''.
| |
| | |
| ''Differential roller screws'', typically variants of the standard and recirculating types, are also commercially available. Differential roller screws modify the rotational speed ratios between the rollers and the screw by varying the flank angles and contact points of the threads or grooves. In that way differential roller screws change the effective lead of the screw. William J. Roantree received a US patent for the "Differential Roller Nut" in 1968.<ref>{{cite patent|US|3406584}}</ref>
| |
| | |
| ===Standard planetary roller screw===
| |
| [[File:Screw-Threaded Mechanism.jpg|thumb|Patent drawing for standard roller screw (1954), with legend.]]
| |
| | |
| The standard planetary roller screw is also known as the non-recirculating roller screw. The lack of axial movement of the roller relative to the nut, and the gearing of rollers to nut, are definitive of the standard type of roller screw.
| |
| | |
| The nut and screw have identical multiple-start threads. The rollers have a single-start thread with an angle matching the nut thread. The matched thread angle prevents axial movement between the nut and the roller as the rollers spin. The nut assembly includes spacer rings and ring gears that position and guide the rollers. The spacer rings, which rotate within the ring gears, have equidistant holes that act as [[Rolling-element bearing|rotary bearings]] for the smooth pivot ends (studs) of the rollers. The ring gears time the spinning and orbit of the rollers about the screw axis by engaging gear teeth near the ends of the rollers. The spacer rings rotate on axis with the screw in unison with the orbit of the rollers. The spacer rings float relative to the nut, axially secured by [[retaining ring]]s, because they spin around the screw at a lower frequency ([[angular velocity]]) than the nut.
| |
| | |
| ====Configuration====
| |
| | |
| Standard roller screws are typically identified by screw diameter (typically ranging from 3.5mm – 200mm) and [[Pitch_(screw)#Lead.2C_pitch.2C_and_starts|lead]] (1mm – 42mm). The threading of the screw (3 – 6 starts) is either rolled (lower capacity) or ground (higher capacity). The diameters of the nut and rollers (7 – 14 in quantity) are simple functions of the screw diameter and lead.
| |
| | |
| Where:
| |
| {| style="margin: 0.75em; width: 90%"
| |
| | <math>s_d =</math> effective screw diameter *
| |
| | <math>t =</math> thread starts on nut and screw
| |
| |-
| |
| | <math>r_d =</math> effective roller diameter
| |
| | <math>l =</math> screw lead
| |
| |-
| |
| | <math>n_d =</math> effective nut inside diameter
| |
| | <math>p =</math> roller thread [[Pitch_(screw)#Lead.2C_pitch.2C_and_starts|pitch]]
| |
| |-
| |
| | colspan = "2" | * effective diameter is also known as [[Pitch_(screw)#Pitch_diameter|pitch diameter]]
| |
| |}
| |
| | |
| The following relationships apply to standard and inverted roller screws:<ref name="cite patent|US|2683379"/>
| |
| | |
| [[File:Common_Configurations_of_Standard_Roller_Screws.jpg|thumb|Common configurations of standard roller screws]]
| |
| | |
| {| style="margin: 0.75em; height: 275px"
| |
| | rowspan="2" | <math>n_d = \frac {s_d \cdot t} {t - 2}</math>
| |
| | rowspan="2" width = "20px" | <math>\therefore</math>
| |
| | valign="bottom" | nut to screw gear ratio
| |
| |-
| |
| | valign="top" | <math>(n_d</math> : <math>s_d) = 1 </math> : <math>(t / (t -2))</math>
| |
| |-
| |
| | rowspan="2" | <math>r_d = \frac {s_d} {t -2}</math>
| |
| | rowspan="2" | <math>\therefore</math>
| |
| | valign="bottom" | roller to screw gear ratio
| |
| |-
| |
| | valign="top" | <math>(r_d</math> : <math>s_d) = 1 </math> : <math>(t - 2)</math>
| |
| |-
| |
| | rowspan="2" | <math>r_d = \frac {n_d} {t} </math>
| |
| | rowspan="2" | <math>\therefore</math>
| |
| | valign="bottom" | roller to nut gear ratio
| |
| |-
| |
| | valign="top" | <math>(r_d</math> : <math>n_d) = 1 </math> : <math> t </math>
| |
| |-
| |
| | rowspan="2" | <math>r_d = \frac {n_d - s_d} {2} </math>
| |
| | rowspan="2" |
| |
| | valign="bottom" |
| |
| |-
| |
| | valign="top" |
| |
| |-
| |
| | rowspan="2" | <math>p = \frac {l} {t} </math>
| |
| | rowspan="2" | <math>\therefore</math>
| |
| | valign="bottom" | ratio of roller thread pitch to
| |
| |-
| |
| | valign="top" | screw lead <math>(p</math> : <math>l) = 1 </math> : <math> t </math>
| |
| |}
| |
| | |
| For example, if
| |
| :Screw: 30mm diameter, 20mm lead, 5 start thread
| |
| then
| |
| :Rollers: 10mm diameter rollers, 4mm thread pitch
| |
| :Nut: 50mm effective diameter.
| |
| | |
| ===Inverted roller screw===
| |
| | |
| The inverted planetary roller screw is also known as the reverse roller screw. The lack of axial movement of the roller relative to the screw, and the gearing of rollers to screw, are definitive of the inverted type of planetary roller screw. This type of roller screw was developed simultaneously with the standard roller screw.
| |
| | |
| Inverted roller screws operate on the same principles of standard roller screws except that the function of the nut and screw is reversed in relation to the rollers. The rollers move axially within the nut, which is elongated to accommodate the full extent of screw shaft travel. The threaded portion of the screw shaft is limited to the threaded length of the rollers. The non-threaded portion of the screw shaft can be a smooth or non-cylindrical shape. The ring gear is replaced by gear teeth above and below the threaded portion of the screw shaft.
| |
| | |
| Aside from the inversion of the relationship of rollers to nut and screw, the configuration and relationships of inverted roller screws match those of standard roller screws.
| |
| | |
| ===Recirculating roller screw===
| |
| [[File:Cage-less_Recirculating_Roller_Screw.jpg|thumb|right|Cage-less recirculating roller screw patent drawing (2006), with legend.]]
| |
| The recirculating type of planetary roller screw is also known as a recycling roller screw. A recirculating roller screw can provide a very high degree of positional accuracy by using minimal thread leads. The rollers of a recirculating roller screw move axially within the nut until being reset after one orbit about the screw. Recirculating roller screws do not employ ring gears. Carl Bruno Strandgren was awarded a US Patent for the recirculating roller screw in 1965.<ref name="cite patent|US|3182522"/>
| |
| | |
| The screw and nut may have very fine identical single- or two-start threads. Recirculating rollers are grooved (instead of threaded) so they move axially during spinning engagement with the threads of the nut and screw, shifting up or down by one lead of thread after completing an orbit around the screw. The nut assembly typically includes a slotted cage and cam rings. The cage captivates the rollers in elongated slots, equally spacing the rollers while permitting rotation and axial motion of the rollers. The cam rings have opposing cams aligned with an axial groove in the wall of the nut. After a roller completes an orbit about the nut it is released into the groove, disengages from nut and screw, and is pushed between the cams to the axial midpoint of the nut assembly (shifting by a distance equal to the lead of the screw). Returned to its starting position, and reengaged to nut and screw, the roller may then orbit the screw once again.
| |
| | |
| In 2006, Charles C. Cornelius and Shawn P. Lawlor received a patent for a cage-less recirculating roller screw system.<ref>{{cite patent|US|7044017}}</ref> As with the traditional recirculating roller screw system, rollers disengage from the screw when they come upon an axial groove in the wall of the nut. The system differs in that the rollers are continually engaged by the nut, and the axial groove of the nut is threaded. Non-helical threads in the axial groove of the nut return the roller to its axial starting position (after completion of an orbit). Non-circular compression rings, or cam rings, at opposite ends of the rollers (roller axles) apply constant pressure between rollers and nut, synchronizing roller rotation and thrusting the rollers into the nut's axial groove. Lacking ring gears and roller cage, cage-less recirculating roller screws can be relatively efficient and, as a result, permit higher dynamic capacities for some screw shaft diameters.<ref>Comparative roller screw load capacity table: CMC v. Rollvis v. SKF [http://www.creativemotioncontrol.com/gallery/pdfs/Competitive_Load_Capacity_Table2011.pdf]</ref>
| |
| | |
| ===Bearing ring roller screw===
| |
| [[File:Spiracon Patent.jpg|thumb|right|Patent Drawing for Spiracon Roller Screw (1986), with legend.]]
| |
| | |
| In 1986 Oliver Saari was awarded a patent for a bearing ring roller screw, commonly referred to by its trademark, Spiracon.<ref>{{cite patent|US|4576057}}</ref> This type matches the orbit of the rollers to the rotation of the nut assembly. The actuator contains more load transfer elements than the other types, a bearing ring and [[thrust bearing]]s, but manufacture of component parts is relatively simple (e.g. gearing teeth may be eliminated).
| |
| | |
| In the other roller screw types above, loads are transferred from the nut through the rollers to the screw (or in the reverse order). In this type of actuator, thrust bearings and a freely rotating internally grooved bearing ring transfer loads between the rollers and the nut.
| |
| | |
| The screw has a multi-start thread. The rollers and encapsulating rotating ring are identically grooved, not threaded, so there is no axial movement between the two. The nut assembly includes a cylindrical housing capped by non-rotating spacer rings. The spacer rings have equidistant holes that act as rotary bearings for the smooth pivot ends (studs) of the rollers. Roller-type thrust bearings between the spacer rings and bearing ring permit free rotation of the bearing ring while transferring the axial load between the two.
| |
| | |
| The rollers act as the “threads” of the nut assembly, causing axial movement of the rotating screw due to their orbital restraint. Screw rotation spins the rollers, which spin the bearing ring, dissipating the load-induced friction along the way.
| |
| | |
| Timothy A. Erhart was awarded a US patent in 1996 for a linear actuator effectively incorporating an inverted bearing ring roller screw.<ref>{{cite patent|US|5557154}}</ref> The screw shaft is grooved the length of and to match the grooved rollers, which travel with the shaft. The bearing ring is elongated and internally threaded for the length of screw shaft travel. The nut assembly housing and sealed end ring forms the exterior of the actuator assembly.
| |
| | |
| ==See also==
| |
| * [[Ball screw]]
| |
| * [[Leadscrew]]
| |
| * [[Linear actuator]]
| |
| | |
| ==References==
| |
| {{Reflist}}
| |
| | |
| ==External links==
| |
| * [http://linearmotion.skf.com SKF Roller Screw website]
| |
| * [http://www.planetel.fr PLANETEL Roller Screw website]
| |
| * [http://exlar.com/TI_ref_rollScrew_oview.html Exlar Roller Screw Description]
| |
| * [http://www.nookindustries.com/rollerscrew/RollerScrewGlossary.cfm Nook Planetary Roller Screw Glossary and Technical Data]
| |
| * [http://www.servo-drive.com/products_servo_actuators_details_en.php Roller Screw Servo Actuator Description]
| |
| * [http://www.rollvis.com/EN/resources/Catal-01-01-2008-AN.pdf Rollvis Satellite Roller Screw Catalog 2008]
| |
| * [http://www.powerjacks.com/Downloads/Product%20Guides/Spiracon-Roller-Screw.pdf Spiracon Roller Screw Catalog]
| |
| * [http://www.creativemotioncontrol.com/roller-screws/patented_design.php CMC Cage-less Recirculating Roller Screw Description]
| |
| * [http://www.consultolsen.com/ch/video_satrollerscrews.html Web Page with Video Showing Standard and Recirculating Roller Screw Assemblies]
| |
| | |
| [[Category:Screws]]
| |
| [[Category:Actuators]]
| |
| [[Category:Positioning instruments]]
| |
While this mindset is certainly understandable, it simply isn't practical at that price point. Various means of transportation come second - from yachts or boats and cars to motorcycles. The trail then follows the side of the glacial Lake Pukaki through to Twizel, the town build in the 60s only to house workers from the Waitaki Hydroelectricity Scheme. If they aren't a know brand, don't panic, I'm certain they'll be fit for purpose, but bear in mind if they look really cheap then you may struggle with things such as adjustment of your gears. Two hunters may choose to use trailers if their distance from the truck is over four or five miles.
There are also single speed mountain bikes that only have one set gear ratio. You want to be pedaling as hard as you can while other riders right next to you are doing the exact same thing. An alternative to Clipless pedals are Mountain Bike shoes with Shimano Pedaling Dynamics (SPD). Cost shouldn't be a factor as a good helmet can be acquired for around $25-$45. However, that being said, many cross country riders prefer hardtail ones because the lighter and stiffer rear ends are better for acceleration and sprinting.
The steeper the angles, the more beneficial it would be for stability and high speed pedaling. It is just much easier to be a participant in a team and enter the race as a whole unit. There are great coaches, who will train you to tweet like a bird in spring or Link in, befriend and get a fan page. If you can't ride from home, park on either side of Galvin Parkway Road at the first intersection north of Van Buren Street (a. If you happen to crash, then you will see that your hands are the first thing that will probably come into contact with the ground.
When discount sales are on, you need to be sure you understand the terms and conditions of your purchase, including warranty information. Then, the shorter and wider teeth as well as the ramps and pegs in a bike are used in sprocket technology to ease the transition of the gear. In the purest sense of the word, a mountain bikes sole mission is to travel "off-road" only. I should have had that Bicycle repair tool with me, becuase when I got home and lowered the seat. With Adventure Kerala ( you will enjoy adventure sports like mountaineering, rapelling, rock climbing, river crossing, and a whole lot of adventure activities.
Together, you will be responsible for forming a life, raising children, making a home. The circumstances will dictate which method to use. Mountain biking amongst the majestic backdrop of the great mountains of Kerala is an unforgettable and thrilling experience. To see more information in regards to Info size bike mountain bike sizing. take a look at our own web-page. Calipers can be actuated with a side pull or center pull. The bike retailer staff will likely be more then glad to expand on and point out the advantages and disadvantages of each design.