Leadscrew

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leadscrew (or lead screw ), also known as screw power or screw translation , is a screw used as a link in the machine, to translate the twisted motion into a linear motion. Due to the large shear contact areas between their male and female members, screw threads have a greater friction energy loss compared to other relationships. They are not normally used to carry high power, but rather for intermittent use in actuator mechanisms and low power positioners. Common applications are linear actuators, slide machines (as in machine tools), vises, presses, and jacks.

Leadscrews are produced in the same way as other threaded forms (they can be rolled, cut, or ground).

The tin screw is sometimes used with a separate nut which is also called a half nut which allows the nut to be released from the yarn and moves axially, regardless of the rotation of the screw, when necessary (as in single point strapping on a manual lathe).

Video Leadscrew

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Power screws are classified according to their thread geometry. V-threads are less suitable for leadscrew than others like ACME because they have more friction between the threads. Their threads are designed to encourage this friction so that fasteners do not loosen. Leadscrews, on the other hand, are designed to minimize friction. Therefore, in commercial and industrial use, V-threads are avoided for leadscrew use. However, V-threads are sometimes successfully used as leadscrews, such as microlathes and micromills.

Square thread

Square threads are named after their square geometry. They are the most efficient, have less friction, so often used for screws that carry high power. But they are also the most difficult to machine, and thus the most expensive.

Acme thread

Acme thread has 29 Â ° thread angle, which is easier to machine than square thread. They are not as efficient as a square thread, because the increased friction is caused by the angle of the thread. ACME threads are generally also stronger than square threads because of their trapezoidal threaded profiles, which provide greater load-bearing capabilities.

Buttress thread

Threaded buttress is a triangular shape. This is used where the force of the load on the screw is applied only in one direction. They are as efficient as square threads in this app, but are easier to create.

Maps Leadscrew

Advantages & amp; loss

The advantages of leadscrew are:

• Ability to carry large loads
• Compact
• Easy to design
• Easy to produce; Special machines are not required
• Great mechanical advantages
• Accurate and accurate linear motion
• Smooth, quiet, and low maintenance
• Minimum number of sections
• Mostly lock themselves

The disadvantage is that most are not very efficient. Because of their low efficiency it can not be used in continuous power transmission applications. They also have a high degree of friction on the thread, which can quickly wear them. For square threads, the nuts should be replaced; for trapezoidal threads, separate beans can be used to compensate for wear and tear.

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Alternative

Alternatives to actuation by leadscrew include:

• Screw ball and roller screws (sometimes categorized as leadscrew rather than contradictory)
• Power liquids (ie, hydraulics and pneumatics)
• Train teeth (eg, worm drives, rack-and-pinion drives)
• Electromagnetic actuation (eg, solenoid)
• Piezoelectric Actuation

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Mechanics

dimana

• T = torsi
• F = memuat pada sekrup
• d _m = diameter rata-rata
• ${\ displaystyle \ mu \,}  ÂÂ$ = koefisien gesekan (nilai umum ditemukan di tabel yang berdekatan)
• l = memimpin
• ${\ displaystyle \ phi \,}  ÂÂ$ = sudut gesekan
• ${\ displaystyle \ lambda \,}  ÂÂ$ = sudut prospek

Based on the equation T _lower it can be found that the self-locking screw when the friction coefficient is greater than the tangent from the lead angle. The equivalent comparison is when the friction angle is greater than the angle of the prospect ( ${\ displaystyle \ phi & gt; \ lambda}$ ). When this is not true the screw will be back-drive , or lower under heavy load.

Efisiensi, dihitung dengan menggunakan persamaan torsi di atas, adalah:

${\ displaystyle {\ mbox {efficiency}} = {\ frac {T_ {0}} {T_ {raise}}} = {\ frac {Fl} {2 \ pi T_ {raise}}} = {\ frac {\ tan {\ lambda}} {\ tan {\ left (\ phi \ lambda \ right)}}}}  ÂÂ$

di mana ${\ displaystyle \ alpha \,}  ÂÂ$ adalah satu setengah sudut utas.

Jika leadscrew memiliki kerah di mana beban naik maka gaya gesekan antar antarmuka harus diperhitungkan dalam perhitungan torsi juga. Untuk persamaan berikut, beban diasumsikan terkonsentrasi pada diameter leher rata-rata (d _c ):

${\ displaystyle T_ {c} = {\ frac {F \ mu _ {c} d_ {c}} {2}}}  ÂÂ$

where ${\ displaystyle \ mu _ {c}}$ is the friction coefficient between the collar on the load and d _c is the average diameter diameter. For the collar that uses pushbutton, friction losses can be neglected and the above equation can be neglected.

Speed ​​Run

Running speed for leadscrew (or ball screw) is usually limited to, at most, 80% of the critical velocity calculated. Critical speed is the speed that surpasses the natural frequency of the screw. For steel balls or steel steel balls, the critical speed is roughly

${\ displaystyle N = {(4.76 \ times 10 ^ {6}) d_ {r} C \ over L ^ {2}}}$

Where

• N = critical speed in RPM
• d _r = the smallest diameter (root) of leadscrew in inches
• L = length between bearing bearings in inches
• C =.36 for one fixed end, one free end
• C = 1,00 for both ends is simple
• C = 1.47 for one fixed end, the simple end
• C = 2.23 for both ends remain

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See also

• Screw the ball
• Fine adjustment screw
• Jackscrew
• Screw rotator

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References

Bibliography

• Bhandari, VB (2007), Machine Element Design , Tata McGraw-Hill, ISBN 978-0-07- 061141 -2 .
Martin, Joe (2004), Table Machining: Basic Approach for Making Small Components on Miniature Machine Tools , Vista, California, USA:
• . Originally published in 1998; content updated with every printing, similar to "revised edition". Currently in fourth printing.
Shitley, Joseph E.; Mischke, Charles R.; Budynas, Richard Gordon (2003), Mechanical Engineering Design (edition 7), McGraw Hill, ISBN 978-0-07-252036-1 Ã, .

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External links

• Power screw analysis

Source of the article : Wikipedia