{"id":1767,"date":"2016-10-11T11:00:28","date_gmt":"2016-10-11T16:00:28","guid":{"rendered":"http:\/\/blog.misumiusa.com\/?p=1767"},"modified":"2016-12-20T11:37:20","modified_gmt":"2016-12-20T17:37:20","slug":"mastering-ball-screws-pt-3-ball-screw-operating-performances","status":"publish","type":"post","link":"https:\/\/us.misumi-ec.com\/blog\/mastering-ball-screws-pt-3-ball-screw-operating-performances\/","title":{"rendered":"Mastering Ball Screws Pt 3: Ball Screw Operating Performances"},"content":{"rendered":"

Friction is one factor in ball screw performance.\u00a0 There are 2 different friction torques affecting screw operation performance.\u00a0 Each friction torque is dependent on the type of feed screw.<\/p>\n

Feed screw is a mechanical element used to convert rotational motion to linear motion, or to generate large forces. The types and required performances are as follows.<\/p>\n\n\n\n\n\n
Feed Screw<\/td>\nLead Screw<\/td>\nA feed screw with the same contacting arrangement as a surface contact slide bearing.<\/td>\n<\/tr>\n
Ball Screw<\/td>\nA feed screw with the same arrangement as a point contacting rolling motion bearing.<\/td>\n<\/tr>\n
Hydrostatic Screw<\/td>\nA feed screw that transmits forces in non-contacting arrangement via air or hydraulic fluids.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Ball screw\u2019s operating performance is characterized by its very small friction resistances. This is due to its structure that transmits forces with rolling motion of the steel balls similar to ball bearings. When given the load and lead screw dimensions, the following formula gives you the torque generated.<\/p>\n

\"\"<\/p>\n

L = Ball Screw Lead<\/p>\n

P = Load<\/p>\n

(1) Static Friction Torque<\/strong><\/p>\n

The static friction torque is a static friction resistance during rotary motion.\u00a0 The ball screw\u2019s static friction torque occurs right when the feed screw begins to turn where the steel balls slightly slide instead of roll.\u00a0 This sliding in the screw groove is what generates the static friction causing the ball screws to wear.\u00a0 The static friction torque differs depending on the rotational direction (forward or reverse) of the screw shaft.\u00a0 It also differs with the position of ball re-circulation paths (positioned low or high, etc.).<\/p>\n

(2) Dynamic Friction Torque<\/strong><\/p>\n

Dynamic friction torque is the friction resistance in dynamic condition and is affected by the amount of preloads determined by steel ball size in relation to the screw groove size as well as lubricant characteristics.\u00a0 It will also vary according to the screw shaft rotational speed.\u00a0 In the case of oversized ball arrangement, the dynamic friction torque dramatically increases depending on the oversize amount, (See Figure 1a).\u00a0 In the case of double nut arrangement, larger number\u00a0of steel balls used and longer length of contacting screw groove reduces dynamic friction torque variations due to averaging effect, (See Figure 1b).<\/p>\n

\"Figure<\/p>\n

(3) Friction Torque Variations<\/strong><\/p>\n

Friction torque variations affects motor\u2019s speed variations, therefore linear motion velocity irregularities and positioning accuracy variations can be caused.\u00a0 Allowable torque variation rate is defined in JIS B 1192.\u00a0 For example, a C3 grade ball screw with an effective thread length of 4000mm or less with reference torque of 0.2~0.4 Nm is allowed a torque variation of \u00b145%.\u00a0 This is a guideline to follow when specifying ball screws in applications and designs.<\/p>\n

Thus far, ball screw characteristics, preloads and performance have been reviewed, up next the optimization of ball screw speed is examined, stay tuned!<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Friction is one factor in ball screw performance.\u00a0 There are 2 different friction torques affecting screw operation performance.\u00a0 Each friction torque is dependent on the type of feed screw. Feed screw is a mechanical element used to convert rotational motion to linear motion, or to generate large forces. The types and required performances are as follows. Feed Screw Lead Screw […]<\/p>\n","protected":false},"author":46,"featured_media":1779,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false},"categories":[6],"tags":[323,324,80,325,166],"aioseo_notices":[],"gutentor_comment":0,"_links":{"self":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1767"}],"collection":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/users\/46"}],"replies":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/comments?post=1767"}],"version-history":[{"count":5,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1767\/revisions"}],"predecessor-version":[{"id":1778,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1767\/revisions\/1778"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media\/1779"}],"wp:attachment":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media?parent=1767"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/categories?post=1767"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/tags?post=1767"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}