{"id":1331,"date":"2015-10-23T13:07:39","date_gmt":"2015-10-23T18:07:39","guid":{"rendered":"http:\/\/blog.misumiusa.com\/?p=1331"},"modified":"2021-11-02T17:00:44","modified_gmt":"2021-11-02T22:00:44","slug":"criteria-in-actuator-selection","status":"publish","type":"post","link":"https:\/\/us.misumi-ec.com\/blog\/criteria-in-actuator-selection\/","title":{"rendered":"Re-examining Precision and Repeatability Criteria in Actuator Selection"},"content":{"rendered":"

One of the main design challenges faced during the early design stages of automated mechanical systems deals with the precision and repeatability needs of components and sub-components.\u00a0 Sometimes, these two design considerations tend to dwarf all others in becoming the only items considered in the selection of an actuator for mechanical system<\/a> design. \u00a0The temptation is to simply select an actuator rated to the highest possible degree of precision, rated to the highest degree of reliability.\u00a0 However, this approach is fundamentally flawed and can result in the engineer designing for an actuator<\/a> with un-needed levels of precision, adding significant, unnecessary costs and complexities to the design.<\/p>\n

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MISUMI LS Series Medium Accuracy Actuator<\/figcaption><\/figure>\n

The antidote for this pitfall lies in understanding the fundamental differences between the definitions of precision and repeatability in actuator selection.\u00a0 Repeatability is a function of the degree to which the actuator is able to duplicate a commanded position, quite literally a measure of the reliability of the actuator in a sense.\u00a0 Precision, in contrast, is a measure of the smallest incremental resolution that the actuator is able to achieve.\u00a0 The key to actuator selection<\/a> lies in understanding when high degrees of precision are truly needed and when more moderate precisions coupled with a machine that can achieve these positions to a high level of repeatability can perform the same job for significantly less cost.\u00a0 The concept of repeatability, however, requires a bit of explanation due to the fact that the number found on a typical actuator specification sheet is quoted as a plus\/minus tolerance.\u00a0 This number literally means that according to the defining statistical standard, ISO 9283:1998, the actual \u201ctrue\u201d position of the actuator will fall within this range 99.8% of the time.<\/p>\n

Generally speaking, a typical \u201chigh-precision\u201d positioning actuator<\/a> operated by a stepper motor is able to achieve positions in the range of 1 m (~40in), in some cases, even more precision is achievable.\u00a0 However, key limitations make the device only useful for a narrow range of applications.\u00a0 Typically devices such as these are only rated for loads on the order of 20-30lb, making the positioning of \u00a0large equipment and machinery to these levels difficult and costly to achieve.\u00a0 These types of actuators are also significantly more expensive than standard single axis actuators; for a standard actuator with a positioning precision around 40 m (~0.0016 in), the cost can be as much as 40% less than a similar micro-positioning actuator.\u00a0 Actuators rated to these more modest precision levels such as these are also capable of operating under much higher (10-20X) loads.<\/p>\n

\"lineareinheiten\"<\/a>
MISUMI LX Series High Precision Ball Screw Actuator<\/figcaption><\/figure>\n

Without citing specific numbers, the same rule is generally applicable to repeatability specs. \u00a0Given an actuator with a high precision rating, the actuator is de facto placed under higher repeatability demands in order to meet these levels of precision.\u00a0 For example, a \u201chigh precision\u201d actuator with a precision of 40m (0.0016in), possesses a typical repeatability around plus\/minus 4m (~0.0016in), which is ten times the precision of the actuator.<\/p>\n

In light of these specifications, it is essential that the engineer carefully select an actuator that is appropriate for each desired application.\u00a0 The \u201chigh precision\u201d positioning actuators are typically only employed in industries such as printed-circuit and medical equipment manufacturing as well as precision industrial inspection devices.\u00a0\u00a0 Unless the system must operate on these sorts of microinch scales, a \u201chigh-precision\u201d actuator will be unnecessary and excessively costly. \u00a0In contrast, more traditional uses of mechanical actuators would encompass applications that are designed to achieve simple lifting and positioning functions, akin to something like a screw jack stand.\u00a0 These sorts of macro-sized automation application needs have driven advances in more traditional actuator technology that has yielded a class of actuators that is able to achieve the levels of precision necessary for such applications very reliably.\u00a0 In these sorts of applications, reliability actually ends up being the more limiting factor in order to ensure that the actuator can achieve the intended positioning every time that it is required to do so.<\/p>\n

\"MSA-628_noBkgd-RGB_448<\/a>
MISUMI MSA Series Belt Drive Actuator<\/figcaption><\/figure>\n

In conclusion, it\u2019s important to remember that today actuators that are fabricated from advanced manufacturing methods such as precision screw thread grinding are available in quality materials such as high strength stainless steels and are able to cost effectively achieve excellent levels of precision extremely reliably, even for high load applications.\u00a0\u00a0 Additionally, selecting an actuator solely on precision without carefully considering the application can lead to an over designed, expensive system that could have been achieved with significantly less cost by employing a quality, slightly lower precision actuator.\u00a0 Admittedly, these sorts of actuators may not be able to match the precision of a comparable \u201chigh precision\u201d stepper motor driven actuator; nevertheless, the engineer can be confident that these actuators will be more than sufficient to meet \u00a0both the precision and reliability needs of a vast majority of automation applications.<\/p>\n

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

One of the main design challenges faced during the early design stages of automated mechanical systems deals with the precision and repeatability needs of components and sub-components.\u00a0 Sometimes, these two design considerations tend to dwarf all others in becoming the only items considered in the selection of an actuator for mechanical system design. \u00a0The temptation is to simply select an […]<\/p>\n","protected":false},"author":46,"featured_media":1333,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false},"categories":[1136],"tags":[37,289,12],"aioseo_notices":[],"gutentor_comment":0,"_links":{"self":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1331"}],"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=1331"}],"version-history":[{"count":5,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1331\/revisions"}],"predecessor-version":[{"id":10743,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/1331\/revisions\/10743"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media\/1333"}],"wp:attachment":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media?parent=1331"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/categories?post=1331"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/tags?post=1331"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}