{"id":128,"date":"2018-04-12T08:28:23","date_gmt":"2018-04-12T08:28:23","guid":{"rendered":"http:\/\/tis-eg.com\/en\/?p=128"},"modified":"2018-04-12T08:30:59","modified_gmt":"2018-04-12T08:30:59","slug":"servomotor","status":"publish","type":"post","link":"https:\/\/tis-eg.com\/en\/servomotor\/","title":{"rendered":"Servomotor"},"content":{"rendered":"
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A\u00a0servomotor<\/b>\u00a0is a\u00a0rotary actuator<\/a>\u00a0or\u00a0linear actuator<\/a>\u00a0that allows for precise control of angular or linear position, velocity and acceleration.[1]<\/a><\/sup>\u00a0It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.<\/p>\n

Servomotors are not a specific class of motor although the term\u00a0servomotor<\/i>\u00a0is often used to refer to a motor suitable for use in a\u00a0closed-loop control<\/a>system.<\/p>\n

Servomotors are used in applications such as\u00a0robotics<\/a>,\u00a0CNC machinery<\/a>\u00a0or\u00a0automated manufacturing<\/a>.<\/p>\n

Mechanism<\/span><\/h2>\n<\/div>\n

A servomotor is a\u00a0closed-loop<\/a>\u00a0servomechanism<\/a>\u00a0that uses position feedback to control its motion and final position. The input to its control is a signal (either analogue or digital) representing the position commanded for the output shaft.<\/p>\n

The motor is paired with some type of\u00a0encoder<\/a>\u00a0to provide position and speed feedback. In the simplest case, only the position is measured. The measured position of the output is compared to the command position, the external input to the controller. If the output position differs from that required, an\u00a0error signal<\/a>\u00a0is generated which then causes the motor to rotate in either direction, as needed to bring the output shaft to the appropriate position. As the positions approach, the error signal reduces to zero and the motor stops.<\/p>\n

The very simplest servomotors use position-only sensing via a\u00a0potentiometer<\/a>\u00a0and\u00a0bang-bang control<\/a>\u00a0of their motor; the motor always rotates at full speed (or is stopped). This type of servomotor is not widely used in industrial\u00a0motion control<\/a>, but it forms the basis of the simple and cheap\u00a0servos<\/a>used for\u00a0radio-controlled models<\/a>.<\/p>\n

More sophisticated servomotors use optical\u00a0rotary encoders<\/a>\u00a0to measure the speed of the output shaft[2]<\/a><\/sup>\u00a0and a variable-speed drive to control the motor speed.[3]<\/a><\/sup>\u00a0Both of these enhancements, usually in combination with a\u00a0PID control<\/a>\u00a0algorithm, allow the servomotor to be brought to its commanded position more quickly and more precisely, with less\u00a0overshooting<\/a>.<\/sup><\/p>\n

Servomotors vs. stepper motors<\/span><\/h3>\n

Servomotors are generally used as a high-performance alternative to the stepper motor. Stepper motors have some inherent ability to control position, as they have built-in output steps. This often allows them to be used as an open-loop position control, without any feedback encoder, as their drive signal specifies the number of steps of movement to rotate, but for this the controller needs to ‘know’ the position of the stepper motor on power up. Therefore, on first power up, the controller will have to activate the stepper motor and turn it to a known position, e.g. until it activates an end limit switch. This can be observed when switching on an\u00a0inkjet printer<\/a>; the controller will move the ink jet carrier to the extreme left and right to establish the end positions. A servomotor will immediately turn to whatever angle the controller instructs it to, regardless of the initial position at power up.<\/p>\n

The lack of feedback of a stepper motor limits its performance, as the stepper motor can only drive a load that is well within its capacity, otherwise missed steps under load may lead to positioning errors and the system may have to be restarted or recalibrated. The encoder and controller of a servomotor are an additional cost, but they optimise the performance of the overall system (for all of speed, power and accuracy) relative to the capacity of the basic motor. With larger systems, where a powerful motor represents an increasing proportion of the system cost, servomotors have the advantage.<\/p>\n

There has been increasing popularity in closed loop\u00a0stepper motors<\/a>\u00a0in recent years.[citation needed<\/span><\/a><\/i>]<\/sup>\u00a0They act like servomotors but have some differences in their software control to get smooth motion. The main benefit of a closed loop stepper motor is its relatively low cost. There is also no need to tune the\u00a0PID controller<\/a>\u00a0on a closed loop stepper system.<\/sup><\/p>\n

Many applications, such as\u00a0laser cutting<\/a>\u00a0machines, may be offered in two ranges, the low-priced range using stepper motors and the high-performance range using servomotors<\/p>\n

Motors<\/span><\/h2>\n

The type of motor is not critical to a servomotor and different types may be used. At the simplest, brushed permanent magnet DC motors are used, owing to their simplicity and low cost. Small industrial servomotors are typically electronically commutated brushless motors.[10]<\/a><\/sup>\u00a0For large industrial servomotors, AC induction motors are typically used, often with\u00a0variable frequency drives<\/a>\u00a0to allow control of their speed. For ultimate performance in a compact package, brushless AC motors with permanent magnet fields are used, effectively large versions of\u00a0Brushless DC electric motors<\/a>.<\/p>\n

Drive modules for servomotors are a standard industrial component. Their design is a branch of\u00a0power electronics<\/a>, usually based on a three-phase MOSFET or IGBT\u00a0H bridge<\/a>. These standard modules accept a single direction and pulse count (rotation distance) as input. They may also include over-temperature monitoring, over-torque and stall detection features.[12]<\/a><\/sup>\u00a0As the encoder type, gearhead ratio and overall system dynamics are application specific, it is more difficult to produce the overall controller as an off-the-shelf module and so these are often implemented as part of the main controller.<\/p>\n

Control<\/span><\/h2>\n

Most modern servomotors are designed and supplied around a dedicated controller module from the same manufacturer. Controllers may also be developed around\u00a0microcontrollers<\/a>in order to reduce cost for large-volume applications.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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A\u00a0servomotor\u00a0is a\u00a0rotary actuator\u00a0or\u00a0linear actuator\u00a0that allows for precise control of angular or linear position, velocity and acceleration.[1]\u00a0It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors. Servomotors are not a specific class of motor although the […]<\/p>\n","protected":false},"author":1,"featured_media":130,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18],"tags":[],"class_list":["post-128","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-articles"],"_links":{"self":[{"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/posts\/128","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/comments?post=128"}],"version-history":[{"count":1,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/posts\/128\/revisions"}],"predecessor-version":[{"id":129,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/posts\/128\/revisions\/129"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/media\/130"}],"wp:attachment":[{"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/media?parent=128"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/categories?post=128"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tis-eg.com\/en\/wp-json\/wp\/v2\/tags?post=128"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}