Basic Motion Control - An Introduction to Stepper Motors

Stepper motors are brushless, synchronous electric motors that converts digital pulses into mechanical rotation. Due to their lower cost, high reliability, high torque at low speeds, and rugged construction, they are found in both industrial and commercial applications.

The Basic Idea

Every revolution of a stepper motor is divided into a discrete number of steps. The motor is sent a pulse for each step. Typically a single rotation is 200 steps or 1.8 degrees of rotation per step. Since a stepper motor can only take one step at a time, and each step is the same size, the motor's position can be controlled without feedback. Obviously, as the pulse frequency increases the discrete step movement will change into continuous rotation - with the speed directly proportional to the pulse frequency.

Why Use a Stepper Motor?

1) Open-loop control makes the motor simpler and less costly to control.

2) The rotation angle of the motor is proportional to the input pulse.

3) Precise positioning and repeatability of movement.

4) Wide ranges are available since the speed is proportional to the frequency of the input pulses.

5) Quality stepper motors have an accuracy of 3 to 5% of a step and this error is non-cumulative step to step.

6) Excellent response to starting/stopping/reversing.

7) If the windings are energized the motor has full torque at standstill.When the load is directly coupled it is possible to achieve very low speed synchronous rotation.

8) High MTBF - since there are no contact brushes in the motor.

Types of Step Motors

There are three basic types: variable reluctance, permanent magnet, and hybrid. Hybrid motors combine the best characteristics of the other two types. They are constructed with toothed stator poles and a permanent magnet rotor. Standard hybrids have 200 rotor teeth and rotate at 1.8 degrees per step. Because they exhibit high static torque, high dynamic torque and run at very high step rates, they are used in a wide variety of applications including: computer disk drives, printers/plotters, machine tools, pick and place machines, automated wire cutting and wire bonding machines.

Modes of Operation

Operating modes include Full, Half and Microstep. The step mode output of any stepping motor is dependent on the design of the driver.

Full Step: Standard hybrid stepping motors have 200 rotor teeth, or 200 full steps per revolution of the motor shaft which equals 1.8 degrees per step. Normally, full step mode is achieved by energizing both windings while alternately reversing the current. One pulse from the driver is equivalent to one step.

Half Step: The step motor rotates at 400 steps per revolution. One then two windings are alternately energized, causing the rotor to rotate half the distance, or 0.9 degrees. Half step mode will produce a smoother rotation than full step but the tradeoff is less torque. (approx. a 30% reduction).

Microstep: Microstepping drives are capable of dividing one step into 256 'microsteps', providing 51,200 steps per revolution or 0.007degrees per step. Microstepping is typically used in applications that require accurate positioning and smooth motion over a wide range of speeds. Again, improved motion control is traded off against torque.

Series or Parallel Winding Connection

Stepper motor windings may be connected in series or parallel. Series connection provides greater torque at low speeds. Parallel connection lowers the inductance providing increased torque at faster speeds.

Driver Output Limiting

The available motor torque vs. speed depends on the driver output voltage. Since the driver output can be rated up to twenty times higher than the motor voltage, the drive should be current limited to the step motor rating.

Indexer Overview

The indexer, or controller, provides step and direction outputs to the driver. Most applications require that the indexer also manage acceleration, deceleration, steps per second and distance.

The indexer is capable of receiving high-level commands from a host and generating the necessary step and direction pulses to the driver. Communication to the indexer is usually via a RS-232 or RS485 port. However, it can also monitor inputs from external Go, Jog, Home and Limit switches.

Indexer Stand-Alone Operation

An indexer can also operate independent of the host. Once a program is loaded into the controller it can be initiated from remote operator HMI's or auxiliary I/O.

Closed loop applications that require stall detection and exact motor position capability will often be pre-packaged with a driver, power supply and optional encoder

Multi-Axis Motion Control

Multi-axis systems are used where a motion control application will have more than one stepper motor. A typical multi-axis networking hub may have up to four stepper drives connected to it; each drive will be connected to a separate stepper motor. The hub provides coordinated movement for applications requiring a high degree of synchronization (i.e. circular or linear interpolation).

Converting Rotational to Linear Motion Control

Where linear motion is required a lead screw/worm gear drive system can be connected to a rotary stepper motor. If the lead screw pitch is equal to one inch per revolution and there are 200 full steps per revolution the resolution of the lead screw system is 0.005 inches per step. Finer resolution is possible by using microstepping mode.

Basic Motion Control - An Introduction to Stepper Motors

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Basic Motion Control - An Introduction to Stepper Motors

Basic Motion Control - An Introduction to Stepper Motors
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Basic Motion Control - An Introduction to Stepper Motors

Basic Motion Control - An Introduction to Stepper Motors

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Logitech Z323 2.1 Speaker analysis and test

Logitech Z323 2.1 Speaker analysis and test

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Logitech Z323 2.1 Speaker analysis and test
This is a review of the Logitech Z323 2.1 speaker system. They cost me £35 from Comet and they are amazing, especially for such a cheap price! They have 3 in...
Logitech Z323 2.1 Speaker analysis and test

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The Importance of Grammar and Verbal Tense in ESL Teaching

Grammar and ESL Teaching: Past and Present Tense

Introduction

The teaching of grammar as part of ESL programs is important; while it is a debated subject, it has been demonstrated that "natural learners" of second languages do not become proficient in the language if they do not understand the basic structure as provided by grammar studies. Hinkel and Fotos (2002) note that individuals over a "critical period" of age 15 are at risk for this problem, as are individuals who acquire enough of the second language to be able to communicate even with grammar deficiencies, and many individuals who learn English as their second language do not receive the negative feedback that would let them know they are doing something wrong that they would receive in a structured situation (18).

The purpose of this paper is to provide a review of the literature to demonstrate the importance of thorough attention to verbal tense.

Literature Review

Plotnik discusses the effect of tense: every narrative has a base tense, one that moves the action of the communication forward. The use of the tense establishes the mood for the conversation or the story being told - past tense is traditionally the storyteller's medium, in which events have taken place and people have acted out their destinies. There is a finite basis to expired time. Present tense, on the other hand, promotes a feeling or mood of immediacy and the potential for change or flexibility (Plotnik, 2003).

According to Mc Carthy and Carter (2002), communication involves relational aspects and the desire to express oneself politely and indirectly (as opposed to bluntly), often manifests itself in tense forms that are part of the knowledge of correct grammatical construction. These include verbs in a progressive context such as want, like, have to and so forth. The range of tense helps individuals to create communication with relational, interpersonal meaning. The speaking strategy of tense creates a relationship between the speaker, the event and the listener that can either involve or detach the participants from the event and each other. Understanding and correctly using the past and present tense has the potential of significantly increasing not only effective communication of verbal and written messages, but also of correctly and proactively establishing relational aspects of events and situations that it is an important part of proactive grammar instruction.

Limitations in the development of the English past tense affix -ed have been well-documented in ESL students across a variety of language tasks, including spontaneous conversations, elicited productions, sentence completion, sentence recall, production of nonsense forms, writing samples, and grammaticality judgments. Specifically, "the morphophonological component of English tense marking represents the patterns children need to extract from the input in order to produce the various forms associated with past tense. Specifically, children have to learn to "add -ed " to regular verb stems and recognize the various alternative phonological processes involved in indicating the past tense of irregular verbs."

There is a semantic contrast between tenses under three headings, location in time, factuality and backshifting. The primary use of the past tense indicates a situation in which "actions, events, processes, relations, states of affairs or whatever a clause expresses" are dynamic (in which case they 'take place') or static in which case they 'obtain'...The past tense may be more directly indicated by an expression including time such as "yesterday", a definite time in which the topic of the sentence occurred. Use of the past tense remarks on something that has happened, but does not necessary indicate that the situation continues into the present.

Huddleston (1984) noted that past time is an inherently relational concept; the past tense inflection indicates that the time the situation or even took place is past in relationship to another time, usually at the time the sentence is said or written. The time of the situation in the present tense will normally be present or future, and may also be expressed in temporal terms (such as now, next week) or by a subordinate when clause such as 'when she gets here, I am going to talk to her', indicating future. One important use of the subordinate clause is restricted to cases when the future situation in which the predicted event will take place is assured - Huddleston uses the example "He is ill next week" as a nonsensical misuse of the present tense as opposed to the action verb in "We leave for Paris next week" (145). This example shows how incorrect usage of past and present tense can not only impair communication and understanding, but have the potential to affect the "face" of the speaker/writer in social and work settings as well.
Quirk, Greenbaum, Leech, & Svartik (1995) identified five major classes of alternations used in the making of English past participles.

The first class includes all regular verbs (e.g., cleaned, kicked, smashed) and a large set of irregular verbs, and is composed of those verbs whose past tense and past participle forms are identical (e.g., brought, built, caught, had, left, kept, said, taught, thought, told). The second class contains high frequency irregular verbs such as hit, cut, and put that remain unchanged across their present, past, or past participle forms. For a third class of irregular verbs, the past participle is generated via the affixation of -en to their past tense form. This class includes verbs like beaten, broken, spoken, stolen. For the fourth class of irregular verbs, the - en morpheme is affixed to the present tense form (e.g., blown, eaten, taken, thrown). A final class of irregular verbs uses participle forms that are distinct from both their present and past tense forms (e.g., been, drunk, gone, written, ridden).

Redmond (2003) notes that production of the English past participle requires command of four advanced grammatical contexts: the passive, the present perfect, the past perfect, and the past modal. From syntactic and semantic perspectives, each of usage is considered complex relative to simple active sentences because they require speakers to coordinate multiple relations between tense, voice, aspect, and mood within the verb phrase.

Ionin and Wexler's 2002 research amongst 20 child ESL learners found that they almost never produce incorrect tense/agreement morpohology. Also, the researchers noted, "the L2 learners use suppletive inflection at a significantly higher rate than affixal inflection, and overgenerate be auxiliary forms in utterances lacking progressive participles (e.g., they are help people).
A grammaticality judgment task of English tense/agreement morphology similarly shows that the child ESL learners are significantly more sensitive to the 'be paradigm' than to inflection on thematic verbs. These findings suggest that tense is present in the learners' grammar, and that it is instantiated through forms of the be auxiliary. It is argued that omission of inflection is due to problems with the realization of surface morphology ... it is furthermore suggested that second language learners initially associate morphological agreement with verb-raising and, thus, acquire forms of be before inflectional morphology on in situ thematic verbs (95).

Conclusion

The correct use of tense is an important skill for adult ESL individuals to have and the lesson plans developed to address this directly will help them communicate effectively with co-workers and people in the community as to what they want and need, what they have had and have done and also to establish their identity based on their past history and future wants.

It is important for ESL students to learn grammar so that they are able to express personal thoughts in the appropriate syntax. Effective use of syntax is important to show different attitudes and express power and identity. Some incorrect forms of grammar may even be interpreted by the listener/reader as being rude or impolite. The more precisely an individual can express their thoughts and meanings, the more effective their communication will be, and the more potential for success they will have in their interpersonal and business communications throughout their lives.

References

Hinkel E. and Fotos, S. (Eds.) (2002). New perspectives on grammar teaching in second language classrooms. Mahwah, N.J.: Lawrence Erbaum Associates.

Huddleston, R. (1984). Introduction to the grammar of English. New York: Cambridge University Press.

Ionin, T. and Wexler, K. (2002). Why is 'is' easier than '-s'?: acquisition of tense/agreement morphology by child second language learners of English. Second Language Research, 18(2): 95-136.

McCarthy, M. and Carter, R. (2002). Ten criteria for a spoken grammar. In: Hinkel E. and Fotos, S. (Eds.) New perspectives on grammar teaching in second language classrooms. Mahwah, N.J.: Lawrence Erbaum Associates.

Plotnik, A. (2003). Tense counts! Writer, 116(10): 17-18.

Quirk, R., Greenbaum, S., Leech, G., and Svartvik, J. (1995). A comprehensive grammar of the English language. New York: Longman.

Redmond, S.M. (2003). Children's productions of the affix -ed in past tense and past participle contexts. Journal of Speech, Language and Hearing Resources, 46(5): 1095-109.

This article brought to you courtesy of www.research-resource.com

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How to use the AUX jack to angle up your MP3 amateur in your Subaru

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How to use the AUX jack to angle up your MP3 amateur in your Subaru

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BMW X3 (E83) '03+ iPod / iPhone Kit / Mediabridge / DUO Install Guide

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www.bavsound.com | This video covers the complete process for installing a BSW iPod Kit, DICE Mediabridge or DUO Multimedia Kit in an X3 BMW (other late model BMWs are similar but we release specific videos all the time). Simple to install, these kits provide iPod/iPhone connectivity, Bluetooth voice and music streaming, USB input, Aux Input and Satellite Radio (in the case of the DUO, iPhone/iPod and Sat Radio Only) in your 3 Series or M3. Each kit is different so visit www.bavsound.com for more info.
BMW X3 (E83) '03+ iPod / iPhone Kit / Mediabridge / DUO Install Guide

BMW X3 (E83) '03+ iPod / iPhone Kit / Mediabridge / DUO Install Guide

BMW X3 (E83) '03+ iPod / iPhone Kit / Mediabridge / DUO Install Guide

BMW X3 (E83) '03+ iPod / iPhone Kit / Mediabridge / DUO Install Guide