SIST EN 894-3:2002+A1:2008
(Main)Safety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 3: Control actuators
Safety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 3: Control actuators
This European Standard gives guidance on the selection, design and location of control actuators so that they are adapted to the requirements of the operators, are suitable for the control task in question and take account of the circumstances of their use.
It applies to manual control actuators used in equipment for occupational and private use. It is particularly important to observe the recommendations in this European Standard where operating a control actuator may lead to injury or damage to health, either directly or as a result of a human error.
Sicherheit von Maschinen - Ergonomische Anforderungen an die Gestaltung von Anzeigen und Stellteilen - Teil 3: Stellteile
Diese Europäische Norm enthält Empfehlungen über die Auswahl, Gestaltung und Anordnung von Stellteilen, um eine Anpassung an die Anforderungen des Operators, die Eignung für die in Frage kommenden Steuerungsaufgaben und die Einsatzbedingungen zu berücksichtigen.
Sie gilt für handbetätigte Stellteile an Arbeitsmitteln für gewerbliche und private Zwecke. Es ist besonders wichtig, die Empfehlungen dieser Europäischen Norm zu berücksichtigen, wenn die Betätigung eines Stellteils entweder direkt oder aufgrund eines menschlichen Fehlverhaltens zu Verletzungen oder gesundheitlichen Schäden führen kann.
Sécurité des machines - Exigences ergonomiques pour la conception des dispositifs de signalisation et des organes de service - Partie 3: Organes de service
La présente norme européenne donne des recommandations sur la sélection, la conception et l’emplacement des
organes de service de telle sorte qu’ils soient adaptés aux exigences des opérateurs et qu’ils conviennent à la tâche
impliquant la commande concernée en tenant compte de leurs conditions d’utilisation.
Elle s’applique aux organes de service manuels utilisés avec les équipements à usage professionnel et privé.
Le respect des recommandations de la présente norme européenne est particulièrement important lorsque
l’utilisation d’un organe de service peut induire des risques en matière de santé et de sécurité, soit directement,
soit suite à une erreur humaine.
Varnost strojev - Ergonomske zahteve za načrtovanje prikazovalnikov in krmilnih stikal - 3. del: Krmilna stikala
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Sicherheit von Maschinen - Ergonomische Anforderungen an die Gestaltung von Anzeigen und Stellteilen - Teil 3: StellteileSécurité des machines - Exigences ergonomiques pour la conception des dispositifs de signalisation et des organes de service - Partie 3: Organes de serviceSafety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 3: Control actuators13.180ErgonomijaErgonomics13.110Varnost strojevSafety of machineryICS:Ta slovenski standard je istoveten z:EN 894-3:2000+A1:2008SIST EN 894-3:2002+A1:2008en,fr01-december-2008SIST EN 894-3:2002+A1:2008SLOVENSKI
STANDARD
SIST EN 894-3:2002+A1:2008
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 894-3:2000+A1
October 2008 ICS 13.100; 13.180 Supersedes EN 894-3:2000 English Version
Safety of machinery -Ergonomics requirements for the design of displays and control actuators - Part 3: Control actuators
Sécurité des machines - Exigences ergonomiques pour la conception des dispositifs de signalisation et des organes de service - Partie 3: Organes de service
Sicherheit von Maschinen - Ergonomische Anforderungen an die Gestaltung von Anzeigen und Stellteilen - Teil 3: Stellteile This European Standard was approved by CEN on 3 February 2000 and includes Amendment 1 approved by CEN on 14 August 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36
B-1050 Brussels © 2008 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 894-3:2000+A1:2008: ESIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 2 Contents Page Foreword.3 1 Scope.4 2 Normative references.4 3 Terms and definitions.4 4 Selection procedure.7 5 Task evaluation and information collection.7 6 Intermediate selection of control families.17 7 Identification of suitable control types.21 8 Additional information for the design of manual control actuators.32 Annex A (informative)
Example of the use of this standard.35 Annex ZA (informative)
!!!!Relationship between this European Standard and the Essential Requirements of EU Directive 98/37/EC, amended by 98/79/EC"""".39 Annex ZB (informative)
!!!!Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC"""".40
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 3 Foreword This document (EN 894-3:2000+A1:2008) has been prepared by Technical Committee CEN/TC 122 "Ergonomics", the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by April 2009, and conflicting national standards shall be withdrawn at the latest by December 2009. This document includes Amendment 1, approved by CEN on 2008-08-14. This document supersedes EN 894-3:2000. The start and finish of text introduced or altered by amendment is indicated in the text by tags ! " This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s). !For relationship with EU Directive(s), see informative Annexes ZA and ZB, which are integral parts of this document." According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 4 1 Scope This European Standard gives guidance on the selection, design and location of control actuators so that they are adapted to the requirements of the operators, are suitable for the control task in question and take account of the circumstances of their use. It applies to manual control actuators used in equipment for occupational and private use. It is particularly important to observe the recommendations in this European Standard where operating a control actuator may lead to injury or damage to health, either directly or as a result of a human error. 2 Normative references This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references subsequent amendments to, or revisions of, any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments). EN 292-1, Safety of machinery - Basic concepts, general principles for design - Part 1: Basic terminology, methodology. EN 292-2, Safety of machinery - Basic concepts, general principles for design - Part 2: Technical principles and specifications. EN 574, Safety of machinery - Two hand control devices -Functional aspects – Principles for design EN 614-1, Safety of machinery - Ergonomic design principles - Part 1: Terminology and general principles. EN 894 – 1, Safety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 1: General principles for human interactions with displays and control actuators. EN 894 – 2, Safety of machinery - Ergonomics requirements for the design of displays and control actuators - Part 2: Displays. prEN 1005-3, Safety of machinery - Human physical strength - Part 3: Recommended force limits for machinery operation. EN 1050, Safety of machinery - Risk assessment. ISO 447, Machine tools - Direction of operation of controls. IEC 60447, Man-machine interface (MMI) - Actuating principles. 3 Terms and definitions For the purposes of this European Standard, the following terms and definitions apply: 3.1 control actuator the part of the control actuating system that is directly actuated by the operator, e.g. by applying pressure [EN 894-1]
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 5 3.2 manual control actuator a control actuator adjusted or manipulated by human hand to effect change in a system, e.g., push-button, knob, steering wheel. Touch sensitive actuation is not included. 3.3 control type a range of control actuators with the same movement and grip characteristics, and fulfilling similar task requirements 3.4 control family a group of control types 3.5 operator the person or persons given the task of installing, operating, adjusting, maintaining, cleaning, repairing or transporting machinery [EN 292 -1] 3.6 task (work task) an activity or activities required to achieve an intended outcome of the work system [EN 614-1] 3.7 control task an activity where a control actuator is used to achieve a task goal
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 6
Figure 1 — Overall selection process for manual control actuators
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 7 4 Selection procedure Many types of manual control actuators are available from push-buttons to hand wheels. Each type is suited to particular task requirements and to certain operator capabilities. Environmental factors (e.g. illumination, vibration) and organisational factors (e.g. team work, workstation separation) also have to be considered. To ensure safe and efficient operation, correct selection of control actuators is important. The following describes a systematic procedure that will enable designers and manufacturers to select manual control actuators meeting their specific requirements. The selection procedure involves three steps which are carried out in an iterative manner. These are: task evaluation and information collection; intermediate selection of control families; identification of suitable control types. The main steps in the selection procedure are shown in figure 1. An example of a form for recording the results of the evaluation is shown in figure 2. Clause 5 describes the information that is required in order to select appropriate control actuators, clauses 6 and 7 then describe how this information is used in order to make the selection. 5 Task evaluation and information collection 5.1 Requirements and characteristics The division of tasks between the operator and the equipment should have been determined early in the design process in accordance with the recommendations in EN 614 -1 and EN 894 -1. There are general and specific requirements imposed by a task which normally cannot be changed. If it is not possible to find a suitable control actuator for a specified task then the allocation of this task or the task itself has to be reconsidered. The task requirements considered in this European Standard are ones that experience has shown to be most important in selecting manual control actuators, as follows: General task requirements a) Accuracy required in positioning the manual control actuator (accuracy); b) Speed of setting required (speed); c) Force/torque requirements (force). Specific task requirements d) Need for visual checking of manual control actuator setting (visual check); e) Need for tactile checking of setting (tactile check); f) Need to avoid inadvertent operation (inadvertent operate); g) Need to avoid hand slipping from manual control actuator (friction); SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 8 h) Need for operator to wear gloves (use with gloves); i) Need for easy cleaning (ease of cleaning). The general task requirements are used to identify classes of suitable control actuators. The specific task requirements are used in selecting individual control actuators within these classes. In order to evaluate the task requirements the classification scheme illustrated in table 1 should be used. This differentiates between 5 different levels from 0 to 4. Table 1 — Classification scheme for evaluating task requirements CODE SYMBOL Degree of requirements 0
Negligible
1
Low
2
Average
3
High
4
Very high
The task requirements do not need to be evaluated precisely, therefore the detailed evaluation procedure given in 5.2 and 5.3, show classification systems that have been found to be sufficiently accurate. The characteristics of the various types of control actuator need to be considered to determine the available selection options. This standard gives information on both movement characteristics and grip characteristics. In many cases some of the characteristics will have been predetermined by the task requirements. Movement characteristics: j) Type of movement; k) Axis of movement; l) Direction of movement; m) Continuity of movement; n) Angle of rotation for continuous rotary movements > 180° Grip characteristics: o) Type of grip; p) Part of hand applying force; q) Method of applying force. The above categories a - q are used throughout this standard. The shorter descriptions given in brackets after the full descriptions are used in table headings where space is limited.
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 9 DESCRIPTION OF INFORMATION Subclause Degree of Requirement (Classification) Remarks
0 1 2 3 4
General Task Requirements 5.2
a) Accuracy 5.2.1
b) Speed 5.2.2
c) Force 5.2.3
Specific task requirements 5.3
d) Visual check 5.3.1
e) Tactile check 5.3.2
f) Inadvertent operate 5.3.3
g) Friction 5.3.4
h) Use with gloves 5.3.5
i) Ease of cleaning 5.3.6
Movement characteristics 5.4
j) Type of movement 5.4.1 Linear Rotary
k) Axis of movement
5.4.2 x y z x y z
l) Direction of movement 5.4.3 +/- +/- +/-+/-+/- +/-
m) Continuity of movement 5.4.4 Continuous Discrete
n) Angle of rotation for continuous rotary movement > 180° 5.4.5 Yes No
Grip characteristics 5.5
o) Type of grip (see fig 4) 5.5.1 ContactPinch Clench
p) Part of hand applying force 5.5.2 Finger Hand
q) Method of applying force 5.5.3 Normal Tangential
Figure 2 — Example of form for recording information used in the selection procedure for manual control actuators
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 10 5.2 Determination of general task requirements a) to c) The following subclauses describe the procedures for completing the recording form in figure 2. The method for assigning each general task requirement to a class in table 1 is described. All acceptable requirements should be entered on the recording form (see figure 2). 5.2.1 Task requirement a:) Classification of accuracy (accuracy) The accuracy required shall be assigned to one of the classes shown in table 1. The accuracy required in the operation of a manual control actuator is determined by the task that has to be performed. Accuracy is influenced by a number of factors, the most important of which is continuity of movement required i.e. whether action of a manual control actuator takes place in discrete steps or continuously. Adequate feedback of information to the operator is necessary to minimise mistakes in positioning. High accuracy is inconsistent with high force application and this selection procedure takes this into account. Thus, a requirement for high force and high accuracy together will not lead to the successful selection of a suitable manual control actuator. Where control actuators are used frequently or for long durations accuracy requirements are increased.
Accuracy in positioning relates to the accuracy of positioning a manual control actuator itself. Accuracy in the positioning of the controlled component may be increased by mechanical means e.g. gears. In this case a high accuracy of positioning of the controlled component may be achieved by use of a manual control actuator capable of only low accuracy. 5.2.1.1 Discrete manual control actuator movements
A discrete manual control actuator movement is one where the manual control actuator can only be moved to a number of fixed positions e.g. rotary switch, on/off switch. The error in selecting the correct position increases with the number of discrete positions. Thus two positions shall be rated as "negligible" requirements whilst 24 positions shall be rated as "high" requirements. Manual control actuators with more than 24 discrete positions should be avoided. Accuracy can be improved by, for example, feedback to the operator of information on the current value of the controlled variable, by clear labelling of manual control actuator positions, by placing the manual control actuator where it can be easily seen and moved. For manual control actuators a visual indication of the function of each position should be provided either by labels or a display. Positions should not be indicated by numbers (1, 2 etc) or letters (A, B etc) to indicate a function, since this requires the operator to remember the related functions and leads to mistakes. Labels 1,2 etc. may be used where the value of the variable controlled varies from position to position at least on an ordinal scale. This becomes more important as the number of discrete positions increases. Labels and displays shall be designed in accordance with the requirements in EN 894 -2. When selecting control actuators whose functions are critical for avoiding injury or damage to health it is especially important that these requirements are followed. 5.2.1.2 Continuous manual control actuator movements Where movement of a manual control actuator corresponds to a continuous change in a controlled variable, the extent to which the variable deviates from the required value is a measure of error. The probability of making an error depends mainly on the time allowed to complete the task (speed), availability of feedback of information to the operator, and operating force. SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 11 For continuous control actuator movements, appropriate feedback of information to the operator shall be provided, for example by indicating the direction and speed of the component controlled. This may be achieved by a display, by movements of other objects relative to the operator e.g. movement of the surroundings when driving a vehicle, movement of a lathe tool, or by other suitable means. Where tasks have to be completed at speed e.g. continuous tracking of a target, high accuracy can only be achieved by provision of low force demands as well as visual feedback of information. For continuous tracking tasks the requirements for accuracy in positioning the manual control actuator shall be rated as "very high" requirements. The direction of movement of manual control actuators relative to the controlled component shall be in accordance with ISO 447 (for machine tools), IEC 60447 (for electrical equipment) and EN 894 -2. 5.2.2 Task requirement b): Classification of speed (speed) The speed of operation required shall be assigned to one of the classes shown in table 1.
The time to complete a manual control actuator movement is composed of two components: time to reach and grasp the manual control actuator and time to make the control movement. The former of these depends on the position of the manual control actuator relative to the operator and the type of grip necessary for its operation. In general, manual control actuators requiring contact grip are quicker to operate than manual control actuators requiring pinch grip which are quicker than manual control actuators requiring clench grip. For emergency situations it is essential for actuation to be as quick as possible. A mushroom shaped actuator operated by hand contact is therefore recommended for emergency stop functions on machinery. High speed of operation is inconsistent with a high force requirement, and the highest speeds can only be obtained when the force is lowest. Thus for continuous tasks, such as keyboard operation, where high speed is necessary the operating force should be kept low. The specification of high speed and high force requirement together will not lead to the successful selection of a suitable manual control actuator. 5.2.3 Task requirement c): Classification of force/torque (force) Control actuators may be used to move parts of a machine. In some circumstances large forces may be needed to move these parts. Some machine designs allow mechanical or power assistance to minimise the load on the operator when using the control actuator. Where this is not possible the magnitude of the force or torque required to operate the manual control actuator shall be assigned to one of the classes shown in table 2. The symbols in this table are used later in the evaluation process, therefore it is recommended that the appropriate symbol be recorded. Where control actuators are used frequently or for long durations force requirements are increased. Table 2 — Classification of force/torque for the selection of manual control actuators
CODE
SYMBOL
FORCE (N) OR TORQUE (N.m) DEGREE OF REQUIREMENTS 0
<10 N <0,5 N.m Negligible
1
>10 to <25 N >0,5 to <1,50 N.m Low 2
>25 to <50 N >1,50 to <3,0 N.m Average 3
>50 to <80 N >3,0 to <5,0 N.m High 4
>80 to <120 N >5,0 to <50 N.m Very high
SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 12 5.3 Determination of specific task requirements d) to i) The following subclauses describe the procedures for completing the recording form in figure 2. The method for assigning each specific task requirement to a class in table 1 is described. Some of these characteristics may have been specified earlier in the design process. The designer should note on the recording form those characteristics which have been predetermined. Any characteristics which have to be excluded because of decisions earlier in the design process should also be noted on the form. Assigning a high classification to some requirements may prevent high classifications being achieved for other requirements, e.g. a "very high" requirement for "friction" may not be compatible with "very high" for "ease of cleaning". Because of this it is important to ensure that the requirements that are most critical from a safety point of view are met before considering less crucial aspects. Where incompatible requirements are identified it will be necessary to reconsider the task design or where this is not possible then to reduce the requirements for the less important aspects. All acceptable degrees of requirements should be entered on the recording form. 5.3.1 Task requirement d): Need for visual checking of manual control actuator setting (visual check) In the operation of manual control actuators it is important to have feedback to the operator that the correct control action has been performed. This may be accomplished for example, by a change in reading of a display, a visual or audible change in the process being controlled etc. It is often advantageous to ensure that the setting of the manual control actuator can be visually checked, particularly where movement is in discrete steps and no other form of feedback is provided. The need for visual checking of the manual control actuator setting shall be assigned to one of the classes shown in table 1. 5.3.2 Task requirement e): Need for tactile checking of setting (tactile check)
In some situations where the operator's vision is fully occupied or the control actuator is located away from the operator's field of vision, it is important for the position of manual control actuators to be readily identified by touch. Identification by touch can also be useful in reinforcing other forms of information feedback to the operator where safety critical functions are involved. The need for tactile checking of the manual control actuator setting shall be assigned to one of the classes shown in table 1. 5.3.3 Task requirement f): Need to avoid inadvertent operation The importance of avoiding inadvertent operation of a manual control actuator depends on the consequences of such accidental operation. It is particularly important where injury or damage to health may result. This standard gives information on the degree of difficulty in inadvertently operating a control actuator itself. In some circumstances, where very high risks are present, this may not be considered sufficient. In such cases the following measures should be considered: locate manual control actuator in a recess; shroud the manual control actuator e.g. cover to prevent access of parts of body larger than the hand, surround manual control actuator with a collar; use manual control actuators that are operated in two movements at right angles to each other; use a lock-out system; SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 13 use two hand controls. For details see EN 574. The need to avoid inadvertent operation shall be assigned to one of the classes shown in table 1. 5.3.4 Task requirement g): Need to avoid hand slipping from manual control actuator (friction) Where manual control actuators are used continuously or frequently, it is important, for reliable operation and safety, to ensure that the operator's hand does not slip on the manual control actuator's surface. This will be particularly important where a requirement for high force application has been identified. The need to avoid slippage of the hand on the manual control actuator shall be assigned to one of the classes in table 1. 5.3.5 Task requirement h): Need for operator to wear gloves Whether or not an operator needs to wear gloves depends on the process. The need for gloves shall be assigned to one of the classes shown in table 1. Where no gloves are required this factor may be classified as "negligible" requirements (see table 1). Where thick gloves need to be worn continuously, as for example where metal components have to be handled frequently or for long durations, the factor should be classed as "very high". 5.3.6 Task requirement i): Need for easy cleaning In some applications, for example on machinery for food processing, it is important to ensure that all parts, including manual control actuators, are easy to clean. The need for ease of cleaning shall be assigned to one of the classes shown in table 1. Where hygiene needs to be considered this factor may be classified as a "high" to "very high" requirement depending on its importance. 5.4 Specification of movement characteristics A manual control actuator may be located in many positions relative to the operator. For equipment to be used by a standing operator there will be a series of normal operating positions, any one of which may be assumed in making the evaluations described in this standard. For a seated operator, the evaluation should be made relative to the preferred seat position. The recommendations given in this European Standard are valid for control actuators placed in the space immediately in front of the operator. Caution should be exercised in applying the standard outside these limits. Where doubt exists, user trials should be conducted (see EN 614- 1). The right-angled axis system to be used in the evaluation is shown in figure 3. SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 14
Figure 3 — Axis systems for linear and rotary movements
Five characteristics (j, k, l, m, n) relate to the determination of movement. Their evaluation requires description of the location of movement in space. It is intended that only those restrictions on movement characteristics that are imposed by the initial design specification should be entered on the recording form (see figure 2). All acceptable characteristics should be entered on the recording form. 5.4.1 Movement characteristic j) linear or rotary The type of movement required from the manual control actuator is in one of two groups according to whether the movement is essentially linear or rotary over the distance the hand will move. In this sense, long levers are classified as linear. Where earlier specifications or consideration of postural constraints restrict the type of movement, either 'linear' or 'rotary' should be entered on the recording form (see figure 2). 5.4.2 Movement characteristic k) axis of movement: The axis of movement is the axis, along or around which movement takes place relative to the operator (see figure 3). It is necessary to consider the possible postures the operator may adopt and the movements of the operator's upper body when using the manual control actuator. Where earlier specification or consideration of postural constraints restricts the axes of movement, the possible movement axes should be entered on the recording form. The predominant movement should be classified as x, y or z relative to one of the three axes shown in figure 3. 5.4.3 Movement characteristic l) direction of movement: The direction of movement is the direction to actuate the control relative to the axis as shown in figure 3. "+" and "-" directions are indicated for both linear and rotary movements. Where earlier specification or consideration of postural constraints restricts the direction of movement, the possible movement directions should be entered on the recording form. Where the operator is required to move the manual control actuator in both directions "+/-" should be recorded. SIST EN 894-3:2002+A1:2008
EN 894-3:2000+A1:2008 (E) 15 5.4.4 Movement characteristic m) continuity of movement: Continuity of movement describes whether the operation is continuous or takes place in discrete steps e.g. a multi-position switch. Where earlier specification restricts whether either continuously variable controls or controls which operate in discrete steps are used then this should be in
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