Roymech engineering encyclopedia

Human Controls and man/machine interfaces

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Machine Interfaces & Associated Controls

This page provides notes on man machine interface controls


The notes below are outline notes based on information obtained from a variety of sources.     I have listed the relevant european standards.  The notes on this page have not yet been checked against the standards.    It is recommended that for final detail design, reference is made to the standards.

Relevant Standards

BS EN 894-1:1997 :Safety of machinery. Ergonomics requirements for the design of displays and control actuators. General principles for human interactions with displays and control actuators
BS EN 894-2:1997: Safety of machinery. Ergonomics requirements for the design of displays and control actuators. Displays
BS EN 894-3:2000: Safety of machinery. Ergonomics requirements for the design of displays and control actuators. Control actuators
BS EN 894-4:2010: Safety of machinery. Ergonomics requirements for design of displays and control actuators. Location and arrangement of displays and control actuators

Size of lettering and Symbols

Below are list suggested for sizes of letter and symbols to be used on controls and machines used in well illuminated areas..
Black letters against white background are clearer to read in normal daylight conditions.   In relatively dark conditions white letters on a dark background are better.

Distance from Eye (mm)Height of Letters or Figures (mm)
Less than 500 2.5
501 to 9005.0
901 - 18009.0
1801- 360018.0
3601 - 600030.0
Control Directions

Rotary Controls.. The accepted direction for rotary controls is Clockwise motion of control to increase the variable. Anti-clockwise motion to decrease the variable...

In direction controls Anti-clockwise motion results in a turn to the left in forward motion and clockwise motion result in turning to the right in forward motion..

Lever controls.. The accepted direction for linear controls is movement forward,to right or up to increase variable and movement towards you, to left or down to reduce variable...

Relationship Between Controls & Displays


Push Buttons..

A push button can be arranged for operation by finger or by hand..
Suggested dimensions..

Diameter..(finger operation)12 -15 mm
Diameter..(emergency stop )30 -40 mm
Travel....(finger operation)03 -10 mm motion.(finger)2.5 - 5.0 N
Diameter...(hand operation)60mm
Travel...(hand operation)10mm motion.(hand)10 N

Toggle Switches

Toggle switches should only have two positions "on" and "off" they should preferably be located on vertical panels with vertical toggle motion.
The angle of motion should be about 45o
Diameter.. 3 - 25mm
The length..12- 50mm
Resistance to movement..2.5 - 15N


Large levers are sometimes used where significant operating forces are required.
Maximum forward and back motion 90ototal.
Maximum forward and back motion 350mm total.
Maximum lateral motion 45o total.
Maximum lateral motion 150mm total.
Maximum operating force 130N forward and back.
Maximum operating force 90N sideways.


Rotating Knobs

Rotating knobs provide a convenient method of controlling variables.  They should conveniently fit the hand , be easy to rotate, and should not impair viewing.

Two options are available knobs 1) Rotating Switches with indented motion (click stops) and 2) continuous motion knobs.

Rotating Switches.
Successive positions should not be less than 15o apart if the knobs are controlled by a pointer in view.
Successive positions should not be less than 30o apart if the knobs are controlled by a feel.

Suggested Design Parameter.

Diameter..35 -75 mm
Continuous resistance0.15Nm
Maximum torque)320 Nm
Resistance (at clicks)...12-18N
Angle for each step...15o to 40o

Continuous Motion Knobs
Continuous motion knobs allow precise regulation and allow control using finger or hand grip i.e delicate movement or rough movement..

Suggested design parameters

Diameter..(finger operation)10 -30 mm
Diameter..(whole hand )35 -75 mm
Height....(finger operation)15 - 25 mm
Height ...(Hand Control) 30 - 50 mm
Diameter...(hand operation)60mm
Max turning torque...(small knobs)0.8Nm
Max turning torque...(large knobs)3.2Nm

rotating knob

Pointed Bar Knobs

Arrow shaped , pointed bar knobs allow settings to be made quickly and conveniently...

Suggested design parameters

Length..25mm min.
Thickness25 mm max.
Height..12 - 70 mm

Pointed Bar Knob


Handwheels allow large forces to be applied because two hands can be used and gearing can be included for slow movement.

Suggested design parameters

Diameter 180- 530mm
Dia of rim 20 to 50mm
No of Spokes Minimise
Resistance (min) 20N
Resistance (max) Single Handed 135N
Resistance (max) Two Handed 225N

Cranked Handwheel

Rotating cranked wheels allow for operating of machines over long movements using continuous rotation of the crank.    The gearing between the crank and the motion may be fine or coarse and may be switched between ratios.   A crank handle allows fast motion and the handwheel can be used for more precise motion.

Suggested design parameters

Radius of crank for low toque ( up to 200 RPM) 60 - 120mm
Radius of crank for high toque ( up to 160 RPM)150 - 220mm
Radius of crank for quick setting up to 120mm
Resistance Torque (120mm rad. Crank) 0.5 to 2.5 Nm
Resistance Torque (240mm rad. Crank) 3.0- 4.0 Nm
Handle diameter 25-30mm
Handle Length (one handed) 80 to 120mm
Handle Length (two handed) 190 to 250mm


Angular Mounting of Monitors

These sketches are very dated and should only be used for general guidance