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Much more than an automatic line, a manual Position requires a lot of attention during its study. Poor design will result in accidents at work, MSD, demotivation, deterioration of the social climate and loss of productivity.

Introduction

Designing a manual production line requires a thorough study, especially on ergonomic aspects.

1 – Choose the type of Position

The first step is to define the type of manual Position that we want. There is no ideal posture: Staying in the same position for a long time is painful. According to international standards, any maintenance of a position for more than 4 hours is considered a painful posture.

This is why, regardless of the type of Position chosen, it will be appropriate to develop situations that allow the operator to ” move “1.

There are four different types of Position to choose from:

  • Sitting
  • Standing
  • Sitting/Standing
  • Standing-Support-buttocks

 

Ergonomically speaking, the best is the seated-standing Position . Man not being ” Intended “to hold a stationary position, this position ensures the least constraint and facilitates mobility. The standing-support-buttocks Position is also very interesting because it ensures a good weight distribution thanks to the fact that we rest on 3 supports.

Ergonomics, however, is not the only criterion. Not all positions are suitable for all situations. The diagram below traces the process of choosing the type of Position .

Notion of Anthropometry

The study of ” Dimensions » Human is the basis of the set of ergonomic data that we must take into account when designing a manual Position . There is a whole range of French, European or international standards defining postures, dimensions…

The set of data we give here is based on these standards and corresponds to 90% of the French population.

Standing height

Fist

Elbow

Shoulder

Eyes

Size

F

H

F

H

F

H

F

H

F

H

Minimum

710

745

945

1030

1255

1365

1430

1550

1540

1660

Average

760

805

1040

1115

1360

1470

1545

1665

1655

1780

Maximum

825

880

1115

1215

1470

1585

1645

1785

1760

1905

Seated size

Size

Eyes

Shoulder

Elbow

Leg

Size

F

H

F

H

F H

F

H

F

H

F

H

Minimum

800

860

690

750

515 565

205

230

385

425

480

525

Average

860

915

745

800

565 605

235

250

435

475

535

580

Maximum

920

970

805

850

620 650

275

280

475

525

580

635

For a standing Position

Height of the work plan

The height of the work surface (dimension A in the drawing below) is defined according to the operations and the working environment in which we are. We have to take into account:

  • The level of precision of the work to be carried out: the more precise it is, the higher the work plan. This will allow the elbows to be stable.
  • The vision requirement: at the most we will need to see elements (small parts, quality control…), at the most the work plan will have to be high.
  • The weight of the objects: at the most the weight is high, at the most the work surface must be low. It is considered that under 3kg, “ repetitive ” work can be done. Beyond that, we have two options:
    • Make specific arrangements: frequent breaks, help with handling…
    • The height according to the size of the object2. So if the object measures 150mm high, the height of the countertop will be:

      1075 – 150/2 or 1000 mmm

  • the need to have a great freedom of movement: for some operations, the operator needs space (large object, many…).
  • male or female staff: If the staff is female, the dimensions shown below should be lowered by about 100 m

Minimum height

Maximum height

Need for vision or precision work

1 050 mm

1 554 mm

Work without specific weight, precision or vision stress

930 mm

1 195 mm

Need to have a great freedom of movement

800 mm

1 000 mm

Weight of the object > 3 Kg

810 mm

1 075 mm

 

Generally speaking, it is advisable to have an adjustable work plan to take into account all the morphology.

Space for Feet

The space for the feet must be sufficient to be able to be upright while being against the work surface. The dimensions are:

Comfort Acceptable Unacceptable
D 0 to 300 mm 300 to 500 mm + 500 mm
E 0 to 300 mm 300 to 500 mm + 500 mm
B + 130 mm 50 to 130 mm -50 mm
C + 210 mm 0 to 210 mm -0 mm

Working depth

The maximum depth of reach corresponds to the extended arm distance. It is advisable to promote the work in the comfort zone corresponding to the mobility space of the forearms keeping the arm along the body and the elbow at 90 °. In standing position, the reach area is slightly more important by a possible bending of the trunk of 20 ° maximum (Trunk comfort zone). It should be noted that the Position must have a minimum depth of 800 mm to allow sufficient room for the tools and parts.
Work with two Hands Work with one hand
Comfort Acceptable Unacceptable Comfort Acceptable Unacceptable
In 170 at 300 300 at 700 -from 170 and + from 700 170 at 300 300 at 700 -from 170 and + from 700
B 60 ° 60 °
C 200 at 900 900 at 1300 -From 200 and + from 1300 600 at 1100 1100 at 1500 -600, + of 1500
D Minimum total depth of 800

 

For a seated Position – stand-up buttocks

The sitting/standing Position is similar to the standing Position in terms of sizing. It is preferred because it allows good mobility while leaving the possibility of resting the legs.

Height of the work plan

In the specific case of the seated-standing Position , the dimensions are reduced by about 100 mm compared to a standing Position , considering that we are sitting on the buttock support.

Minimum height

Maximum height

Need for vision or precision work

950 mm

1 454 mm

Work without specific weight, precision or vision stress

830 mm

1 095 mm

Need to have a great freedom of movement

700 mm

900 mm

Weight of the object > 3 Kg

710 mm

975 mm

 

Space for Feet

The space for the feet and on the other hand much larger to allow the leg to be slightly forward because of the possibility of being in support on the buttocks. It should be noted that the support must have an inclination of about 15 ° in relation to the horizontal.

 

Comfort Acceptable Unacceptable
B + from 750 650 at 750 -From 650
C + from 600 500 at 600 -From 500
D 400 at 570 285 at 400 -From 285
E 630 at 840 -From 630 and + from 840
F 0 to 300 300 at 500 + from 500
G 0 to 300 300 at 500 + from 500

 

* Dimension A is the height of the work plan seen previously.

Footrests VS. Foot-Rest

We bring your attention to the footrest: this one by its name, bears a connotation of rest. But far from his function. Indeed, for ergonomic reasons, it is necessary to have the ankles at right angles with the shins. For this reason and avoid confusion, it is better to prefer the term “pose-feet“.

Working depth

The work depths are strictly the same as for a standing Position .

For a seated Position

Finally, the last possibility, the seated Position . Often recommended for work requiring a lot of precision and little effort, it has the advantage of being the most restful.

Height of the work plan

The height of the work surface depends on a main criterion: The possible setting of the seat. Indeed, if it is not adjustable, then we will take a fixed height of 720 mm.

However, if the seat is adjustable in height, then the height must be in a range between 495 and 820 mm, knowing that at the most the work surface is high, at the most the precision work is possible.

Space for Feet

The space for the feet should be as large as possible to allow them to move and ensure good blood circulation. For this reason, we indicate here minimum values below which one should not go, but the maximum values are ” “Infinite” for most dimensions. 

Minimum Maximum
B 480
C-leg space at foot height 755
D-height of the feet on the support 0 165
E-space for legs at knee height 550
F-Necessarily adjustable 370 575
G 0 to 300 500
H 0 to 300 500
Foot width back view 790
Space for foot movements under the seat 285

Position Depth

Comfort Acceptable Unacceptable
In 170 at 300 300 at 500 -170 and + of 500
B -60 ° 60 to 80 ° + 80 °
C 600 at 1 100 1 100 at 1 500 -from 600 and + from 1 500
D Minimum total depth of 800

The sitting-standing Position

The sit-up Position is very similar to the seated Position . It has the same general dimensions. You just need an adjustable seat that can be at least 15cm from the bottom of the table. It is also required to provide foot support that is 15 ° from the ground and about 45cm from the seat.

The efforts

To design a Position is to take into account the ergonomic constraints. This will help with the principles of the Therbligs to “workout” the job and then carry out evaluations (see below) more precise to ensure the comfort of the Position .

The efforts

For highly repetitive movements (more than once per minute), the maximum weight to be moved is 3kg. Beyond that, for frequent movements, we come out of the recommendations of the standards and tools of the ergonomics. To study the different postures, we will use the OCRAtool.

To limit the impact of these efforts, we can:

  • Limit the efforts to be exerted on the controls, using pneumatic or hydraulic electric relays rather than mechanical controls requiring a more important support force.
  • Reduce effort by using suitable tools, such as a portable screwdriver rather than a screw driver.
  • Put in place aid for lifting, for example, a spring or a cylinder to facilitate the movement of a bonnet.

Charging Port

In the case of less repetitive load or load beyond 3Kg, we will rely on other tools (Niosh equation, Standard X35-109 that will tell us the maximum recommended weight based on a number of criteria.

However, generally speaking, we will retain the following elements :

Regular Effort

Occasional Effort

Female 15 – 18 years old and 45 – 65 years

10 Kg

12 Kg

Women 18 – 45 years and men 15 – 18 years

12.5 Kg

15 Kg

Male 45 – 65 years

20 Kg

25 Kg

Male 18 – 45 years old

25 Kg

30 Kg

The joint beaches

It is also necessary to respect the joint beaches of comfort. The synthesis proposed below is an ” average ” of data from the following different tools: RULA, OSHA, OCRA, Standard 1005-4 and 1005-5.

Description

Comfort Zone

Acceptable area

Area to be banned

Bending/extending the handle

0 °

± 15 °

+ 15 ° or-15 °

Radial and ulnar deflection of the handle

0 °

± 15 °

+ 15 ° or-15 °

Bending the forearm

60 to 100 °

-60 ° and + 100 °

Supination/pronation of forearm

0 to 30 °

30 to 45 °

+ 45 °

Shoulder bending

0 to 20 °

20 to 90 °

+ 90 °

Shoulder Extension

-20 to + 20 °

0 to-20 °

-20 °

Shoulder abduction

0 °

± 20 °

+ 20 °

Inter/Exter Rotation of the shoulder

0 °

0 °

+ 0 °

Bending the trunk

0 ° to 20 °

20 to 60 °

+ 60 °

Lateral inclination of the trunk

0 °

± 10 °

+ 10 ° or-10 °

Trunk Rotation

0 °

± 10 °

+ 10 ° or-10 °

Bending of the blow

0 to 10 °

10 to 20 °

+ 20 °

Extension of the coup

0 °

0 °

+ 0 °

Neck Rotation

0 °

± 10 °

+ 10 ° or-10 °

Tilt of the shot

0 °

± 10 °

+ 10 ° or-10 °

Container design

The format of the container is an important factor to take into account. The recommended dimensions are as follows:

Recommended

Acceptable

Unacceptable

Width

≤ 350 mm

350 to 500 mm

> 500 mm

Length

≤ 550 mm

550 to 1 000 mm

> 1 000 mm

Height

≤ 250 mm

250 to 400 mm

> 450 mm

 

It should be noted that if the container cannot be in the recommended dimensions then the following rules apply:

  • If the weight is > 10kg : The container must have the ” acceptable ” dimensions.
  • If the weight is < 10kg : You may have a container with ” unacceptable ” dimensions.

The visual fields

At the Position , important and useful elements (safety lights, production indicators…) must be in the visual field. This helps to limit the risk of errors, to reduce uncomfortable postures and unnecessary displacements. However, it must be ensured that the visual and audible signals are not in excess, or that the operator is in a mental overload.

The basic rules

Beyond all these figures, some common sense rules must be respected:

  • Reduce travel distances
  • Reduce the amplitude and the number of movements.
  • Reduce the effort required for each movement.
  • No extreme postures of the joints.
  • No movements where the arms lie above the level of the heart.
  • The hand should not be used as a typing tool.
  • No sudden effort or rapid rise in intensity.
  • No use of fingertips for traction or thrust pressure operations of more than 2 DaN.
  • Eliminate all risks of injury (cut, scratch, shock…).
  • Reduce the vibrations produced by the tools and relieve the maintenance.
  • Mechanize Parts Maintenance operations.
  • Provide ” Micro-time ” in the work cycle without activity to rest.
  • Use the body weight to act on the controls.
  • Choose the lower limbs to make a high effort.
  • Allow the possibility of changing postures regularly.
  • Minimize kneeling or squat postures as much as possible.
  • Provide stops for orders requiring precise stops.
  • Make sure to take care of the tools and the adapted parts: wide and comfortable handles, no grasp of the fingertips…

Source

1 – INRS (2008) – Working sitting or standing

2-Standard NF X35-104

NF EN ISO 14 738

INRS ED79

F. Dapitan (2011)-Ergonomic approach

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