Ergonomics can basically be understood as the adaptation of work to the physiological and psychological characteristics of human beings. Especially in warehouse and production logistics, disregarding ergonomic principles can lead to less efficient and even less safe work situations. The detrimental risks of this are gaining notoriety.

Within both warehouse logistics and production logistics, ergonomics can have a major impact on the work situation. This relates to both work performance and work safety. Here, safety should not be seen directly as a life-threatening situation, but rather as a circumstance where physical injury can occur. And in many cases, this can be of a long-term nature.

Because the results of good or bad ergonomics are seemingly less measurable, this important aspect of work science is treated rather lightly.
But more and more insight is gained into the measurability of ergonomic aspects and the possibilities for improvement, where we can also observe that there is a direct relationship between a good ergonomic situation and the efficiency improvement of work.

Ergonomic aspects warehouse logistics
The human element plays a major role in work within warehouse logistics. Here, a number of types of work can be imagined. But the most important work with regard to ergonomics can be seen as order picking work. In which we can focus on one-dimensional picking.

If we look at the top view of the average male order picker, see Figure 1, a number of maximum lines of movement that can originate from the order picker become visible.

Figure 1: Top view of average male order picker

Here, it is important to note that the average length of the arm from the shoulder tip to the fingertips is 78 cm. Measured from the armpit to the fingertips, it is 73 cm on average. The latter measurement mainly determines the physical reach, but not yet the ergonomic grip depth.

The centre of the hand, which is about 12 cm from the fingertips, partly influences the ergonomic grasp depth with an upright body position. Thus, the ergonomic grip depth can be determined to be approximately 61 cm. This human size affects the time spent and effort of the gripping action, this at the occurring gripping depths.

Ergonomics versus grip depth
As indicated earlier, ergonomics has a direct relationship with the optimisation and efficiency improvement of operations. To this end, it is necessary to understand the time studies carried out in the process.

Figure 2: Chart grip depth

To illustrate the importance of this aspect, we can first refer to the graph showing reach depth in Figure 2. This graph clearly shows that, up to a reach depth of 50 cm, there is an almost directly proportional relationship between the time taken and the reach depth.
Once the 50 cm reach depth is exceeded, there is already a progressively variable increase in time, which becomes more pronounced particularly beyond the >60 cm mark.

The increase in time spent after the gripping positions located at >60 cm depth is mainly due to the fact that the body has to make a bending movement to perform the gripping action.

Between the gripping depths of 60 and 120 cm, a significant difference can even be observed with the front end. And all this is mainly related to the physical constitution of the human being (order picker). It can thus be observed that in situations with high order picking frequencies, the ergonomic aspect of the gripping depth can play an important role and deserves further attention.

Ergonomics versus grip height
In addition to the grip depth already described, grip height, in combination with grip depth, also plays an important role. For further consideration of this aspect, reference can be made to the ergonomic gripping height of the average male order picker, see Figure 3.

Figure 3: Ergonomic grip height male order picker

From this image, it can be seen that a height range of 221 cm can be achieved in a stretched position. This height range affects the gripping height during order picking.

If we place the relevant dimensional figure in front of a racking pattern, the gripping movement will involve a bend of the hand that has a radius of about 20 cm. This creates a maximum grasping height of 221-20=(201), say 200 cm. This grip height will still be affected to some extent by the grip depth.

Next, it is important to know where the optimum grip height is located. If we take another look at the ergonomic measurement figure in Figure 3, we see that the pivotal point of the shoulder has a height of 141 cm. The length of the upper arm can thereby be set at 32 cm, bringing the position of the hand to around 109 cm.

When bringing the forearm forward, this for performing a gripping movement, the front part of the forearm and hand will make a descending movement, which is related to physical constitution of the human being. This will ultimately involve a grasping height of about 100 cm, which can be considered a favourable ergonomic grasping height.

We get the minimum practicable gripping height by combining a kneeling and bending movement, with the items possibly placed on a ground pallet. In principle, the minimum practicable gripping height can be set at around 15 cm.

Figure 4: Graph of grip height

Looking at the graph in Figure 4, we see relatively significant differences at the indicated heights. This creates a functional relationship with the grip depths indicated on the graph grip height Figure 2.

Indeed, taking something at a grip depth of about 105 cm creates a grip time of 5 seconds (see Figure 2). That gripping time is then the starting point for calculating the gripping time at the various heights. Here we can observe that at a grasping height of about 100 cm (see Figure 4) there is no determining influence from the grasping depth time, as this is the ergonomic grasping height.

For example, if there is a gripping time of 4 seconds, this can be projected onto the gripping height graph (Figure 4). We can then read in the progression via the curve, the subsequent grasping times.

The functional relationship between grip depth and grip height can thus be used to determine the most optimal ergonomic position. In which further consideration should be given to ergonomic locations and collection frequencies.

Comment:
The time studies processed in the graphs are based on article weights of 0.4 to 1.0 kg. For heavier weights, this will progressively increase variably.

Workplace ergonomics
To further substantiate the importance of the ergonomic aspects described so far, reference can be made to an occupational aspect. This in the occurring postures and loads. We can characterise this as the occurring need for rest allowance.

If labour is performed, fatigue will occur. For example, if a deep grasping movement is performed, at a lower location, with relatively heavy weights, it will require a greater effort. As a result, significant fatigue will occur. This fatigue and other movements should be compensated by some form of rest allowance.

When performing the grip depths and grip heights already described, the position of the bones of the bones will undergo regular changes. Here, forces will be carried out by the muscles, causing the bending and stretching movements.

Because the muscles are close to the bones, unfavourable leverage ratios will occur. As a result, the forces exerted by the muscles will be significantly greater than the effective forces exerted by the limbs.

However, these movements require some form of energy, which is created by burning a substance called glycogen. The glycogen is transported in glucose form through the blood to the muscles.

The combustion process creates a certain amount of energy. This combustion process will take place much less if the muscles do not have to provide any or only limited labour.

The combustion process, however, requires oxygen. Keeping vital functions such as circulation, respiration and digestion going requires very little oxygen.

Any kind of muscle work does require a certain amount of oxygen. The greater the muscle activity, the greater the oxygen consumption and thus the energy consumption.

Previous occupational and medical studies have established, that the limit of taxability lies at an average energy consumption of 4 Kcal/minute during a working day. In such a situation, there is no need for rest to recover from fatigue. However, this is the case with the order picking movements already covered and shown. These movements are also expressed in Table 1.

Table 1: Rest allowance under load

From Table 1, it is clearly observable what large differences arise to the need for rest allowance at the indicated order picking ratios and loads. Under characteristic A, B and C the movements are expressed which relate to the graph Figure 2 and the graph Figure 4.
The inclusion of this rest allowance can consist of: working less fast for a certain period of time or taking complete rest, to achieve the body's recovery.

Conclusion and recommendation:
Ergonomics should not be seen as an academic description but as a physical matter which we can characterise as a law which is expressed. This requires an optimal approach.

We can also turn a blind eye to the aspects discussed so far. However, we should remember that human energy can be used alternatively. That is, energy given for certain work cannot be given to other work. Water used to make tea can, normally, no longer be used to make coffee.

The recommendation that can be given is to optimise by intensity of picking operations based on the ergonomic starting points. This with regard to ergonomic location determination.

Thus, a situation can be achieved with:

• Limited human effort;
• Efficient order picking operations;
• Faster turnaround time;
• Preventing low back pain;

Ergonomic aspects production logistics
Production logistics is mostly based on two basic principles, which we can characterise as:

• The functional set-up;
• The line layout.

This with the variants applicable here.

We can think of the functional arrangement as a production mode in which the machining method is taken as the starting point. This creates groups of machines that can perform an identical operation. Here we can think of a group of lathes, a group of drilling machines, etc.

As far as materials handling is concerned, there will therefore always be movements, intermediate stops and manual handling that can affect ergonomic aspects.

Line assembly can be described as a production method in which successive operations are performed. An important advantage of this mode of production is that there will be low movements and limited buffering.

Where, for example, in an assembly/assembly sector, there is handling of large or heavy parts, the so-called line arrangement offers a good possibility. This is because line assembly involves successive operations. The handling-intensive parts can be handled efficiently within this line principle. There are no additional intermediate operations and forms of intermediate storage in such a situation, which in principle will result in ergonomically sound handling and good space utilisation.

However, this can raise the problem of correct system alignment, i.e. the alignment between successive operations.

Figure 5: Ergonomic working method in line assembly

Figure 5 provides an illustration of the desired system harmonisation. Here, a so-called overhead conveyor system is used as the system technology within the production line layout. This is an assembly line for central heating boilers.

The overhead system is a very good system for a line arrangement. As already indicated, the problem in a line arrangement is the coordination between the activities (machining) between them. But the main issue here is the impact this system principle will have on the all-important ergonomic production method.

From the line principle with this system technology, the full integration of workplace operations should therefore be pointed out here. If we review Figure 5 again, it can be seen that the workstation has a drop section, see yellow arrow on the image. This is a vertically movable section of the overhead system with the machining frame. This creates a situation almost identical to the posture shown under characteristic B of table 1. Also, the semi-finished products to be processed are brought to a minimum distance from the assembly worker, eliminating the need for deep movements.

Thus, an ergonomically correct working method is obtained within the line layout. Also it is possible for the assembly worker to be seated by means of a pendulum seat, further saving human energy, see feature D and E of table 1.

The implementation of this system technology largely depends on the loads to be moved and the distances to be covered in the process. For the situation shown in Figure 5, a monorail is sufficient. Given the weights of the semi-finished products and the distances between them, the frames can be moved manually. Only a slight pushing force is required to move the 4 to 6 frames. Similarly, the power and free principle can suffice, with one drive taking place per frame.

And this is just one example where optimisation is achieved between systems technology and ergonomics in a production environment . Nevertheless, numerous solutions in the occurring situations can be thought of, in which ergonomics has an important influence.

Author: Gerben W. Esmeijer - consultant/director at logistics consultancy Esmeijer BV.