Merford Cabs Designs a State-of-the-Art Operator Cabin for Cranes Unloading Ships
Operators of material handling equipment in the steel and aluminium industries, for example, contend with radiation, heat and dust, as well as visibility, posture and ergonomic issues that come with working long, demanding shifts. Such conditions call for special attention to the design of an operator’s working environment.
Crane operators control a whole range of processes. Each process has different specifications with regard to the cab and the operator’s seat. In the case of unloading raw materials from ships, visibility, reflection and bad posture affect the performance and health of the operator.
Stimulated by requests from users, Merford has designed a new operator cabin which is specially suited for ship unloader cranes. Working together with crane operators, engineers and supported by scientific institutes and industrial designers, Merford analysed the sitting position and the lines of sight of existing cabins. It was clear many different sitting positions were used and lines of sight were being blocked by the position of the cabin, the operator seat and the structure of the cabin.
Cranes are often operated with open windows to improve visibility and allow the operator to relate to the sound of the engine and working environment. This creates a risk that polluted exhaust emissions can enter the cabin.
With the new cab design, operators have the benefit of temperature control. It has been proven, Merford says, that people perform at their best at 23 to 24°C. It has been demonstrated, it adds, that lowering or raising the temperature by 5°C reduces performance by about 9 percent (Seppänen et al. 2003). The new cabin is equipped with the new Merford Climate Unit to create perfect working conditions. The Merford Filter Unit, meanwhile, limits the concentration of harmful gases.
Shell around the operator
The cab creates a shell around the crane operator, protecting him from environmental influences (heat and cold, incoming light, dust, gases, noise, vibrations, movements and pollution, etc).
The cabin meets ISO standard 11226 and achieves optimal air and temperature control, while the Merford Ergoseat meets the P5-P95 working directive in the Netherlands.
Crane operator seats usually derive from designs from other industries, Merford says. Anthropometry (the measurement of the human individual) played an important role in the design of the new cabin. Statistical data about distribution of body dimensions were used. As an example, the required height adjustment of a seat should be about 5 inches to fit both a large male and a small female (difference in lower leg length).
Merford analysed routine actions, including posture, of a crane operator to achieve an ergonomic layout of the controls. 3D software was used to show visibility from the operator’s perspective. This led to the use of anti-reflective glass and a bottom window which can only be opened to clean the windows, limiting pollution.
The height of the consoles needed to be adjustable in relation to the seat. Anthropometrical data mandates the forward-backward position of the master switches also needed to be adjustable. Experience teaches that it is helpful to have a seat arrangement that allows the operator to stand up and sit down while continuing operation.
When sitting, body weight is transferred to the seat. A portion of the weight is also transferred to the floor, back rest and armrests. The location of transferred weight is the key to good seat design. When the proper areas are not supported, sitting in a seat all day can put unwanted pressure on the back, causing pain. More likely, lower back and neck problems occur when crane operators are working in extreme postures. This is especially true for crane operators who are constantly looking downward. This can result in fatigue, physical complaints, loss of efficiency, and even damage and/or dangerous situations.
ISO 11226, Ergonomics — Evaluation of Static Working Postures, shows the maximum back inclination in relation to "holding time" if the crane operator is not using an upper body support. As an example, the maximum holding time is 2.5 minutes when the back inclination is 40° (Fig. 1). If the crane operator works in a dynamic environment (shocks and vibrations, horizontal movements), the loads on the lower back increase even more. An upper body support is highly recommended in this case.
In a laboratory test environment, data was recorded relative to the posture of 10 test persons. They were observed working in both traditional seat arrangements and the Ergoseat (a seat arrangement with upper body support via the arms, as shown in Fig. 3). The data was used as input for biomechanical analyses. To make it possible to do the calculations, the anatomic data of the test persons were also recorded, and the loading on both the cushion and armrests was measured during the computer task. Figs. 4 and 5 illustrate the biomechanical context of the traditional working posture of a crane operator (Fig. 4) and, in the new posture (Fig. 5), he/she can adopt in the Ergoseat with upper body support via fully adjustable armrests/consoles.
In the traditional seat, the lower back is under significant stress because the back muscles need to generate forces to counteract the forward torque of the upper body. However, in the seat with the adjustable consoles, a significant portion of the weight of the trunk, head, arms and hands is carried at the armrests. The mechanical loading on the lower back is thereby reduced by more than 50 percent. The further forward the operator leans, the more this reduction may be. Another clear advantage of the Ergoseat with adjustable consoles is the potential variation in shoulder load over the course of the day.
Crane operators may vary the load on their shoulders (and lower back) by varying the extent to which they lean on the arm support (ranging from total support to none). Hence, internal structures in the back and shoulder can recover during work, and fatigue is reduced. In contrast, in the traditional situation, the load on the shoulders and lower back is constant and continuous while the operator is working.