The case study presents an industrial development project on a static concept. The purpose of the development was to remove repetitive failures in the power train system of the hydraulic grab and improve the product reliability.
The grab is suspended by a rope system from an overhead crane [Figure 7.1]. The primary use of the crane is to transport community waste from a pit to an oven at waste-to-energy plants.
83 Figure 7.1 An overhead crane and hydraulic grab in waste-to-energy plant to move
community waste from pit to oven (Konecranes Plc).
The main function of the grab, opening and closing the jaws, is actuated by hydraulic cylinders. An electrical motor inside the grab operates the bidirectional pump, which generates the working pressure and fluid flow to and from the cylinders. The power supply to the grab is provided via a cable, accommodating the length variations during lifting movement by wounding the cable on the drum of the hoisting machinery, simultaneously with the hoisting ropes.
7.3.1 Problem description
The power train system of the grab was mechanically simplified; the opening and closing movement of the jaws was arranged by changing the rotation direction of the motor. This operation principle eliminated the need for any control devices in the grab, as a specific hydraulic block with relief valves fulfilled the functional requirement [Figure 7.2].
Figure 7.2 Original grab control and actuating system, based on the change of the rotation direction of the electric motor (Konecranes Plc).
The existing power train is the result of a single disciplinary approach; the bidirectional use of the motor matches with jaw movements, additionally all sensitive components (the phase change contactor of the power supply) can be located on the crane level beyond the rough environment of the grab. However, the arrangement has caused continual problems for the power train system and led to a call for improvements. The identified problems were:
• Overheating of the electric motor.
• Breakages of the coupling between the motor and pump.
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• Failures, leakages and the jamming of the hydraulic block.
The root causes of problems were investigated and recognized to be the consequence of the motor starting and the activation of jaw movements against full load, as well as the repetitive change of the rotation direction of the motor on each working cycle. Both of these cause additional motor and hydraulic system heating, which were the ultimate sources of failure. The original operating principle was simple and done well in its early stages. However, during the life span of the grab, many upgrades on grab size and capacity have occurred and it seems obvious that the concept scaling, architecture and part structure have reached their limits. Earlier development actions had been taken in a single- disciplinary way, e.g. mechanical breakages had been solved by reinforcing the components.
The development task includes constraints to restrict the solution landscape;
• The change of the grab interface to the crane must be limited to a minimum to ensure changeability to existing installations.
• Power requirements shall not be greater and thus affect the dimensioning of the existing power supply system of the crane.
• Power supply means to the grab via the power cable shall not be changed to a different type due to the cable coiling system.
Constraints with the space inside the grab, power requirements, cooling, control and power supply caused that the problems cannot be solved by component sizing, thus an alternative concept was necessary.
The new power train system consists of a unidirectional hydraulic pump and a separate valve system that directs the oil flow to meet the jaw movements. The actuation of the valve system was controlled in a new way, enabling the change of the operation principle.
The control commands to the valve system were carried through the power supply cable.
The command signal was arranged on the crane level so that a short interruption of one supply phase was caused, which was identified at the grab and interpreted correctly so as to allow the operation of valves and ensure that they let the drive grab jaws open, close or keep steady [Figure 7.3].
Figure 7.3 New grab control and actuating system, including innovative control message transmittal through power supply phases (Konecranes Plc).
The new control system enables to construct the power train system in a manner that enables the continuous run of the motor and pump and removes additional load peaks that cause excessive heating. The new operating principle removes problems and additionally enables the decrease of motor size due to lower torque requirements at start-up.
85 Additionally, a shorter response time was achieved due to action by the immediate availability of the hydraulic pressure and flow. The main constraint with the crane interface was maintained as the power cable was unchanged; however additional control electronics should be installed.
7.3.2 Synthesis
The new solution was developed based on an invention and was also awarded a patent. The change involved a different part structure thus remaining the function structure the same.
The new sub-system combination and control system introduced the changed operating principle. However, the innovation was not consciously created by using any systematic method, at the time of creation it was purely the result of individual intuition. A retrospective study was carried out with the purpose of understanding how the innovator may have unconsciously collected and organized the information and ended up with a new solution. Capturing and imitating the mental process provides direction and advice for developing a general method for incremental product development.
The start-up of the development process analyzed the defects and problems. It was found that the scaling of the power train system was the root cause. The operation modes of the grab and jaws opening and closing were executed by rotating the pump and the motor back and forth. The repetitive starts of the motor; as the power and inertia increase, acceleration and deceleration generated excessive heating due to tight encapsulation. In addition, loaded starts and stops against pressure relief valves generated repetitive load peaks. Finally, after several upgrades, the design margins within the space limitations were exceeded.
A linear design approach to this problem would solve it through the analysis of design properties and parameters. Simulations and dimensioning could be used to find out the operation limits by means of forces and thermal capacity. The improvements may have been a new heat exchanger, special materials or motor technology. Alternatively, an obvious solution would be a common hydraulic circuit with a continuous running motor and pump with a separately controllable valve block. However, this alternative was constrained because of the power supply cable had only four wires for the power supply and could not be used due to interchangeability. Wireless data transfer systems were considered, but they were rejected due to reliability issues in rough environments.
The case identifies a typical problem in industrial development; a feasible solution to an original problem or root cause creates a new problem or is restricted by constraints. The case study also showed that constraints may transform the problem from one discipline to another; as here the original mechanical problem may be solved but then creates a control system problem. However, the nature and formulation of the problem changed which may cause a shift in the solution landscape beyond the competence of the original problem owner.
If we approach the case retrospectively from the inventor’s view, the situation is a kind of transformation process from problem to solution. Before the intuition, when the invention took place, the critical phase was how the opportunity was identified. Referring to the problem solving methods (Goldratt 1990), the problem verbalization and search for the root cause are the key elements towards finding a solution. Constraints, contradictions and interactions create the means which stimulate creativity with the exploration for new solutions. However, creativity is not enough, there is a need to provide guidance or focus on what in the solution space can be changed. A problem’s definition and analysis provide a deep technical context and this has to be able to be utilized for a more systematic approach than just relying on intuition.
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Human creativity played an important role in this case, because multi-disciplinary workgroups, brainstorming or other creativity techniques were not used. However, the inventor has deep and broad experience within engineering and specifically in the mechanical discipline. Therefore, the question is; how did the inventor end up with an invention from another discipline? The focus of this study is technical and is not extended to the human brain, even if it is the key element for the result. By focusing on the information and the problem and the eventual solution an approach for determining the seeds for the idea was developed and is presented below.
The inventor understood that the earlier development had led to the current situation and due to the static design a totally new product development would be very difficult. The new solution introduces a new way of transferring the control commands to the hydraulic valve block, enabling the construction and operation of the valve system with reliable commercial components. Accordingly, the new solution involves an additional discipline into the system, control logics and with this the operation principle of the power train system was changed.
The problem solving logic applies the multi-disciplinary approach which enables the opportunity identification to change the operating principle.
Even though there is no documented systematic exploration within and between disciplines in this case, it is feasible, with logical reasoning, that this is what took place. In developing this approach further, a path from problem to solution may be presented [Figure 7.4]
Figure 7.4 Transformation process from problem to solution utilizing multi- disciplinary mapping as opportunity identification and idea generation.
It is proposed that the information processing and multi-disciplinary mapping takes place prior to the opportunity identification and idea generation phases. This mapping includes the recognition of the function activity chain, which actually describes the operating principle of the system. The mapping identifies the interactions among and between each technological discipline in the system and as a consequence enables the recognition of opportunities and seeds for ideas in a more systematic way.