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95 requires a huge amount of additional steel resulting in a high cost impact on material and work. Consequently, the increased weight will affect the sizing of other components. Alternative solutions to increase rigidity include changing a structural section to lighter and more rigid lattice type. This solution is not preferred due to increased fatigue properties and a more demanding manufacturing process and inspection requirements.
• Solution 2: Decrease the force impulse by reducing the gantry travel acceleration impact. Theoretically, this solution provides an almost linear effect; doubling the acceleration ramp time will decrease the impulse to half. However, this is in conflict with the requirements and specification and will significantly decrease the performance of one product function.
The most obvious solution of single-disciplinary alternatives led to a dead-end. However, an opportunity was identified for improving structural behaviour through an innovative solution:
• Opportunity: The acceleration time of the crane movement is longer than the oscillation time of the natural frequency. The acceleration impulse increases the displacement amplitude when acting in the same direction and decreases when moving in opposite directions. Arranging the impulse in a pre-determined sequence during acceleration may be utilized to decrease the harmful effect.
• The innovative solution: The shape of the acceleration ramp value was stepped to match the structural oscillation turning points by use of a lower acceleration value when oscillation and impulse move in opposite directions and a higher value when their directions are the same. The total acceleration ramp time remains the same, but an in-built dampening effect was achieved [Figure 8.4].
Figure 8.4 The impact of changing the acceleration ramp shape from linear (before) to stepped (after) to reduce dynamic amplification and initiated structural sway (Konecranes Plc).
The innovative solution was easy to implement with the control system, as the required sequence with ramp times and acceleration values could be calculated from the structural data. However, the solution involves three technological areas to be considered:
• Mechanical system; Steel structure and machinery. No changes required, however a possible change exists because the acceleration increase requires higher torque from the travel machinery. However, this operation mode is not the determinative loading case and the necessary margin exists.
96
• Electrical power train; Electric motors and their converters. No changes required, however the same possible threat as with the mechanical system.
• The control system requires the interpretation and processing of user commands and sensor information and a detailed event execution in digital format to the electrical power train. A moderate change in the sub-program of the acceleration ramp generator, instead of one linear ramp was also needed, and a three-step ramp was developed with unique parameters for each crane according to its natural frequency.
The birth of this innovative solution came purely through intuition - at least the inventor did not consciously follow any systematic method. However, retrospectively all obvious elements for the opportunity identification existed and they are evaluated to find out if any systematic method can be found. The evaluation of the case produced several observations and resulted in some conclusions:
• The technical system presented is a static multi-disciplinary concept.
• The nature of the problem or opportunity was an unspecified, dissatisfied property of the technical system, which came out in the operation and was a part of an experienced behaviour.
• The unexpected appearance of dissatisfactory properties was a consequence of partial optimization and weight minimization within one technological discipline. The original design with a linear top-down development method and its division into single functions principally aimed to match one product property to one design parameter (axiomatic principle), which then failed to be applicable within a multi-disciplinary product. The separate development of systems may provide a more controllable process but also lead to the proliferation of such functional compatibility.
• The prerequisite to identify the opportunity was to perceive the total function, and interactions and impacts between different technological systems and the functional execution chain during the action mode changes.
• The implementation of the solution took place in a sub-concept level of the product, in an activity where functional decomposition and structure do not penetrate.
• Functional structure and decomposition into sub-structures or sub-systems do not recognize impacts on other sub-structures.
• The solution was within all constraints and almost ideal, the cost impact practically zero.
• The solution was implemented within a different technological discipline to the one it appeared in.
• A creative technique, brainstorming was used for idea generation, but this failed due to lack of systematic or value creating processing in the existing concept.
Observations and question; can a generic product’s development processes and methods respond to the industrial demand for developing static multi-disciplinary concepts? Based on earlier considerations, it is claimed that:
97 i. The initiation of an incremental development results from a problem or an
opportunity within an existing concept and not a need as with new product development.
ii. Incremental development focuses on a static concept, where the sub-systems or each discipline have been thoroughly optimized during the life cycle of a product.
iii. With static and multi-disciplinary concepts, the potential development opportunities may be identified with sub-system or discipline integrations.