November 2015 Archives

In the stage of moving onto the detailed parts drawing from the assembly drawing, it is necessary to make the parts shape design as easy as possible to assemble. This section introduces points on designing easy-to-assemble components.

• The machine used for assembly parts can guarantee the machining precision of approximately ±0.1 to 0.2mm even as the general tolerance. Therefore, it is possible to design easy-to-assemble components by altering their shapes without providing a dimensional tolerance.
• [Fig.1] illustrates an example of easy-to-assemble components designed with the assembly guides in order to ensure the parallel precision of the two components. If you stack and assemble two sets of this component, the assembled components will have the better precision in the vertical direction as well. For details, see #46.

• [Fig.2] is an example of the assembly guide parts drawing (workpiece holder) using locating pins. This is a case example of the parts requiring the assembly precision to keep the workpiece in place.
• In this case, two of the four fixing screw holes can be used as a guide hole of the locating pins.

To improve your skills of designing an automation device, it is necessary to gain as much design experience as possible and to increase your knowledge by learning about various types of automation devices.However, especially with the stiffness design required for the high degree of precision in positioning and machining, the designers are expected to have the implicit knowledge that can be acquired through working with advanced design structures.This section introduces points on preparing drawings by incorporating the stiffness into the design structure.

• A force applied to all the mechanical devices including the automation device has a point of application.
• In most cases, the mechanical devices are designed with the enhanced performance of assembly and machining work using this point of application.
• In the case of a mechanical device that drives at a high speed, the inertia force applies at the position where the acceleration changes.
• The machining and inertia forces are balanced with the reaction forces that work in the opposite direction. This is why the mechanical device itself is able to stand still in a stable position.
• The mechanical device must have the sufficient structural strength that is larger than the reaction forces.When you design a structure that is strong enough to overcome the reaction force, the strength must be guaranteed throughout the usage period of the mechanical device.

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• To incorporate the greater structural strength than the reaction force into the design drawing, multiply the thrust value by the safety factor and adopt the machine dimensions that can withstand the reaction force several times greater than the actual thrust.
• However, the strength calculated by the above method will be applied to the major design components only (support components, screws, rack unit, etc.) without being reflected to all the related parts.
• To incorporate the stiffness design in the actual designing stage, create a drawing of a particularly important component at 1.0x magnification. It is important to view the drawing so that you can avoid the intuitively weak structure when you design the detailed shape (See [Fig.2]).
• We tend to magnify the drawing of a complex component in the design process. However, if we do this, it is important to know that using a different magnification compromises our intuition to assess the stiffness design accurately (See [Fig.3]).