The story behind the development of EBARA Densan ultraprecision screw rotors

EBARA Densan Ltd. was founded as a fully-owned subsidiary of EBARA Corporation, an environment-conscious company focusing on the realization of "sustainable society", and has established track records for wind- and water-power machinery systems, water-treatment systems, environmental protection systems, and semiconductor manufacturing equipment in the areas of information, communications, and control.

Under the corporate philosophy of "striving to make broad and comprehensive contributions to society by providing excellent technologies and the best services in the fields of water, air, and the environment", the company has been playing an important role in developing better environmental infrastructures. The Mechatronics Division of the company, a key player in these activities, utilizes its long-accumulated technologies of rotating machinery and electrical equipment control to develop products such as compact fluid machinery and permanent-magnetic motors that boast small sizes and high efficiencies.

The air blowers used in the small-size fuel cells for home use originally developed by the Mechatronics Division require high efficiency, low cost, and ultra-long life for the flow range and rated pump head. With the goal of meeting these difficult challenges, EBARA Densan has been working on the development of a biaxial positive-displacement screw-type blower that does not incorporate a timing gear.

"Two screw rotors in a meshed arrangement (photo 1) are used; however,in actuality the blades are delicately designed to not come in contact with each other. This requires highly accurate, precise molding during manufacturing," says Yasuo Narui of Mechatronics Office of the company.

With rotors being made in an increasingly diverse range of materials in addition to the conventional aluminum, such as thermosetting-resin rotors, "It has become difficult to apply past accumulated experience in conventional design and processing." (Mr. Narui). As a countermeasure, it is required to thoroughly check the shapes in the early stages and feed back any detected defects to the die design, processing, and molding processes. The company therefore introduced a Konica Minolta non-contact 3D digitizer for assessing the shape at the prototype stage.

Other brands of digitizers were considered as well; however, they required too much time to compare measured data against the CAD data, and failed to meet the needs of the company. More importantly, highly accuratedigitizing is essential for verifying any molding errors and defects of the ultraprecision rotors. To this end, aluminum and other glossy materials should be scanned without needing to use an antireflection spray. The KONICA MINOLTA RANGE7, the latest non-contact 3D digitizer model, was the solution that satisfied their demanding requirements, such as accuracy,usability, and the capability to measure glossy surfaces, which were conventionally difficult to measure with optical digitizers. In addition, RANGE7 was "superior in terms of cost effectiveness", says Mr. Narui.

According to Mr. Narui, the company intends to broaden the scope of RANGE7 utilization. "In addition to screw rotors, we look to expand the use of RANGE7 to casings, bearings, nozzles and other parts in the future. Through dimensional assessment in prototype stages, we expect RANGE7 to contribute to the streamlining of development, reviews of manufacturing methods, and reductions in the costs of parts."