Mitsubishi Heavy Industries Machine Tool Co., Ltd., a part of Mitsubishi Heavy Industries (MHI) Group, has developed new models of hobbing and gear shaping machines with highly accurate machining to manufacture precision reduction gears for robots. These new products, marketed as the “FR Series,” respond to the rapidly growing need for highly precise and efficient manufacturing of strain wave gears [1] and other precision reduction gears for robots. The full-fledged launch will begin in August 2020, with the unveiling at an online seminar scheduled for September.
The name “FR Series” is derived from “Fine Pitch for Robot, Reducer.” The units were developed based on MHI Machine Tool’s existing models, more than 2,000 of which have been delivered to the automotive industry and other manufacturers. The market expansion for industrial and life support robots in recent years has led to a sharp rise in demand for the high precision, small module [2] gears inside the precision reduction gears used in the joints of these robots. Two types of gears are used in these reduction gears (an external tooth gear and an internal tooth gear), and MHI Machine Tool has added to its lineup a hobbing machine to create the external gear and a shaping machine to make the internal gear. In contrast with conventional mass-production gears typically used in the automotive industry, which have modules (gear tooth sizes) of 1-4 and accuracy requirements of ISO class 8 or 9, gears for robots require greater precision, with modules of 1 or below and an ISO class of 3 to 6. The FR Series was specifically designed to meet these demands.
MHI Machine Tool’s hobbing machines use direct-drive motors [3] for both the main spindle to which the cutting tool (hob) is attached and the work table spindle holding the workpiece along with advanced control technology. By limiting the machine tool error to the greatest extent possible, this system achieves a pitch error [4] of just 1 micrometer (μm) [5]. Compared with precision gear cutting, accuracy has been raised three classes (from about ISO 6 to ISO 3). Also, the fast cutting speed with up to 8,000 rpm (revolutions per minute) shortens the processing time by about a third, contributing to greater productivity.
The shaping machines use high-precision worm gears for the cutter head and a work table that comprise the core components. Further, strict management values in the machine’s assembly precision has raised the precision class for the gear working by two levels (from about ISO 6 to ISO 4), providing high gear precision.
MHI Machine Tool is using its strength in manufacturing both gear-cutting machines and cutting tools to not only offer machines to manufacture the high-precision gears used in precision reduction gears for robots, but with its comprehensive solutions for gear machining — including cutting tools to ensure optimal cutting, processing know-how, and automated systems — is contributing to the manufacturing of high-precision gears.
MHI Machine Tool completed its first hobbing machine in 1962, and over nearly six decades, has continually developed new products and technologies. This track record and degree of contribution to the market has raised the company’s standing, and at the end of June, it led to MHI Machine Tool being selected for inclusion in the “Global Niche Top Companies Selection 100” by the Ministry of Economy, Trade and Industry (METI). Going forward, as an industry leader and as a manufacturer of the gear machine tools that support a wide range of industries, MHI Machine Tool will continue to lead the way in manufacturing.
Notes
[1] Strain wave gears (strain wave reduction units), also called Harmonic Drive® strain wave gears, comprise an internal elliptical disc called the wave generator, surrounded by a thin elliptical gear with external teeth called the flexspline, which in turn is surrounded by a perfectly round cylindrical circular spline with internal teeth. The rotation of this gear produces an internal wave motion, generating a significant reduction ratio.
[2] Module (m) is a unit representing the size of the gear tooth. It is derived by dividing the diameter (mm) of the pitch circle by the number of teeth.
[3] Direct-drive mechanism motors use the torque coming from a motor without passing through a gearbox or other mechanism in order to control driving loss due to friction and reduce wear on parts.
[4] Pitch error in a gear is an indicator of the spacing between the teeth of a gear and its adjoining gear. The smaller the pitch error, the smoother the gears work together.
[5] In-house machining result with GE15FR Plus (Workpiece data: Module 0.5mm; Number of teeth 100; Torsion angle: 0°; Tooth width: 15mm)
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