3. Strain Wave Gear Interface Design
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This section of the article series &#;Capabilities of the Strain Wave Gear Division at ILJIN&#; describes the interface of a strain wave gear (SWG) and is also the last part in this series.
The most common interface is the screw connection. The strengths and weaknesses can be summarized as:
Strength:
· Detachable connection
· Easy to assemble and disassemble
· Reusable
· Scalable (thread type / strength class)
Weakness:
· Expensive and time-consuming preparation of the connection (holes / threads)
· Component weakening in the bolt area
· Unsuitable for small surfaces and areas that are difficult to reach
· Preload loss during setting and creepage (loosening of screws)
The upper figure shows an example of a SWG with screw connections at the flexible gear, internal gear and cam interface. While the internal gear and the cam connection usually do not require increased attention, the flexible gear interface of the cup type can cause serious problems. The main problems of the cup flexible gear are the small pitch circle diameter (PCD) and the limited space for the screw connection. In general, the bolt head, nut and washer should not exceed the diameter D which is the outer diameter of the flexible gear flange. Sometimes there might be a clamping ring necessary. The figures below show an example how to solve this problem:
The combination of small PCD´s and high torques lead into high shear forces in the parting line of the screw connection. These shear forces need to be absorbed to prevent a malfunction in the form of a slip between the connection parts. The common practice to prevent slip is to use either dowels or to increase the friction in the parting line of the connection. A friction disk (shown in the picture on the left) can multiply the friction and can be a cost &#; effective solution.
Another commonly used interface, especially at the flexible gear, is a spline connection. The strengths and weaknesses can be summarized as:
Strength:
· Resistant against high torque and shock load
· Less component weakening compared to bolt connections
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· Fewer components compared to bolt connections
Weakness:
· Radial forces in the connection can cause widening
· Limited reusability
· Assembly is more difficult compared to bolt connections (press fit)
The upper figure shows an example of a SWG with a spline connection at the flexible gear interface. For some reasons these spline connections are mainly seen in automotive applications whereas robotic applications mainly show bolt connections.
However, this is only an extract of the possible interface designs. There are several additional connection systems that are suitable to the SWG like e.g.:
· Hirth coupling
· Press fit
· Tolerance ring
· Clamp bushing
· Fether key
· &#;
ILJIN has the experience to guide the customer to find suitable interfaces for all kinds of applications and a wide range of possibilities to machine the parts according to specific requirements.
Summary - Capabilities of the Strain Wave Gear Division at ILJIN Motion & Control GmbH
The article series &#;Capabilities of the Strain Wave Gear Division at ILJIN Motion & Control GmbH&#; gives a rough overview about the complexity of SWG design and the daily tasks of the R&D Team. Drop-in replacement gears from size 35mm (14 / 1,4 inch) to 102mm (40 / 4,0 inch) are validated and ready to order. Beside the drop-in replacement of state-of-the-art SWG´s ILJIN Motion & Control GmbH can offer the full service to engineer your drive solution to a class leading and outstanding performance. Especially tailor-made, high-volume products perfectly match ILJIN's automobile-driven history and structure.
The High-voltage Rotary Actuators feature compact size, high precision, and ample hollow space, simplifying selection, design, and manufacturing for clients. The series includes the basic model with a standard medium hole, single encoder, and no brake, and the standard model with an extra-large medium hole, dual encoders, and a brake.
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