Capsuled Rotary Joint with Wireless Electrical and Contactless Mechanical Transmission
Publication Date: 2014-Jul-18
The IP.com Prior Art Database
Normally the hollow shaft or complex cable routing is used to promise the lifetime of the cable. And cable bench test is required to evaluate the design. Dynamic sealing is needed to isolate the device and environment. Hard to design the cable routing, even with the time and cost consuming bench test. Dynamic sealing is not so reliable after long-term running. In addressing the problem, it is provided a capsulted rotary joint with 1. wireless electric and contactless mechanical transmission, for easy cable routing and sealing solution, without complex and time consuming bench test. 2. the whole joint can be enclosed as a module with only a static sealing, easy to assemble, easy to manufacture and easy to maintain. 3. no rotation limitation. It brings about the advantages as 1) a new design module for ABB product, such as industrial robot, mining machine, etc., with new technologies, to keeping leading position, especially for the product used in the extreme environment. 2) save a lot effort in new product design and test in cable routing. 3) increase the reliability and reduce the cost in sealing solution by removing dynamic sealing.
Capsuled rotary joint with wireless electrical and contactless mechanical transmission
CNCRC/MEC/Jiafan Zhang, 2014-01-22
The rotary joint is a fundamental element in multi-link systems, such as robots, CNC machines, etc. Generally, a rotary joint consists of a motor-like actuator, gear-like transmission mechanism and cable for power and signal transmission to the end-effector.
Unlike the static cable underground, there are stringent demands on cables used in rotary joint with the motion of the joint. Cables flex in one or more of the four basic motions, as shown in Figure 1. Because the copper in the cable has poor resistance to repeated stressing, even if the stress is kept below its ultimate yield point, a lot effort is put on the design of the cable routing in the rotary joint, to promise the cable to eventually survive from millions of repeated bending and twisting movement. Figure 2 lists some established routing solutions, by employing hollow shaft, for example, in existing designs.
Figure 1 Four basic motion of cable
a) b) c)
Figure 2 Traditional cable routing solutions. a) Cable routing with hollow shaft; b) Routing with arc shaft; c) Routing with U-shape
However, due to lack of accurate fatigue model to predict the lifetime of cables, the only way to indicate the feasibility of cable routing is by cable bench test. In the test, the candidate cables are arranged in the same routing and driven to follow the similar movement in the rotary joint repeatedly. Up to millions of cycles, this kind of test always takes a quite long time.
On the other hand, sealing for such a rotary joint is another headache when designing a facility for extreme environment, such as clean room, under water, or to meet high demanding in food grade or high IP protection. Besides the sealing on the gearbox, normally an extra sealing is involved between the link 1 and link 2, to isolate interfering stuff bilaterally, as shown in Figure 3. Because of the relative movement between both links, a dynamic shaft sealing should be used here. This high quality and high demanding sealing is much more complex and expensive than a static sealing. After a long-term repeated rotary movement, it leaves unsure in leakage. To avoid disaster resulted from leakage of the sealing by any chance, especially in the food grade environment, special lubricant meeting food grade standards is introduced. It leads to more challenges in design and test, with higher cost. Additionally, the dynamic shaft sealing itself is a source to generate interfering articles due to its wear.
Figure 3 Conventional rotary joint structure with dynamic shaft sealing
It relates to a capsuled rotary joint, with wireless electrical and contactless mechanical transm...