1.Brief introduction of harmonic drive gear reducer
A harmonic drive gear reducer is a compact, high-ratio speed-reducing device that uses harmonic motion, or vibration, to achieve high precision and high torque in a lightweight package. It consists of three main components: a wave generator (input), a flexspline (a flexible, externally toothed gear), and a circular spline (a rigid internally toothed gear). The wave generator's elliptical shape deforms the flexspline, causing its teeth to engage with the circular spline's teeth for power transmission.
2.Working process of harmonic drive gear reducer
1.Wave generator rotation: After the wave generator is installed into the inner hole of the flexspline, since its length is slightly larger than the diameter of the inner hole of the flexspline, the flexspline is formed into an oval shape.
2.Engagement and disengagement: When the wave generator rotates counterclockwise, the flexspline rotates clockwise. The gear teeth of the flexspline will mesh with or mesh out of the gear teeth of the rigid spline during the deformation process, forming a continuous simple harmonic wave motion.
3.Deceleration effect: Since the deformation of the flexspline is a continuous simple harmonic waveform on the unfolded diagram of the flexspline circumference, the ratio of the number of rotations of the wave generator to the number of rotations of the flexspline is the value of the harmonic gear reducer. The reduction ratio is very large.
3.Outstanding features of harmonic drive gear reducer
1.The harmonic drive gear ratio is large. Single-stage harmonic gearing transmission speed ratio range from 70 to 320, in some devices, can reach 1000, and multi-stage transmission speed ratio up to 30,000 or more. It can be used not only for deceleration but also for speed-increasing occasions.
2.It has a high load-bearing capacity. This is because the number of teeth engaged at the same time in the harmonic gearing transmission, the number of teeth engaged at the same time in the double-wave transmission can reach more than 30% of the total number of teeth, and the flexible wheel is made of high-strength materials, and the teeth and teeth are in contact with each other.
3.High precision harmonic transmission. Because the number of teeth meshed at the same time in the harmonic gear transmission, the error is averaged out, so that multiple teeth meshing has a mutual compensation effect on the error, and the transmission accuracy is high. In the case of the same gear accuracy level, the transmission error is only about 1/4 of the ordinary cylindrical gear transmission. At the same time can be used to change the radius of the wave generator to increase the deformation of the flexible wheel so that the tooth gap is very small, and can even achieve no side gap meshing, so the harmonic gear reducer transmission clearance is small, suitable for reverse rotation.
4.Harmonic drive gearbox has high efficiency and smooth motion. Since the teeth of the flex wheel make uniform radial movement during transmission, the relative slip speed of the teeth is still extremely low even if the input speed is high. Therefore, the wear of wheel teeth is small and the efficiency is high (up to 69%~96%).
5.The structure of the harmonic drive is simple, the number of parts is small, and it is easy to install. There are only three basic components, and the input and output shafts are coaxial, so the structure is simple and easy to install.
6.It is small in size and light in weight. Compared with a general reducer, the volume of the harmonic gear reducer can be reduced by 2/3 and the weight by 1/2 when the output torque is the same.
7.Harmonic gearing can transmit motion to confined space. Using the flexible characteristics of the flexible wheel, the wheel transmission is incomparable to other transmissions.
4.Optimization methods of harmonic drive gear reducer
1.Wave generator and flexspline profile optimization: Designing the wave generator to minimize stress in the flexspline, which is often achieved through a non-elliptical closed convex curve profile that distributes stress more evenly.
2.Multi-objective optimization: Using algorithms like NSGA-II to simultaneously improve multiple goals, such as increasing stiffness and torque capacity while decreasing weight and stress.
3.Finite Element Analysis (FEA): Employing FEA to model the stress and deformation in the flexspline and bearings under assembly and operational loads, and to perform modal analysis to understand natural frequencies and avoid resonance.
4.Structural parameter adjustments: Analyzing the impact of changing structural parameters, like the length and wall thickness of the flexspline's cylindrical section, to improve torsional stiffness and reduce stress.
5.Advanced materials: Using composite materials, such as combinations of carbon and glass fibers, to reduce the weight and improve the stiffness of the flexspline.
6.Lubrication modeling: Developing mathematical models that account for factors like mixed lubrication, contact geometry, and surface roughness to improve performance and predict lubrication-related issues like fatigue and wear.
7.Dynamic modeling: Creating models that can predict dynamic behavior like transmission error under variable loads and speeds, which is critical for applications like space robotics.
8.Torque estimation: Developing methods to estimate output torque by calibrating the inherent flexibility of the drive without adding extra components. This can be done using new compliance models or by training neural networks with data from motor and load-side encoders.
9.Parametric optimization: Analyzing the influence of different tooth profile parameters, such as tooth face radius and flank radius, to optimize performance for specific applications.
10.Accelerated life testing: Using statistical methods, like maximum likelihood functions combined with genetic algorithms, to optimize parameters for durability and lifetime prediction based on test data.
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