Robot Knee Screw Actuator With Low-Inertia Hip-Mounted Drive
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing robotic systems face limitations in responsiveness and performance due to high rotational inertia in electromechanical actuators, particularly in screw actuators used for knee joints, which affects the robot's ability to achieve high accelerations and maintain balance under external disturbances.
Innovation Solution
The implementation of a screw actuator with a planetary roller screw mechanism, where the motor is positioned closer to the hip joint, reducing distal mass at the knee joint and using a harmonic drive transmission with integrated overload protection to minimize rotational inertia, allowing for higher acceleration capabilities and improved responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a traditional electromechanical actuator with high rotational inertia is used at the knee joint, then the actuator can provide sufficient torque, but the robot's responsiveness and acceleration capability are reduced
Solution Approach 1:
The actuator system is segmented into two separate actuators: one located at the hip joint and another at the knee joint. This segmentation allows the hip actuator to provide the necessary torque through mechanical advantage while the knee actuator maintains low rotational inertia for high responsiveness and acceleration capability.
Solution Approach 2:
The solution moves the primary torque-generating actuator from the knee joint to the hip joint, utilizing the hip's larger moment arm to generate the required knee torque. This spatial repositioning in another dimension (from distal to proximal location) resolves the contradiction between torque and acceleration.
2Reliability
If the motor is positioned at the knee joint, then direct torque control is achieved, but the distal mass increases reducing responsiveness
Solution Approach 1:
The control function is segmented between two actuators: the hip actuator provides primary torque generation with precise control, while the knee actuator provides fine-positioning control with low inertia. This functional segmentation maintains torque control precision while improving responsiveness.
Solution Approach 2:
The hip actuator serves as an intermediary that provides the majority of torque through the thigh link, allowing the knee actuator to be smaller and more responsive while still achieving precise torque control through coordinated operation.
3Speed
If a harmonic drive transmission is used to reduce rotational inertia, then acceleration capability improves, but the system becomes more complex
Solution Approach 1:
The transmission complexity is segmented and distributed across two actuators rather than concentrated in one. Each actuator uses a harmonic drive, but the overall system achieves the desired performance with two simpler units rather than one complex high-ratio transmission.
Solution Approach 2:
The gear ratio parameter is changed from a single high-ratio transmission to two lower-ratio transmissions in sequence. This parameter change reduces the complexity of each individual harmonic drive while maintaining the overall torque multiplication and acceleration capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the effective rotational inertia at the knee joint, enhancing the robot's responsiveness and performance by allowing higher accelerations and torque capabilities while protecting against overload conditions.
Implementation Method 1
the screw shaft is rotatable within the nut... Rotation of the motor causes the screw shaft to rotate, which further causes (a) the nut and the carrier to travel along an axis of the screw shaft
Implementation Method 2
The implementation of a screw actuator with a planetary roller screw mechanism... to minimize rotational inertia, allowing for higher acceleration capabilities
Implementation Method 3
using a harmonic drive transmission with integrated overload protection to minimize rotational inertia
Data Source
AI summary
A robot leg assembly including a hip joint and an upper leg member. A proximal end portion of the upper leg member rotatably coupled to the hip joint. The robot leg assembly including a knee joint rotatably coupled to a distal end portion of the upper leg member, a lower leg member rotatably coupled to the knee joint, a linear actuator disposed on the upper leg member and defining a motion axis, and a motor coupled to the linear actuator and a linkage coupled to the translation stage and to the lower leg member. The linear actuator includes a translation stage moveable along the motion axis to translate rotational motion of the motor to linear motion of the translation stage along the motion axis, which moves the linkage to rotate the lower leg member relative to the upper leg member at the knee joint.