Direct Drive Actuator Planetary Nut Backlash Elimination
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Solution Overview
Problem
Existing rotary-to-linear motion actuators face issues with backlash, wear, complexity, high cost, and limited life, which hinder their performance in applications requiring high stiffness, slew rates, and frequency responses.
Innovation Solution
The development of direct-drive electromechanical rotary-to-linear actuators featuring a helically threaded planetary-nut-and-shaft arrangement, with a magnetically permeable central shaft and neodymium-iron magnets, and a backup motor for fail-safe operation, eliminates backlash and reduces complexity and cost by eliminating gear trains and incorporating a redundant power source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional gear trains and mechanical linkages are used in rotary-to-linear actuators, then motion conversion is achieved, but backlash and wear occur reducing precision and reliability
Solution Approach 1:
The patent replaces traditional mechanical gear trains and linkages with a direct-drive electromagnetic motor system. The motor's rotor is directly coupled to the planetary nut, eliminating intermediate mechanical components that cause backlash and wear. This substitution maintains motion conversion functionality while achieving backlash-free operation and reduced mechanical complexity.
Solution Approach 2:
The patent extracts and removes the gear train and intermediate mechanical linkages from the actuator system. By taking out these problematic components, the design achieves direct-drive operation where the motor rotor directly drives the planetary nut through threaded engagement, eliminating the sources of backlash and mechanical wear.
2Reliability
If redundant backup motor is added for fail-safe operation, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent incorporates a backup motor in advance to prevent system failure. The backup motor is pre-configured and can immediately take over if the primary motor fails, providing fail-safe operation. This beforehand preparation ensures continuous operation without interruption, addressing the reliability requirement for critical applications.
Solution Approach 2:
The patent changes the system configuration from a single motor to a dual motor arrangement with specific control parameters. The backup motor is integrated with control circuitry that monitors primary motor status and automatically switches operation, changing the system's operational parameters to achieve fail-safe capability while managing the added complexity through intelligent control.
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 solution provides backlash-free operation, increased stiffness, higher slew rates, improved frequency responses, and extended life, while maintaining reliability and efficiency, making them suitable for demanding applications like flight control and industrial automation.
Implementation Method 1
an electric motor, including a stator fixed in the housing and a rotor supported for rotation relative to the stator
Implementation Method 2
The drive unit comprises an elongated central shaft coupled to the rotor for conjoint rotation therewith and has a plurality of helical threads on an external surface thereof
Implementation Method 3
a plurality of planetary rollers, each having a helical thread on an external surface thereof that is complementary to and in engagement with both a thread of the shaft and a thread of the nut
Data Source
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AI summary
Direct drive electromechanical rotary-to-linear actuators include one or more electric motors mounted in a housing. Each motor includes a stator and a rotor. The motor drives a planetary drive mechanism that includes an elongated central shaft having one or more helical threads on an external surface coupled to the rotor for conjoint rotation. A planetary nut having helical threads on an internal surface is disposed concentric to the shaft, and a plurality of planetary rollers are disposed concentrically between the shaft and the planetary nut. Each of the rollers has a helical thread on an external surface that is complementary to and in engagement with a thread of the shaft and a thread of the nut. Rotation of the rotor is converted with mechanical advantage into linear movement of the planetary nut. The actuators provide backlash-free operation, higher stiffnesses, slew rates and frequency responses, and better overall efficiency.