Reciprocating Mowing Sickle Drive With Frequency-Tuned Spring Stiffness
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Solution Overview
Problem
Conventional mowing sickle drive systems face challenges in compactness and efficiency due to the large space required for inertia compensation, with direct proportional relationships between input speed and knife bar speed leading to non-optimum cutterbar operation, and coil springs generating unnecessary opposing forces at low speeds.
Innovation Solution
A mowing sickle drive system with a knife bar driven by a linear motor and equipped with a spring having a variable modulus of elasticity, controlled by a flow control valve, to adjust restoring forces based on drive frequency, reducing wear and energy consumption by minimizing stiffness at low speeds and maximizing it at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional mechanical sickle drive systems with flywheels are used for inertia compensation, then the rapid changes in inertia are compensated, but the drive system requires large space and extends laterally outside the cutterbar width
Solution Approach 1:
The patent extracts the inertia compensation function from the mechanical drive system and relocates it to a separate hydraulic system. The hydraulic cylinder with variable stiffness spring provides inertia compensation independently from the drive mechanism, allowing the drive system to be more compact while maintaining reliability.
Solution Approach 2:
The patent introduces a hydraulic cylinder as an intermediary mechanism between the drive motor and the knife bar. This hydraulic intermediary absorbs the inertial shocks and provides smooth force transmission, enabling compact drive system design without sacrificing inertia compensation capability.
2Reliability
If coil springs are used for inertia compensation in linear electric motor systems, then the stresses upon the motor and linkage are reduced, but unnecessary opposing forces are generated at low speeds where inertia is low
Solution Approach 1:
The patent employs a variable stiffness spring mechanism that dynamically adjusts its stiffness based on operating conditions. At high speeds with high inertia, the spring provides full stiffness for stress reduction. At low speeds with low inertia, the stiffness is reduced or eliminated, avoiding unnecessary opposing forces and energy loss.
Solution Approach 2:
The patent changes the physical parameter of spring stiffness dynamically. By varying the stiffness parameter according to drive frequency and inertial demands, the system optimizes both stress reduction and energy efficiency across different operating conditions.
3Device complexity
If the cutterbar is driven at speeds directly proportional to other header-mounted components, then the drive system is simplified, but the cutterbar is often driven at a non-optimum speed for the encountered crop conditions and ground speed
Solution Approach 1:
The patent makes the drive system universal by enabling the linear electric motor to operate independently from other header components. The motor can be controlled at variable speeds optimized for different crop conditions and ground speeds, while still providing inertia compensation through the hydraulic system, thus achieving both operational flexibility and cutting efficiency.
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
The system allows for efficient operation at variable speeds, reducing wear and energy consumption by dynamically adjusting the spring's stiffness in response to changing inertia, enabling the knife bar to be driven at speeds proportional to the forward speed while maintaining optimal performance.
Implementation Method 1
a spring connected to the knife bar for applying a restoring force to the knife bar toward a neutral position when in motion, wherein the spring has a variable modulus of elasticity that is controlled dependent upon the drive frequency
Implementation Method 2
the knife bar carries inertia when driven in a reciprocating motion
Implementation Method 3
European Patent Application Publication 2,976,936 discloses a mowing sickle drive system that includes a linear electric motor configured for driving the knife bar in a reciprocating linear motion
Implementation Method 4
controlled by a flow control valve, to adjust restoring forces based on drive frequency
Data Source
AI summary
A mowing sickle drive system comprises a knife bar supported by a frame and drive apparatus operable to drive the knife bar in a reciprocating linear motion at a variable drive frequency. A spring is coupled to the knife bar for applying a restoring force to the knife bar toward a neutral position when in motion. The spring has a variable modulus of elasticity that is controlled dependent upon the drive frequency.