Variable Frequency Drive Torque Control for Non-Cylindrical Load Wrapping
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Solution Overview
Problem
Conventional wrapping machines face challenges in maintaining adequate containment force for non-cylindrical loads due to erratic speed changes and variations in packaging material demand, leading to issues like packaging material breaks and inefficient wrapping, especially with the use of AC motors which struggle to modulate torque effectively.
Innovation Solution
A torque control algorithm constrained by a speed window is used to control the dispense rate of a packaging material dispenser, maintaining a substantially constant torque for the dispenser motor while operating within a speed window based on the rate of relative rotation between the dispenser and the load, utilizing an AC variable frequency drive (VFD) without the need for separate tension sensing devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional speed control methods are used for AC motors in wrapping machines, then the system is simpler to operate, but the torque modulation capability is insufficient leading to packaging material breaks and inconsistent containment force
Solution Approach 1:
The patent applies dynamics by transitioning from fixed-speed AC motor operation to variable-speed operation with continuous torque modulation. The VFD enables the motor to dynamically adjust its speed and torque output in real-time during the wrapping cycle, allowing the system to adapt to changing load conditions and maintain consistent packaging material tension throughout the wrapping process.
Solution Approach 2:
The patent implements parameter changes by modifying the electrical parameters of the AC motor through the VFD. The controller adjusts frequency, voltage, and torque parameters dynamically during operation, enabling precise control of the packaging material dispense rate and tension without requiring mechanical modifications to the motor itself.
2Reliability
If the dispense rate of packaging material is not properly controlled, then the system operates simpler without complex control algorithms, but containment force becomes inconsistent and packaging material breaks occur
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual dispense rate and comparing it to the target dispense rate calculated by the control algorithm. The controller adjusts the VFD output based on this feedback to maintain consistent packaging material tension and prevent breaks, creating a closed-loop control system that automatically corrects deviations from the desired wrapping parameters.
Solution Approach 2:
The patent applies preliminary action by pre-calculating the target dispense rate and torque requirements before the wrapping operation begins. The control algorithm determines the optimal speed and torque profile in advance based on the desired containment force, allowing the system to proactively adjust parameters rather than reactively responding to deviations during operation.
3Reliability
If torque control is not implemented, then the system has fewer control parameters, but the dispense rate varies causing packaging material breaks and loose wrapping
Solution Approach 1:
The patent replaces mechanical torque control mechanisms with an electrical control system. Instead of using mechanical friction devices, clutch-brake assemblies, or complex mechanical linkages to control torque, the system uses a VFD to electrically control the AC motor's torque output, simplifying the mechanical structure while enabling more precise and flexible torque modulation.
4Ease of repair
If AC motors are used instead of DC motors, then maintenance is reduced and cost is lowered, but torque modulation capability is limited
Solution Approach 1:
The patent introduces the VFD as an intermediary device between the power source and the AC motor. This intermediary enables the AC motor to achieve the torque modulation capability previously only available from DC motors by converting fixed-frequency power into variable-frequency, variable-voltage power that can precisely control motor torque and speed during the wrapping operation.
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 approach ensures consistent torque and efficient wrapping by adapting to the changing demands of non-cylindrical loads, improving containment force and reducing packaging material breaks, while also simplifying the system by eliminating the need for costly force sensing devices.
Implementation Method 1
controlling an AC variable frequency drive (VFD) to maintain a substantially constant torque for a dispenser motor while maintaining a speed of the dispenser motor within a speed window
Data Source
AI summary
A method, apparatus and program product utilize a torque control algorithm constrained by a speed window to control the dispense rate of a packaging material dispenser when wrapping a non-cylindrical load with packaging material. In particular, a dispenser motor of the packaging material dispenser that is controlled by a VFD may be driven to maintain a substantially constant torque, while also constrained to operate within a speed window that is based at least in part on a rate of relative rotation between the packaging material dispenser and the load.