Suspension Work Platform Hoist Variable-Frequency Control
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Solution Overview
Problem
Traditional suspension work platform hoist systems lack control over acceleration and deceleration, leading to jarring movements, equipment wear, and safety risks, while also suffering from voltage drops and unauthorized access.
Innovation Solution
A suspension work platform hoist system with variable acceleration and deceleration control, incorporating a variable frequency drive and reactive power reducing input power system, along with tilt and emergency descent controls, and authorization systems to ensure safe and controlled operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional across-the-line starters are used in hoist motors, then the system is simple and reliable, but the platform experiences instantaneous acceleration from standstill to full speed which is jarring and dangerous to occupants and roof beams
Solution Approach 1:
The variable frequency drive system performs preliminary action by gradually increasing the motor speed from zero to full speed before the platform reaches full velocity, rather than instantaneously switching to full speed. This controlled ramp-up of frequency and voltage prevents jarring acceleration while maintaining system reliability.
Solution Approach 2:
The system transitions from static across-the-line starting to dynamic variable frequency control, allowing the motor speed to be continuously adjusted during operation. This enables smooth acceleration and deceleration profiles that adapt to operational requirements while protecting occupants and structural elements.
2Productivity
If traditional single-speed motors are used in hoists, then the system is simple and cost-effective, but the platform velocity cannot be adjusted to reduce repeated starting, stopping, and reversing that causes equipment wear and safety hazards
Solution Approach 1:
The variable frequency drive enables the motor to operate at multiple speeds rather than a fixed single speed. This dynamic speed control allows the platform to maintain optimal velocities for different operational phases, reducing unnecessary stops and starts that cause equipment wear and improve overall productivity.
Solution Approach 2:
The system changes the operational parameters of the motor by varying frequency and voltage to achieve different speed levels. This allows continuous adjustment of platform velocity to match operational requirements, eliminating the inefficiencies of repeated acceleration and deceleration cycles.
3Length of moving object
If hoists are positioned several hundred feet from power sources, then the system can reach distant work areas, but voltage drop through conductors causes motors to overheat, fail prematurely, stall, and requires boost transformers
Solution Approach 1:
The variable frequency drive system replaces the need for mechanical boost transformers by using electronic control to compensate for voltage drop. The VFD monitors and adjusts output voltage to maintain proper motor operation over long distances, eliminating the need for additional electrical equipment and improving reliability.
4Ease of operation
If traditional hoist systems operate at full speed continuously, then the system is simple to control, but the platform approaches elevation at full speed and stops instantaneously causing repeated hunting before desired elevation is obtained
Solution Approach 1:
The variable frequency drive performs preliminary deceleration action by gradually reducing motor speed before the platform reaches the target elevation. This controlled slowdown prevents the platform from approaching at full speed and eliminates the need for instantaneous stopping, thereby preventing repeated hunting and improving elevation control precision.
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 provides smooth and controlled elevation changes, reduces equipment wear, minimizes safety hazards, and ensures authorized access, while maintaining efficient power factor and emergency safety features.
Implementation Method 1
The variable acceleration motor control system achieves the acceleration control by converting the constant frequency input power to a variable frequency power supply connected to the motors
Implementation Method 2
The suspension work platform hoist system may include a reactive power reducing input power system that reduces the reactive power and produces a hoist system power factor of at least 0.95 when operating at a steady state full-load condition
Data Source
AI summary
A suspension work platform hoist system for raising and lowering a work platform is provided. The system incorporates at least one hoist attached to the work platform and in electrical communication with a hoist control system having a monitoring and diagnostic system to monitor and record at least one of a plurality of operating characteristics of the hoist. The hoist control system may further include a safety lock out system that requires authentication of an operator prior to the hoist control system causing movement of the hoist system.