Vacuum Turbomolecular Pump Overspeed Protection via EMF
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Vacuum turbomolecular pumps face a high risk of overspeed accidents due to the potential for the rotor to exceed nominal rotational frequencies, posing safety hazards and requiring complex and costly redundant safety systems.
Innovation Solution
A vacuum turbomolecular pump with a constant low supply voltage to the motor control, limiting the rotational frequency to 1.3 times the nominal frequency, and a protective device that monitors and adjusts the voltage to prevent overspeed, including an EMF evaluation module and signal generator to ensure the rotor does not exceed safe operational limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second independent rotational frequency control device is added to prevent overspeed, then safety is improved, but device complexity and cost increase considerably
Solution Approach 1:
The system uses its own electromotive force (EMF) signal, which is naturally generated during motor operation, as the basis for overspeed protection. The EMF evaluation module processes this self-generated signal to detect overspeed conditions, eliminating the need for external sensors or independent control devices. The motor control unit itself performs the safety function by evaluating the EMF signal and initiating shutdown when necessary.
Solution Approach 2:
The motor control unit is designed to perform multiple functions: it controls the motor operation during normal operation and simultaneously serves as the overspeed protection device by evaluating the EMF signal. This multi-functionality consolidates what would traditionally require separate independent control systems into a single integrated unit, reducing overall system complexity while maintaining safety.
2Reliability
If the pump rotor is armored to protect against high kinetic energy from detached rotor parts, then safety is improved, but manufacturing effort and cost increase greatly
Solution Approach 1:
The system prevents the dangerous condition (rotor detachment at high speed) from occurring in the first place by continuously monitoring the EMF signal for overspeed conditions. By detecting and responding to overspeed before rotor detachment can occur, the invention eliminates the need for protective armor that would be required if the system relied solely on physical protection measures.
3Reliability
If the supply voltage is limited to a constant low value, then overspeed is prevented, but the maximum rotational frequency is reduced
Solution Approach 1:
The system dynamically adjusts the evaluation threshold for the EMF signal based on the nominal rotational frequency and limit rotational frequency parameters. By changing the parameter (EMF limit value) rather than permanently limiting the supply voltage, the system maintains full power availability for normal operation while preventing overspeed through intelligent evaluation of the EMF signal against predefined thresholds.
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 solution effectively prevents overspeed by limiting the rotational frequency, reducing the risk of accidents and eliminating the need for a second speed control system, ensuring the pump's safety with minimal additional effort and cost.
Implementation Method 1
a maximum rotational frequency is automatically set in that the voltage or electromotive force (EMF) induced by the permanent magnet of the rotor in the stator coils becomes so great that the maximum standing driving force is fully compensated
Data Source
Figure 1
AI summary
A vacuum turbomolecular pump (10) is driven by a brushless direct current drive motor (16), which has stator coils and a permanent magnetic-exited motor rotor. When rotating, the motor rotor produces an electromotive force oriented counter to the direction of rotation. A motor controller (22) is provided, which is connected to the stator coils and which generates a current from the supply voltage, this current being impressed into the stator coils. In addition, a rotary frequency regulator (32) is provided that limits the rotary frequency (f) of the drive motor (16) to a nominal rotary frequency (fN). A power supply (20) is provided, which is connected to the motor controller (22) and which supplies a constant direct current voltage as a supply voltage for the motor controller (22). The power supply (20) is designed so that the constant supply voltage (UV) is low enough that at a limit rotary frequency (fG), the electromotive force is equal to the drive force that can be maximally generated by the motor controller (22) and by the stator coils. The limit rotary frequency (fG) is less than 1.3 times the nominal rotary frequency (fN). As a result, the motor output is limited and the rotary frequency of the drive motor (16) is physically restricted to a limit rotary frequency (fG) in a reliable manner.