Stack Gas Probe Counterweight Droop Control
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Solution Overview
Problem
Existing automated probes for measuring stack gas flow velocity face challenges in robustness, accuracy, and minimizing droop due to increased mass and complexity, particularly in large diameter stacks, where multiple test ports are needed to accommodate the probe's range and cantilevered structure.
Innovation Solution
An automated probe system with a square tube and sensing tip, featuring a gripper assembly for translation and a servo-motor powered mechanism for rotation, constrained to prevent turning during translation, and a slewing ring bearing assembly for yaw adjustment, allowing precise positioning with reduced droop and increased robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the probe is extended to reach larger distances in large diameter stacks, then the measurement range is improved, but the probe droop increases due to cantilever mass
Solution Approach 1:
A counterweight assembly is provided that applies a counterbalancing force to offset the gravitational force acting on the extended probe mass. The counterweight is positioned and sized to create an opposing moment that prevents the probe from drooping below the maximum allowable angle, enabling the probe to be extended to greater lengths without excessive droop.
Solution Approach 2:
The counterweight is pre-positioned and pre-balanced to compensate for the probe mass before the probe is extended to its full measurement distance. This preliminary balancing action ensures that when the probe is extended to reach large diameter stacks, the droop is already compensated for, maintaining measurement stability throughout the extended range.
2Stability of the object's composition
If probe stiffness is increased to minimize droop, then the droop angle is reduced, but the probe mass and dimensions increase requiring more substantial mechanisms
Solution Approach 1:
Instead of increasing probe stiffness and mass to reduce droop, a counterweight assembly is used to apply a counterbalancing force that offsets gravitational effects. This approach maintains probe flexibility and lower mass while achieving the same droop control through external counterbalancing rather than internal stiffening.
Solution Approach 2:
The counterweight assembly acts as an intermediary mechanism between the probe and the gravitational force. Rather than making the probe itself stiffer and heavier, the counterweight mediates the gravitational effect by providing an opposing force, allowing the probe to remain lightweight while still controlling droop.
3Ease of operation
If more powerful prime movers are used to translate and turn the heavier probe, then the probe positioning capability is improved, but the device complexity and power requirements increase
Solution Approach 1:
The counterweight assembly reduces the net force required from the prime movers by offsetting the gravitational load on the extended probe. This allows smaller, less complex motors to be used while maintaining the ability to translate and rotate the probe through its full range of motion, reducing both power requirements and mechanism complexity.
Solution Approach 2:
The counterweight is pre-configured to balance the probe mass before positioning operations begin. This preliminary balancing reduces the dynamic load on the prime movers during translation and rotation, allowing for simpler motor designs and reduced complexity in the drive mechanism while maintaining full positioning capability.
Data Source
AI summary
A system and method for the automated measurement of properties related to a stack gas stream, flow velocity for example. A probe assembly (24) is introduced into a stack through a test port and operated by an automated mechanism mounted on the test port to position a sensing tip (28) at various locations within the gas stream at proper yaw angle. A framework (30, 32, 34, 36) of the automated mechanism provides bearing support for the probe assembly while allowing the probe assembly to translate on the framework along an axis but constraining the probe assembly from turning on the framework about the axis. With a gripper assembly (44) gripping the probe assembly and another gripper assembly (56) released, a linear actuator (40) can move the gripper assembly (44) along the axis to translate the probe assembly on the framework. A motor (70), also mounted on the framework, can turn a pinion (66) that is in mesh with a toothed segment (64) of a ring gear (62) that attaches to the stack port so that the motor (70) can turn the framework and probe assembly together about the axis.