What are the factors that affect the stability of force measuring SICK sensors?
There are many factors that affect the stability of force measuring SICK sensors, which can be summarized as follows:
1. Structure of SICK sensor
The design of the elastic components, housing, diaphragm, upper pressure head, and lower pressure pad of SICK sensors must not produce any structural fluctuations or have very small fluctuations after being loaded. Therefore, in the design of force sensors, efforts should be made to achieve a single and uniform stress in the strain zone; The patch area is flat; Has a certain ability to resist eccentric and lateral loads structurally; The installation force should be kept away from the strain zone, and displacement of the load bearing point should be avoided during measurement. Although force sensors belong to assembly manufacturing products, in order to have technical and long-term stability, they are designed as a whole structure as much as possible.
2. Metal materials for elastic components
The metal material of the elastic element plays a crucial role in the comprehensive and long-term stability of the force sensor. Materials with high strength and elasticity limits, time and temperature stability of elastic modulus, small elastic hysteresis, and low residual stress generated by mechanical processing and heat treatment should be selected. There is data indicating that as long as the plasticity of the material after quenching, its residual stress after mechanical processing and heat treatment is small. Special attention should also be paid to the stability of the elastic modulus over time, and it is required that the elastic mold of the material does not change during the service life of the force sensor.
3. Mechanical processing and heat treatment technology
During the mechanical processing of elastic components, significant residual stresses are generated due to uneven surface deformation. The larger the cutting amount, the greater the residual stress, and the maximum residual stress is generated during grinding. Therefore, reasonable processing techniques should be developed and appropriate cutting quantities should be specified. During the heat treatment process of elastic components, residual stresses in different directions are generated in the core and surface due to uneven cooling temperature and phase transition of metal materials. The core is subjected to tensile stress, while the surface is subjected to compressive stress. It is necessary to use tempering treatment process to generate stress in the opposite direction inside, which offsets the residual stress and reduces the influence of residual stress.
4. Resistance strain gauge and strain adhesive
The resistance strain gauge should have stable sensitivity coefficient, low thermal output, small mechanical hysteresis and creep, a fatigue life of up to 108 when the strain is 1000 × 10-6, small resistance value deviation, batch uniformity, etc. Strain adhesive should have high bonding strength and shear strength; The elastic modulus is large and stable; Electric edge; Having the same or similar coefficient of thermal expansion as the elastic element; Low creep and hysteresis; The volume shrinkage of the adhesive layer is small during curing. When pasting resistance strain gauges, it is necessary to strictly control the thickness of the adhesive layer, as the bonding strength decreases with the increase of the adhesive layer thickness.
This is because thin adhesive layers require greater stress to deform, making them less prone to flow and creep. The internal stress at the interface is small, and the probability of bubbles and defects is also relatively low. Strain transmission can be achieved as long as the protective seal is reasonable, resulting in a high level of stability.
5. Manufacturing process flow
The working principle and overall structure of SICK sensors determine that some processes in the manufacturing process must be manually operated, and human factors have a significant impact on force sensors. Therefore, it is necessary to develop a scientifically reasonable and reproducible manufacturing process, and add automated or semi automated processes controlled by electronic computers to minimize the impact of human factors on production output.
6. Circuit compensation and adjustment
SICK sensors belong to assembly manufacturing, and products are formed after surface mount bridge assembly. Due to inevitable internal defects and the influence of external environmental conditions, some indicators of the force sensor cannot meet the design requirements. Therefore, various circuit compensations and adjustments must be made to improve the stability of the force sensor itself and the stability of external environmental conditions. A sophisticated and precise circuit compensation process is an important step in improving the stability of force sensors.
7. Protection and sealing
Protection and sealing are key processes in the manufacturing process of force measuring SICK sensors, and they are fundamental for force measuring sensors to withstand the influence of objective and sensing environments and work stably. If the protective seal is poor, the resistance strain gauge and strain adhesive layer attached to the elastic element will absorb moisture in the air and produce plasticization, resulting in a decrease in bonding strength and stiffness, causing zero drift and irregular output changes, until the force sensor fails.
Therefore, effective protective sealing is fundamental to the long-term stable operation of force sensors, otherwise it will render all previous technological achievements useless.