The force measuring sensor is composed of three parts: one or more elastic bodies that can produce deformation after being subjected to force, a strain gauge that can sense this deformation, and a bridge circuit. It also includes adhesive that can fix the strain gauge on the elastic body and conduct the strain, as well as sealing glue that can protect the electronic circuit. Below we will briefly introduce the factors that affect the stability of force measuring sensors.
The structure of the force measuring sensor
The design of the elastic element, shell, diaphragm, upper pressure head, and lower pressure cushion of the force measuring sensor must ensure that there is no performance fluctuation or minimal performance fluctuation after being loaded in the structure. Therefore, in the design of the force measuring sensor, efforts should be made to ensure that the stress and strain are uniform and consistent in the strain area, and the chip parts are preferably flat. The force measuring sensor should have a certain ability to resist eccentric load and lateral load in the structure. The installation force should be far away from the strain area, and the displacement of the load-bearing point should be avoided during the measurement. Although the force measuring sensor belongs to the assembly manufacturing product, in order to ensure better technical performance and long-term stability, it should be designed as a whole structure as much as possible.
Metal material of the force measuring sensor elastic element
The metal material of the elastic element plays a key role in the comprehensive performance and long-term stability of the force measuring sensor. Materials with high ultimate strength and elastic limit, good time and temperature stability of elastic modulus, small elastic hysteresis, and small residual stress generated by mechanical processing and heat treatment should be selected.
Mechanical processing and heat treatment of the force measuring sensor elastic element
During mechanical processing, the elastic element produces large residual stress due to uneven surface deformation. The greater the cutting dosage, the greater the residual stress, and the grinding process produces greater residual stress. Therefore, reasonable processing technology and appropriate cutting dosage should be formulated. During heat treatment, the elastic element produces residual stress with different directions in the core and surface due to uneven cooling temperature and metal material phase transformation. The core is subjected to tensile stress and the surface is subjected to compressive stress. The residual stress must be offset by internal opposite-directional stresses through tempering process to reduce the influence of residual stress.
Manufacturing process of the force measuring sensor
The working principle and overall structure of the strain-based force measuring sensor determine that some processes must be manually operated in the production process, and human factors have a significant impact on the quality of the force measuring sensor. Therefore, a scientific and reasonable manufacturing process must be established, and automatic or semi-automatic processes controlled by electronic computers should be added to reduce the impact of human factors on product quality as much as possible.
Compensation and adjustment of force measuring sensor circuit
The strain-based force measuring sensor belongs to assembly manufacturing, and after chip assembly, it forms a product. Due to some defects inside and the impact of external environmental conditions, some performance indicators of the force measuring sensor cannot meet the design requirements. Therefore, various circuit compensation and adjustments must be carried out to improve the stability of the force measuring sensor itself and its stability to external environmental conditions. A perfect and sophisticated circuit compensation process is an important part of improving the stability of the force measuring sensor.
Protection and sealing of the force measuring sensor
Protection and sealing are crucial processes in the manufacturing process of the force measuring sensor, and are the fundamental guarantee for the force measuring sensor to withstand objective environmental and induction environmental impacts and work stably and reliably. If the protection and sealing are not good, the resistance strain gauge and strain bonding adhesive layer attached to the elastic element will absorb moisture in the air and become plasticized, causing the bonding strength and stiffness to decrease, resulting in zero drift and irregular output changes, and even leading to the failure of the force measuring sensor. Therefore, effective protection and sealing is the fundamental guarantee for the long-term stable operation of the force measuring sensor, otherwise all the achievements of various processes will be futile.
Stability processing of the force measuring sensor
In addition to dealing with the influence of the above factors, an important way to improve the stability of the force measuring sensor is to adopt various technical measures and process methods, simulate the use conditions, and carry out effective artificial aging tests to release as much residual stress as possible and reduce the performance fluctuation to a minimum.