The generation and adjustment of four corner errors in parallel beam type weighing sensors

The generation and adjustment of four corner errors in parallel beam type weighing sensors

With the vigorous development of industries such as e-commerce and express delivery, and the growing demand for accurate measurement of electronic scales, the four-corner error problem of parallel beam load cells, as the core component of electronic scales, has received much attention. Today, let's take an in-depth look at the "past and present" of the four-corner error of parallel beam load cells and tips for adjustment~

### 1. How does the four-corner error occur?
When a parallel beam load cell works, the elastic body deforms under load, and the bonded resistance strain gauges subsequently produce resistance changes, which are converted into voltage signals by a Wheatstone bridge to achieve weighing. However, due to the eccentric load caused by different placement positions of objects, additional strain is easily introduced when strain gauges are bonded in the strain area, thereby generating four-corner errors.

There are many factors affecting the four-corner error:
- **Material and manufacturing**: Uneven aluminum alloy raw materials for producing the elastic body of the sensor, or differences in the resistance strain generated by resistance strain gauges during production, can "lay mines" for four-corner errors.
- **Bonding deviation**: If the bonding position of the resistance strain gauge deviates from the preset force center, or the bonding symmetry does not meet the design requirements, the voltage signal output by the Wheatstone bridge will differ, directly leading to four-corner errors.
- **Environmental impact**: Changes in environmental temperature and humidity will interfere with the aluminum alloy elastic body. Uneven temperature causes inconsistent deformation of the elastic body, and humidity makes the strain gauges damp, causing the output signal to deviate from the actual value, thereby affecting the four-corner error.

### 2. How to reduce errors?
- **Material and process optimization**: Select high-quality aluminum alloy elastic body materials, design temperature compensation circuits, and do a good job in the sealing process after strain gauge bonding to reduce environmental humidity interference and reduce the impact of errors from the source.
- **Bonding precision**: Some manufacturers rely on manual fine bonding and adjustment of strain gauge positions; some enterprises also use machine vision and computer control for precise positioning and bonding to improve the bonding precision of strain gauges.

### 3. What are the tricks for error adjustment?
The formula for the maximum strain in the strain area of a parallel beam elastic element is [formula]. Based on this, regardless of the eccentric load error caused by any factor, it can be attributed to the inconsistency in the cross-sectional dimensions ( b ) and ( h ) at the resistance strain gauge in the strain area. Fine-tuning these two dimensions can correct the eccentric load error and adjust the four-corner error.

At the same time, the structural dimensions of the sensor elastic body (such as hole diameter, elastic element thickness ( b ), hole spacing ( L ), etc.) will affect the sensitivity output. During the semi-finished product stage, the thickness ( b ) of the elastic element has a significant impact on the sensitivity, and adjusting it can achieve a wide range of adjustment; adjusting the hole spacing ( L ) has a small impact and is suitable for fine-tuning. In actual production, the four-corner error adjustment is often achieved by slightly adjusting the thickness of the patch area.

### 4. Model simulation experiment verification
Simulate the HBM PW2DC3/72kg parallel beam aluminum alloy load cell, install it on a tooling and load a 24kg load for testing. After the initial test, parameter assignment to the model, and adjustment of the thickness of the strain gauge patch area, then test again. It is found that adjusting the thickness of the patch area can change the force on the target point, realize the adjustment of the four-corner error, and verify the effectiveness of the adjustment method~

### 5. Intelligence is the future direction
At present, most of the four-corner error adjustment in China relies on manual work, which has high requirements for technology and experience. In the future, it is necessary to accumulate a large amount of data and build an automatic control system. At the same time, efforts should be made in aspects such as innovation in elastic body material technology, improvement of strain gauge bonding precision (machine vision + nanoscale etching), and high and low temperature compensation (AI algorithm) to build a high-precision load cell technology system, promote the upgrading of downstream products such as electronic scales, and support the development of industries such as logistics and retail~