Читать книгу Industry 4.1 - Группа авторов - Страница 42

Cutting force is an intuitional physic quantity that affects the machining quality and product quality the most. This force generated from the relative motions between the cutting tool and workpiece is necessary to form the shape of the workpiece, this relationship is illustrated in Figure 2.3. Any change occurred in the cutting‐tool paths, heat, weight, tension, or structure of the material during the cutting operation can be directly reflected on the cutting force. Thus, the cutting force is considered to be the best indicator to perform the monitoring of cutting‐tool/equipment condition and prediction of the workpiece accuracy.

Figure 2.3 Relative motion between a cutting tool and a workpiece.

Observing Figure 2.3, the electrical strain gauge, or the so‐called piezoresistive sensor, detects forces or strains on the target device and converts the amount of the deformation into an electrical signal. As shown in the right side of Figure 2.3, the electrical resistance element changes its resistance length once the strain gauge is elongated or contracted under the external force. Through this direct measurement, the strain gauge provides extremely accurate and rapid response of the forces and strains that happened in the movement direction of cutting‐tool. The excellent durability and stability also enable them to be operated in harsh environment. Figure 2.3 demonstrates an example of the adhesive‐backed strain‐gauge installation, which can be directly attached to the tool holder to monitor the torque and force on the cutting tool during the operations.

Many similar sensor types derived from the same working principle of strain‐gauge technology, such as strain gauge‐based pressure transducer and dynamometer are also commonly used in the machining factories. The tool dynamometer or force dynamometer is also frequently adopted as a sensor for monitoring cutting force signals. The sampling rate usually ranges from 1 to 100 kHz.

The installation of a force dynamometer is illustrated in Figure 2.4, which has to be fixed on the machining table. The performance is also sensitive to the installation direction, humidity, temperature, or long‐time usage. Yet the installation process of the dynamometer is tedious because of its intrusive nature, which may deteriorate the machining performance. In addition, a dynamometer may reduce the working space and available machining conditions so that it is not acceptable and practical in the industry.

Figure 2.4 Installation of a Dynamometer.