Application of closed-loop control technology in double disc grinding machine in grinding accuracy improvement

The closed-loop control technology of double disc grinding machine has become the core means to break through the bottleneck of traditional machining accuracy through real-time monitoring and dynamic adjustment. During the grinding process, factors such as grinding wheel wear, thermal deformation and workpiece clamping errors accumulate micron-level deviations, while the open-loop system can only rely on the passive execution of preset procedures and is unable to cope with real-time perturbations. The essence of closed-loop control lies in the construction of a ‘perception-decision-execution’ feedback link, for example, through high-precision displacement sensors (such as laser interferometer or capacitive probe) real-time acquisition of the workpiece size and grinding wheel position data, and compared with the theoretical model, the CNC system drives servo motors to compensate for the error. A bearing collar processing case shows that the closed-loop control can compress the workpiece parallelism error from ± 5μm to ± 1.5μm, and the yield rate increased by more than 20%.

The layout and selection of the sensor network is the basis of closed-loop control. In a double disc grinding machine, key monitoring points include the axial position of the grinding wheel, workpiece thickness, grinding force and vibration amplitude. For example, an inductive displacement sensor with nanometer resolution integrated at the end of the grinding wheel spindle captures the axial runout of the grinding wheel at the micron level in real time; while a piezoelectric force sensor installed on the workpiece fixture monitors the dynamic change of the grinding force and prevents surface burns due to cutting overload. A German high-end grinder manufacturer adopts multi-sensor fusion technology to synchronise grinding force, temperature and vibration data into the control unit, and eliminates noise interference through Kalman filtering algorithms, so that the confidence level of the feedback signal reaches 99%.

The design of real-time feedback and dynamic compensation algorithm directly determines the response speed and accuracy of the closed-loop system. The traditional PID control is difficult to adapt to the nonlinear disturbances in the grinding process (e.g. wheel passivation, material hardness fluctuations) because of the fixed parameters. For this reason, adaptive control algorithms have been introduced. For example, fuzzy logic-based controllers can automatically adjust the feed rate according to the rate of change of the grinding force, and when a sudden increase in the grinding force is detected, the system reduces the feed rate by 30% within 10ms, avoiding vibration patterns on the surface of the workpiece. A more cutting-edge solution is to combine machine learning technology to train a prediction model through historical machining data to predict grinding wheel wear trends and compensate in advance. An experiment has shown that this technology can extend grinding wheel life by 40 per cent, while reducing the number of dressings by 30 per cent.

Thermal error compensation is another important application scenario for closed-loop control in double disc grinding machines. The heat generated by high-speed grinding leads to micron-level thermal expansion of components such as the bed and spindle, and the traditional temperature compensation model relies only on a limited number of temperature measurement points with limited accuracy. The new generation system combines distributed fibre-optic temperature sensors on key structures (e.g. spindle bearings, guide rails) with a finite element thermal deformation simulation model to predict the amount of thermal expansion in real time and drive linear motors to compensate for it in the reverse direction. After adopting this technology, a semiconductor equipment manufacturer has reduced the workpiece thickness fluctuation from ±3μm to ±0.8μm for 8 hours of continuous machining, achieving sub-micron stability.

Intelligent integration further expands the application boundaries of closed-loop control. For example, embedding the machine vision system into the closed-loop link allows online inspection of the workpiece surface after grinding is completed, and if local unground areas are found, the system automatically triggers the secondary machining process without manual intervention. In addition, digital twin technology can preview the effects of different compensation strategies through real-time interaction between virtual models and physical equipment. In an automotive parts production line, the digital twin-driven closed-loop system reduced commissioning time by 70%, while reducing the standard deviation of machining consistency from 1.2 μm to 0.4 μm.