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Percussion rock drills have been widely used mainly for blast hole drilling in mineral extraction, tunnel excavation, and underground development. To advance the performance and efficiency of rock drills, it is essential to understand the complex mechanisms of percussive rock drilling: hydraulic mechanisms in a drill body, elastic wave propagation and attenuation in rods and rod joints, dynamic bit penetration into rock, and the effects of thrust, rotation, and flushing. This paper focused on and detailed the bit penetration into rock. Some theories concerning the penetration characteristics of rock drill bits were presented such as elastic contact theory, slip line field theory, and fracture theory. Recent authors’ studies on static and dynamic penetration tests with a single button were introduced as an elementary drilling process of a bit in which a number of buttons are embedded. Then, recent authors’ studies on dynamic penetration tests with a button bit were introduced with the calculation method of force and penetration depth at the bit tip and with the results of force-penetration curves. The loading and unloading phases of the curves were modeled by convex functions, and their variation was discussed with the relation between the force-penetration curves of a bit and buttons. Important future research issues on the bit penetration into rock were presented for the further progress of percussive rock drilling.

In response to the issues of overheating of the shell and insufficient impact energy of the hydraulic rock drill, this paper focuses on the hydraulic rock drill with alternating front and rear return chambers. By establishing nonlinear and linear dynamic models, the influence of stroke amount and flow compensation on the hydraulic system is investigated, and an optimization method for impact characteristics is proposed. Considering factors such as hydraulic clamping force, fluid leakage, and rock properties, a feedback control numerical model is established for the impact system. This model is based on principles drawn from wave dynamics and fluid dynamics theories. It elucidates the dynamic characteristics of the impact piston, reversing valve, and high-pressure accumulator. Combining three linear models, this study investigates the influence of the advance amount of the return signal chamber and the gas pre-charge pressure of the high-pressure accumulator on the impact characteristics. A thorough laser experiment has been created to evaluate the actual rock drilling capabilities of the impact system. Proposed optimal parameters are tested experimentally to compare the impact performance before and after the enhancement. The results indicate an increase in impact power, validating the effectiveness of the proposed improvement method.

Data-driven fault diagnosis is an essential technology for the safety and maintenance of rock drills. However, since the signals acquired from a rock drill have different distributions, which arise due to their variable operating conditions, the classification performance of any data-driven method is diminished; this is called the domain-shift issue. This paper proposes a new domain-adaptation-based fault diagnosis scheme to solve the domain-shift problem. The proposed method introduces a data-cropping technique to mitigate the difference in the length of the data measured from a rock drill for each impact cycle. To extract invariant features for all operating conditions, the proposed method combines two methods: a domain adversarial neural network and minimization of the maximum mean discrepancy (MMD) between the features from different domains. In addition, a soft voting ensemble is used to reduce the model uncertainty. The proposed method shows superior performance when validated with a rock drill dataset; the proposed approach was ranked in 2nd place in the 2022 PHM Conference Data Challenge.

To optimize and improve the impact performance of a hydraulic rock drill, it is helpful to test the stress waves of the drill and analyze the impact energy, impact frequency, and energy utilization rate. For this study, a stress wave test bench was designed and built, according to international standards, in order to study the impact process of a hydraulic rock drill under the working pressures of 18 MPa and 23 MPa. The impact energy, impact frequency, and energy utilization rate of two different hydraulic rock drill pistons in low, middle, and high gear were analyzed using a control variable method. The results demonstrate that the impact stress waves of the rock drill periodically occur in the drill rod, and then decay exponentially until they become close to zero. Moreover, the amplitude of the incident stress wave determines the rock-breaking ability of the drill. The impact energy of the short piston is greater than that of the long piston, with a maximum average value of 346.1 J; the impact frequency of the long piston is higher than that of the short piston, with a maximum average value of 62 Hz; and the energy utilization rate of the short piston is higher than that of the long piston, with a maximum average value of 56.92%, which is close to the theoretical ideal efficiency. Therefore, it can be concluded that the impact performance of a hydraulic rock drill can be effectively tested using the proposed horizontal bench, and that piston characteristics and the working pressure are the main factors affecting impact performance. Accordingly, when developing a hydraulic rock drill, it is advisable to select a shorter piston and a higher working pressure, thus allowing the drill to provide good impact performance.

This study presents a novel method for fault diagnosis of a hydrostatic rock drill. Hydraulic rock drills suffer from both domain discrepancy issues that arise due to their harsh working environment and indivisible difference. As a result, fault diagnosis is very challenging. To overcome these problems, we propose a novel diagnosis method that combines both data-driven and signal-process-based methods. In the proposed approach, data-driven methods are employed for overall fault classification, using domain adaptation, metric learning, and pseudo-label-based deep learning methods. Next, a signal-process-based method is used to diagnose the specific fault by generating a reference signal. Using the combined approach, the fault-diagnosis performance was 100%; the proposed method was able to perform well even in cases with domain discrepancy.

Hydraulic rock drills are widely used in drilling, mining, construction, and engineering applications. They typically operate in harsh environments with high humidity, large temperature differences, and vibration. Under the influence of environmental noise and operational patterns, the distributions of data collected by sensors for different operators and equipment differ significantly, which leads to difficulty in fault classification for hydraulic rock drills. Therefore, an intelligent and robust fault classification method is highly desired. In this paper, we propose a fault classification technique for hydraulic rock drills based on deep learning. First, considering the strong robustness of x−vectors to the features extracted from the time series, we employ an end−to−end fault classification model based on x−vectors to realize the joint optimization of feature extraction and classification. Second, the overlapping data clipping method is applied during the training process, which further improves the robustness of our model. Finally, the focal loss is used to focus on difficult samples, which improves their classification accuracy. The proposed method obtains an accuracy of 99.92%, demonstrating its potential for hydraulic rock drill fault classification.

Large pulsation and impact occur during the working process of hydraulic rock drill, which has a negative influence on the system. Aiming at this phenomenon, the related characteristics of hydraulic fluid inertia are studied in this paper. The dynamic model of impact and reversing mechanism of rock drill is established. Through the parameter analysis of the model, the concepts of hard parameter quantity and soft parameter quantity are proposed. The influence coefficient C of the initial section of crevice flow including the influence of fluid inertia is deduced, and the comprehensive factors such as hydraulic oil velocity, unstable flow and friction resistance are analyzed, The value of soft parameter quantity ζ is (ξ+1) ~ (ξ+ 1.5)。The pressure test of the working chamber is designed and 7 groups of data are obtained. Through data analysis, the influence of C on the simulation results is obtained, which has a great influence on the reversing valve. The deviation of simulation data of left and right valve chamber pressure is increased from ± 8% to ± 3%. It has a certain impact on the impact piston. The deviation of simulation data increases from ± 5% to ± 3%, and has little impact on the accumulator. The deviation of simulation data increases from ± 4% to ± 3%. [ABSTRACT FROM AUTHOR]

Workers in the rock face stabilisation sector are exposed to high levels of vibration from pneumatic rock drills, which can lead to vibration injuries. The work situation is also ergonomically challenging since the work often is performed on steep cliffs with heavy equipment and a substantial degree of dust exposure. To reduce exposure to vibrations, the equipment has been redesigned, including the machine’s handle, feeding hoist and the implementation of a reciprocating mass generating a counter force to reduce the vibrations. As a side project, a dust removal device was also developed. It was shown that vibration and dust exposure can be substantially reduced.

To optimize and improve the impact performance of a hydraulic rock drill, it is helpful to test the stress waves of the drill and analyze the impact energy, impact frequency, and energy utilization rate. For this study, a stress wave test bench was designed and built, according to international standards, in order to study the impact process of a hydraulic rock drill under the working pressures of 18 MPa and 23 MPa. The impact energy, impact frequency, and energy utilization rate of two different hydraulic rock drill pistons in low, middle, and high gear were analyzed using a control variable method. The results demonstrate that the impact stress waves of the rock drill periodically occur in the drill rod, and then decay exponentially until they become close to zero. Moreover, the amplitude of the incident stress wave determines the rock-breaking ability of the drill. The impact energy of the short piston is greater than that of the long piston, with a maximum average value of 346.1 J; the impact frequency of the long piston is higher than that of the short piston, with a maximum average value of 62 Hz; and the energy utilization rate of the short piston is higher than that of the long piston, with a maximum average value of 56.92%, which is close to the theoretical ideal efficiency. Therefore, it can be concluded that the impact performance of a hydraulic rock drill can be effectively tested using the proposed horizontal bench, and that piston characteristics and the working pressure are the main factors affecting impact performance. Accordingly, when developing a hydraulic rock drill, it is advisable to select a shorter piston and a higher working pressure, thus allowing the drill to provide good impact performance. [ABSTRACT FROM AUTHOR]