Contact between the tool and the workpiece during machining has a significant effect on the vibration characteristics of the machine tools. In this study, contacting rate is defined as the contact time per unit time based on the detected contact between the tool and workpiece during the excitation tests, and relationship between the contacting rate and vibration characteristics is investigated. As a result, it was confirmed that the natural frequency increased significantly when the contacting rate was over 90%, and the vibration damping increased significantly when the contacting rate was in the range of 0-10%.
Infrastructure facilities have been deteriorating and require a vast number of inspections conducted by skilled engineers. Inspection robots are required because of a shortage of skilled engineers. In order to improve the inspection efficiency of outdoor infrastructure facilities, an omni-directional mobile robot that can move freely in all directions has been investigated. However, it is necessary to design a vibration isolation mechanism because the accuracy of the positional inspection of underground objects is adversely affected by vibration in an outdoor environment. We have constructed an experimental setup to evaluate the vibration properties of the wheel. The acceleration characteristics due to the difference between the direction of movement and the speed of the omni-wheel have been evaluated. It was confirmed that periodic vibration occurred by each moving direction of the Omni wheel.
A unique machining knowledge has led to several different perspectives between planners and operators as regards in designing a machining process plan. All precedents have shown the need to maintain a suitable machining process plan. Commercial Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) systems have facilitated the manipulation of 3D models to generate a machining process plan. The open Advanced Programming Interfaces (APIs) are also helpful in tailoring decision support systems to determine process plans. This study proposes an emergent system to generate flexible machining process plans. The proposed system considers the integration between design and manufacturing perspective to produce relevant machining process plan. The generation of process plans begins by considering the total removal volume of the raw material, estimating the removal features, thus analyzing and ordering several candidates of machining process plans. The total machining time and number of setups from each machining process plan candidate is analyzed and evaluated. Eventually, the proposed system is tested using several prismatic 3D models of a workpiece to show the outcomes.
Energy consumption of numerical control (NC) machine tools is one of the key issues in modern industrial field. This study focuses on reducing the energy consumed by a five-axis machining center by changing only the workpiece setting position. Previous studies show that the movements along each axis in five-axis machining centers depend on the workpiece setting position, regardless of whether the same operation is performed. In addition, the energy consumptions required for the movements are different along each axis. From these considerations, an optimum workpiece setting position that can minimize the energy consumed during these motions is assumed to exist. To verify this assumption, in this study, the energy consumed by the feed drive systems of an actual five-axis machining center is first measured and then estimated using the proposed model in this study. The model for estimating the energy consumption comprises the friction, motor, and amplifier losses along each axis. The total energy consumption can be estimated by adding the energy consumptions along each axis. The effect of the workpiece setting position on the energy consumption is investigated by employing the cone-frustum cutting motion with simultaneous five-axis motions. The energy consumption that depends on the workpiece setting position is first measured and then estimated. The results confirm that the proposed model can estimate the energy consumption accurately. Moreover, the energy consumption is confirmed to depend on the workpiece setting position; the minimum energy consumption is found to be 20% lower than the maximum one.
Several methods of evaluating the motion accuracy of the rotary axes of five-axis machining centers have been proposed in past studies. Because it is known that particular motion errors exist near motion direction changing points, it is important to evaluate the behavior of the rotary axes near these points. However, the influence of the motion error of the translational axes is included in conventional evaluation results because the translational axes reverse at the motion direction changing points about the rotary axes. In this study, a measurement system for evaluating the dynamic characteristics of the rotary axes near the motion direction changing points about these axes, excluding the influence of the translational axes, was developed. The measurement tests were also conducted using this measurement system for evaluating the dynamic characteristics of the tilt axis near the motion direction changing points about this axis. In addition, an actual machining test was conducted to evaluate the influence of the motion errors of the tilt axis near the motion direction changing points. As a result, it was confirmed that the behavior of the tilt axis near the motion direction changing points can be evaluated by using the proposed measurement method. It was also confirmed that the influence of the motion error on the machined surface is related to the size and shape of the tool and the geometric relationship between the motion error and the machined surface. It was also confirmed that the machined shape does not always contain defects when motion errors exist depending on the relationship between the motion error and the machined surface.
There are some kinds of mathematical models of feed drive mechanism for machine tools. We modeled a feed drive mechanism by using the most popular model which is for two degrees of freedom, and proposed a simple friction model by considering the balance of the driving force and friction force. As a result of simulation using the model, the simulated circular trajectory was in agreement with the actual trajectory and the quadrant glitch was well expressed. However, the out put torque of the motor cannot be expressed in the simulation. In addition, the frequency response cannot be expressed with the parameters identified by the step response.
The workpiece setting is an important issue in process planning for 5-axis machine tool. However, in order to know the workpiece setting is proper or not, several NC programs for machining operation have to be prepared for trial-and-error examination to select the most suitable NC program by the trial cutting or the virtual machining simulation. In order to reduce the huge amount of time and effort for this trial-and-error determination method, the most suitable workpiece setting has to be determined first. In this study, the decision method is proposed to predict the machinable space using a virtual machine tool model, virtual cutting tool models, and the Form Shaping Function. In addition, the measure of accessibility of the cutting tool can be visualized. As the result, workpiece setting can be determined in the early stages of process planning.
