NC controllers use different types of compensation systems to improve motion accuracy of feed drive systems against pitch error, friction, backlash, and elastic deformation. Compensators for static error, such as pitch and squareness errors, are tuned semiautomatically. However, for dynamic error such as quadrant glitches and vibration, parameter tuning takes too much time. In this study, motion trajectory measurement for parameter tuning using accelerometers has been proposed. In the methods, displacements of each axis can be obtained from measured accelerations along each axis. Although the obtained displacements include some errors, such as setting error, sensitivity error, and integral error in numerical integration, the errors can be compensated for based on the feedback positions measured simultaneously. To confirm the feasibility of the proposed methods, measurement tests using a grid encoder are carried out. Results of the measurements confirm that the circular trajectories and vibrations can be measured by the proposed method. Automatic parameter tuning method for the backlash compensator is also proposed.
The contact between a tool and workpiece during machining has a significant effect on the vibration characteristics of machine tools. This study proposes a method for detecting contact between a tool and workpiece, and demonstrates applications of the detection. To detect the contact between the tool and workpiece, this study used the change in the contact electrical resistance in a metal-to-metal contact corresponding to the true contact area. The contact resistance between the tool and workpiece was connected in series with a buffer resistance, and the degree of separation was defined based on the change in the ratio of a voltage applied to the circuit under a constant current flow. Two types of applications were demonstrated in this study; one was an analysis of the influences of the contact state on the vibration characteristics, and the other was contact detection during milling operations. In the first demonstration, a contacting ratio was defined based on the contact time per unit time and degree of separation based on the tool-workpiece contact as detected during an excitation test, and the relationship between the contacting ratio and vibration characteristics was examined. It was confirmed that the natural frequency increases significantly when the contacting ratio exceeds 90%, and that the damping characteristics increase significantly when the contacting ratio is in the range of 0–10%. For the second demonstration, a milling test using a face mill with the same detection circuit confirmed that the system could detect contact during intermittent cutting and the changes in contact conditions associated with the occurrence of chattering vibration. It is expected that the developed method can be used to monitor machining conditions.
Unexpected problems may occur on the finished surface machined by the 5-axis machining centers, because of geometric and dynamic synchronous errors of the machine. In this study, actual ball-end milling tests of hemispheres and its finished surface simulations considering the different geometric errors and different position loop gain of feed drive systems were carried out, in order to clarify the influence of the errors onto machined surface. As the results, it is clarified that the influence of geometric errors onto the machined surface is depending on the relationships between the movement of the axes and the surface geometry. In addition, the dynamic synchronous error also influences the machined surface when the velocity of translational and rotational axes changed rapidly.
In this paper, an autonomous compensator for the quadrant glitch was developed, and its effectiveness is verified through simulation and experiments. The autonomous compensator composes of the newly developed torque following compensator and the friction compensator, which was already developed by our group. The principle of the developed torque following compensator is to correct the difference between an ideal torque and an actual torque with changing of torque due to friction changes. Only the developed compensator was applied to the controller, and simulation and experiment were conducted. As the results, it is found that the height of quadrant glitches only decreases up to about 50 %. However, the developed compensator can effectively correct the fluctuation of the height of quadrant glitches due to friction change and the difference of the heights by the friction force change has considerably become small. Then, the friction compensator was used together with the torque following compensator. Thus, it was confirmed that the quadrant glitches effectively disappeared.
NC machine tools generate desired shapes by relative motion control between tool and workpiece. Since several tool paths exist in machining products with NC machine tools, it is difficult to plan the suitable motion path for the machining. This study investigates the energy consumption of feed drive systems of NC machine tools during the machining operation. In this study, an evaluation method to predict the energy consumption for a given motion path patterns is proposed. The results of this study confirmed that the proposed method can evaluate the power efficiency of each motion path based on its energy consumption.
A new methodology to revise cutting conditions for machining operation planning has been developed in this study. In order to automate machining operation planning, reuse of cutting conditions in the past previous machining operations was proposed in our previous study. However, assessment and revision of cutting conditions are required to apply the referred cutting conditions for the objective machining operation. For the assessment of cutting conditions, an acceptable area of cutting conditions (AACC) is calculated. The AACC is restricted by several constraints such as spindle power capacity and maximum feed speed of machine tools, torsional and bending strength of cutting tools and so on. In the case that the referred cutting conditions stay in the AACC, the referred cutting condition can be applied for the objective machining operation without any revision. In the case that the referred cutting conditions stay out the AACC, the referred cutting conditions should be revised for the objective machining operation. In this study, the referred cutting conditions are revised to keep machining time, surface roughness (cusp height) and tool life as much as possible. In this paper, the restriction by the spindle power capacity of machine tools is confirmed in cutting experiments. Also, the revision of the referred cutting conditions is performed for the objective machining operation.
Abstract Non-adherent cells, such as hematopoietic cells and lymphocytes, are important research subjects in medical and biological fields. Therefore, a system that enables the handling of non-adherent cells in solutions in the same manner as that of adhering cells during medium exchange, exposure to chemicals, washing, and staining in imaging applications would be useful. Here, we report a ‘Cell Dome’ platform in which non-adherent cells can be enclosed and grown in the cavities of about 1 mm diameter and 270 μ m height. The domes consist of an alginate-based hydrogel shell of 90 μ m thickness. Cell Domes were formed on glass plates by horseradish peroxidase-mediated cross-linking. Human leukaemia cell line K562 cells enclosed in Cell Domes were stable for 29 days with every 2–3 days of medium change. The enclosed cells grew in the cavities and were stained and differentiated with reagents supplied from the surrounding medium. Additionally, K562 cells that filled the cavities (a 3D microenvironment) were more hypoxic and highly resistant to mitomycin C than those cultured in 2D. These findings demonstrate that the ‘Cell Dome’ may be a promising tool for conveniently culturing and evaluating non-adherent cells.
