Daisuke Kono

Nano-positioning Drive with Piezoelectric Actuator Integrated into Support Bearing Unit of Ball Screw

This paper presents a new fine positioning device with a piezoelectric actuator integrated into the support-bearing unit of a ball screw. By moving the outer race of the support bearing, the piezoelectric actuator gives a preload to the bearings, which translates the screw shaft and table. Since the rotation of the screw shaft gives coarse motion to the table, the whole system can perform the positioning of the table in a long stroke with a high resolution. On the developed system, open loop and closed loop tests are carried out to evaluate its positioning performance. It was found that the piezoelectric actuator translates the table in the order of nanometers in the open loop test and the designed closed-loop control system can control the table position with a resolution of 20 nanometres.

Measurement of Contact Stiffness for Stiffness Estimation of Machine Tool Supports

The contact stiffness is measured at interfaces of several materials that are often used for the machine tool support. Models of machine tool supports and contact stiffness are described. Then, a measurement method of the contact stiffness is proposed according to the model and demonstrated. The unit normal contact stiffness is 1-2×106 N/mm/mm2 for general steel and cast iron. The unit normal contact stiffness is pSuperscript textositively correlated with the longitudinal elastic modulus. The unit tangential contact stiffness is 1/10-1/5 of the unit normal contact stiffness and not correlated with the elastic shear modulus. The surface roughness of the specimen should be small to reduce the dispersion of the measured unit contact stiffness.

Development and Evaluation of a High-Precision Machining Center with Friction-Less Drives

In order to realize high-speed and high-precision machining, the enhancement of the motion accuracy of NC machine tools is required. It is effective to minimize the friction forces imposed on drive systems to enhance the motion accuracy. From this viewpoint, we developed a high precision machining center using linear motors and hydrostatic guideways for its drive system. The disturbance forces on the developed machining center are measured to evaluate the fundamental motion characteristics. Contouring error trajectories in high-speed circular motions of small radii are also measured for the evaluation of roundness.

Linked Ball Bar for Flexible Motion Error Measurement for Machine Tools

A measuring instrument, Linked Ball Bar (LBB), is developed to measure machine tool motion errors quickly, flexibly, and robustly. The LBB employs the concept of double ball bar (DBB) and measures the distance between two balls attached to the spindle and table. The problem of short measurement range, the drawback of the DBB, is solved using a link. The measurement accuracy of the LBB is investigated. The analytical resolution of displacement measurement using the LBB is under 30 nm when the displacement direction coincides with the sensitivity direction. The difference between the LBB and the laser interferometer is less than 1 μ m in the center measurement range of 75 mm. The repeatability of the LBB is±0.4 μm and is at the same level as the interferometer. The kinematic error of a five-axis machine tool is measured using the LBB to demonstrate its validity. The parallelism between the C-axis and Z-axis identified using the LBB agrees with the result measured using the cylindrical square. The difference between the LBB and the cylindrical square is about 10 μ m/m at the maximum. The LBB can provide quick and flexible measurements of the motion errors of five-axis machine tools.

Dynamic Characteristics of Ultra-Precision Machine Tools (Evaluation for Stiffness of Guideways by Impact Test)

This study discuss the dynamic stiffness of guideways of a ultra-precision machine tools.V-V roller guideways have been employed in ultra-precision machine tools, as they can provide very smooth motion and good straightness. Recently, general linear ball guideways are also employed in ultra-precision machine tools. In the design of the machines, it is necessary to obtain the stiffness of these guideways. Therefore an identification method of the guideway stiffness is verified in this paper. In this method, the guideway stiffness is identified from the natural frequency of the moving body. First, the impact test is carried out for an ultra-precision machine tool to obtain the vibration mode of its moving body. Next, a simple vibration model is developed based on the obtained vibration mode to identify the equivalent stiffness of the guideways. Then, the static stiffness of the guideways is measured for the verification of the identified equivalent stiffness. For further verification, natural frequencies of the moving body are calculated by FEM with the identified equivalent stiffness and compared with the measured natural frequencies. The identified equivalent stiffness agreed well with the measured static stiffness. Furthermore, the natural frequencies were calculated almost correctly with the identified equivalent stiffness.

Evaluation of Surface Roughness in High-Speed Shaping of Ni-P

A flat surface was machined by shaping to investigate the influence of the cutting speed on surface finish. When the cutting speed was 10-30 m/min, the surface roughness deteriorated because fine valleys with a depth of 40-200 nm were caused. Because the pitch of the valleys was almost equal at different cutting speeds, it was concluded that the valleys were not caused by the natural vibration of the machine tool. The velocity of the tool tip was measured by a laser Doppler vibrometer to compare the tool motion and the work piece profile. The periodical velocity change of the tool corresponded to the pitch of valleys. When a work piece with higher phosphorus content was machined, the valleys were not caused at a cutting speed of less than 30 m/min. It is estimated that the smoothness of chip removal has an influence on the emergence of valleys.

Investigation of Copying Rate of Tool Motions on Workpiece Profile

The copying characteristic of the tool motion on the workpiece profiles is investigated. Assuming that the workpiece profile consists of sinusoidal-wave components, the amplitude ratio between the workpiece profile and the tool motion is defined as copying rate . An experiment was conducted to identify in shaping of electroless plated nickel. With polycrystalline diamond tools, the copying rate was obtained as =1.16. The result indicates that the amplitude of the workpiece profile can be larger than that of the tool motion. Shaping of slot profiles was carried out to investigate the influences of depth of cut, rake angle and relief angle on the copying characteristic. The depth of slot was larger than the tool displacement in the Z-direction by 0.1-0.4 μm when the rake angle was -5 degrees and the relief angle was 12 degrees.