Machining Performance of Robot-Type Machine Tool Consisted of Parallel and Serial Links Based on Calibration of Kinematics Parameters

This study aims to calibrate the posture of a robot-type machine tool comprising parallel and serial links using a kinematics error model and verify the machining performance based on the measurement results of a machined workpiece calibrated with kinematics parameters. A robot-type machine tool (XMINI, Exechon Enterprises LLC) is used in this study. Typically, the performance required of a robot-type machine tool is not only dimensional accuracy but also the contour accuracy of the machined workpiece. Therefore, in this study, we first construct a forward kinematics model of a robot-type machine tool and identify the kinematics parameters used in it via spatial positioning experiments using a coordinate measuring machine. Based on the parameter identification results, we calibrate this robot-type machine tool and evaluate its machining performance in terms of the dimensional accuracy and contour accuracy of the machined workpiece.

Drudgery reduction in operation of cleaner-cum-grader: An ergonomic intervention

A pedal-operated cleaner-cum-grader having common bicycle chain-sprocket mechanism to get the speeds of 240 and 720 rpm of eccentric shaft and blower shaft, respectively for the desired cleaning/grading of grains was developed earlier by CIAE, Bhopal. Also, in order to utilize the human energy in more efficient way through pedalling mode, CIAE has recently developed a dynapod. The dynapod is a pedal operated rotary device, which can be used as an interface between human worker and any rotary-type machine. The developed dynapod was used to operate the cleaner-cum-grader to assess the drudgery reduction in its operation in comparison to original pedalling mechanism. The dynapod was interfaced with the cleaner-cum-grader by carrying out minor modifications in the original unit. Eight male agricultural workers with mean stature and weight as 168.4 cm and 54.4 kg, respectively participated in the study. The cleaner-cum-grader was used for cleaning and grading of soybean grains. Heart rate of the workers was measured during operation of cleaner-cum-grader using the dynapod as well as the original pedalling mechanism. Mean working heart rate during operation of machine with original pedalling mechanism was 114 beats min-1 as against 108 beats min-1 in case of pedalling with dynapod. The work pulse (ÄHR) with the original pedalling mechanism was 35 beats min-1 as against 29 beats min-1 during pedalling with dynapod. The output capacity of the machine increased from 303 kg h-1 in case of original pedalling mechanism to 345 kg h-1 with dynapod. Considering the cardiac cost as well as output of the machine, the drudgery reduction by using dynapod with cleaner-cum-grader was about 25.4% as compared to the original pedalling mechanism.

Forward Kinematics Model for Evaluation of Machining Performance of Robot Type Machine Tool

Robot-type machine tools are characterized by the ability to change the tool posture and machine itself with a wider motion range than conventional machine tools. The motion of the robot machine tool is realized by simultaneous multi-axis control of link mechanisms. However, when the robot machine tool performs a general milling process, some problems that affect the machining accuracy occur. Moreover, it is difficult to identify the motion errors of each axis, which influence machining accuracy. Thus, it is difficult to adjust the servo gain and alignment error. In addition, the machining performance is unidentified because of the rigidity differences when the posture changes. In this study, the focus was on robot-type machine tools consisting of a serial and a parallel link mechanism. A geometric model is described, and the forward kinematics model is derived based on the geometric model. Machining tests were then carried out to evaluate the machining accuracy by measuring the machined surfaces and the simulated motion of the tool posture based on the proposed forward kinematics model to identify the mechanism that affects the machined surface roughness and surface waviness. As a result, it was shown that the proposed model can separate and reproduce the behavior of each axis of the machine. Finally, it was clarified that the behavior of the second axis has a great influence on the tool posture and machined surface.

Study on the dynamic identification method of the weak part of the bar-shaped combined structure

The weak part of the stiffness of machine tool combined structure is the key to improve the stiffness of machine tool. To overcome the static deformation with difficulty acquisition, the paper chooses machine tool combined structure which can be equivalent to one-dimensional bar structure, and a weakness index (WI) is proposed to identify the weak part of the stiffness by means of the dynamic hammer test method. Based on the bar structure as a numerical example, the weak parts are modeled as EA reduction in stiffness while the mass is maintained at a constant value. Thorough finite element (FE) method simulations are performed to assess the robustness and limitations of the method in several scenarios with single and multiple weakness. On the crossbeam of gantry type machine tool, the sensors are used to collect vibration data, the structural modal parameters are obtained by singular value decomposition (SVD) technique, and the dynamic characteristics are systematically reconstructed by using modal state space method to obtain stiffness data at zero-frequency. Then, the weak part of the structural stiffness is identified by the weakness index. Finally, the comparison of FE simulations and experiment results are provided to illustrate the working of the method.

Effect of Microshot Peening on Fatigue Strength of Austenite Stainless Steel

The effects of the peening conditions on the surface characteristics and fatigue strength of stainless steel were investigated by microshot peening (MSP). In recent years, MSP technology has attracted attention. The use of MSP technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. However, the effect of MSP technology on stainless steel has not been much studied. In the present study, an air-type machine was used. The media used was high-carbon cast steel (490 HV) and Fe-Cr-B alloy (1130 HV), with an average diameter of 0.1 mm. The peening time was in the range of 0 - 100 s. Four types of stainless steels, SUS304, SUS304L, SUS316, and SUS316L, were tested. The workpieces were annealed at 1100 K for 1.2 ks in air. In the measurement of fatigue strength, the workpieces were machined in hour-glass shape. As the results, surface roughness of the workpieces treated by MSP was small. Work hardening was evident to the depth of approximately 0.2 mm from the surface. This depth was about twice the diameter of shot media. However, the effect of the peening time on the hardness distribution was not large. The compressive residual stress was added in the surface vicinity. It is assumed that the fatigue limit had increased because the work hardened layer was formed near the workpiece surface.

New microforce generating machine using electromagnetic force

This paper reports a new microforce generating machine under development at NMIJ, AIST. We proposed a new microforce generating method by referring to the principle of the Kibble balance experiment and planned to apply it to a rotary type machine. Microforce in the micronewton and millinewton range can precisely be generated using this newly developed machine.