To realize autonomous machining, it is necessary to focus on machining tools and also on the automation of process planning in the preparation stage. This study proposes a process planning system that automatically defines the machining region and determines the machining sequence. Although previous studies have explored computer-aided process planning, only a few have considered geometric tolerances. Geometric tolerances are indicated on product drawings to eliminate their ambiguity and manage machining quality. Geometric dimensioning and tolerancing (GD&T) is a geometric tolerance standard applied to a three-dimensional computer-aided design (3D CAD) model and are expected to be used for the digitization of manufacturing. Therefore, this study developed an automated process planning system by using GD&T as a sequencing constraint. In the proposed system, the machining sequence is automatically determined by the geometrical constraints, which indicate whether the tool can approach, and GD&T, which indicates the geometric tolerance and datum in a 3D CAD model. A case study validated the proposed method of automated process planning constrained by GD&T. The result shows that the proposed system can automatically determine the machining sequence according to the geometric tolerance in a 3D CAD model.
Bicycles have been recognized for their advantages such as low environmental impact, health improvement, and maintenance of transportation function in times of disaster, and demand for bicycles is increasing as social conditions change. The pedaling of a conventional bicycle nowadays turns a crank to rotate the front gear, which is transmitted to the rear gear by a chain, and turns the rear axle to rotate the rear wheel. Since bicycles require human power to pedal, a structure that allows bicycles to be pedaled with a low load has been considered so that more people can easily use bicycles. This study developed a new bicycle power transmission system that enables bicycles to be pedaled with a low load without using gearbox or external power such as motor. In order to verify the effectiveness of the newly developed bicycle power transmission device, a prototype bicycle with the proposed device was fabricated and tested. Participants quantitatively evaluated the physical load with and without the device by pedaling the bicycle. The experimental results showed that the developed bicycle power transmission device can reduce the physical load.
This study investigated a musculoskeletal model that includes the function of the antagonistic muscles and biarticular muscles and models muscles acting across the hip, knee and ankle joints, simultaneously. Furthermore, this study can be applied to dynamic motions. One vertical jump trials were conducted to validate the proposed model. Electromyograms (EMGs) of tibials anterior, gastrocnemius, soleus, rectus femoris, vastus lateralis, semimembranosus, biceps femoris, short head and gluteus maximus were used to compare with the estimated muscle forces. The results showed that the muscle forces estimated by the proposed method had a stronger correlation with EMGs than those of an optimization method. The correlations of the proposed method and the optimization method were 0.4 and 0.01 of TA, 0.95 and 0.86 of GAS, 0.95 and 0.93 of SOL, 0.94 and 0.01 of RF, 0.93 and 0.97 of VAS, 0.83 and 0.91 of SM, 0.75 and 0.01 of BFSH and 0.95 and 0.92 of GMAX. Thus, the proposed method was considered to successfully estimate the muscle forces during vertical jumping.
A method to calculate tool path uniquely for roughing using a flat drill is proposed. A flat drill is a drill with a flat tip. Unlike a square end mill, it cannot feed a tool laterally, but it is suitable for machining to feed a tool longitudinally. The advantage offered by the flat drill is expected to reduce machining troubles, such as tool breakages and chatter vibration, owing to the axial sturdiness of the tool. Furthermore, it can be used to machine lapped holes that cannot be machined with a normal drill owing to its flat tip. Hence, roughing using a flat drill by drilling multiple holes at constant intervals is proposed herein. Furthermore, in this method, a tool path for semi-finishing is generated only on the remaining region. A cutting experiment is conducted to validate the effectiveness of the proposed method. The result of the cutting experiment confirmed the effectiveness of the proposed method based on the machining time and the productivity of machining multiple products simultaneously.
Abstract A method to extract the machining region from 3D CAD model in STL (Standard Triangulated Language) format and automatically generate tool path is proposed. At first, this study proposes a method to extract the machining region and obtain the geometrical feature such as convex shape or concave shape from only the 3D CAD model in STL format. The STL format has only triangular mesh data and drops all the information which is necessary to extract the removal volume for machining and the geometrical characteristics. Furthermore, the triangular mesh size is non-uniform. Then, the contour line model, in which the product model is minutely divided on the plane along any one axial direction and represented by points at intervals below the indicated resolution obtained from the contour line of the cross section of the product, is proposed. Subsequently, this study proposes a method to determine the machining conditions for each extracted machining region and automatically generate tool path according to the obtained geometrical feature of the machining region.
Abstract It is expected that the vibration characteristics of NC machine tools are affected by the contact between the tool and the workpiece during the cutting operations. However, the influences of the contact have not been clarified up to now. In this study, a method to evaluate the contacting effect and evaluated results are described. Frequency response of a vertical type milling machine during cutting operation is evaluated in this study. The evaluation tests of the contacting effect are carried out with and without cutting operations. In order to clearly evaluate the influence of the contact between a tool edge and a workpiece, boring operations of 50 mm diameter are carried out. The frequency responses are measured by using feed motor torque. Impulse signal is applied to the motor torque command during the cutting operations to oscillate the machine tool, and the axial acceleration of the table is measured to obtain the frequency responses. The impulse signal can be applied by refereeing the spindle rotational angle to control the relationships between the cutting edge and workpiece surface. As the results of the evaluations, it is clarified that the proposed method can evaluate the influence of the contact adequately. The natural frequency slightly increases and the vibration amplitude decreases when the tool contacts with the workpiece, regardless of whether non-cutting or cutting. It has also been confirmed that the vibration amplitude of the frequency characteristics is changed due to the contact length and the relative direction of the cutting edge.
A new method of the process planning for end-milling operation considering product design constraints in this study. In our previous study, the process planning system, in which the Total Removal Volume is divided by the planes parallel with the XY, YZ or ZX planes to analyze machining sequence from top to bottom of the target product, is proposed. In this study, the process planning system, in which the Total Removal Volume is divided by all planes (including slope planes) existing on the target product, is proposed. Furthermore, the product design constraints or the designer's intention such as separate through holes which have the same central axis to be slide bearing is considered. A case study was conducted and the result showed that the proposed method can generate efficient multiple process plans for the machining operation. These multiple process plans or machining sequences are available to select adaptively the most suitable process plan or machining sequence under the several conditions such as the machine tool to be used and the product design constructions.
Since cutting force acts on feed drive and spindle drive systems as force disturbance, feed speed and spindle speed are changed. As the results, cutting force is also changed. In this study, a coupled simulation method of the vibration of machine tool, the dynamic behaviors of feed and spindle drive systems and the cutting force is developed. Simulation results are compared with the experimental results, and it is confirmed that the vibration of the feed and spindle drive systems due to the cutting force can be simulated by the proposed method. It is also confirmed that the cutting force influenced by the vibrations can be expressed.
