Improving repeatability of coordinate measuring machines with shaped command signals

Performance of coordinate measuring machines (CMMs) is adversely effected by structural vibrations. The effect of input shaping, a method of reducing residual vibration, on the quality of CMM measurements has been investigated. Measurements of a CMM show a reduction of structural deflection when input shaping is used. Additional tests indicate that input shaping improves measurement repeatability over a large range of operating parameters.     

Calibration of coordinate measuring machines

For over three years the Physikalisch-Technische Bundesanstalt has been investigating the numerical error correction of cmms, and the relationships between problems in this area and in the calibration of these machines. It has been determined that calibration is possible, for pre-defined conditions, but that the calibration is applicable only to the particular measuring task and conditions. This paper describes the mathematical model used by PTB and gives results of tests on a cmm.     

Modelling of pretravel for touch trigger probes on indexable probe heads on coordinate measuring machines

This paper presents a pretravel model for touch trigger probes mounted on indexable probe heads, which can rotate and tilt the probe into a number of orientations for coordinate measurements on coordinate measuring machines (CMMs). Pretravel accounts for the majority of touch trigger probe errors and is caused by bending deflection of the stylus shaft. A trigger force model is derived and used to model bending deflection of the stylus shaft at the trigger instant. Only one model parameter needs to be calculated using the probe calibration data. Experimental data associated with thirteen probe orientations were used to validate the model. It is shown that the model can effectively predict pretravel distances associated with various probe approach directions. The standard deviations of prediction errors are less than 0.71 µm, indicating that the proposed model can be used to compensate for pretravels occurring in touch trigger probe applications.     

Efficient inspection planning for coordinate measuring machines

The coordinate measuring machine (CMM) has been recognized as a powerful tool for dimensional and geometric tolerance inspection in the manufacturing industry. The power of the CMM depends heavily on an efficient inspection plan that measures a part in minimal time. This paper proposes CMM inspection planning that can minimize the number of part setups and probe orientations and the inspection feature sequence. In our planning, a greedy heuristic method is adopted to obtain the minimal number of part setups and probe changes. Meanwhile, a continuous Hopfield neural network is developed to solve the inspection feature-sequencing problem. The proposed method was successfully implemented and tested using a machine spindle cover part. The results show that the proposed method can achieve excellent performance compared to the other methods.     

Factors affecting component measurement on coordinate measuring machines

It can often be difficult to find a complete relationship between the specified performance of a coordinate measuring machine (cmm) (see Fig 1) and actual results obtained, because of unexplained differences between them. This report explain one method of identifying these differences and discusses some sources of error which may give rise to them.     

Selection of coordinate measuring machines by the neural network method

In this paper, a method for the selection of coordinate measuring machines is developed first, a neural networks training algorithm with conditional attributes through gradually adding training examples is proposed as the neural networks machine learning model for the selection of coordinate measuring machines. A learning model using conditional attributes was used in this study, which divides a problem into either an attribute or a decision. Through the input of attribute values, the system can present the required decision by inference. With this model, the training of the system can produce acceptable results. This learning model is also used to establish a multiple decision type selection system for coordinate measuring machines to assist the user in choosing an appropriate coordinate measuring machine.     

关节类坐标测量机关键技术及进展

关节类坐标测量机具有便携性好、质量轻、测量范围大等优点,广泛应用于汽车工业、航空航天、模具制造、大型装备装配等领域的质检工作。关节类坐标测量机由6或者7个旋转关节串联而成,靠近基座的关节一般装有力平衡机构,提高了关节类坐标测量机的易操作性;其测角系统由安装在各旋转关节上的高精度角度编码器实现;光学扫描测头应用于关节类坐标测量机上实现了复杂曲面的非接触快速测量;为得到精确的测量模型,研究了多种建模和参数辨识方法并由不同国际组织提出了关节类坐标测量机的性能评价标准。最后介绍了关节类坐标测量机的关键技术和未来发展趋势。     

Measuring probe alignment errors on cylindrical coordinate measuring machines

This note describes a method for measuring probe alignment errors on precision cylindrical coordinate measuring machines. Specifically, this method is used to determine the minimum distance between the line of travel of the center of a spherical probe tip and the axis of rotation of a rotary axis. Within the Timken facility, we refer to this error as intersection error [Bryan JB. Private communication; 7 June 1992]. In addition to intersection error, this method determines the position along the probe line of travel at which the center of the probe tip passes nearest to the axis of rotation. This position is commonly referred to as probe offset error. It is used to adjust the probe location such that its radial position is zero where it intersects (or nearly intersects) the axis of rotation. In this way, the probe tip location is datumed to the axis of rotation.     

A feature-based inspection planning system for coordinate measuring machines

A feature-based inspection planning system is proposed in this research to develop more efficient measuring methodology for a CMM for complicated workpieces having many primitive form features. The proposed strategy is composed of two stages; global inspection planning and local inspection planning stages. In the global inspection planning stage, the system generates an optimum inspection sequence of the features in a part. The sequence is determined by analyzing the feature information such as the nested relations and the possible probe approach directions of the features, and by forming feature groups. A series of heuristic rules are developed to accomplish it. In the local inspection planning stage, each feature is decomposed into its constituent geometric elements, and then the number of sampling points, the locations of the points and the optimum probing sequence are determined. Also, an effective collision avoidance methodology is proposed. After required simulation, the effectiveness of the proposed system is verified .     

A novel artifact for testing large coordinate measuring machines

We present a high-accuracy artifact useful for the evaluation of large CMMs. This artifact can be physically probed by the CMM in contrast to conventional techniques that use such purely optical methods as laser interferometers. The system can be used over large distances; for example, over 4 meters, with an uncertainty of less than one part per million. The artifact is relatively inexpensive, robust for use in reasonable industrial environments, and significantly reduces testing time over traditional step gauge measurements.     

A two-dimensional test body for calibration of coordinate measuring machines

A two-dimensional test body having cross-aligned hollow cones has been developed for automatic calibration of coordinate measuring machines (CMMs). Two hours are sufficient for the measurement of translatory and rectangularity errors of a CMM by means of the test body. In this paper the principles of measurement of such erros using the test body are described These principles can be utilized on the assumption that one knows the exact values of the test body, so the calibration procedures for the test body are also described.     

Research on optimal measurement area of flexible coordinate measuring machines

When we measure a workpiece in the optimal measurement area of the flexible coordinate measuring machines (FCMMs), the measuring precision can be improved. The flexible CMM’s measuring space is given. Then its spatial error distribution model is build by using support vector machine theory. Finally, the two solutions of the optimal measurement area are discussed and solved through experiments. The high precision measurement results can be realized by using a low-precision measuring machine without any increase in hardware manufacturing cost. This is of great theoretical value and practical significance for the flexible CMM’s further development.     

基于便携式坐标测量机的大齿轮测量方法

针对目前便携式坐标测量机测量大齿轮的采样策略和评定算法存在的不足,设计了两种特殊的辅助标尺一渐开线标尺及螺旋线标尺.利用设计的两种标尺在大齿轮齿面上对齿廓及螺旋线的测量点进行标注,开展了齿轮的在位重复性测量的实验研究.利用关节臂坐标测量机及激光跟踪仪测量系统在德国计量研究院研制的1 m外径齿轮样板上开展了测量实验,采用INVOLUTE Pro对采样数据点进行评定,给出了测量结果及测量不确定度.测量实验表明,基于新的齿轮测量方法,关节臂坐标测量机比激光跟踪仪测量系统测量结果更为精确,测试结果与标定值最大相差8.16 μm.实验结果验证了提出方法的有效性,为便携式坐标测量机在大齿轮测量领域的应用提供了依据.     

Development of a fast mechanical probe for coordinate measuring machines

To decrease inspection times of workpieces, not only do coordinate measuring machines (CMMs) need to operate faster, but also the mechanical probing process requires attention in this field. This paper shows that impact forces attributable to probing are much higher than generally accepted measurement forces, which can result in workpiece damage. Furthermore, it is shown that probe tip bouncing can slow down the probing process and requires mechanical damping to reduce it. Based upon these findings, a fast mechanical probe system has been developed, equipped with an optical measurement system able to measure six degrees of freedom at high speed. The probe system is suitable for high-speed, single-point measurements as well as scanning purposes. The measurement uncertainty of the prototype is approximately 1 μm for probing speeds up to 70 mm/s.