Motor Feed Research Articles

Feed forward control of back bead for root gap variation in V-groove welding without backing plate

The stable back bead in a first layer of the one-side multilayer welding is important to obtain a good quality of welding. For this purpose, the switch back welding method was applied for the root gap from 1 mm to 5 mm in V groove welding without the backing plate. This method requires the cooperative control of power source, wire feed motor and robot manipulator by the personal computers. The validity of welding conditions for each root gap were confirmed by observing the arc and the weld pool, and the back bead appearance. Next, the feed-forward control of the back bead for the root gap variation was discussed. The root gap on start and end points of welding were detected by using the spot laser sensor. The welding conditions, welding current, wire feed rate, weaving width, forward/backward stroke of the switch back motion and stroke speed, were continuously controlled corresponding to the root gap variation, and the stable back bead was obtained by the fundamental experiment regardless of changing the root gap from 4.4 mm to 1.9 mm.

An investigation of the characteristics of the stationary feed motor current in NC machines

The cross-feed directional cutting force acts normal to the machined surface of a workpiece. It is important to estimate and control this force, since it directly affects the machined surface. However, using the current supplied to a stationary motor to predict the cutting state poses difficulties, because of the current's somewhat undesired behaviour. In this paper, a largely empirical approach was used to help resolve this problem. We show that the current's undesired behaviour is related to infinitesimal rotations of the motor. Subsequently, the relationship between the current and the cutting force was identified with an error of less than 15%. The predictions obtained using two machine tools with different characteristics were compared to confirm the validity of the method when investigating the characteristics of the stationary feed motor current.

Estimating cutting force from rotating and stationary feed motor currents on a milling machine

The feed motor current of a machine tool contains substantial information about the machining state. The current has been used as a measure of cutting forces in much previous research; however, this indirect measurement of the cutting forces was feasible only in a low frequency range up to about 60 Hz when milling machining. In this paper, the bandwidth of the current sensor was expanded to 130 Hz. The unusual current behavior between 45 and 60 Hz was examined and analyzed. It is necessary to estimate the cross-feed directional cutting force that is normal to a machined surface, since it directly affects the error of that surface. However, because of the undesired behavior of the stationary motor current, difficulties are encountered when using it to estimate the cutting state. An empirical approach was used to resolve this problem. As a result, we show that the current is related to the infinitesimal rotations of the motor, and it is this that causes the undesired behavior of the current. Subsequently, a relationship between the current of the stationary feed motor and the cutting force normal to machined surface was identified with an error of less than 20%.

ESC 공정으로 제작된 금형강의 가공특성연구

Machining characteristics of tool steels manufactured by electro slag casting process has been investigated in this study. For the estimation of machinability, turning and drilling tests are carried out. The chip shapes at various velocities are investigated for the comparison of turning workabilities of tool steels because the chip shapes reflect characteristics of cutting resistance. In case of drilling test, feed motor currents measured by a hall sensor are used as a measure for the drilling resistance. The machining characteristics of the tool steels are strongly correlated with tensile properties. such as tensile strength. hardness, and ductility. In case of turning workability, it was found to be favoured by the higher tensile strength, while the opposite is true for the drilling workability. The electro-slag casted materials show better turning workability in the viewpoint of chip shapes and, the quenching-tempered electro-slag casted material has relatively better drilling machinability than that of the annealed one.

バッキングレスＶ開先継手におけるルートギャップ変動に対する裏ビードのフィードフォワード制御

The stable back bead in a first layer of the one-side multilayer welding is important to obtain a good quality of welding. For this purpose, the switch back welding method was applied for the root gap from 1 mm to 5 mm in V groove welding without the backing plate. This method requires the cooperative control of power source, wire feed motor and robot manipulator by the personal computers. The validity of welding conditions for each root gap were confirmed by observing the arc and the weld pool, and the back bead appearance. Next, the feed-forward control of the back bead for the root gap variation was discussed. The root gap on start and end points of welding were detected by using the spot laser sensor. The welding conditions, welding current, wire feed rate, weaving width, forward/backward stroke of the switch back motion and stroke speed, were continuously controlled corresponding to the root gap variation, and the stable back bead was obtained by the fundamental experiment regardless of changing the root gap from 4.4 mm to 1.9 mm.

Motion control for linear motor feed drives in advanced machine tools

Minimum-time path optimization (MTPO) and minimum-time tracking control (MTTC) have previously been introduced as effective strategies for controlling high-speed machine tools [D. Renton, M.A. Elbestawi, High speed seruo control of multi-axis machine tools, Int. J. Machine Tools Manuf. 40 (2000) 539–559]. It has been argued that the effectiveness of these strategies is due to their ability to accommodate the dominating saturation effects in control of high-speed machine tools. In this paper the application of MTPO and MTTC to linear-motor-driven machines is examined. It is found that the attention paid to saturation limits by MTPO and MTTC strategies provides significant performance improvements for linear-motor-driven machines. Issues such as improved stiffness to periodic disturbances, improving holding torque through heat-reducing commutation methods and improved sensor feedback are also examined.

Feed Cutting Force Estimation from the Current Measurement with Hybrid Learning

It is very important to use reliable and inexpensive sensors to obtain useful information about manufacturing processing, such as cutting force, for monitoring automated machining. In this paper, the feed cutting force is measured using an inexpensive current sensor installed on the a.c. servo motor of a CNC turning centre. The factors that affect a feed drive system are analysed in detail, and a model of the feed drive system for estimating feed cutting force is presented. The feed cutting force is estimated using feed motor current measurement and neuro-fuzzy techniques. Experimental results demonstrate that this method can accurately estimate feed cutting force within an error of 5%.

Current-sensor-based feed cutting force intelligent estimation and tool wear condition monitoring

Tool wear condition monitoring has the potential to play a critical role in ensuring the dimensional accuracy of the workpiece and prevention of damage to cutting equipment. It could also help in automating cutting processes. In this paper, the feed cutting force estimated with the aid of an inexpensive current sensor installed on the AC servomotor of a computerized numerical control tuning center is used to monitor tool wear condition. To achieve this, the feed drive system is modeled, using neuro-fuzzy techniques, to provide the framework for estimating the feed cutting force based on the feed motor current measured. Functional dependence of the feed cutting force on tool wear and cutting parameters are then expressed in the form of a difference equation relating variation in the feed cutting force to tool wear rate. The computerized system automatically compares successive feed cutting force estimates and determines the onset of accelerated tool wear in order to issue a request for tool replacement. Experimental results show that the tool wear condition monitoring is effective and industrially applicable.

Real-time tool condition monitoring using wavelet transforms and fuzzy techniques

Wavelet transforms and fuzzy techniques are used to monitor tool breakage and wear conditions in real time according to the measured spindle and feed motor currents, respectively. First, continuous and discrete wavelet transforms are used to decompose the spindle and feed ac servo motor current signals to extract signal features so as to detect the breakage of drills successfully. Next, the models of the relationships between the current signals and the cutting parameters are established under different tool wear states. Subsequently, fuzzy classification methods are used to detect tool wear states based on the above models. Finally, the two methods above are integrated to establish an intelligent tool condition monitoring system for drilling operations. The monitoring system can detect tool breakage and tool wear conditions using very simple current sensors. Experimental results show that the proposed system can reliably detect tool conditions in drilling operations in real time and is viable for industrial applications.

構造振動を考慮したリニアモータサーボ系の設計 状態フィードバックを用いた安定化補償器の設計

Linear motor feed drives are considered as the ideal drives with no-transmission, no-backlash and smooth motions. But if they are applied to dynamically complicated machines such as machining centers or cantilever type XY robots, the servo systems are influenced by the structural vibrations. The vibrations inspired by tracking motion aggravate the motion and position accuracy. Some of them are detected by position sensors and destabilize the servo loop. This paper deals with the design method of stabilizing controllers for the linear motor servo drives under the influence of structural vibrations. The feed drives are modeled and analyzed taking structural vibrations into account, and stabilizing controllers are designed based on the modem control theory. A reduced order controller is also designed and compared to the classical PI compensators in terms of servo characteristics. Observer based full state feedback controller and local state feedback controller are found to be effective through simulation and experiment.

Indirect Cutting Force Measurement Considering Frictional Behaviour in a Machining Centre Using Feed Motor Current

In machine tools, friction exists between the table and the guideways, and in ballscrews. In this paper, feed motor current is measured by a hall effect current sensor. It is used to calculate the motor torque which, in turn, is the frictional torque at steady state. Some frictional phenomena are studied in feed drive systems of a horizontal machining centre, such as the relationship between feedrate and frictional torque, the relationship between frictional torque and table feed position, and the slideway cover effects on frictional torque. Considering all these frictional phenomena, the relationship between the feed force and the feed motor current is obtained. Feed force can be estimated well from the feed motor current considering frictional behaviour. The relationship between the cutting force and the feed motor current is slightly different during up milling and down milling, because y(vertical) directional cutting force changes the frictional force.

Drill wear monitoring based on current signals

This paper presents a simple method for on-line wear state monitoring and tool replacement decision-making using spindle motor and feed motor current signals in drilling. In the paper, the effects of tool wear as well as cutting parameters on the cutting current signals are analyzed. The models on the relationship between the current signals and the cutting parameters are established under different tool wear states with a partial experimental design and regression analysis. Finally, a fuzzy classification method is used to classify the tool wear states so as to facilitate defective tool replacement at the proper time. The validity and reliability of the method are verified by experimental results.

Tool wear detection with fuzzy classification and wavelet fuzzy neural network

In the paper, a new method of tool wear detection with cutting conditions and detected signals is presented, which includes the model of wavelet fuzzy neural network with acoustic emission (AE) and the model of fuzzy classification with motor current. The results of tool wear estimated by cutting conditions and detected signals (spindle motor current, feed motor current and AE) are fused by fuzzy inference. Experimental results show that the method of tool wear detection is reliable and practical.

Stability of Turning Processes with Actively Controlled Linear Motor Feed Drives

Using linear motors as machine tool feed drives has the potential of enhancing machining performance by eliminating gear related mechanical problems and increasing speed and accuracy, but introduces a stability concern due to a strong dynamic feedback interaction between the machining process and the drives. This paper investigates the stability aspect of this dynamic interaction and the use of active damping to achieve machining stability in turning. Various necessary and sufficient conditions for stability at all cutting speeds are derived, and have been used to study the effect of damping and gear reduction in system stability. The interaction of the cutting process with the tool servo loop is seen to have significant instability consequences in systems with small drive gear reductions. Both theoretical stability and experimental cutting results are presented for PD and PID regulation. Results show that actively controlled linear motors can provide sufficient dynamic stiffness for stable turning operation.

Increasing Availability and Efficiency by Monitoring the Cutting Process in a Lathe During Production with Limited Manpower

In a machine tool equipped with DC motors for the spindle and feed movements, the armature currents in the drive motors adjust themselves to the total load torque on the motor shafts. It is possible to detect load variations on the machine's cutting tool by measuring the armature currents in the machine's (in this case a lathe) spindle and feed motors. By studying the no-load currents in the drive motors for the spindle and the feed systems, it is possible to monitor their condition. This permits scheduled stoppages for service and maintenance. Variations are obtained in the armature currents in the motors when the tool undergoes wear. By calculating the change in direction of the cutting force resultant per unit time within one cut during the machining process, it is possible to determine a suitable time for an automatic tool change before the tool becomes unusable. Monitoring of the tool permits the use of smaller safety margins in the choice of speeds and feeds and enables the tool to be used for a maximum cutting time. An automatic tool change eliminates lost machining process time due to tool breakdown during an unmanned shift. Tool monitoring contributes both to a higher machine availability and to a higher degree of efficiency in the cutting process. Monitoring of the cutting process via the armature currents is limited to a relatively slow monitoring during rough machining. This is due to the fact that the armature currents in the drive systems have poor dynamics and sensitivity for variations in the load on the tool.

Monitoring and Adaptive Control of Cutting Process by Means of Motor Power and Current Measurements

This study is carried out to establish the feasibility of motor power and current measurements for ACO, ACC and monitoring. The dynamics of measured power and current signals from the spindle and feed motors of an NC lathe and a machining center is investigated to establish the response of power and current variations due to tool wear, tool breakage and vibrations. An extensive investigation of two commercially available adaptive control systems (based on motor current measurement) - one on an NC lathe and the other on a machining center is conducted with the aim of exploring practical aspects when employing such systems in workshop environment.

Evaluation of DC Servo Machine Tool Feed Drives as Force Sensors

Unmanned machine tools as part of an automated factory require reliable, inexpensive sensors to provide machine and process information to the controller. The electric current in the DC motor of a CNC machine tool can be inexpensively measured and used to calculate the tool/workpiece cutting force and the forces associated with drive system components. In order to characterize the bandwidth, sensitivity and accuracy of current monitoring on the feed system of a CNC lathe, a dynamic lumped parameter model of this sensor system is developed. The model is used to identify the system components that have a dominant effect on the behavior of the sensor. Tests were conducted in order to determine the model parameters, verify the model, and determine the signal-to-noise (S/N) ratio of the sensor. The bandwidth of this sensor is predicted to be 80 Hz. Tests show that the S/N ratio is low but can be improved by a trade-off with the system bandwidth. The bandwidth is limited by the characteristics of the SCR amplifier. In addition, the sensitivity and accuracy of calculating the feed force component of the cutting force from the total current used by the feed motor is limited by the pitch of the ball screw and friction coefficient variations in the slide. Feed system design changes, to improve the S/N ratio of the feed system as a tool and machine force sensor, are discussed.

Paper Feed Control for Drum-type X-Y Plotter

Slip between paper and drum leads to drawing quality deterioration in a drum-type x-y plotter. From this view point, this paper presents a formulation for a paper feed control system consisting of a vacuum column and paper feed motors, the analytical paper position and paper tension variation in the vacuum column, and the comparison of numerical results with experimental data. It particularly explains that paper friction force in the vacuum column seriously influences the dynamic characteristics of the system and finally describes the critical velocity in thigh speed x-y plotters.

Avon No. 8—A Supercritical-Pressure Plant

Abstract This paper describes the 250,000-kw supercritical-pressure addition to the Avon Plant of The Cleveland Electric Illuminating Company. Special features of the third supercritical-pressure unit designed for an American central station include the use of a monotube once-through boiler, combination motor and turbine-driven boiler feed pumps, extruded pipe for main steam leads, condenser by-pass demineralization system, and a high-temperature water-heating system for the plant addition.