Ball Screw Shaft Research Articles

Tracking Control of Flexible Ball Screw Drives With Runout Effect and Mass Variation

Most machine tools rely on precision ball screw drives to accurately position the workpiece relative to the tool. The quality of the machining outcome depends significantly on the tracking performance of the workpiece position over a desired trajectory. This paper addresses the minimization of the tracking error in a ball screw drive system in the presence of dynamic variations. Three sources of dynamic variations are considered: mechanical flexibility, runout of the ball screw shaft, and workpiece mass change during operations. Dynamic variations due to flexibility and runout are related to the workpiece position which is continuously measurable, while the variation caused by the workpiece mass change is uncertain. The ball screw drive system affected by dynamic variations is expressed as an uncertain linear model with time-varying parameters. Based on this model, servo controllers are designed such that their parameters are adjusted in real time by the measurable workpiece position to improve the tracking performance and that their performance is maintained robustly over uncertain mass variation. The importance of taking into account flexibility and runout of the shaft, as well as mass variation, explicitly in controller design is demonstrated through a ball screw drive experimental setup.

Improvement of Positioning Error on a Ball Screw by Cooling System

A high speed ball screw system generates more heat naturally and resultant more thermal expansion, which adversely affects the accuracy of positioning. Therefore, an air cooling system was set in ball screw shaft in this paper to dominate the thermal error and achieve temperature equilibrium faster. In order to estimate the thermal error of ball screw system and effectiveness of air cooling system, thermal behavior models of finite element method and modified lumped capacitance method were developed separately which includes the heat generation power of the main heat source of the ball screw system and other boundary conditions. The completed models were used to simulate the temperature distribution, thermal deformation and air cooling performance. Compared with experiments, it is shown that these methods can well predict the air cooling performance.

Thermal error forecast and performance evaluation for an air-cooling ball screw system

In machine tools such as numerical control machines, thermal error in the ball screw induces a direct position error. A high-speed ball screw system naturally generates more heat and results in greater thermal expansion, adversely affecting the accuracy of positioning. In this paper, we discussed the placement of an air cooling system in a ball screw shaft to overcome thermal errors and achieve temperature equilibrium faster. In order to estimate the thermal error of the ball screw system and effectiveness of the air cooling system, thermal behavior models using the finite element method (FEM) and a modified lumped capacitance method (MLCM) were developed separately. This included heat generation from the main heat source of the ball screw system and other boundary conditions. The completed models were used to simulate temperature distribution, thermal deformation and air cooling performance. Comparing the experiments shows that these methods can well predict thermal behavior of the ball screw system and air cooling performance. And the positioning accuracy will significantly improve with the use of the air cooling system in the ball screw drive system.

A thermal model of a ball screw feed drive system for a machine tool

The feed drive system is a major heat source of machine tools, which results in considerable thermal drift at the tool. Therefore, there is a need to establish a scientific and systematic model that can be used to predict the temperature distribution of the feed drive system. In this research, considering the thermal contact resistance between the bearing and its housing, an integrated thermal model has been developed by the aid of the finite-element method to analyse the temperature distribution of a ball screw feed drive system, in particular the theoretical determination of power losses caused by the friction in ball screw pair, rolling bearings, and guide ways. Thermal boundary conditions including the convective heat transfer coefficients and heat flux have been obtained using the Fourier's law. Results reveal that the ball screw shaft surface has a uniform temperature rise of 4.2 °C under a given condition. The temperature rise agrees with the data obtained by an infrared thermometer.

ボールねじ軸の自動ラップ盤の開発(第3報):熟練作業者によるボールねじ軸ラップ加工におけるラップトルク測定

ボールねじ軸の自動ラップ盤の開発(第3報):熟練作業者によるボールねじ軸ラップ加工におけるラップトルク測定

A Multiple Purpose Soil Testing Apparatus

Abstract A relatively compact soil testing system that is capable of performing monotonic/cyclic triaxial and torsional simple shear tests has been developed. A high-torque direct-drive, servo/stepper motor is used to provide the driving force. Under the servo mode, the motor could be controlled to provide a constant torque, which is used in stress-controlled tests. Strain-controlled tests are conducted using the stepper control mode. To perform triaxial tests, the rotational motion of the motor is transformed into linear motion using a preloaded ball screw shaft. A preloaded ball spline shaft directly attached to the motor is used to perform torsional simple shear tests. Because there are no gears in the driving system, there is no backlash during reversals of loading directions. The motor is equipped with an encoder and an indexer. The extremely rigid driving system and high resolution of the encoder enable the linear and rotational displacement to be monitored through the encoder/indexer system. Test control and data logging are fully automated using a personal computer. This paper provides details of the apparatus. A set of strain-controlled test data are presented to demonstrate capabilities of the new apparatus.

Determinant Factors of Efficiency of a Motor-Driven Ventricular Assist Device

Limiting factors of the system efficiency of an electric-motor-driven ventricular assist device (VAD) consisting of a brushless dc motor and a ball screw in the actuator were analyzed from the balance of force and torque in the pump and actuator. The results suggested that several mechanical components in the actuator should be improved to increase the efficiency. According to the suggestion, rotor material was changed from stainless steel to a lighter engineering plastics; smaller ball bearings were used to reduce rotor inertia; the ball screw was changed from rolled- to ground-execution type; the friction loss in the anti-rotation column inside the ball screw shaft was reduced by changing sliding mechanism to rolling one. These improvements elevated the total system efficiency from 11% to 15%. The new system cleared durability testing of longer than 900 h. More elaborate assembly of the mechanical components of the actuator would increase the efficiency.

A Motor-driven Ventricular Assist Device Controlled with an Optical Encoder System

An electric motor-driven ventricular assist device has been developed for long-term use inside the body. The system is composed of a pusher-plate-type blood pump and an actuator consisting of an electrical motor and a ball screw. Cyclic change of the direction of motor rotation makes a back-and-forth axial movement of the ball screw shaft. The shaft, which is detached from the pump diaphragm, pushes the diaphragm via a pusher plate to eject blood during systole; blood is sucked by the diaphragm resilience during diastole. Using the output signals from a newly designed, incremental-type, miniature optical rotary encoder mounted inside the actuator, the input voltage of the motor is optimally controlled referring to the phase difference between the current position of the moving rotor and the electrical reference signal of the rotation generated by a microprocessor-based controller. In vitro performance tests indicated that the system fulfills required specifications. The maximum efficiency was 11%, which was about twice as high as that obtained with the previous open-loop prototype system. In the air, the surface temperature of the actuator elevated to 20 degrees C above the room temperature. An acute in vivo test showed its feasibility as a left ventricular assist device. Analysis of the energy loss in each component of the system indicated that redesign and precise assembly of the mechanical parts could increase the system efficiency.