MOTOR WITH INTEGRATED BALLSCREW SHAFT AND NUT TO SUPPORT COLLIMATOR X-RAY CONDITIONING
Publication Date: 2016-Nov-22
The IP.com Prior Art Database
A device having a motor with an integrated ballscrew for X-ray conditioning applications, such as pre-patient collimator is disclosed. The device includes a motor with a directly mounted precision ballscrew shaft and a ballnut having re-circulating balls for smooth and accurate motion control.
The present disclosure relates generally to X-ray imaging and more particularly to a motor with integrated ballscrew shaft and nut to support collimator X-ray conditioning.
Generally, ballscrew shaft designs require mounting the ends of the shaft on a fixed end rigid support as depicted in Figure 1. Bearings are required on both shaft ends to allow the shaft to rotate relative to the supports. A motor driving this ballscrew shaft is also mounted to a rigid support. A flex coupling is used to account for small misalignment between the motor shaft and ballscrew so that the ballscrew can be reliably rotated with minimal variation in torque. Such conventional ballscrew shaft designs require flex couplings and have a high part count contributing to complexity, cost, assembly time and potential reliability issues.
Further, conventional stepper motor designs use leadnut shafts, for example ACME or screw threads or have a bare shaft extension, for example a short stub shaft as depicted in Figure 2. Leadnuts have backlash i.e. gaps between the nut and shaft to allow the shaft to rotate without binding. The inherent backlash in a leadnut design is not preferred for precision applications such as positioning X-ray conditioning parts. Furthermore, a bare shaft requires a flex coupling to be installed. For many applications, the addition of a flex coupling to the bare motor shaft and ballscrew shaft leads to increased physical mounting space requirements.
Also mounting a feedback device or encoder in ballscrew design presents challenges in long-term reliability, cost and complexity. Typically the encoder is mounted to a shaft extension on the ballscrew, or directly to the motor. When mounted to a shaft extension, the alignment of the encoder is critical and requires accurate machining or a flexible coupling. This arrangement requires physical packaging space which is not always feasible, especially in high g-force environments such as Computed Tomography. A motor-mounted encoder is a more secure mounting configuration for the encoder, but ballscew shaft rotational accuracy may be affected if a flex coupling is used between the motor stub shaft and ballscrew shaft.
It would be desirable to have an improved design for a device having the motor, shaft and encoder coupled directly without intermediate flexible connections to obtain maximum positioning accuracy in X-ray conditioning applications.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 depicts a conventional ballscrew shaft design requiring mounting the ends of the shaft on a fixed end rigid support.
Figure 2 depicts conventional stepper motor designs using leadnut shafts, for example ACME or screw threads and a bare shaft extension, for example a short stub shaft.
Figure 3 a device including a motor with a directly mounted precision ballscrew shaft and a ballnut having re-circulating balls for...