Maintenance of digital horizontal coordinate boring machine

The relationship between positioning accuracy and machining accuracy

Digital display and CNC horizontal boring machines (production coordinate horizontal boring machines), especially the positioning accuracy of the linear motion of the machining center (MC), are the main indicators that comprehensively reflect the accuracy of the machine tool, which directly affects the quality of the processed parts.

The positioning accuracy of machine tools includes two aspects: positioning accuracy and repeated positioning accuracy. CNC horizontal boring machines, production coordinate boring machines, and machining centers that require coordinate accuracy all have this requirement. The definitions of positioning accuracy and positioning error are as follows:

Positioning accuracy refers to the actual positional accuracy achieved by the main components of a machine tool at the required motion endpoint.

The error between the actual position and the theoretical position is called positioning error.

Machine tool moving parts http://www.btjxjt.com The content of position detection includes angle, length, angular displacement, and displacement, as well as the classification of position detection components.

The numerical control system mainly consists of two parts: the control machine and the servo mechanism. The servo system is used to receive the feed signal sent by the controller, convert it into an analog quantity, and drive the workbench through power amplification, so that the workbench can make precise positioning or strict relative movement according to the specified track. Essentially, it is a displacement servo system. The position control servo system can be divided into four types based on the presence or absence of detection and feedback of the regulated quantity: open-loop, feedback compensation open-loop, closed-loop, and semi closed-loop systems. Different systems have different positioning accuracies.

Factors affecting the positioning accuracy of machine tools

The factors that affect the positioning accuracy of machine tools include measurement systems, control systems, feed systems, and structural systems,

(1) The measurement system factors, such as errors in precision line rulers, induction stepper and other components, measurement devices and reading errors, all affect the correctness of the position of moving parts.

(2) The control system indicates the ability of the servo system to accurately execute positioning instructions. The fluctuation of switch time and action start stop time of servo system components affects the dispersion of positioning errors.

(3) The feed system is affected by factors such as clearance in the feed components, rigidity of transmission parts, and friction characteristics of bearings and guide rails, resulting in insensitive areas and insufficient rigidity of the feed system. After being subjected to force, it causes elastic deformation and positioning errors.

(4) The geometric shape and mutual position error of the working surface of structural system factors, such as the Abbe error caused by the standard length ruler used in the measurement system not being in a straight line with the measured length, affect the positioning accuracy.

There are two types of positioning errors: random and non random. The randomness caused by the clearance, elastic deformation, and geometric accuracy of transmission components in the measurement system and feed system can be solved by compensation or elimination. The fraction of start stop time of servo components, changes in friction characteristics of guide rails and bearings, and other factors have non random properties that cannot be ruled out. The length dimension error of the transmission reference element and the straightness error of the linear motion trajectory of the moving parts are reflected in one-way and two-way positioning, while the clearance error and elastic deformation of the transmission reference element, torque transmission element, and motion guide rail pair only occur in two-way positioning.

The above factors have no impact on the control system error during manual control, and the influence of the feed system is not significant