CNC Machine Control Unit

Transcription

1 NC Hardware a

2 NC Hardware

3 CNC Machine Control Unit

4 Servo Drive Control

5

6 Hydraulic Servo Drive Hydraulic power supply unit Servo valve Servo amplifiers Hydraulic motor

7 Hydraulic Servo Valve

8 Hydraulic Servo Drive Hydraulic cylinders: linear motion A drastic increase of fluid volume in the cylinder causes the system dynamic response to become sluggish due to bulk modulus effect Hydraulic motors: rotary motion The motor is operated at higher speed and is geared ddown and coupled dto the lead screw.

9 Permanent Magnet Stepping Motor Low velocity : 500 rpm with 500 pulses/sec Low velocity : 500 rpm with 500 pulses/sec The rotor lag must not be to allowed exceed one-half the step size

10 Mode of Operation Single Step Mode 5 steps/sec Slue Mode Continuous Motion

11 Three Phase Variable Reluctance Stepping Motor It uses a toothed iron wheel such that it can be made in any shape. However, it gives less torque than the PM motor

12 Brushed DC Servo Motor

13 Brushed DC Servo Motor The motor has four main components: permanent magnets in the stator, armature windings in the rotor, brushes, and a commutator. T K I sin m e a where T m is the motor torque, K e is the motor constant, is the magnetic flux density, I a is the armature current, is the angle between magnetic field vector and current vector. A typical DC servo motor circuit can be described by the following equation. di a Va Kb Ra I a La dt The torque equation is T m Advantages: Disadvantage: J J ) ( f f ) ( m l m l inexpensive, easy to be controlled. brush replacement, electrical noise, poor thermal dissipation, high rotor inertia.

14 Brushless DC Servo Motor The windings of a brushless motor are located in the stator, and the permanent magnets are mounted on the armature. Two commonly used electronic commutation schemes are the optical-disk and Hall-effect method.

15 FanucTaiwan.comcom /j /d t/l t l

16 FANUC 控 制 器 18i-MB

17 Control Loop

18 Contouring Accuracy

19 Parameter setting

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21 Controller Auto-tuning

22 Machine Axes and Coordinate Systems The positioning of a workpiece on a CNC machine axis identification coordinate systems positioning systems machine coordinates work coordinates

23 Machine Axis Identification Axis: a line segment used to orient a space or a geometric object.it can be regarded as a reference line from which distances or angles are measured in a coordinate system. The Cartesian coordinate system is normally used to define the movements e on CNC C machines. Two types of axis movement: linear and rotary motion.

24 Z axis Z axis The z-axis is always coincident with or parallel to the axial centre line of the main machine rotating spindle. +Z: the direction in which the tool moves away from the workpiece.

25 X axis Theaxisparalleltothelongest dimension of the primary machine table. +X: +X movement is to the right when viewed from the spindle axis with the observer facing the supporting column (for vertical Z-axis) axis). View dir.

26 +X movement is to the right when viewed from the spindle axis in the direction of workpiece (for horizontal Z-axis). View dir.

27 Relationship between table motion and cutter motion Moving the cutter to the right (+X) in relation to the table requires moving the table to the left (- X). To avoid confusion, a part programmer can always consider the motion in terms of the cutter moving along the part, regardless of whether it is the cutter or moves.

28 Primary Rotary Axes: A, B and C A, B and C are used to indicate rotary motions about the X, Y and Z axes, respectively. The thumb rule is used to determine the direction of rotation. Many CNC machining centers are characterized by three linear axes and one rotary axis

29 Coordinate Systems In CNC applications, two coordinate systems can be used to identify the critical points that define a workpiece: the Cartesian coordinate system and the polar coordinate system. Cartesian coordinate system: In single quadrant positioning, preferred by many part programmers, all position are located in the 1st quadrant.

30 Polar coordinate system: The angle is positive when measured in the counterclockwise direction from the positive X axis.

31 The use of polar rotation to drill a series of holes along a circle Coordinate system rotation and machining of Coordinate system rotation and machining of symmetrical part feature using polar rotation

32 Positioning System Absolute positioning system Incremental position system

33 Reference coordinate Machine reference point: Initial setup of the machine As the reference point for other coordinate system As the tool change position

34 Reference return point: accurately predetermined in each moving axis by limit switch to allow the machine table or spindle to be returned to. Work reference points: (G92) The origins of the workpiece coordinate systems Program reference points: (G92) These positions are chosen by the programmer to locate all other points in the part program