Nema 23 Stepper CNC Motor
Nema 23 Stepper CNC Motor
In automation, what is the difference between PLC, NC, and CNC (in layman’s terms)? Is one more advanced than another, or are the controllers used for different machinery?
Manual machines are controlled by an arrangement of Cams and gear wheels. Simple linear trajectory of the part being machined or the tool being used can be controlled through hand operated or automated wheels that are connected to screws or rack and pinion arrangements. Complex paths are usually controlled by some kind of a cam follower device which follows a master template. Precision was realised by very high reduction ratio gear sets, which enabled movement of the resolution of microns by rotating a hand wheel by one turn or a fraction of a turn using marked dials or dial wheels. This arrangment requires great manual skills and hard stops to make precise features. It is analogous to an analog system.
Numerical controlled machines on the other hand use servo motors, encoders and ball screws. The servo motor can be instructed to rotate even as little as a fraction of a degree. Normally used ball screws have a pitch of around 10mm. Therefore one rotation of the ball screw moves the part or tool by 10 mm. By precisely controlling the rotation, even movement as small as nanometeric resolution can be obtained on modern machines. Most normal modern machine tools can make movements of 1 micron resolution quite reliably. The encoders provide a closed loop feedback to the servo motor driver, which makes for very precise positioning and thereby great accuracy of the machined part. These instructions can be numerical, and hence I suppose the name Numerical control.
Usually, the tool and the part are moved relative to each other by manipulating three servo motors on the x,y and z axes, which are linear axes. More complex movements can be achieved by incorporating rotary axes around the linar axes which are termed a,b and c axes. Very few machine tools have rotary axes, but that seems to be changing these days.
In a Numerically controlled machine, the trajectory (also known as tool path) and its velocity (also known as feed rate) is controlled by simultaneosly varying the speed and direction of the servo motors which control the linear and rotary axes. This involves complex trignometric and velocity calculations in real time based on real time feed back from the encoders. These calculations are carried out by the numerical controller in real time.
In the early days of Numerically controlled machines I suppose not much interaction was possible between the machine controller and humans. As has been pointed out, communication was rather limited through punch cards or tape. I suppose the machines only contained the Motion control kernel and not much else beyond that. Programs had to be manually written at the most basic level and fed into the machines.
Modern CNC machines however are much more advanced and have full fledged PCs which permit all kinds of interaction with the user. they can be networked throug ethernet, RS232, accept Compact flash cards, USB drives etc.
Personally, I dont see much difference between NC machines and CNC machines except in their ability. CNC machines accept programs in the form of G Codes which are instructions that provide the direction and speed for the tool trajectory. Many modern CNC permit high level programming of complex parts at the machine interface itself. Many common features are inbuilt as parametrized canned cycles
(Edit) I forgot to address what a PLC is, so here it is. PLC (Programmable Logic Controller) is a ruggedized industrial computer. PLC has a series of inputs and outputs which can be as few as 4 to 8 to may be a hundred or more through addon Input Outpu (IO) modules. The inputs receive signals from sensors and outputs activate motors, valves, signals, through relays and switches. The PLC works on a sequential scan cycle. The PLC examines the inputs for their signal status, which is mostly binary (on or off) and based on the logic programmed into it, activates the outputs. PLCs can also control servo and stepper motors. Their programming is in a strange language which looks like a circuit diagrams involving relays. It seems the PLC was developed to replace the cumbersome circuit of relays which was used to control early machine automation. CNC machines also have a PLC to control all the peripherals, interlocks and signals. For eg. a PLC may prevent a chuck from being declamping on a cnc turning machine when it is in operation. PLCs are good enough for many kinds of automation without requiring NC or CNC.
Cloudray Stepper Motor Series has set the standard for quality, reliability, and durability in stepping motors. The precision of our Torque Power motors is matched only by the dependability of their performance. All Torque Power motors are bi-directional and totally enclosed with permanently lubricated ball bearings for long-lasting, smooth operation.
Fast Response,Better Acceleration Performance
Thanks to a robust design they can be selected for the harshest environments. Precise, open-loop, speed and position control can be achieved with the application of full step, half step, or microstepping electronics.
Stepping angle is adjustable( rang in 18°±5%）， 0.9 °stepper motor's stepping angle is smaller, fineness is higher and positioning is more accurate.Avoiding vibration,runs more smoothly and gets lower noise.
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