CNC Motion Controller

Complete 4 Axis Motion Controller setup

 

 

 

 

 

Bipolar 4X Axis Micro Stepper Motor PWM Control RCF-V10

Step and direction control is by far the most common PC based CNC Machine motor controller.  There are many companies that offer motor controller circuits and systems; we recommend using a motor controller that is made or purchased with Step and Direction Circuit design, and capable of using a PC Parallel port for control.  This is the most common design, which means you will many choices of control software to use, like Mach, EMC , Turbocnc

PC Parallel port or USB:

Currently, the most common control software and motor controllers will use the PC parallel port (25 pin connector printer port).  USB controllers are available but are still a rare item, and do not work reliably, as of yet, using a true parallel port is best,  

Do It Yourself Motor CNC Machine Controller:

If you have some knowledge of electronic components, there are many motor controller kits which only require soldering.  But DIY kits, that include all parts and a have circuit board, can be successfully completed, with only novice skills.  There is nothing more satisfying than building anything from scratch, but electronics are a different animal and mistakes can cost money, and injury.  So unless you are familiar with all aspects of electronics and know what you are doing we do not recommend tackling it with your first machine.  Buying a pre-made controller will be more expensive, but will give you the knowledge of what to expect if you ever decide to make one yourself.

Chopper Current Motor Controller:

A chopping circuit  can limit the current, without getting electronic components too hot, and will be much more efficient.  Often called PWM, (Pulsed Width Modulation) PWM will switch the operating voltage on and off,at high frequencies; this routine is called pulsed width modulation.  The on time will determine how much current gets through to the motors. PWM control is best for  stepper motor control, and is considered newer technology.

Resistive Current  Controller:

Normally, with stepper motors, the voltage is set  higher than the voltage rating of the motor - a way of limiting the current going to the motors, is to use a current limiting resistor.  These motor controllers  are called L/R drivers, L=Inductance, R=Resistance.  This resistor is placed in series with the winding, and will take some current from the motor and will dissipate it with heat.

Integrated Control:

Integrated control means the motor controller is embedded and will accept commands from the host computer "direct connect" during the motion process.  Communication, operator interface and the I/O functions are  separate elements of the system.  The motion  is done by the computer and in this case the controller acts as an independent device.  CNC (computer numerical control) applications are well suited for integrated control because the data input is "dynamic", or changing frequently.

Motor Step Modes:

Stepper motor controllers can have different  step modes - full, half and micro-stepping.  The type of step mode output of any motor is dependent on the motor controller and motors

Full Step:

Standard stepping motors have 200 full steps per revolution of the motor shaft.  Dividing  200 steps into the 360 degree rotation equals a 1.8 degree full step angle.  Normally, this full step mode or 1 pulse from the controller will equal 1 step

Half Step:

Half step means the controller will send is rotating at 400 steps per revolution. In this mode, one winding is energized and then two windings are energized alternately, causing the rotor to rotate at half the distance, or 0.9º's.  Half stepping is a more practical solution however, in industrial applications. Although it provides slightly less torque, half step mode reduces the amount "jumpiness" inherent in running in a full step mode.

Micro-stepping:

Micro-stepping is a relatively new stepper motor technology that can control the current  degree that will subdivide the number of positions between a single step.  Micro-stepping is a function of the electronic motor controller, it will enable one single step of the stepper motor to be divided into multiple steps, giving the stepper motor more resolution, and a smoother operation; most newer and higher quality motor controllers will have this function.  Micro-stepping is typically used in applications that require accurate positioning and a fine resolution, over a wide range of speeds.  Micro-stepping will make a stepper motor run more smoothly and more accurately.

Controlling External Devices

E-Stop

E-stop stands for Emergency Stop there are a few ways to E-Stop a machine when the motion is going wrong or is about to, Mach3 control software has a large button that will immediately stop all motion, this is considered a software controlled e-stop. A hardwired e-stop is a physical button or switch that is wired and connected to an input of a breakout board and can be configured  to stop all motion, a physical hardwired switch is a more reliable way to e-stop a machine than a software e-stop

Breakout Board:

A breakout board is used to isolate and extend the parallel port, for external devices like limit switches, and turn things on and off, like a rotary tool, automatic clamping, vacuum table, or whatever device you want to control while running your machine.  Most pre-made motor controllers will have connection points for  external devices, but if the DIY controller is made a breakout board would be advisable.  An optoisolated breakout board will isolate connections to protect your computer port from accidental short-circuits. The optoisolated circuit  sends the signal through a LED, and will receive the light with a phototransistor.  When the parallel port switches the signal to on or high, an LED will turn on - the phototransistor sees the light  and relays the signal.  Your computer’s sensitive electronics are  isolated from your external devices. The input signals are transmitted with light and not through hard wired connections, so any higher destructive voltages or accidental shorts will never reach your sensitive computer electronics.  Breakout boards are not an absolute must, but will help to protect your PC.

Charge Pump:

A charge pump is an electronic circuit board which is a safety device used  on PC based CNC.  A control like  Mach will send a 12.5 KHz signal through one of the computers parallel port pins. A charge-pump board will act like a traffic light, if the charge pump sees a 12.5 KHz signal it will continue; but, as almost everyone knows, Windows can do unexpected things like stall, crash, blue screen.  When any issues with Windows happens and Mach looses control, the charge pump board will stop all motion to the machine.  A charge pump when wired correctly to the relay board will disable the relay board during PC start up, until the control program has control over the port. 
 

CNC Limit and Home Switches:

Limit switches are used for two purposes, one is to stop machine over travel; a slide can only travel as per its design.  Using a limit switch will tell the control software when it is at its maximum travel limit, and to stop all motion before a crash occurs.  Limit switches are not mandatory but will help in a crash.  The second use, for a limit switch, is homing - this function is used at start up, or in between cuts.  Homing will set a reference point or machine zero for the starting point; homing is a useful feature for making multiple parts when using fixtures.  It will reference all motion from the same point every time, eliminating the need to manually find an exact starting point.

Parallel Port Description and Pin Outs Interface Chart

Pin No    Name Direction
1 Strobe Out
2 Data0 In/Out
3 Data1 In/Out
4 Data2 In/Out
5 Data3 In/Out
6 Data4 In/Out
7 Data5 In/Out
8 Data6 In/Out
9 Data7 In/Out
10 nAck In
11 Busy In
12 Paper-Out In
13 Select In
14 Linefeed Out
15 nError In
16 nInitialize Out
17 nSelect-Printer Out
18-25 Ground -

Stepper Motors:   The stepper motor is an electro-magnetic device that converts pulses of electricity into mechanical shaft rotation. Stepper motors are low cost, with high reliability, high torque at low speeds and a simple construction. Some disadvantages in using a step motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed. Stepper motors have multiple coils, when a specific coil is energized in the proper order, the motor will step in the appropriate direction , a typical stepper motor will usually have 200 steps to make up one turn. Because of this design, stepper motors can keep count without the need of an encoder making electronic controls for stepper motors fairly simple and making them ideal for low cost and easy use. Motor Mechanical Power Ratings: Motor power ratings are measured in ounce inches or (oz.in.) example: A 100oz.in. rated motor simply means, if an arm was attached on the motor shaft sticking out one inch from center and if a 100 ounce weight was hung from the end of the arm the motor will lift it. How to Select and Identify Stepper Motors: Bipolar Stepper Motors: Bipolar Stepper Motors will have 4 wires. They produce more torque and will require a more complicated, electronic control circuit to run properly. They are used in more applications, because can develop more speed and power than Unipolar motors. Unipolar Stepper Motors: A unipolar stepper motor will have 5 or 6 wires. The drawback to using a unipolar drive, is its limited capability to energize all the windings, at any one time. This means the torque will be reduced by around 40% compared to other motors. Unipolar motors are good for applications that operate at lower step rate speeds. Variable Reluctance Stepper Motors: Variable reluctance stepper motors or Hybrid motors are the simplest to control over other types of stepper motors. Their drive sequences simply energize each of the windings in order, one after the other. Comman Stepper Motor Frame Sizes for a CNC Machine: NEMA 17 NEMA 23 NEMA 34 Connecting Stepper Motors: Series Connected: There are two ways to connect a stepper motor, in series or in parallel. A series connection provides a high inductance and will give higher performance at low speeds. Parallel Connected: A parallel connection will lower the inductance but increase the torque at faster speeds. Motor Resonance: Motor resonance is a condition where vibration or oscillation will cause missed steps and noisy operation on your CNC machine. Naturally all stepper motors will have more vibrations, as they are moving in a series of steps, this can cause resonance; it can be caused for various reasons that include: incorrect electronic pulse timing of the steps, loose components. There are many types of dampening hubs that can be installed to stop this issue. Inductance: Stepper motors are rated in terms of inductance. A high-inductance motor will provide a greater amount of torque at low speeds and a low inductance motor will be opposite. Sizing a CNC Machine Motor: Sizing a motor is important when selecting a stepper motor or servo motor - having more power will always be a better choice. Not having enough power can cause overheating in servos, and can cause stalling in a stepper motor. It is always difficult to calculate the exact power requirements needed to drive slides on a machine, as there are many factors to consider, like slide friction, lead screw pitch and nut friction, and size of machine - these will all effect what size and power are needed in general with DIY machines the most common motor frame is a Nema23 the range of this size frame will be from approximately 100oz.in. to 500oz.in. Servo Motors for CNC: Servo motors are generally the standard in most high end systems, they can come in many sizes and are either brush or brushless. Because a servo motor is basically a dc motor, it cannot count position on it's own; it will need what is called an encoder, an encoder can be rotary or linear , a rotary encoder is usually mounted to the motor shaft and a linear encoder will be mounted to the slide or table. The purpose of an Encoder is to count the pulses or position, for example: if a rotary 1000 count encoder is used, it will count 1000 pulses per one turn of the motor. This count is sent back to the motor controller electronics, for the controller to position the motor. This routine is called the PID Control Loop. Servo Motor control is much more complicated to perform, a servo motor controller system will cost much more than a stepper motor controller.     NEMA Motor Frame Mounting Dimensions  inch    Dimension NEMA 17 NEMA 23 NEMA 34  NEMA 42 Motor Shaft Diameter 0.1968 0.250  0.375 0.625 Motor Shaft Length 0.945 0.81 1.25 1.380 Pilot Diameter 0.866 1.500 2.875 2.186   Pilot Length 0.080 0.062 0.062 0.062   Mounting Bolt Circle 1.725 2.625 3.875 4.950   Bolt Hole Size 4-40 0.195 0.218 0.281 Bolt Hole Distance  square 1.220 1.856 2.740 3.500