Kreutz-4 4 Axes DIY Bipolar Micro stepper: Introduction

The Kreutz-4 four axes bipolar micro stepper set was designed to provide a ready solution for CNC retrofit integrators and DIY CNC machine builders. It includes the PC Interface Board and four high power bipolar power stages.

Optionally, a simple DIY external Interface board could be added for expanded functionality, as well as a more complete (non DIY) External interface board that includes isolated I/O and two SPST 30 Amperes 240Vac relays (or SSR interface) for Spindle/ Vacuum/ Cooling pump, 0-10V isolated analog Spindle speed output, E-Stop Safety circuit, power supply soft-start, DC power supplies sequencing and monitoring, and a regenerative energy dump driver.

K-4 Bipolar Micro-stepper Design Goals

• SIMPLICITY: It is designed to be a plug in solution with expansion and upgrade capabilities. Originally intended to be a kit, soon it outgrew the DIY kit concept while we were adding new features. The original one board with through-hole components concept became a five boards set with SMD components completely assembled and tested.
• LOW COST: The original target price was $150.00 for a four axes kit. Soon it was evident that the price was not realistic. We ended up fixing a new target price of $285.00 for the four axes kit, that price was still the price the first 25 sets of the Rev3.02SMD (manually assembled and tested) were sold. (Not available anymore, design has being sold. Updated 04/2012)
• HIGH PERFORMANCE: Originally it was intended to capitalize on the translator developed for the Mardus-Kreutz boards, later more features were added, like: Automatic Slow/Fast decay mode, Torque Loss display, independent power supply monitoring on each power stage, CPLD based fixed frequency chopper with adjustable average current versus PWM duty cycle. The power stage is “silent”.
• 48 volts 5 Amperes maximum per phase Bipolar Micro-Stepper output stages.
  Once the design was split into five boards, it was decided that the translators resided on the PC interface board. The idea was to make them compatible with the M-K boards. Actually it is really simple to utilize mixed Bipolar and Unipolar micro-stepper output stages; the only difference is the interface cable.

K-4 PC Interface board

The PC interface board, also called the K-4 Interface, has B.O.B. (Break Out Box) functionality and interfaces four independent bipolar power stages or a combination of K-4 Bipolar micro-stepper (48V / 5 Amperes) power Stages and Mardus-Kreutz Unipolar Micro-Stepper (80Volts /8 Amperes) power stages. The design includes an expansion port (20 pin IDC connector) on the interface board, in order to provide access to the non used LPT port pins for functions like: axis limit switches, home switches, scanning probes, spindle speed control, spindle power control, vacuum or cooling pumps, etc.

General Characteristics:

Kreutz-4 Rev3.02SMD (K-4) is a Bipolar Micro-stepper, Chopper current control, 4 axes set (5 PCBs) intended for low cost CNC or robotic applications. The Basic set offers Break Out Board functionality as well as four individual Bipolar Power Output boards.

The main advantages of the K-4 hardware configuration are:

1. Low Cost.


2. No need to buy extra boards for basic CNC or robotic applications.


3. Individual Power boards are easily and economically replaceable.


4. Sophisticated features include: Individually selectable micro-step modes, reference current "morphing" versus rotational speed, automatic torque compensation, automatic stand-by current reduction, individual motor voltage and current adjustment for each axis.


5. Basic protection/safety includes: 2500 V Opto-isolation & RF signal isolation, Over-current, Over and Under-Voltage, and Over-Temperature protection. Reverse voltage protection on the 12Vdc input. Charge Pump feature (watch-dog).


6. There is no need to open the PC or get another external power supply in order to provide the required non-isolated +5 Volts (supplied by using a standard USB cable between the PC and the PC-interface board).


7. Customizable platform for O.E.M. or Value Added resellers.


8. Easy and economical upgrade path to higher output bipolar or unipolar power boards.


9. Optional External Interface board could be added later for additional control, power and safety features.

General K-4 Specificacions:

• Accepts 4 or 8 wires motors (and 6 wires motors leaving one wire disconnected on each phase)
• Operating Modes: Full Step, 1/2, 1/4, 1/8, 1/16, 1/10, 1/5.
• Opto-isolated Inputs and Outputs (except External Output interface signals). RF isolated Step-direction signals up to 2500 volts.
• +3.3 Volt or+ 5 Volt PC interface (jumper selectable).
• Automatic torque compensation.
• Automatic Reference waveform "morphing" .
• Active average current compensation adjustment.
• Firmware Upgrade capability built in.
• External Output connector for interfacing the rest of the LPT port pins.
• Idle current reduction (50%) after 1 second inactivity independently for each axis.
• Charge-Pump (watch dog) circuit disables the outputs if the 12 KHz signal is not received from the software, protecting against Software "freezes" and LPT cable disconnections.
• A logic LOW at the EMG_STOP pin will disable all Axes and trigger a software E-Stop by pulling pin 10 of the Lpt port LOW.
• A Fault signal received from any of the Axes will trigger an Emergency Stop

The K-4 PC interface board includes the "translators" for the four axes, as well as low voltage (12Volts) power distribution for the power boards. All the PC Lpt port signals used on the board are isolated by means of opto-isolation or RF Isolation up to 2500 Volts. The "Charge Pump" approx. 12Khz signal, coming from the PC software, enables the four axes (which are also individually enabled or disabled by programming jumpers) and the output controlling signals. Optionally one Active High Enable signal at pin 1 of the LPT port could be jumper programmed to activate all the individual outputs, instead of the charge pump signal.

Individual Axis Specifications:

• Maximum Step rate: 100 Khz
• Minimum Step and Direction pulse width = 2 uSec @ 100 Khz.
• Step and direction signals are Active "High" (Low to High Transition).
• 40 Khz chopper frequency.
• Over current and over temperature protection.
• Automatic phase Current Decay mode controlled by CPLD.

Low Voltage Power supply:

There is only one required connection to the externally regulated +12 Volt DC power supply, and it is on the "PC Interface board" (The 12 Vdc 2 Amps regulated power supply is provided by the User).

• K-4 requires a +12 Volts (2 Amperes) Regulated Power supply. This power supply is monitored to be between 14 Volt and 8.5 volts, otherwise the power board’s output is disabled.
• The +12 Volt Power supply input on the PC Interface Board is protected against reverse polarity and >14.2 Volts surges. A 2.5 Amps (25 mm) Fast fuse is recommended between the external regulated power supply and this input.
• Internally regulated +5 volt power supply is derived, on each board, from the +12 V power supply, it is monitored by the Micro-controller’s brown-out protection circuit which will reset the micro-controller when the +5 volt power supply voltage is under 4.3 Volts.

Bipolar Power boards:

Note: The following power stage design have been sold (about 3 years ago)  I currently don't hold the rights to distribute schematics and/or firmware. You can still use the K-4 PC interface board  for the Mardus-Kreutz power stages which is a DIY solution. K-4 Pc interface and M-K unipolar (up to 80V - 8 Amps) micro-step power stage's schematics, gerber files and firmware are available for free. 

(Updated 04/20/2012)

Bipolar Power Board ( 5 Amps).

Specs:

1. 48 Volts Absolute Maximum Motor voltage including Power Supply ripple and Back EMF (Over 47 Volts the output is disabled by the monitoring/safety circuit on each individual power board).
2. 15 Volts minimum motor voltage (under 15 Volts the output is disabled)
3. 5 Amperes (peak) Maximum phase current per axis.
4. Current Reference is individually adjustable by potentiometers and measured on individual test points for each coil.
5. Average current compensation adjustment potentiometer on each Power board.

Indicators:

• PC power LED
• "Torque Loss". LED Turns on when the motor current can not follow the reference, indicating torque loss at the corresponding speed or speed range. LED brightness indicates relative loss (Brighter indicates less torque available).
• Firmware Ready LED (for each axis), Service/Adjustment blinking LED.
• Axis Disabled LED (for each axis)
• Stand-by Current reduction LED (for each axis)
• Charge Pump OK LED
• E-Stop LED
• Low Voltage Power LED (on every Power board)

Other Features:

1. Works with any Step-Direction software with the ability to setup individual LPT port pin functions.
2. RoHS compliant.
3. Individual or Simultaneous control of all axes.
4. Power On reset.
5. On board 5 Volts voltage regulation (on each individual board)
6. PC +5Volts is supplied by the PC's USB port using a standard USB cable (using USB-B connector on the interface board), it is used on the non-isolated part of the PC interface board.

Note: Heat-sinks are not included. Dimensions for a suggested heat-sink will be shown on the documentation.

The DIY Translator 

The completely assembled K-4 PC interface board  100% compatible with the DIY M-K unipolar micro-step power stages, yet another option was also designed for the DIY inclined: The individual K-41DIY Translator.

Features:

• Operating Modes: Full Step, 1/2, 1/4, 1/8, 1/16, 1/10, 1/5.
• Opto-isolated Fault signal, RF isolated Step-direction signals (up to 2500 volts).
• Automatic torque compensation.
• Automatic Reference waveform "morphing" .
• Firmware Upgrade capability built in.
• Idle current reduction (50%) after 1 second inactivity independently for each axis.
• An optically isolated Fault signal Output
• An Active Low isolated Enable input.
• 3.3V and 5 V B.O.B. logic compatible.

A new DIY bipolar power stage is being designed using a different technology... stay tuned. (04/2012).

(will continue...)