Motor Controller

Figure 23: Ocean Control KTA-190 Serial Stepper Motor Controller. (www.oceancontrols.com.au)

The KTA-190 serial stepper motor controller (Figure 23) from Ocean Controls provides an easy interface for controlling bipolar stepper motors from a personal computer. With inexpensive USB to serial converters it is able to be controlled through a USB port (alternatively a KTA-205 parallel port interface can be used for a parallel connection). The KTA-190 allows for a total of four stepper motors to be controlled independently (or collectively) off the one board, with the ability to connect up to four serial stepper motors controller boards together allowing the user individual control of a up to16 motors. 2 KTA-190 motor controllers were required to provide communication to the 5 motors.

The KTA-190 controller requires a 12V DC power source and has an ATMega 168 microcontroller on-board, which is connected via a MAX232 chip (ensuring the incoming signals are in the microcontroller range of 0 – 5V). Limit switch inputs have pull up resistors, with step and direction outputs connected through a 74HC245 buffer chip. Dip switch SW1 identifies which board is being addressed when more than one serial stepper board is in use. The controller

has a 9 pin female D-connector, with a 10 pin IDC header onboard giving an interface for additional controllers to be connected.

Custom software (alternatively serial terminal software) is used to send commands to the controller board, via a serial port (or USB port when using a USB to serial adaptor). A board rate of 9600, 8 data bits, 1 start, 1 stop bit and no parity (9600, 8, N, 1) was required for communication. ASCII commands are sent to the controller board in the format:

@AA CMND XXXXCR

Where: @AA is the address of the motor required to be controlled (between 01 and 16)

CMND is the command required to be executed (refer Table 1) XXXX is the parameters of the CMND (refer Table 1)

CR is the carriage return bite (0x0D)

Alternatively, a single command can be sent to the desired controller board to control all four motors simultaneously using the following format:

@AA CMND WWWW XXXX YYYY ZZZZCR

Where: @AA is the address of the controller board (01, 05, 09, 13) CMND is the command required to be executed (refer Table 1) WWWW is the parameters of motor 1 (refer Table 1)

XXXX is the parameters of motor 2 (refer Table 1) YYYY is the parameters of motor 3 (refer Table 1) ZZZZ is the parameters of motor 4 (refer Table 1) CR is the carriage return bite (0x0D)

Command (CMND) Description

POSN Set the position that motor AA is currently at to be XXXX

where XXXX is between -99,999,999 and 99,999,999

PSTT Returns the position of motor AA

AMOV Move motor AA to the absolute position XXXX

where XXXX is between -99,999,999 and 99,999,999

RMOV Move motor AA relatively from the current position by XXXX

where XXXX is between -99,999,999 and 99,999,999

STOP Stop motor AA immediately

STAT Get the status of the motors see “Status Command Detail”

ACCN Set the maximum stepping rate of motor AA to XXXX where

XXXX is between 0 and 9999 see ”Acceleration”. If the value for ACCN is 0 or less than RATE then no acceleration or deceleration occurs

ACCI Set the Acceleration interval of motor AA to XXXX where

XXXX is between 1 and 9999 see ”Acceleration”

RATE Set the minimum stepping rate of motor AA to XXXX where

XXXX is between 1 and 9999 see ”Acceleration”

DRON Turn Direction output (D1-D4) associated with AA on for XXXX

* 0.131mS. If XXXX is -1 output will be on until a ‘DROF’ command is received

DROF Turn Direction output (D1-D4) associated with AA off

immediately from ‘DRON’ command

DRST Returns time remaining of ‘DRON’ command in time intervals,

or -1 if it is on permanently

OPTN Bit 1 of the parameter turns Verbose mode on and off, bit 2

turns Checksum mode on and off. Valid addresses are 01, 05, 09 and 13. See the section on the Option Command

ACCF When set to 1 the alternate Acceleration Curve is used, when

set to 0 the standard Acceleration Curve is used.

SAVE Saves RATE, ACCI, ACCN, ACCF and OPTN parameters to

EEPROM, which are then automatically loaded on the next power up. Valid addresses are 01, 05, 09 and 13.

REL1 Turns Relay 1 ON when parameter is 1, Turns Relay 1 OFF

for all other parameters. Valid addresses are 01, 05, 09 and 13.

REL2 Turns Relay 2 ON when parameter is 1, Turns Relay 2 OFF

for all other parameters. Valid addresses are 01, 05, 09 and 13.

KTA-190 controller has a status command (which is sent in the same way as any other command), and responds with an integer, which when converted to 12 bit binary, providing the real-time status of the controller board being investigated.

@AA STAT

MSB 11 10 9 8 7 6 5 4 3 2 LSB

L4 L3 L2 L1 D4 D3 D2 D1 M4 M3 M2 M1

Table 2: Representation of the binary number returned from the status command.

Where: M represents the movement of the motor (1 = moving, 0 = stopped) D represents the Direction of the motor (1 = forward, 0 = reverse) L represents the status of the limit switch (1 = closed, 0 = open) In the event a binary number is less than 12 digits, 0 are added to the beginning. i.e. 1001110 = 000001001110.

Each motor connected to the KTA-190 has the ability to have a limit switch input, to ensure the motors do not travel out of range. Since the limit switches have a pull up resistor they only require a ground connection to activate, thus ensuring they will work even if power is cut to the entire system. Each motor can have multiple limit switches, provided they are connected in parallel. When a switch is activated, the corresponding motor will stop, and only move one step at a time until the switch is deactivated. This ensures no damage is done to the application and allows the motors to be homed.

The ability to control the speed and acceleration of any stepper motor is important. The KTA-190 has the ability to control both, by manipulating the acceleration settings by sending the appropriate command. The acceleration and final speed is determined by the commands ACCN, ACCI, and RATE. The motor starts stepping one step every ACCN interval, decreasing by the ACCI interval every step until RATE, with the opposite occurring when decelerating. By default the controller has the following settings: ACCN = 50, ACCI = 2, and RATE = 10.

Figure 24: KTA-190 Accleration example. Source: www.oceancontrols.com.au