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| ST Home | Application Specific for Motor Control | Integrated Power Stages | practiSPIN SW & HW | ||
Integrated Power Stages - powerSPIN™
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The practiSPIN™ evaluation environment consists of three main components.
 In operation, the ST7 microcontroller on the interface board communicates with the user interface across an RS232 link to the PC and generates the real time control signals for the driver ICs. The PC based software sends all of the commands to the ST7 across the RS232. The PC software can also update the firmware in the ST7 across the RS232 link. The system uses this in application programming of the ST7 flash to provide the flexibility to support many devices or applications. Each device or application has their own dedicated firmware that can be downloaded into the flash memory. The practiSPIN™ system will automatically determine if the appropriate firmware is loaded in the ST7. Each supported device has a dedicated evaluation board. This board includes the power connections and all required external components for the device and connects to the ST7 across a 34 Pin ribbon cable. The circuitry on the dedicated evaluation board is generally the configuration shown as the typical application on the data sheet. In some cases adjustments are provided on the board to set the operating conditions that are not controlled by the software. Generally these boards may also be connected to the users system also to test the user's firmware.  When you first start up the practiSPIN™ system you get a screen like the one shown here. The first screen allows you to select the communication port that will be used to communicate with the ST7 board using the port selection drop down box, the powerSPIN™ product and the type of motor you will be evaluating. The software now displays the user interface for the selected motor type. The example here is for the stepper motor with L6208 as the target device and set appropriate operating values for the motor.  Using the control panel we can select the operating conditions for the application. Starting at the upper left we have a stepping mode selection. From the control panel we can select full step (normal) half step or micro stepping mode (micro stepping is only supported for the L6208). Other controls on the top line let the user select the direction of rotation and the decay mode during recirculation. The actual movement parameters are selected in the second and third row of controls. The controls on the second row allow the user to set the top speed and the acceleration and deceleration rate. The typical run profile for a movement includes an acceleration ramp, constant velocity run and deceleration ramp as shown here. All of these parameters are set on the control panel. In many applications the torque needed to accelerate and decelerate is significantly larger than that required for the constant speed running so the designer may want to drive the motor with a higher current during the acceleration and deceleration time and then drop the current to a lower level during the constant speed portion of the movement to reduce the dissipation. The control panel allows the user to set the current, as a percentage of the maximum value determined by the hardware, for each portion of the movement and the holding time. When motor settings have been defined one can start and stop the motor by simply clicking on the RUN and STOP Micro stepping operation is obtained with two reference signals generated by a pair of D/A implemented by filtering the PWM outputs of the two counter/timers in the ST7. Using the 8-bit resolution of the PWM up to 1/64 micro stepping can be achieved. The second control screen allows the user to operate the stepper in an indexing mode. The table on the right of the screen is used to define the movement sequence. Two settings are required for each movement. The distance of the movement, defined as the number of steps from the current position, and the wait time before the next step is started. A positive number of steps will move the motor forward and a negative number will move the motor in the reverse direction. At any time during the operation I can change the speed or acceleration settings and the new setting will take effect at the start of the next movement. Using this mode with a repetitive movement you can evaluate the accuracy of the movements and the ability of the system to maintain step accuracy. Now let's look at at how DC motor are supported.  Generally DC motors are operated in voltage mode with the microprocessor providing a PWM output to control the motor. For the practiSPIN™ system since we do not know the type of feedback that will be used in the system we have chosen to implement an open loop speed control in which the duty cycle of the PWM output is set directly by the user on the control panel. Since the powerSPIN™ family of devices are all dual bridges, they can be operated to drive either two DC motors, as we show here, or connected in parallel to drive on DC motor.The practiSPIN™ supports both configurations. The user can select the motor direction and whether the driver applies a breaking or allows the motor to coast freely to a stop. The user can also set the output PWM duty cycle directly on the voltage control and the motor current as a percentage of full scale on the current control. Here we have a system set up with the L6206 driving two small DC motors. By clicking on Run we can run either or both of the motors. By toggling the forward/reverse switch we can reverse the direction of the motor. By changing the voltage setting we are selecting the PWM duty cycle and thereby changing the effective voltage drive to the motor. We can also set the current control to regulate the peak current. This mode can be used to simulate a toque control technique. If I set the voltage to 100% and turn down the current I can demonstrate the torque control. The control panel for operating the two bridges in parallel looks similar to the one shown here but has only one motor panel.  For BLDC motors the system supports the L6235 and L6229 driver ICs and the control panel and features are similar to the DC motor drive control panel and features.In addition to driving the motors, the practiSPIN™ includes a program to assist in the thermal evaluation of the application. The software is set up to take the operating conditions from the application including the power supply voltage, motor characteristics and some information about the movement profile and use this to calculate the dissipation and operating junction temperature of the device. The software also considered the mounting configuration and package type when calculating the operating temperature point and provides an useful “first cut” estimation on whether the actual application conditions are acceptable. The analysis can be conducted in Steady State conditions as well as in single pulse or repeated pulse conditions, allowing a vast coverage of practical situation encountered.  Within the powerSPIN™ all the technical papers (data sheets and application notes) can be navigated from the main menu.
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