APPLICATION-SPECIFIC FUNCTION: MOVE SFC STEP
This function is used to set up a move step for a motor controlled by the PLC to a position specified on the TARGET input.
The motor is controlled by the following three outputs (symbolized by the green/blue/red dots on the icon):
ON (0 or 1): The motor runs when the ON signal is at 1. Otherwise, it stops (with optional braking depending on the motor configuration)
DIRECTION (0 or 1): Indicates the direction of motor rotation (1 clockwise, 0 anticlockwise)
SPEED (0 to 30000): Indicates the motor speed in rpm
Note 1: When several move steps are linked, it is possible to combine their motor control signals using the MOTOR MULTIPLEXER function. For information on the MOTOR MULTIPLEXER function, click on the following link: Motor multiplexer
The move consists of 5 steps:
Move parameters:
HIGH SPEED (0 to 30000): Indicates high speed in rpm (see note 2)
LOW SPEED (0 to 30000): Indicates low speed in rpm (see note 2)
Note 2: In order to bring the speed output within the PWM range [0..255], a GAIN block must be inserted just before the analog output controlling the motor speed. This block should be set to 255/N where N is the maximum motor speed. For information on the GAIN block, click on the following link: GAIN block
ACCELERATION (0 to 2767): Indicates the speed increment on each PLC cycle (see note 3)
DECELERATION (0 to 2767): Indicates the speed decrement on each PLC cycle (see note 3)
Note 3: The standard PLC cycle is 10 ms. Setting acceleration to 10 will make the motor accelerate by 10 rpm every 10 ms, hence from 0 to 1000 rpm in 1 second. If the cycle is 20 ms, then the motor will accelerate from 0 to 1000 rpm in 2 seconds
APPROACH (0 to 32767): Indicates the distance before the target during which the motor decelerates and then approaches at low speed before stopping (notes 4 and 5)
TARGET (-32768 to 32767): Indicates the value to be reached on the POSITION input in order for the move to be deemed complete (see note 4)
Note 4: (EXAMPLE) Motors in the CROUZET 80040xxx and 80080xxx brushless range generate 12 pulses per revolution.
A position of 1200 therefore corresponds to 1200/12=100 motor rotations.
If the motor is fitted with a gearbox with ratio 10, the geared motor output shaft will therefore make 100/10=10 rotations.
And if the output shaft drives a belt on a 40 mm diameter pulley, this belt will advance by 10 x 3.14 x 40 = 1256 mm = 1.256 m
Note 5: For optimum stopping, adjust the APPROACH parameter so as to obtain a short plateau at low speed before stopping.
If the plateau does not exist, increase the APPROACH parameter.
If the plateau is unnecessarily long, reduce the APPROACH parameter.
If the motor slows down too abruptly, reduce the DECELERATION parameter
If a status token is present at STEP INPUT 1 or STEP INPUT 2, it is stored immediately in the function step, switching the ON output controlling the motor to 1.
This token remains stored in the step until the move is complete. In this case, the status token crosses the transition and disappears from the step. The ON output is set to 0 and the token is then available on the STEP TRANSITION OUTPUT and can be stored in the step or steps connected downstream of this output.
Depending on the DIRECTION OF MOVEMENT option, the move is performed as follows:
Note 6: This function is based on the convention that DIRECTION = 1 makes the motor rotate in order to make the POSITION value increase, and vice versa. This is the case with CROUZET brushless motors. In cases where the motor or its rotation sensor do not respect this convention, a NOT relay should be placed just before the logic output controlling the motor direction.
CAUTION, if this convention is not respected, the motor will rotate indefinitely, which could move the system it is driving beyond its limits.
There is is no guarantee that the function will work correctly when the speed output is forced to values in excess of 30000, whether by manual forcing or when using a display.
For more information about SFC charts and this function, see: SFC chart help
Parameterisation box/Comments tab