As I stated previously ...

When the Photo-Sensor sends the "STOP" signal to the Motor Controller,
the Motor Controller changes from a Precise Dispensing Velocity to a Precise Deceleration Rate down to Zero Velocity.
Zero Velocity will occur within +/-1 encoder Counts of the expected Encoder Count,
giving a very constant / fixed over-shoot distance ( in Encoder Counts ) from the Photo-Sensor Signal.

Given the Precise Dispensing velocity when the STOP signal is received and
a precise Deceleration Rate from the Dispensing Velocity down to Zero Velocity then
the motor will stop the coupon at exactly the same position every time, within +/-1 Encoder Count.

Now simply move the Photo-Sensor, as needed, to align the perforation of the Coupon.

Precise Dispensing Velocity + Stop Signal + Precise Deceleration Rate = exact repeatable stopping point after the Photo-Sensor signal
The Motor Controller works units of "Encoder Counts per Unit Time".

It is better to have controlled acceleration ramps and deceleration ramps = easy on the gears.
Full torque Hard Start and Hard Stop will cause extra wear and tear on the gears, etc.

As I stated in message #66...
A Closed-Loop Servo or a Stepper Motor makes more sense here.

 

As I stated previously ...

When the Photo-Sensor sends the "STOP" signal to the Motor Controller,
the Motor Controller changes from a Precise Dispensing Velocity to a Precise Deceleration Rate down to Zero Velocity.
Zero Velocity will occur within +/-1 encoder Counts of the expected Encoder Count,
giving a very constant / fixed over-shoot distance ( in Encoder Counts ) from the Photo-Sensor Signal.

Given the Precise Dispensing velocity when the STOP signal is received and
a precise Deceleration Rate from the Dispensing Velocity down to Zero Velocity then
the motor will stop the coupon at exactly the same position every time, within +/-1 Encoder Count.

Now simply move the Photo-Sensor, as needed, to align the perforation of the Coupon.

Precise Dispensing Velocity + Stop Signal + Precise Deceleration Rate = exact repeatable stopping point after the Photo-Sensor signal
The Motor Controller works units of "Encoder Counts per Unit Time".

It is better to have controlled acceleration ramps and deceleration ramps = easy on the gears.
Full torque Hard Start and Hard Stop will cause extra wear and tear on the gears, etc.

As I stated in message #66...
A Closed-Loop Servo or a Stepper Motor makes more sense here.

Yeap, applying a gradual duty cycle pwm during accel/deceleration should do the trick

 

There is s-curve velocity start and stop profiles.

 

Energy consumption braking, reverse connection braking and regenerative power generation braking are commonly used in the electric braking of dc motor.

Energy consumption braking is to maintain the dc motor excitation power remains the same. Cut off the running motor armature power supply, and then connect an additional brake resistance. The composition of the circuit, the mechanical energy into heat consumption in the armature and brake resistance, forcing the motor to stop. Reverse braking is to change the direction of the electromagnetic torque by changing the polarity of the voltage at both ends of the armature or the direction of the excitation current, so as to form the braking torque and force the motor to stop running.