Novanta i401, Руководство пользователя

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CONTROL SIGNALS PAGE | 64
laser was on (lasing) during the last 200 microsecond (
μ
s) interval. If the lasers on time was greater than
the preset tickle value, then no tickle pulse is generated because the PWM signal was sufficient to
maintain a plasma state. If no PWM signal was applied during the 200-
μ
s measurement period (or was
shorter than the preset tickle value), internal circuitry generates a tickle pulse such that the laser always
receives a pre-set amount of RF drive averaged over any 200-
μ
s interval.
Pulse Width Modulation (PWM)
Pulse Width Modulation, or PWM, controls laser power by varying the duty cycle of I401’s RF amplifiers,
which in turn control the time-averaged RF power applied to the laser. The percentage of optical output
increases as duty cycle increases (at a constant PWM frequency) or as PWM frequency decreases (at a
constant duty cycle).
I401 lasers are designed to operate at Command signal base frequencies up to 100 kHz; however, the
choice of PWM frequency depends on the user’s specific application. In the majority of laser applications,
the UC-2000’s default Command signal frequency of 5 kHz has proven to work well. When considering
Command frequencies at 5 kHz or below, please review Marking/engraving operation later in this
section. For high-speed motion applications that cannot tolerate any ripple in the optical beam response
but still need adjustable power levels, we recommend the use of higher PWM frequencies, up to 100 kHz
maximum.
Command signal
The modulated Command signal applied between Pin 9, PWM Input, and Pin 1, PWM Return, of the User
I/O connector on the i401 laser has three parameters: signal amplitude, base frequency, and PWM duty
cycle. By changing these parameters, you can command the beam to perform a variety of marking,
cutting, welding, or drilling operations.
The first Command signal parameter, signal amplitude, is either logic low—corresponding to laser beam
off, or logic high—corresponding to beam on. The laser off voltage, typically 0 V, can range from 0.0 V
to +0.8 VDC while the laser on voltage, typically 5 V, can range from +3.5 V to +6.7 VDC.
Base frequency, the second parameter, is the repetition rate of the PWM input signal. The standard base
frequency is 5 kHz, which has a period of 200 µ s. Maximum PWM frequency is 100 kHz. The third
Command signal parameter, PWM duty cycle, is the percentage of the period that the Command signal
is high. For example, if the Command signal’s amplitude (at 5 kHz) is high for 100 μ s and low for 100 μ s, it
has a 50% duty cycle; if the amplitude is high for 190 μ s and low for 10 μ s, it has a 95% duty cycle. Figure
3-4 illustrates typical PWM Command signal parameters.
Warning: Serious Personal Injury
Always use shielded cable when connecting your PWM signal source to the laser’s PWM connections.
In electrically noisy environments, long lengths of unshielded wire act like an antenna and may
generate enough voltage to trigger un-commanded lasing.