Performance Motion Devices Juno MC71112, Руководство пользователя

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Drive & DC Bus Safety
82
Juno Step Motor Control IC User Guide
13
Figure 13-4:
Current
Foldback
Processing
Example
Setting continuous current limit and energy limit to less than the maximum available from the amplifier circuitry is
useful if the required current limit is due to the motor, rather than to the drive electronics.
The instantaneous state of current foldback (whether the foldback limit is active or not) is available in the Drive Status
register. In addition, if a foldback event has occurred, this event is recorded in the Event Status register.
Example
A particular motor has an allowed continuous current rating of 3 amps. In addition, this motor can sustain a temporary
current of 5 amps for 2 seconds.
In this example the continuous current limit would be set to 3 amps, and the energy limit would be set to:
Energy Limit = (peak current
2
- continuous current limit
2
) * time
Energy Limit = (5
2
A
2
- 3
2
A
2
) * 2 Sec
Energy Limit = 32A
2
Sec
Following the current scaling example in Section 9.2.2, “Current Signal Scaling” the programmed continuous current
limit would be 3.0 A * .625 * 32,767 / 10.0A = 6,144.
The programmed energy limit value must convert seconds to Juno current loop cycles (19,531 cycles/sec) and must
factor in the scaling of Juno’s programmed energy limit value which is 1/2
31
. This gives:
Programmed Energy Limit = 32 A
2
Sec * (1.25 * 32,768 / 10A)
2
* 19,531 cycles/Sec * 1/2
31
Programmed Energy Limit = 4,883
Current foldback, when it occurs, may indicate a serious condition affecting motion stability, smoothness, and per-
formance. It is the responsibility of the user to determine the appropriate response to a current foldback event.
0
30
20
10
10
5
0
10
5
0
Commanded
Current
Amps
Continuous
current limit
exceeded
Integrated
energy limit
exceeded
Amps
Amp 2 -sec
Output
Current
Integrated
Energy
Time