AMIS-30624 I2C Microstepping Motordriver
Data Sheet
15.4 Motion Detection
Motion detection is based on the back emf generated internally in the running motor. When the motor is blocked, for example when it
hits the end-position, the velocity and as a result also the generated back emf, is disturbed. The AMIS-30624 senses the back emf,
calculates a moving average and compares the value with two independent threshold levels: Absolute threshold (AbsThr[3:0] ) and
Delta threshold (DelThr[3:0] ). Instructions for the correct use of these two levels in combination with three additional parameters
(MinSamples, FS2StallEn and DC100SDis) are outside the scope of this datasheet. Detailed information is available in a dedicated
white paper “Robust Motion Control with AMIS-3062x Stepper Motor Drivers”, available on http://www.amis.com/.
If the motor is accelerated by a pulling or propelling force and the resulting back emf increases above the Delta threshold (+ ∆THR),
then <DelStallHi> is set. When the motor is slowing down and the resulting back emf decreases below the Delta threshold
(- ∆THR), then <DelStallLo>is set. When the motor is blocked and the velocity is zero after the acceleration phase, the back emf is
low or zero. When this value is below the Absolute threshold, <AbsStall> is set. The <Stall> flag is the OR function of
<DelStallLo> OR <DelStallHi> OR <AbsStall>.
Velocity
Vbemf
+ ∆THR
Vmax
Motor speed
- ∆THR
Vbemf
Vbemf
Vmin
Vbemf
t
t
DeltaStallHi
DeltaStallLo
VABSTH
Back emf
t
t
t
AbsStall
t
Figure 22:Triggering of the Stall Flags in Function of Measured Back emf and the Set Threshold Levels
Table 24: Truth Table
Condition
<DelStallLo>
<DelStallHi>
<AbsStall>
<Stall>
Vbemf < Average - DelThr
Vbemf > Average + DelThr
Vbemf < AbsThr
1
0
0
0
1
0
0
0
1
1
1
1
The motion will only be detected when the motor is running at the maximum velocity, not during acceleration or deceleration.
If during positioning a mechanical obstacle is detected (stall), an (internal) hardstop is generated. The motor will stop immediately and
as a consequence the <StepLoss> and <Stall> flags are set. The position in the internal counter will be copied to the ActPos register.
All flags can be read out with the GetFullStatus1.
If Stall appears during DualPosition then the first phase is cancelled (via internal Hardstop) and after timeout (26.6ms) the second
phase at Vmin starts.
Important Remark:
Using GetFullStatus1 will read AND clear the following flags: <Steploss>, <Stall>, <AbsStall>, <DelStallLo>, and
<DelStallHi>. New positioning is possible and the ActPos register will be further updated.
Motion detection is disabled when the RAM registers AbsThr[3:0] and DelThr[3:0] are empty or zero. Both levels can be programmed
using the I2C command SetStallParam in the registers AbsThr[3:0] and DelThr[3:0]. Also in the OTP register AbsThr[3:0] and
DelThr[3:0] can be set using the I2C command SetOTPParam. These values are copied in the RAM registers during power on reset.
AMI Semiconductor – Apr. 2007, Rev 3.1, M-20664-003
37
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