DOKK / manpages / debian 12 / linuxcnc-uspace / bldc.9.en
BLDC(9) HAL Component BLDC(9)

bldc - BLDC and AC-servo control component

loadrt bldc cfg=qi6,aH

This component is designed as an interface between the most common forms of three-phase motor feedback devices and the corresponding types of drive. However, there is no requirement that the motor and drive should necessarily be of inherently compatible types.

Each instance of the component is defined by a group of letters describing the input and output types. A comma separates individual instances of the component. For example loadrt bldc cfg=qi6,aH.

Input type definitions are all lower-case.

n No motor feedback. This mode could be used to drive AC induction motors, but is also potentially useful for creating free-running motor simulators for drive testing.

h Hall sensor input. Brushless DC motors (electronically commutated permanent magnet 3-phase motors) typically use a set of three Hall sensors to measure the angular position of the rotor. A lower-case h in the cfg string indicates that these should be used.

a Absolute encoder input. (Also possibly used by some forms of Resolver conversion hardware). The presence of this tag over-rides all other inputs. Note that the component still requires to be be connected to the rawcounts encoder pin to prevent loss of commutation on index-reset.

q Incremental (quadrature) encoder input. If this input is used then the rotor will need to be homed before the motor can be run.

i Use the index of an incremental encoder as a home reference.

f Use a 4-bit Gray-scale patttern to determine rotor alignment. This scheme is only used on the Fanuc "Red Cap" motors. This mode could be used to control one of these motors using a non-Fanuc drive.

Output type descriptions are all upper-case.

Defaults The component will always calculate rotor angle, phase angle and the absolute value of the input value for interfacing with drives such as the Mesa 8I20. It will also default to three individual, bipolar phase output values if no other output type modifiers are used.

B Bit level outputs. Either 3 or 6 logic-level outputs indicating which high or low gate drivers on an external drive should be used.

6 Create 6 rather than the default 3 outputs. In the case of numeric value outputs these are separate positive and negative drive amplitudes. Both have positive magnitude.

H Emulated Hall sensor output. This mode can be used to control a drive which expects 3x Hall signals, or to convert between a motor with one hall pattern and a drive which expects a different one.

F Emulated Fanuc Red Cap Gray-code encoder output. This mode might be used to drive a non-Fanuc motor using a Fanuc drive intended for the "Red-Cap" motors.

T Force Trapezoidal mode.

The component can control a drive in either Trapezoidal or Sinusoidal mode, but will always default to sinusoidal if the input and output modes allow it. This can be over-ridden by the T tag. Sinusoidal commutation is significantly smoother (trapezoidal commutation induces 13% torque ripple).

To use an encoder for commutation a reference 0-degrees point must be found. The component uses the convention that motor zero is the point that an unloaded motor aligns to with a positive voltage on the A (or U) terminal and the B & C (or V and W) terminals connected together and to -ve voltage. There will be two such positions on a 4-pole motor, 3 on a 6-pole and so on. They are all functionally equivalent as far as driving the motor is concerned. If the motor has Hall sensors then the motor can be started in trapezoidal commutation mode, and will switch to sinusoidal commutation when an alignment is found. If the mode is qh then the first Hall state-transition will be used. If the mode is qhi then the encoder index will be used. This gives a more accurate homing position if the distance in encoder counts between motor zero and encoder index is known. To force homing to the Hall edges instead simply omit the i.

Motors without Hall sensors may be homed in synchronous/direct mode. The better of these options is to home to the encoder zero using the iq config parameter. When the init pin goes high the motor will rotate (in a direction determined by the rev pin) until the encoder indicates an index-latch (the servo thread runs too slowly to rely on detecting an encoder index directly). If there is no encoder index or its location relative to motor zero can not be found, then an alternative is to use magnetic homing using the q config. In this mode the motor will go through an alignment sequence ending at motor zero when the init pin goes high It will then set the final position as motor zero. Unfortunately the motor is rather springy in this mode and so alignment is likely to be fairly sensitive to load.

Hall sensor signal 1
Hall sensor signal 2
Hall sensor signal 3
Indicates that the selected hall pattern gives inconsistent rotor position data. This can be due to the pattern being wrong for the motor, or one or more sensors being unconnected or broken. A consistent pattern is not neceesarily valid, but an inconsistent one can never be valid.
Fanuc Gray-code bit 0 input
Fanuc Gray-code bit 1 input
Fanuc Gray-code bit 2 input
Fanuc Gray-code bit 3 input
PWM master amplitude input
The phase lead between the electrical vector and the rotor position in degrees
Set this pin true to reverse the motor. Negative PWM amplitudes will alsoreverse the motor and there will generally be a Hall pattern that runs the motor in each direction too.
Frequency input for motors with no feedback at all, or those with only an index (which is ignored)
The current to be used for the homing sequence in applications where an incremental encoder is used with no hall-sensor feedback
Encoder counts input. This must be linked to the encoder rawcounts pin or encoder index resets will cause the motor commutation to fail.
This pin should be connected to the associated encoder index-enable pin to zero the encoder when it passes index. This is only used indicate to the bldc control component that an index has been seen.
A rising edge on this pin starts the motor alignment sequence. This pinshould be connected in such a way that the motors re-align any time that encoder monitoring has been interrupted. Typically this will only be at machine power-off. The alignment process involves powering the motor phases in such a way as to put the motor in a known position. The encoder counts are then stored in the offset parameter. The alignment process will tend to cause a following error if it is triggered while the axis is enabled, so should be set before the matching axis.N.enable pin. The complementary init-done pin can be used to handle the required sequencing.

Both pins can be ignored if the encoder offset is known explicitly, such as is the case with an absolute encoder. In that case the offset parameter can be set directly in the HAL file.

Indicates homing sequence complete.
Output amplitude for phase A
Output amplitude for phase B
Output amplitude for phase C
Output bit for phase A
Output bit for phase B
Output bit for phase C
High-side driver for phase A
High-side driver for phase B
High-side driver for phase C
Low-side driver for phase A
Low-side driver for phase B
Low-side driver for phase C
High-side driver for phase A
High-side driver for phase B
High-side driver for phase C
Low-side driver for phase A
Low-side driver for phase B
Low-side driver for phase C
Hall 1 output
Hall 2 output
Hall 3 output
Fanuc Gray-code bit 0 output
Fanuc Gray-code bit 1 output
Fanuc Gray-code bit 2 output
Fanuc Gray-code bit 3 output
Phase angle including lead/lag angle after encoder zeroing, etc. Useful for angle/current drives. This value has a range of 0 to 1 and measures electrical revolutions. It will have two zeros for a 4 pole motor, three for a 6-pole, etc.
Rotor angle after encoder zeroing etc. Useful for angle/current drives which add their own phase offset such as the 8I20. This value has a range of 0 to 1 and measures electrical revolutions. It will have two zeros for a 4 pole motor, three for a 6-pole, etc.
Current output, including the effect of the dir pin and the alignment sequence.
Direction output, high if /fBvalue/fR is negative XOR /fBrev/fR is true.
Absolute value of the input value

state machine output, will probably hide after debug
state machine output, will probably hide after debug
The number of encoder counts per rotor revolution.
The number of motor poles. The encoder scale will be divided by this value to determine the number of encoder counts per electrical revolution.
The offset, in encoder counts, between the motor electrical zero and the encoder zero modulo the number of counts per electrical revolution
The encoder offset measured by the homing sequence (in certain modes)
The angle, in degrees, applied to the commanded angle by the drive in degrees. This value is only used during the homing sequence of drives with incremental encoder feedback. It is used to back-calculate from commanded angle to actual phase angle. It is only relevant to drives which expect rotor-angle input rather than phase-angle demand. Should be 0 for most drives.
Commutation pattern to be output in Hall Signal translation mode. See the description of /fBpattern/fR for details.
Commutation pattern to use, from 0 to 47. Default is type 25. Every plausible combination is included. The table shows the excitation pattern along the top, and the pattern code on the left hand side. The table entries are the hall patterns in H1, H2, H3 order. Common patterns are: 0 (30 degree commutation) and 26, its reverse. 17 (120 degree). 18 (alternate 60 degree). 21 (300 degree, Bodine). 22 (240 degree). 25 (60 degree commutation).

Note that a number of incorrect commutations will have non-zero net torque which might look as if they work, but don't really.

If your motor lacks documentation it might be worth trying every pattern.

Phases, Source - Sink
pat B-A C-A C-B A-B A-C B-C
0 000 001 011 111 110 100
1 001 000 010 110 111 101
2 000 010 011 111 101 100
3 001 011 010 110 100 101
4 010 011 001 101 100 110
5 011 010 000 100 101 111
6 010 000 001 101 111 110
7 011 001 000 100 110 111
8 000 001 101 111 110 010
9 001 000 100 110 111 011
10 000 010 110 111 101 001
11 001 011 111 110 100 000
12 010 011 111 101 100 000
13 011 010 110 100 101 001
14 010 000 100 101 111 011
15 011 001 101 100 110 010
16 000 100 101 111 011 010
17 001 101 100 110 010 011
18 000 100 110 111 011 001
19 001 101 111 110 010 000
20 010 110 111 101 001 000
21 011 111 110 100 000 001
22 010 110 100 101 001 011
23 011 111 101 100 000 010
24 100 101 111 011 010 000
25 101 100 110 010 011 001
26 100 110 111 011 001 000
27 101 111 110 010 000 001
28 110 111 101 001 000 010
29 111 110 100 000 001 011
30 110 100 101 001 011 010
31 111 101 100 000 010 011
32 100 101 001 011 010 110
33 101 100 000 010 011 111
34 100 110 010 011 001 101
35 101 111 011 010 000 100
36 110 111 011 001 000 100
37 111 110 010 000 001 101
38 110 100 000 001 011 111
39 111 101 001 000 010 110
40 100 000 001 011 111 110
41 101 001 000 010 110 111
42 100 000 010 011 111 101
43 101 001 011 010 110 100
44 110 010 011 001 101 100
45 111 011 010 000 100 101
46 110 010 000 001 101 111
47 111 011 001 000 100 110

Andy Pugh

GPL

2023-02-10 LinuxCNC Documentation