Timer set up as Quadrature encoder - question

Further reading in the Reference Manual, I think this Polarity select bit is mean to select inverted or non-inverted signal of the input channel (TI1 or TI2), and not meant to say the triggering edge (In the CubeMX this should say 'Inverted Input' or 'non-inverted input' instead of Rising Edge  or Falling Edge. And of course the Both Edge selection should be deleted from the pull down box. 

Hello !

The encoder(MCU)  takes as Input  two digital lines  .

 Theese lines carry 2 bit of information.

The information is just edges and states with 90 deg. phase difference.

The encoder gives an output  data also with two bits of information

One bit is the counter revolution and the other bit is the direction.

It is not possible to have 4x resolution without lose the direction.

So if you detect both edges at one channel there will be an ambiguity about the direction because the edge from other channel will be occur at 180 degrees...  in the midle of the two detected edges..  and so on.

In case the polarities are different  the direction changes (it is not something abnormal)

About  'Both Edge selection' in STM32 cube i think also that must be eliminated.

Regards

vf

Hi VF,

'

It is not possible to have 4x resolution without lose the direction.'

4X resolution means the encoder counter has an output count of 4X the resolution lines on the encoder disc or scale; i.e. a 1000-line optical disc will generate a total 4000 counts in one turn of the disc. This is a very common standard in the motion industry. 

'

So if you detect both edges at one channel there will be an ambiguity about the direction because the edge from other channel will be occur at 180 degrees...' 

This is not quite true. In Encoder Mode, the user can select to count only on one input, TI1 (2X resolution) or TI2 (2X res) , or both inputs (4X res), by setting SMS bits of TIMx_SMCR register, and regardless of counting only one or both inputs the counter always triggers on BOTH EDGES, no option about this.

The Direction is determined by the logic state of the other input (90* out of phase from the one having triggering edge). Review the Encoder Mode in the Reference Manual rev1, Figure 170 will show how it works in 4X resulution (4 counts in one period of  input channel).

Best,

Brian

Hi VF,

We're discussing the STM32 Timer works in  Encoder Mode, and so I take encoder as quadrature or 2X encoder, anything with 50% duty signal waveform including washer machine motor encoder, angle sensor or even gyro, as long as their outputs the definition of 2X or 4X encoder signal.

'

In this figure you supposed that the direction is given and you wrote that the resolution is x4. But the direction is not given. It takes at least a whole pulse to have certainty about direction.'

The direction is given within a count unit of the resolution. what do you mean 'a whole pulse'? A full period of TI1 or TI2? The direction is ambiguity only within a 1/4 of the input pulse period, just as the encoder count resolution. The counter in Fig 170 starts from 0 and counting up, and so when the count changed from 0 to 1, we can tell that it's counting up or moving CW, or when it changed from 10 to 9 then it is moving CCW. No direction? In fact there is a register (TIMx_DIR) that can be read for Direction. 

Btw, do anyone know why clicking the ST logo on the upper left corner of this page does not return to ST.com home page? How do you get back to ST home?

Best,

Brian

VF,

So you said there was direction ambiguity for half of a line resolution of the encoder disc (a line resolution is the spatial includes the dark and clear of the lines). No, in quadrature encoder both the count and direction have resolution within ¼ of the lines resolution, not ½ as you think.

Reference to Fig 7 above and during the time t that you highlighted, TI1 doing up, down, up while TI2 stays low, the counter went through 3 events: +1, -1, +1, although in the Fig 7 it doesn’t show the counter is counting during the highlighted zone for some reasons, but I’m pretty sure in reality it counted +1, -1, +1 and the DIR bit changed accordingly.

Best,

Brian