Skip to main content

LUP Student Papers

LUND UNIVERSITY LIBRARIES

DC Motor Control without Encoder - A Ripple Based Approach

Björnberg, Axel LU and Vesterlund, Jonathan LU (2024) In CODEN:LUTEDX/TEIE EIEM01 20241
Industrial Electrical Engineering and Automation
Abstract
The goal of this master thesis was to identify an alternative to shaft encoders as
means of achieving accurate motor velocity and position control for sliding door
systems. While the company had previously explored methods like using backEMF, this thesis investigates counting voltage ripples during the commutation
process in a brushed DC motor. During commutation, one or two pairs of commutator segments contact the brushes simultaneously, periodically changing the motor’s
impedance. With a constant current, this creates a ripple observable on the voltage.
Through a series of experiments, it was possible to produce a clear ripple signal
originating from the commutator commutation. This was done even though high
frequency switching of... (More)
The goal of this master thesis was to identify an alternative to shaft encoders as
means of achieving accurate motor velocity and position control for sliding door
systems. While the company had previously explored methods like using backEMF, this thesis investigates counting voltage ripples during the commutation
process in a brushed DC motor. During commutation, one or two pairs of commutator segments contact the brushes simultaneously, periodically changing the motor’s
impedance. With a constant current, this creates a ripple observable on the voltage.
Through a series of experiments, it was possible to produce a clear ripple signal
originating from the commutator commutation. This was done even though high
frequency switching of the internal H-bridge used for motor control was utilized. By
employing a series of filters and amplifiers, coupled with Arduino microcontrollers,
noise could be removed and the wanted signal amplified. The signal was then used
to produce a square wave representing the commutation ripple. This square wave
could then be read by an Arduino using an interrupt pin.
For the software solutions, a moving average, a finite state machine (FSM), and
a solution to remove multiple readings of a single ripples were used. These software
solutions was used in combination with the circuitry to further increase the accuracy
of the detection and counting of voltage ripple.
The resulting solution provided mostly correct velocity estimations as compared
to the onboard encoder. The difference being the lower resolution and some difficulties in recording all ripples. The performance was adequate at low to medium
velocities, but started to deviate at higher velocities as a result of, amongst other
factors, inadequate sampling rates. Another problem that was observed was the
loss of observable ripples during deceleration. This was theorized to be caused by
the way the signal was sampled from the H-bridge, whereas a differential reading
across the bridge might render better results.
This report shows that voltage ripples can track velocity and position. While the
current solution is insufficient for ripple-based motor control, future research based
on the produced findings might enable its implementation in the future. (Less)
Popular Abstract
Measuring DC motor position without an encoder?
This thesis explores using voltage and current ripples caused during commutation in brushed DC motors for velocity and position estimation, potentially reducing the need for expensive encoders by combining ripple detection with lower-resolution encoders.
Is it possible to avoid having to utilize expensive encoders for velocity and position estimation related to brushed DC motors? This is the question the authors of this thesis asked themselves when they set out to explore possible alternatives. It turns out that the voltage and current across a brushed DC motors are subject to small, repeating, pulsation or “ripples” that occur during the commutation process. This is caused by the fact that... (More)
Measuring DC motor position without an encoder?
This thesis explores using voltage and current ripples caused during commutation in brushed DC motors for velocity and position estimation, potentially reducing the need for expensive encoders by combining ripple detection with lower-resolution encoders.
Is it possible to avoid having to utilize expensive encoders for velocity and position estimation related to brushed DC motors? This is the question the authors of this thesis asked themselves when they set out to explore possible alternatives. It turns out that the voltage and current across a brushed DC motors are subject to small, repeating, pulsation or “ripples” that occur during the commutation process. This is caused by the fact that the brushes can make contact with either one or two commutator segments at the same time, depending upon whether the brushes are transitioning between two commutator segments or not. Because of this the impedance(also induced voltage) changes slightly in a periodical manner that is proportional to the velocity of the motor.
The main problem in using this phenomenon for measuring position and velocity lies in the ability to see them. As such, the authors explored a solution involving analogue filters, amplifiers and microcontrollers in order to find the ripples on a sliding door system, a common application of brushed DC motors. The results were promising at lower to medium velocities, but it was realized that the main problem standing in the way of better results at higher velocities was the limited sampling frequency of the microcontrollers. However, the results still indicate that current or voltage ripples likely can yield adequate velocity measurements. Even though the technique might not completely replace encoders, it might enable companies to use encoders of lower resolution via a combined ripple and encoder approach. Even if speed and position tracking is feasible at low and medium speeds, it is quite more challenging during acceleration and deceleration. (Less)
Please use this url to cite or link to this publication:
author
Björnberg, Axel LU and Vesterlund, Jonathan LU
supervisor
organization
alternative title
DC-motorstyrning utan positionsgivare - en rippelbaserad metod
course
EIEM01 20241
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Encoder Alternatives, Voltage Ripple, Brushed DC Motor, Ripple Detection, Commutation Process, Noise Removal, Arduino Microcontrollers, Velocity Estimation, Position Control, Sliding Door Systems, H-bridge, Signal Filtering, Moving Average, Finite State Machine, BACK EMF, Embedded Systems
publication/series
CODEN:LUTEDX/TEIE
report number
5513
language
English
id
9168761
date added to LUP
2025-02-05 16:49:49
date last changed
2025-02-05 16:49:49
@misc{9168761,
  abstract     = {{The goal of this master thesis was to identify an alternative to shaft encoders as
means of achieving accurate motor velocity and position control for sliding door
systems. While the company had previously explored methods like using backEMF, this thesis investigates counting voltage ripples during the commutation
process in a brushed DC motor. During commutation, one or two pairs of commutator segments contact the brushes simultaneously, periodically changing the motor’s
impedance. With a constant current, this creates a ripple observable on the voltage.
Through a series of experiments, it was possible to produce a clear ripple signal
originating from the commutator commutation. This was done even though high
frequency switching of the internal H-bridge used for motor control was utilized. By
employing a series of filters and amplifiers, coupled with Arduino microcontrollers,
noise could be removed and the wanted signal amplified. The signal was then used
to produce a square wave representing the commutation ripple. This square wave
could then be read by an Arduino using an interrupt pin.
For the software solutions, a moving average, a finite state machine (FSM), and
a solution to remove multiple readings of a single ripples were used. These software
solutions was used in combination with the circuitry to further increase the accuracy
of the detection and counting of voltage ripple.
The resulting solution provided mostly correct velocity estimations as compared
to the onboard encoder. The difference being the lower resolution and some difficulties in recording all ripples. The performance was adequate at low to medium
velocities, but started to deviate at higher velocities as a result of, amongst other
factors, inadequate sampling rates. Another problem that was observed was the
loss of observable ripples during deceleration. This was theorized to be caused by
the way the signal was sampled from the H-bridge, whereas a differential reading
across the bridge might render better results.
This report shows that voltage ripples can track velocity and position. While the
current solution is insufficient for ripple-based motor control, future research based
on the produced findings might enable its implementation in the future.}},
  author       = {{Björnberg, Axel and Vesterlund, Jonathan}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{CODEN:LUTEDX/TEIE}},
  title        = {{DC Motor Control without Encoder - A Ripple Based Approach}},
  year         = {{2024}},
}