1. Sensorless position control of direct driven hydraulic actuators Master’s thesis seminar presentation
Tom Sourander
Aalto University
School of Engineering
Department of Mechanical Engineering

2. Introduction
In the Tubridi, Hyblab research project, original mining loader was retrofitted and full-scale series hybrid electric powertrain prototype was built.
The main target in the EL-Zon project is to investigate Direct Driven Hydraulics (DDH)

3. Background of Zonal hydraulics and Direct Driven Hydraulic (DDH) system
Application of Zonal or Decentralized Hydraulic approach to Off-road machinery:
Realized with Direct Driven Hydraulics

4. Thesis goal Main goal: The method:
Estimate the positions of DDH driven cylinders
Inputs only from servo motor torque and speed measurements
The method:
Cylinder movement calculations by simulation
Use simulation results to calculate cylinder position from measured motor drive data

5. Why sensorless positioning
Position sensors surprisingly expensive
Cylinder embedded sensors increase cost and complexity
Requires deep hole drilling of the piston
Can increase cylinder length
Changing sensors requires to remove the entire cylinder
External sensors more vulnerable to damage
Cabling and connectors problematic in harsh environments
Sensorless system replaces sensors and brings redundancy
Is millimeter accuracy necessary? Is expensive sensor worth it?
Tom Sourander

6. The research platform: EJC-90 mine loader DDH units
Component 1
Electric motor 2
B-side pump 3
A-side pumps 4
Pump pressure relief valve 5
Anti-cavitation valve 6
Safety valves 7
Hydraulic cylinder 8
Battery 9
Motor controller
Tom Sourander

7. Simulation model with Simulink Simscape
Hydraulic dynamics dependent on kinematics
Combine Simscape hydraulic blocks with multibody simulation
Kinematics time consuming to solve analytically
Physical simulation with Simscape multibody blocks

8. Simulation between the pump and cylinders
Electrical
Hydraulic
Mechanical
Rotational speed
Rotational speed
Fluid flow into cylinder – flow losses
Fluid flow into cylinder – flow losses
Cylinder movement
Cylinder movement
Oil temperature
Electric servo motor controller
Pump leakage  flow losses
Pump leakage  flow losses
Change in center of mass
External load mass
Torque
Torque
Fluid pressure
Fluid pressure
Cylinder forces
Cylinder forces
Measure motor torque and speed
Simulate flow losses
Calculate cylinder position

9. Sensorless positioning simulation
Simulate multiple lifting and lowering cycles
Constant cylinder forces from 1 kN to pressure relief valve limit
Oil temperatures from -5 to 80 °C
Motor speeds with low, medium and maximum (6000 rpm) speed ranges
Record cylinder movements by motor turn count in function of mean motor torque (mm/rev by Nm) into lookup tables
Use the lookup tables to estimate cylinder movements in the real system

10. Lookup tables for cylinder movements
Up movement
Down movement

11. Real-time control system
ControlDesk GUI
Control input
Joystick: movement speed
Automation: cylinder position
RTI computer: MicroAutoBox
Motor
Input
Desired motor speed
Control software
(Manual speed control or PID position control)
Motor controller
User
(Joystick or automation)
Position feedback
Calculated cylinder position
Motor controller sensor output:
Rotational speed
Torque
Sensorless position calculation
(Compare to simulation results)
Oil temperature

12. Simulation validation results: Boom and bucket cylinder errors at different loads
Light: ¼ Oil temperature: 40 °C
Medium: ½
High: ¾
Maximum: relief valve limit

13. Results from off-line measurements with soft limits
Boom cylinder, 1040 kg load
Bucket cylinder, 1040 kg load
Measured real and calculated position
Difference between measured and calculated position
Calculated position creeps up due to rough motor control

14. Boom and bucket motor speeds
Small boom motor holding speed causes the boom cylinder creep 14

15. Bucket lower tip position error, 1040 kg load
Orange: Real
Grey: Sensorless

16. Results with sensorless position control
Bucket cylinder position
Boom cylinder position
Bucket cylinder position error
Boom cylinder position error

17. Results with sensorless position control with reference points
Bucket cylinder position
Boom cylinder position
Bucket cylinder position error
Boom cylinder position error

18. Conclusions
Virtual position sensor is fine for centimeter-scale accuracy
Reference point compensation helps with successive cycles
Future work:
More accurate simulation model
Cylinder frictions
Secondary leakages (pressure relief valves)
More attention to acceleration and deceleration phases
Better position and motor controller tuning
More varied and realistic work cycle