Figure 1.
Graphical view of the initial SPECTA concept [
39].
Figure 1.
Graphical view of the initial SPECTA concept [
39].
Figure 2.
Overview of the SPEA architecture, which can be divided into iSPEA and +SPEA. (
a) iSPEA schematic, consisting of parallel branches with springs that can be variably recruited by one motor that moves using a dephased intermittent mechanism, represented by the blue rectangle. (
b) +SPEA schematic, which consists of parallel branches, each with a motor that can variably recruit the spring present in their unit. Additionally, a Non-Backdrivable Mechanism (NBM) is added to lock the motor such that the spring can be tensioned without drawing power from the motor. Adapted from [
31].
Figure 2.
Overview of the SPEA architecture, which can be divided into iSPEA and +SPEA. (
a) iSPEA schematic, consisting of parallel branches with springs that can be variably recruited by one motor that moves using a dephased intermittent mechanism, represented by the blue rectangle. (
b) +SPEA schematic, which consists of parallel branches, each with a motor that can variably recruit the spring present in their unit. Additionally, a Non-Backdrivable Mechanism (NBM) is added to lock the motor such that the spring can be tensioned without drawing power from the motor. Adapted from [
31].
Figure 3.
Overview of the SPECTA actuator for case 2. The blocks with and represent respectively the electromagnetic clutch at the input, the ratchet and pawl system to lock the spring, and the electromagnetic clutch at the output. The electromagnetic clutches are represented by the red boxes, whereas the ratchet and pawl mechanisms—by the blue boxes for clarity.
Figure 3.
Overview of the SPECTA actuator for case 2. The blocks with and represent respectively the electromagnetic clutch at the input, the ratchet and pawl system to lock the spring, and the electromagnetic clutch at the output. The electromagnetic clutches are represented by the red boxes, whereas the ratchet and pawl mechanisms—by the blue boxes for clarity.
Figure 4.
Visualization of the different states of the used locking mechanisms. The blue boxes always represent a ratchet and pawl mechanism and the red boxes always represent an electromagnetic clutch. Here, the visualization of the variable is not shown explicitly, but it is the same as for .
Figure 4.
Visualization of the different states of the used locking mechanisms. The blue boxes always represent a ratchet and pawl mechanism and the red boxes always represent an electromagnetic clutch. Here, the visualization of the variable is not shown explicitly, but it is the same as for .
Figure 5.
View of a specific configuration of the SPECTA actuator. In this configuration, the spring of the first constant torque unit (top branch) is charged by the motor, whereas the spring of the second constant torque unit (lowest branch) is in direct contact with the load. In this example, the constant torque units are coupled to the output axis by a belt (gray band) and for both units, the ratchet and pawl are in their unlocked state. The stiff (continuous torque) unit, which is shown in the middle branch, is coupled directly to the output (load).
Figure 5.
View of a specific configuration of the SPECTA actuator. In this configuration, the spring of the first constant torque unit (top branch) is charged by the motor, whereas the spring of the second constant torque unit (lowest branch) is in direct contact with the load. In this example, the constant torque units are coupled to the output axis by a belt (gray band) and for both units, the ratchet and pawl are in their unlocked state. The stiff (continuous torque) unit, which is shown in the middle branch, is coupled directly to the output (load).
Figure 6.
Comparison of the total energy consumption for moving a 1 DOF link at Nm for an entire range of and . The left part represents the consumption of a SPECTA actuator, whereas the figure to the right represents the consumption of an equivalent stiff actuator. In this simulation, an ideal constant torque spring is assumed. Here, all simulations point out that the most energetic optimal SPECTA is the one where only one spring is recruited, namely, the one that is connected to the high-speed motor.
Figure 6.
Comparison of the total energy consumption for moving a 1 DOF link at Nm for an entire range of and . The left part represents the consumption of a SPECTA actuator, whereas the figure to the right represents the consumption of an equivalent stiff actuator. In this simulation, an ideal constant torque spring is assumed. Here, all simulations point out that the most energetic optimal SPECTA is the one where only one spring is recruited, namely, the one that is connected to the high-speed motor.
Figure 7.
Overview of the gain in total energy consumption for moving a 1 DOF link at Nm for a SPECTA actuator in comparison to an equivalent stiff actuator. In this simulation, an ideal constant torque spring is assumed. The values of energy consumption that are positive represent the regions where a SPECTA actuator uses less energy than the stiff equivalent for the same task. In the regions where the value is smaller than zero, the stiff actuator uses less energy.
Figure 7.
Overview of the gain in total energy consumption for moving a 1 DOF link at Nm for a SPECTA actuator in comparison to an equivalent stiff actuator. In this simulation, an ideal constant torque spring is assumed. The values of energy consumption that are positive represent the regions where a SPECTA actuator uses less energy than the stiff equivalent for the same task. In the regions where the value is smaller than zero, the stiff actuator uses less energy.
Figure 8.
Overview of (a) the angle of each of the units, (b) the rotational speed of the units, (c) the torque of each unit, (d) the states of the ratchet and pawl mechanism of each unit, and (e) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of for a SPECTA with an ideal constant torque spring that is not charged yet.
Figure 8.
Overview of (a) the angle of each of the units, (b) the rotational speed of the units, (c) the torque of each unit, (d) the states of the ratchet and pawl mechanism of each unit, and (e) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of for a SPECTA with an ideal constant torque spring that is not charged yet.
Figure 9.
Torque–angle plot of the constant torque spring behavior used in the simulations.
Figure 9.
Torque–angle plot of the constant torque spring behavior used in the simulations.
Figure 10.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with an ideal constant torque spring.
Figure 10.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with an ideal constant torque spring.
Figure 11.
Overview of (a) the angle of each of the units, (b) the rotational speed of the units, (c) the torque of each unit, (d) the states of the ratchet and pawl mechanism of each unit, and (e) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of with an ideal constant torque spring. In these plots, the subscripts “CT,1” and “CT,2” indicate, respectively, the first and second constant torque unit, the subscript “3” indicates the last (continuous) unit.
Figure 11.
Overview of (a) the angle of each of the units, (b) the rotational speed of the units, (c) the torque of each unit, (d) the states of the ratchet and pawl mechanism of each unit, and (e) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of with an ideal constant torque spring. In these plots, the subscripts “CT,1” and “CT,2” indicate, respectively, the first and second constant torque unit, the subscript “3” indicates the last (continuous) unit.
Figure 12.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with an ideal constant torque spring.
Figure 12.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with an ideal constant torque spring.
Figure 13.
Overview of the gain in total energy consumption for moving a 1 DOF link at Nm for a SPECTA actuator that is ideal in comparison to a SPECTA actuator that has springs which showcase 10% hysteresis. The values of energy consumption that are positive represent the regions where the ideal spring SPECTA actuator uses less energy than the one that has hysteresis for the same task.
Figure 13.
Overview of the gain in total energy consumption for moving a 1 DOF link at Nm for a SPECTA actuator that is ideal in comparison to a SPECTA actuator that has springs which showcase 10% hysteresis. The values of energy consumption that are positive represent the regions where the ideal spring SPECTA actuator uses less energy than the one that has hysteresis for the same task.
Figure 14.
Overview of (a) the rotational speed of the units, (b) the torque of each unit, (c) the states of the ratchet and pawl mechanism of each unit, and (d) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of with a constant torque spring that has hysteresis. In these plots, the subscripts “CT,1” and “CT,2” indicate, respectively, the first and second constant torque unit, the subscript “3” indicates the last (continuous) unit.
Figure 14.
Overview of (a) the rotational speed of the units, (b) the torque of each unit, (c) the states of the ratchet and pawl mechanism of each unit, and (d) the states of the output clutch mechanism of each unit. These simulations were performed for a task angle with a variation of with a constant torque spring that has hysteresis. In these plots, the subscripts “CT,1” and “CT,2” indicate, respectively, the first and second constant torque unit, the subscript “3” indicates the last (continuous) unit.
Figure 15.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with a constant torque spring that has hysteresis. In comparison with case 1, only the Joule losses and gearing losses have changed (increased).
Figure 15.
Overview of the different types of losses. These are (a) the Joule losses, (b) the friction losses, and (c) the gearing losses. These simulations were performed for a task angle with a variation of with a constant torque spring that has hysteresis. In comparison with case 1, only the Joule losses and gearing losses have changed (increased).
Figure 16.
Different views of the constant torque unit that is driven by a high-speed motor (EC4-Pole motor). This unit consists of (1) a DC motor, (2) a torque sensor, (3) an electromagnetic clutch on motor side, (4) a supporting piece for the encoder reader, (5) an optical encoder disc, (6) a constant torque spring, (7) a ratchet and pawl system, (8) a supporting piece with solenoid, (9) an electromagnetic clutch on load side, (10) a pulley, (11) an auxiliary axis for the constant torque spring. (a) Panoramic view of the constant torque unit with high-speed motor. (b) Side view of the constant torque unit with high-speed motor.
Figure 16.
Different views of the constant torque unit that is driven by a high-speed motor (EC4-Pole motor). This unit consists of (1) a DC motor, (2) a torque sensor, (3) an electromagnetic clutch on motor side, (4) a supporting piece for the encoder reader, (5) an optical encoder disc, (6) a constant torque spring, (7) a ratchet and pawl system, (8) a supporting piece with solenoid, (9) an electromagnetic clutch on load side, (10) a pulley, (11) an auxiliary axis for the constant torque spring. (a) Panoramic view of the constant torque unit with high-speed motor. (b) Side view of the constant torque unit with high-speed motor.
Figure 17.
Panoramic view of the constant torque unit that is driven by a high-torque motor (EC Flat motor). Only encoders are included in this unit as measuring tools, no torque sensors.
Figure 17.
Panoramic view of the constant torque unit that is driven by a high-torque motor (EC Flat motor). Only encoders are included in this unit as measuring tools, no torque sensors.
Figure 18.
Different views of the output branch, which contains both the variable torque unit and the output load, which are linked together. This unit consists of (1) a DC motor that is driving the variable torque unit, (2) a connection piece, (3) the output axis, (4) two pulleys to couple the other units to the output axis, (5) a connection piece, (6) a gearbox, (7) bellow couplings, (8) a torque sensor, (9) the load motor. (a) Panoramic view of the output branch (variable torque unit and output load). (b) Side view of the output branch.
Figure 18.
Different views of the output branch, which contains both the variable torque unit and the output load, which are linked together. This unit consists of (1) a DC motor that is driving the variable torque unit, (2) a connection piece, (3) the output axis, (4) two pulleys to couple the other units to the output axis, (5) a connection piece, (6) a gearbox, (7) bellow couplings, (8) a torque sensor, (9) the load motor. (a) Panoramic view of the output branch (variable torque unit and output load). (b) Side view of the output branch.
Figure 19.
Panoramic view of the complete test bench, which contains both constant torque units and the variable torque unit with output. In this setup, one of the constant torque units is turned such that both can deliver positive torque.
Figure 19.
Panoramic view of the complete test bench, which contains both constant torque units and the variable torque unit with output. In this setup, one of the constant torque units is turned such that both can deliver positive torque.
Figure 20.
View of the experimental SPECTA set-up.
Figure 20.
View of the experimental SPECTA set-up.
Figure 21.
Overview of the simulink script that was used to perform the tests. All motors were separately tuned and some safety mechanisms were added.
Figure 21.
Overview of the simulink script that was used to perform the tests. All motors were separately tuned and some safety mechanisms were added.
Figure 22.
Experimental tests of the working range of a constant torque spring that is dimensioned to deliver 0.3 Nm. This theoretical value is indicated in orange, whereas the measured torque is indicated in blue.
Figure 22.
Experimental tests of the working range of a constant torque spring that is dimensioned to deliver 0.3 Nm. This theoretical value is indicated in orange, whereas the measured torque is indicated in blue.
Figure 23.
Overview of the motor torques (after the gearbox) of (a) the first (high-torque motor) unit and (b) the last (continuous torque) unit, together with (c) the torque and (d) velocity values at the output. For each plot, both the simulated (orange) and measured (blue) data are included. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Figure 23.
Overview of the motor torques (after the gearbox) of (a) the first (high-torque motor) unit and (b) the last (continuous torque) unit, together with (c) the torque and (d) velocity values at the output. For each plot, both the simulated (orange) and measured (blue) data are included. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Figure 24.
Overview of (a) the motor current and (b) voltage of the first unit, together with (c) its electrical energy consumption. The (d) motor current, (e) voltage, and (f) electrical energy consumption of the last (continuous torque) unit are also shown. For each plot, both the simulated (orange) and measured (blue) data are plotted. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Figure 24.
Overview of (a) the motor current and (b) voltage of the first unit, together with (c) its electrical energy consumption. The (d) motor current, (e) voltage, and (f) electrical energy consumption of the last (continuous torque) unit are also shown. For each plot, both the simulated (orange) and measured (blue) data are plotted. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Figure 25.
Overview of both the measured (a) and simulated (b) energy losses of the individual units together with the total consumed energy. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Figure 25.
Overview of both the measured (a) and simulated (b) energy losses of the individual units together with the total consumed energy. These data were retrieved when performing/simulating a pendulum task for a task angle and a variation of .
Table 1.
Nomenclature of the SPECTA concept.
Table 1.
Nomenclature of the SPECTA concept.
Symbol | Explanation | Unit |
---|
| Inertia of motor and transmission | kgm |
| Viscous friction coefficient | Nms/rad |
| Torque constant of the motor | Nm/A |
R | Motor resistance | |
| Motor/Spring/Output angle | rad |
| Motor/Spring velocity | rad/s |
| Motor/Spring acceleration | rad/s |
| State of the clutch between (motor and spring)/(spring and output) | / |
| State of the ratchet and pawl mechanisms | / |
U | Motor voltage | V |
I | Motor current | A |
P | Motor power | W |
| Torque level of the CT spring | Nm |
| Maximum hysteresis amplitude of the of the CT spring | Nm |
n | Transmission ratio | / |
| Efficiency function of the transmission | / |
| Maximum efficiency of the transmission | / |
Table 2.
Overview of how the speed of the constant torque spring is defined for case 2 with respect to the clutch, ratchet, and pawl variables. The value 0 represents the upper state of all colored boxes (in
Figure 3), whereas the value 1 represents the lower state of the colored boxes. This explanation is also shown in
Figure 4.
Table 2.
Overview of how the speed of the constant torque spring is defined for case 2 with respect to the clutch, ratchet, and pawl variables. The value 0 represents the upper state of all colored boxes (in
Figure 3), whereas the value 1 represents the lower state of the colored boxes. This explanation is also shown in
Figure 4.
| | | |
---|
0 | 0 | 0 | 0 |
1 | 0 | 0 | |
0 | 1 | 0 | |
0 | 0 | 1 | |
1 | 1 | 0 | |
1 | 0 | 1 | |
0 | 1 | 1 | |
1 | 1 | 1 | |
Table 3.
Overview of the experiments that will be shown in this paper. For the simulations, all details were performed, but only two working points are shown in detail in this paper to avoid repetition. All shown experiments were performed for a gravitational torque () of 15 Nm.
Table 3.
Overview of the experiments that will be shown in this paper. For the simulations, all details were performed, but only two working points are shown in detail in this paper to avoid repetition. All shown experiments were performed for a gravitational torque () of 15 Nm.
Simulations | |
---|
| Case 1 | Case 2 |
---|
What is shown in the paper | | | | |
Energy consumption | | | | |
Specific energy losses | 70 | 10 | 70 | 10 |
+θ, , T, λ and γ | 120 | 20 | | |
Experimental Testing | | | | |
What is shown in the paper | | | | |
All relevant data (Torque, velocity, voltage, current, energy consumption, etc.) | 90 | 5 | | |
Table 4.
Characteristics of the selected high-speed motor (Maxon EC-4pole, Brushless motor, 120 W, part number 311536) and the corresponding gearbox (Maxon GP22HP, part number 370784).
Table 4.
Characteristics of the selected high-speed motor (Maxon EC-4pole, Brushless motor, 120 W, part number 311536) and the corresponding gearbox (Maxon GP22HP, part number 370784).
High-Speed Motor | |
---|
| = | | kgm | | = | 24 | V |
| = | | Nm/A | | = | | A |
| = | | Nms/rad | R | = | | |
| = | | mNm | | = | 25 000 | rpm |
Gearbox | |
i | = | | | | = | | kgm |
| = | 59 | % | | = | | Nm |
Table 5.
Characteristics of the selected high-torque motor (Maxon EC 60 Flat, Brushless motor, 200 W, part number 614949). Since this is a high-torque motor, no gearing is coupled directly to it.
Table 5.
Characteristics of the selected high-torque motor (Maxon EC 60 Flat, Brushless motor, 200 W, part number 614949). Since this is a high-torque motor, no gearing is coupled directly to it.
High-Torque Motor | |
---|
| = | | kgm | | = | 24 | V |
| = | | Nm/A | | = | | A |
| = | | Nms/rad | R | = | | |
| = | 536 | mNm | | = | 6 000 | rpm |
Table 6.
Characteristics of the selected load motor (Maxon RE 50, Brushed motor, 200 W, part number 370,354) and its corresponding gearbox (Maxon GP 62 A, part number 110,506).
Table 6.
Characteristics of the selected load motor (Maxon RE 50, Brushed motor, 200 W, part number 370,354) and its corresponding gearbox (Maxon GP 62 A, part number 110,506).
Load Motor | |
---|
| = | | kgm | | = | 24 | V |
| = | | Nm/A | | = | | A |
| = | | Nms/rad | R | = | | |
| = | 405 | mNm | | = | 9500 | rpm |
Gearbox Load | |
---|
i | = | | | | = | | kgm |
| = | 70 | % | | = | 50 | Nm |