**2. Description of test setup**

The experimental setup uses a speed-controlled electric servo motor drive rotating two hydraulic pumps to directly control the amount of hydraulic oil pumped to the asymmetrical double-acting cylinder MIRO C-10-60/30× 400. The simplified circuit diagram of the experi‐ mental test setup is illustrated in Figure 4. The hydraulic pump/motors P1 and P2 create an input and output flow that depends on the rotating speed of the servo motor. The oil pressure rises to the required level as determined by the payload. During lowering motion, the potential energy of the payload creates a flow that rotates the hydraulic machine P1 as a motor and the hydraulic machine P2 as a pump, and the mechanically connected electric motor acts as a generator, which is controlled by the frequency converter. The speed-controlled generator controls the amount of fluid flow and the position of the payload. The program for the electric drive controls both the electrical and hydraulic sides of the system as there is no conventional valve control.

pump/motors *D*1 and *D*2.

For easier understanding of the real displacements of the pumps, the following ratios *R*A and *R*Q will be defined. In this work, the ratio between the cylinder areas is defined by the following equation:

$$\mathcal{R}\_A = \frac{A\_3}{A\_1}\prime$$

where *A*<sup>3</sup> = *A*<sup>1</sup> − *A*2 is the cylinder area from the rod side. The diameter of the cylinder piston head is *d*1 = 0.06 m and *d*2 = 0.03 m is the diameter of the piston rod, which determines the piston surface areas A1 and A2. According to the datasheet, the cylinder stroke is *l* = 0.4 m.

As previously stated, the pump/motors P1 and P2 are mounted on the same axis, so their speeds are identical. If the pump leakage is ignored, the ratio of the flow rates *R*<sup>Q</sup> can be produced directly from the displacement of the pump/motors *D*1 and *D*2.

$$R\_{\odot} = \frac{D\_2}{D\_1}.$$

Figure 4 illustrates the first prototype of the DDH setup with *R*<sup>Q</sup> ≈0.63 and *RA* =0.75. To test the concept, the components for this prototype were taken off the shelf. ܴ୕ ൌ ܦଶ ଵܦ Ǥ (2) Figure 4 illustrates the first prototype of the DDH setup withܴ୕ ൎ ͲǤ͵ and ܴ ൌ ͲǤͷ. To test the concept, the

double-acting cylinder, (b) wire-actuated encoder, (c) pressure sensor, (d) reversible gear pump/motor P1, (e) pressure sensor, (f) gearbox, (g) PMSM motor/generator, (h) current sensors, (i) frequency converter, (j) tank, (k) pressure sensor, (l) reversible gear pump/motor P2 and (m) pressure sensor in the tank line; (c) the crane is used for the DDH setup as a test platform (side view). **Figure 4.** First prototype of the DDH setup: (a) zoom view;(b) the experimental setup consists ofa) a double-acting cyl‐ inder, b) wire-actuated encoder, c) pressure sensor, d) reversible gear pump/motor P1, e) pressure sensor, f) gearbox, g) PMSM motor/generator, h) current sensors, i)frequency converter, j) tank, k) pressure sensor, l) reversible gear pump/ motor P2 and m) pressure sensor in the tank line; (c) the crane is used for the DDH setup as a test platform (side view).

Figure 4. First prototype of the DDH setup: (a) zoom view; (b) the experimental setup consists of (a) a

Two XV-2M internal gear pump/motors by Vivoil with displacements of 14.4 and 22.8 cm<sup>3</sup> /rev were used, P2 and P1, respectively [20]. The position feedback from the motor is given by means of its in-built incremental encoder (4096 pulses per revolution, resolution 14 bits), and read with the Unidrive SP1406 drive software [21]. It converts Two XV-2M internal gear pump/motors by Vivoil with displacements of 14.4 and 22.8 cm3 /rev were used, P2 and P1, respectively [20]. The position feedback from the motor is given by means of its in-built incremental encoder (4096 pulses per revolution, resolution 14 bits), and read

for a motor speed of 400 rpm and a payload of 150 kg: speed, torque and pressure.

the AC power supply from the line and allows the speed of the permanent magnet brushless servo motor, Unimotor 115U2C manufactured by Emerson Control Techniques, to be set, taking advantage of the information obtained by the feedback device fitted to ensure the rotor speed is exactly as demanded [22]. This experimental setup was tested with a payload of 150 kg at motor speed ranges from 300 to 500 rpm. Figure 5 shows an example of measured data

with the Unidrive SP1406 drive software [21]. It converts the AC power supply from the line and allows the speed of the permanent magnet brushless servo motor, Unimotor 115U2C manufactured by Emerson Control Techniques, to be set, taking advantage of the information obtained by the feedback device fitted to ensure the rotor speed is exactly as demanded [22]. This experimental setup was tested with a payload of 150 kg at motor speed ranges from 300 to 500 rpm. Figure 5 shows an example of measured data for a motor speed of 400 rpm and a payload of 150 kg: speed, torque and pressure.

For easier understanding of the real displacements of the pumps, the following ratios *R*A and *R*Q will be defined. In this work, the ratio between the cylinder areas is defined by the following

> 3 1 , *<sup>A</sup> <sup>A</sup> <sup>R</sup> A* =

where *A*<sup>3</sup> = *A*<sup>1</sup> − *A*2 is the cylinder area from the rod side. The diameter of the cylinder piston head is *d*1 = 0.06 m and *d*2 = 0.03 m is the diameter of the piston rod, which determines the piston

As previously stated, the pump/motors P1 and P2 are mounted on the same axis, so their speeds are identical. If the pump leakage is ignored, the ratio of the flow rates *R*<sup>Q</sup> can be produced

2

As previously stated, the pump/motors P1 and P2 are mounted on the same axis, so their speeds are identical. If the pump leakage is ignored, the ratio of the flow rates *R*Q can be produced directly from the displacement of the

Figure 4 illustrates the first prototype of the DDH setup withܴ୕ ൎ ͲǤ͵ and ܴ ൌ ͲǤͷ. To test the concept, the

Ǥ (2)

1 . *<sup>D</sup> <sup>R</sup> D*=

> ܴ୕ ൌ ܦଶ ଵܦ

(a) (b) (c)

a

d

e

Figure 4. First prototype of the DDH setup: (a) zoom view; (b) the experimental setup consists of (a) a double-acting cylinder, (b) wire-actuated encoder, (c) pressure sensor, (d) reversible gear pump/motor P1, (e) pressure sensor, (f) gearbox, (g) PMSM motor/generator, (h) current sensors, (i) frequency converter, (j) tank, (k) pressure sensor, (l) reversible gear pump/motor P2 and (m) pressure sensor in the tank line;

**Figure 4.** First prototype of the DDH setup: (a) zoom view;(b) the experimental setup consists ofa) a double-acting cyl‐ inder, b) wire-actuated encoder, c) pressure sensor, d) reversible gear pump/motor P1, e) pressure sensor, f) gearbox, g) PMSM motor/generator, h) current sensors, i)frequency converter, j) tank, k) pressure sensor, l) reversible gear pump/ motor P2 and m) pressure sensor in the tank line; (c) the crane is used for the DDH setup as a test platform (side view).

Two XV-2M internal gear pump/motors by Vivoil with displacements of 14.4 and 22.8 cm<sup>3</sup>

were used, P2 and P1, respectively [20]. The position feedback from the motor is given by means of its in-built incremental encoder (4096 pulses per revolution, resolution 14 bits), and read

Two XV-2M internal gear pump/motors by Vivoil with displacements of 14.4 and 22.8 cm3

for a motor speed of 400 rpm and a payload of 150 kg: speed, torque and pressure.

b c

*H*

M

g h i

k

m

l

j

P1, respectively [20]. The position feedback from the motor is given by means of its in-built incremental encoder (4096 pulses per revolution, resolution 14 bits), and read with the Unidrive SP1406 drive software [21]. It converts the AC power supply from the line and allows the speed of the permanent magnet brushless servo motor, Unimotor 115U2C manufactured by Emerson Control Techniques, to be set, taking advantage of the information obtained by the feedback device fitted to ensure the rotor speed is exactly as demanded [22]. This experimental setup was tested with a payload of 150 kg at motor speed ranges from 300 to 500 rpm. Figure 5 shows an example of measured data

f

P1 P2

Figure 4 illustrates the first prototype of the DDH setup with *R*<sup>Q</sup> ≈0.63 and *RA* =0.75. To test the

Q

surface areas A1 and A2. According to the datasheet, the cylinder stroke is *l* = 0.4 m.

directly from the displacement of the pump/motors *D*1 and *D*2.

concept, the components for this prototype were taken off the shelf.

components for this prototype were taken from the shelf.

(c) the crane is used for the DDH setup as a test platform (side view).

equation:

148 New Applications of Electric Drives

pump/motors *D*1 and *D*2.

**Figure 5.** Example of measured data of the first DDH prototype: motor speed, torque, pressure in the pump/motor line P1 and in the pump/motor line P2. For a motor speed of 400 rpm and a payload of 150 kg.

In Figure 5, during the lifting, which lasts from 1 to 7 s, the pressure in the pump/motor P1 is about 2 MPa, which rises by the end to 4 MPa. It is worth remarking that the rise appears to be due to the difference between *R*Q and *RA*. A similar rise also occurs in the pump/motor line P2, from atmospheric pressure to 2.6 MPa.

During the lowering, performed from 7 to 13 s, a drop in the pressure from high pressure to about 1 MPa happens. During the lifting, the motor torque is 7 Nm; during the lowering, the torque is around 1 Nm. The pressure in the tank line is close to atmospheric pressure, as it is supposed to be in an open system.

4

/rev were used, P2 and

/rev

In order to overcome the rise in pressure at the end of the movement and investigate the tankless approach, a new prototype was designed. Figure 6 illustrates the experimental test setup of the second DDH prototype. The system is closed by giving up the tank completely (compare to Figure 2b) and replacing it with a hydraulic accumulator A.

pressure sensor, (d) flow meter, (e) reversible gear pump/motor P1, (f) PMSM motor/generator, (g) reversible gear pump/motor P2, (h) pressure sensor, (i) hydraulic accumulator B, (j) pressure sensor in tank line, (k) current sensors, (l) frequency converter, (m) pressure sensor and (n) hydraulic accumulator A; (b) photograph of DDH setup. Within the framework of this work for the second prototypeܴ୕ ൎ ͲǤ͵ andܴ ൌ ͲǤͷ . It can be seen that the ideal **Figure 6.** (a) Schematics of the setup of the second DDH prototype: a) double-acting cylinder, b) wire-actuated encod‐ er, c) pressure sensor, d) flow meter,e) reversible gear pump/motor P1, f) PMSM motor/generator, g) reversible gear pump/motor P2, h) pressure sensor, i) hydraulic accumulator B, j) pressure sensor in tank line, k) current sensors, l) frequency converter, m) pressure sensor and n) hydraulic accumulator A; (b) photograph of DDH setup.

Figure 6. (a) Schematics of the setup of the second DDH prototype: (a) double-acting cylinder, (b) wire-actuated encoder, (c)

*R*Q = *R*A was not achieved. Therefore, an accumulator B is added to compensate for the displacement difference between the available pump/motors and cylinder areas. **Components used**  In the second prototype, DDH setup an electric motor, an IndraDyn T MST130A-0250-N torque motor from Bosch Within the framework of this work for the second prototype *R*<sup>Q</sup> ≈0.73 and *RA* =0.75. It can be seen that the ideal *R*Q = *R*A was not achieved. Therefore, an accumulator B is added to com‐ pensate for the displacement difference between the available pump/motors and cylinder areas.

### **2.1. Components used**

Nm

ͺuͳͲି m3

\* Short-term pressure during start 1 MPa.

parameters of the hydraulic accumulators.

kW

Rated power Rated torque Maximum torque Nominal speed Maximum speed Pole pairs Torque constant Voltage constant Resistance Inductance 1.2 4.5 13 Nm 2500 4000 rpm 10 1.3 0.085 5.9 Ohm 17.5 mH In the second prototype, DDH setup an electric motor, an IndraDyn T MST130A-0250-N torque motor from Bosch Rexroth, is used. The parameters of the electric motor are shown in Table 1.

Nm/A

V/min-1

Minimum speed Maximum speed

Table 1. IndraDyn T MST130A-0250-N parameters [23].


Table 3. Parameters of the AZMF-12-008U hydraulic pump/motor P2 [24].

/rev 25 MPa 0.3 MPa\* 500 Nm 4000 rpm

Two Parker AD100B20T9A1 diaphragm accumulators are utilized as the initial choices. Table 4 shows the

Leakage-oil pressure

6

ͳͳuͳͲି m3 /rev 25 MPa 0.3 MPa\* 500 Nm 3500 rpm **Table 1.** IndraDyn T MST130A-0250-N parameters [23].

Flow rate Maximum

pressure

Rexroth, is used. The parameters of the electric motor are shown in Table 1.

rpm

Bosch Rexroth AZMF-12-011U and AZMF-12-008U external gear motors are used as hydraulic pumps/motors. The parameters of the pump/motors are shown in Tables 2 and 3.


**Table 2.** Parameters of the AZMF-12-011U hydraulic pump/motor P1 [24].

In order to overcome the rise in pressure at the end of the movement and investigate the tankless approach, a new prototype was designed. Figure 6 illustrates the experimental test setup of the second DDH prototype. The system is closed by giving up the tank completely

i

**B**

m n

frequency converter, m) pressure sensor and n) hydraulic accumulator A; (b) photograph of DDH setup.

**A**

Figure 6. (a) Schematics of the setup of the second DDH prototype: (a) double-acting cylinder, (b) wire-actuated encoder, (c) pressure sensor, (d) flow meter, (e) reversible gear pump/motor P1, (f) PMSM motor/generator, (g) reversible gear pump/motor P2, (h) pressure sensor, (i) hydraulic accumulator B, (j) pressure sensor in tank line, (k) current sensors, (l) frequency converter,

**Figure 6.** (a) Schematics of the setup of the second DDH prototype: a) double-acting cylinder, b) wire-actuated encod‐ er, c) pressure sensor, d) flow meter,e) reversible gear pump/motor P1, f) PMSM motor/generator, g) reversible gear pump/motor P2, h) pressure sensor, i) hydraulic accumulator B, j) pressure sensor in tank line, k) current sensors, l)

Within the framework of this work for the second prototypeܴ୕ ൎ ͲǤ͵ andܴ ൌ ͲǤͷ . It can be seen that the ideal *R*Q = *R*A was not achieved. Therefore, an accumulator B is added to compensate for the displacement difference

Within the framework of this work for the second prototype *R*<sup>Q</sup> ≈0.73 and *RA* =0.75. It can be seen that the ideal *R*Q = *R*A was not achieved. Therefore, an accumulator B is added to com‐ pensate for the displacement difference between the available pump/motors and cylinder

In the second prototype, DDH setup an electric motor, an IndraDyn T MST130A-0250-N torque motor from Bosch

Table 1. IndraDyn T MST130A-0250-N parameters [23].

4000 rpm 10 1.3

In the second prototype, DDH setup an electric motor, an IndraDyn T MST130A-0250-N torque motor from Bosch Rexroth, is used. The parameters of the electric motor are shown in Table 1.

Bosch Rexroth AZMF-12-011U and AZMF-12-008U external gear motors are used as hydraulic pumps/motors.

**Pole pairs**

Table 2. Parameters of the AZMF-12-011U hydraulic pump/motor P1 [24].

/rev 25 MPa 0.3 MPa\* 500 Nm 3500 rpm

Table 3. Parameters of the AZMF-12-008U hydraulic pump/motor P2 [24].

/rev 25 MPa 0.3 MPa\* 500 Nm 4000 rpm

Two Parker AD100B20T9A1 diaphragm accumulators are utilized as the initial choices. Table 4 shows the

Leakage-oil pressure

Leakage-oil pressure

Pole pairs Torque constant

Nm/A

**Torque constant**

Voltage constant

0.085 V/min-1

Minimum speed Maximum speed

**Voltage constant**

0.085 V/

Minimum speed Maximum speed

Resistance Inductance

5.9 Ohm 17.5 mH

min-1 5.9 Ohm 17.5 mH

**Resistance Inductance**

Maximum speed

**Maximum speed**

(compare to Figure 2b) and replacing it with a hydraulic accumulator A.

h

(a) (b)

M

P1 P2

<sup>j</sup> <sup>k</sup>

between the available pump/motors and cylinder areas.

Maximum torque

Flow rate Maximum

**Table 1.** IndraDyn T MST130A-0250-N parameters [23].

**Maximum torque**

Flow rate Maximum

13 Nm 2500

The parameters of the pump/motors are shown in Tables 2 and 3.

pressure

pressure

f g

(m) pressure sensor and (n) hydraulic accumulator A; (b) photograph of DDH setup.

Rexroth, is used. The parameters of the electric motor are shown in Table 1.

Nominal speed

**Nominal speed**

1.2 kW 4.5 Nm 13 Nm 2500 rpm 4000 rpm 10 1.3 Nm/A

rpm

l

a

e

b c d

150 New Applications of Electric Drives

**Components used** 

Rated torque

4.5 Nm

**Rated torque**

**2.1. Components used**

ͳͳuͳͲି m3

ͺuͳͲି m3

\* Short-term pressure during start 1 MPa.

parameters of the hydraulic accumulators.

Rated power

1.2 kW

**Rated power**

areas.

*H*


**Table 3.** Parameters of the AZMF-12-008U hydraulic pump/motor P2 [24].

Two Parker AD100B20T9A1 diaphragm accumulators are utilized as the initial choices. Table 4 shows the parameters of the hydraulic accumulators.


**Table 4.** Parameters of the AD100B20T9A1 hydraulic accumulators A and B.

The pressure was measured with Gems 3100R0400S pressure transducers. The velocity of the cylinder piston was measured with an SGW/SGI wire-actuated encoder by SIKO.

According to the manufacturer, the pump/motors used have an external leakage-oil line with a pressure limitation of 0.3 MPa. During the start, the maximum allowed short-term pressure is 1 MPa. Thus, a detailed investigation of the hydraulic connection of the external leakage line is required.
