The present invention relates to a rotation driving device for a construction
machine, which uses an electric motor to drive a rotational system.
Conventionally, a hydraulic actuator is extensively adapted, in general,
as an actuator of a construction machine. However, a hydraulic driving system using
the hydraulic actuator has a low energy efficiency due to generation of resistance
in a control valve for controlling the direction and flow rate of pressure oil discharged
from a hydraulic pump, generation of a pressure loss in pipes, generation of an
excessive flow in a circuit and the like.
In order to enhance the energy efficiency, thus, it is known to use
an electric motor as the actuator.
In a "turning drive device for construction machine" described in
Japanese Patent Application Laid-Open No. 2001-11897, for example, the electric
motor is used as a rotating motor for rotating an upper rotating body.
However, in the use of the electric motor as the actuator of the construction
machine, responsiveness of the actuator to a lever operation becomes too sensitive,
compared with the hydraulic driving system, although the energy efficiency can be
When the lever is operated in an intermediate range to change the
speed of the electric motor, for example, the electric motor is suddenly changed
in speed, consequently causing hunting or shock.
In case of driving a front attachment by use of the electric motor,
a sudden stop of the electric motor might cause elastic deformation of the attachment,
which in turn leads to a swing-back. In this way, such an excessive sensitive responsiveness
of the actuator to the drive of the electric motor inconveniently deteriorates the
operability rather than in the hydraulic driving system.
To solve such a problem, model follow-up control that is a known technique
can be applied. This technique comprises controlling the actuator, for example,
by use of a normal model such as a primary delay, which can provide an intended
responsiveness, so as to follow up the responsiveness of the normal model.
However, in such a general model follow-up control, a fixed response
delay regularly appears to a lever operation because a linear model such as a simple
primary delay is used as the normal model. Consequently, there still remains the
problem that a delay also accompanies a sudden operation, which disables a quick
acceleration or quick stopping.
Further, in such a simple linear model, the operability cannot be
delicately tuned according to an operator's taste.
DISCLOSURE OF THE INVENTION
The present invention has been attained considering the problems in
a conventional actuator driving device as described above. Accordingly, an object
of the present invention is to provide a rotation driving device for a construction
machine for driving a rotational system by use of an electric motor, which can mildly
respond to operation of a lever in an intermediate range, and swiftly respond to
a quick operation of the lever.
The present invention provides a rotation driving device for a construction
machine comprising an electric motor for driving a rotational system of the construction
machine, an operating member for instructing an operation of the electric motor,
and a controller for controlling the electric motor according to an operation command
from the operating member, wherein the controller has an emulation model for simulating
dynamic characteristics of a hydraulic rotation driving device in real time, and
a control target value as target value for control is calculated from the emulation
model according to the operation command from the operating member to control the
According to the present invention, when the operating member is operated,
the controller simulates, as dynamic characteristics of the hydraulic rotation driving
device, for example, revolving speed or driving torque, or the both thereof in real
time in reference to the emulation model to compute the control target value. The
controller then controls the electric motor, targeting for the control target value,
for example, by speed control or torque control, or the both thereof. Accordingly
to this, even in case of driving the rotational system by the electric motor, the
responsiveness to the operation of the operating member can be made almost equal
to that in the hydraulic driving system.
In the present invention, the emulation model preferably has specifications
of a hydraulic pump, a hydraulic actuator and various valves as hydraulic equipment
In the present invention, an input unit is preferably connected to
the controller, so that each specification in the emulation model can be changed
through the input unit. Accordingly to this, the operability can be tuned delicately
according to an operator's taste.
In the present invention, the emulation model preferably has nonlinear
characteristic of a flow control valve or pressure control valve as a valve.
This nonlinear characteristic enables generation of a proper response
delay, in case of operating a lever as an operating member in an intermediate range,
to prevent generation of hunting, swing-back or shock, and also enables a quick
acceleration or quick stopping, in case of quickly operating the lever, without
almost generating a response delay.
In the present invention, as the power source of the construction
machine, any one or two or more of an external power source, a built-in battery,
an electric motor driven by an engine, and a capacitor are selected.
In the present invention, the construction machine may have, as the
rotational system, concretely, at least one of a rotating system with a rotating
motor as driving source, a hoisting system with a winch motor as driving source,
and a traveling system with a traveling motor as driving source.
BRIEF DESCRIPTION OF THE DRAWINGS
BEST MODE FOR CARRYING OUT THE INVENTION
- Fig. 1 is an apparent view of a hydraulic excavator to which a rotation driving
device of the present invention is applied;
- Fig. 2 is an illustrative view showing the configuration of the rotation driving
device of the present invention;
- Fig. 3 is an illustrative view showing a control flow according to the present
- Fig. 4 comprises (a) and (b) which are a circuit view showing the configuration
of an emulation model shown in Fig. 3, and a table showing each valve characteristic
in the same model, respectively;
- Fig. 5 is an illustrative view showing a conventional control flow;
- Fig. 6 is a graph showing one example of an operation pattern by a conventional
- Fig. 7 is a graph showing the speed response waveform of an electric motor by
the conventional control;
- Fig. 8 is a graph showing the speed response characteristic of the electric
motor by the control according to the present invention;
- Fig. 9 is a graph showing another example of the operation pattern by a control
- Fig. 10 is a graph showing the speed response characteristic of the electric
motor according to the present invention to the operation pattern of Fig. 9; and
- Fig. 11 is an illustrative view showing another control flow according to the
The present invention will be described below in detail based on preferred
embodiments shown in the drawings.
Fig. 1 shows a hydraulic excavator as a construction machine to which
an actuator driving device of the present invention is applied.
In this figure, the hydraulic excavator comprises an upper rotating
body 2 mounted on a lower traveling body 1, and the upper rotating body 2 is adapted
to be rotatable around a rotating axis R.A.
A front attachment 3 is provided on the front part of the upper rotating
body 2. The front attachment 3 comprises a boom 3a, a boom cylinder 3b for raising
and lowering the boom 3a, an arm 3c, an arm cylinder 3d for rotating the arm 3c,
a bucket 3e and a bucket cylinder 3f for rotating the bucket 3e.
A cabin 4 is disposed on the left side of the base end of the front
attachment 3. An engine, hydraulic equipment, a tank and the like (not shown) are
disposed in the rear of the cabin 4, and covered with an equipment cover 5.
Denoted at 6 is an electric motor for rotating the upper rotating
body 2, which is composed of an AC servomotor. The electric motor 6 may be composed
of a DC servomotor. The electric motor 6 is used as the driving source of a rotating
mechanism (rotating system) for rotating the upper rotating body 2.
Fig. 2 shows the configuration of a rotation driving device unit on
the hydraulic excavator.
A reduction gear 7 is connected to the output shaft of the electric
motor 6, and an inertial load (concretely, a rotator, a winch, a traveling body
or the like as a rotational system) 8 is connected to the rotating shaft of the
reduction gear 7.
A controller 9 is adapted so as to give a revolution signal to an
inverter 10a. The inverter 10a controls a rotation of the electric motor 6, and
an encoder 11 detects the revolution of the electric motor 6, and feeds the detected
revolution back to the controller 9 as a signal.
Denoted at 12 is a control lever (operating member) , which is to
be operated by an operator to control the revolving speed of the electric motor
As a power supplying source for driving the electric motor 6, a generator
13a driven by an engine 13, a battery 14, a capacitor 15 and the like are used in
combination. Denoted at 16a is a converter for converting alternating current to
direct current, and 16b and 16c are DC-DC converters for increasing or lowering
In this embodiment, the configuration is adapted to mount the generator
13 on the hydraulic excavator and store electricity in the battery 14. However,
the configuration can be adapted to receive supply of electric power from an external
Denoted at 3b is the boom cylinder, which is shown as one actuator
of the front attachment 3.
Denoted at 17 is a hydraulic pump for supplying pressure oil to the
boom cylinder 3b, and 18 is the other electric motor for driving the hydraulic pump
17. Denoted at 19 is a hydraulic circuit for adjusting the speed and pressure of
the boom cylinder 3b, and 10b is an inverter.
The boom cylinder 3b is driven by the pressure oil supplied from the
hydraulic circuit 19. Accordingly, the other electric motor 18 is not adapted to
drive the rotational system.
A control flow in the controller 9 will be described in reference
to Fig. 3.
The controller 9 computes or calculates, on receipt of a manipulated
variable S of a control lever 12, an actuator revolving speed ωa
in case of a hydraulic driving system with the manipulated variable given by use
of a hydraulic driving system emulation model 9a stored therein.
A speed target value ωref of the electric motor is
determined from the computed revolving speed ωa by use of the following
ωref = ωa×N1/N2
wherein N1 is the speed reduction ratio of the electric
motor system, and N2 is the speed reduction ratio of the hydraulic system.
By using this ωref as the speed target value of the
electric motor 6, PID control is carried out by a PID 9b followed by comparison
with the revolving speed ω determined from the encoder 11, whereby speed feedback
control is carried out.
The content of the hydraulic driving system emulation model is shown
in Fig. 4(a).
In Fig. 4(a), the emulation model mainly comprises a hydraulic pump
20, a hydraulic motor 21, a reduction gear 22 connected to the output shaft of the
hydraulic motor 21, a rotating inertia 23 connected to the rotating shaft of the
reduction gear 22, a control valve 24 for supplying the pressure oil discharged
from the hydraulic pump 20 to the hydraulic motor 21 while controlling its flow
rate and direction, a main relief valve 25, port relief valves 26a, 26b, check valves
27a and 27b, and a bypass valve 28. This figure shows a principal view for normally
rotating the hydraulic motor 21.
The control valve 24 comprises a bleed-off valve (B/O) 29, a meter-in
valve (M/I) 30, and a meter-out valve (M/O) 31. Denoted at 32 is a tank.
In the emulation model, as shown in Fig. 4 (b), a bleed-off opening
(the curve shown by B/O of the same figure) is throttled as the lever manipulated
variable S becomes larger. Contrary to this, a meter-in opening (the curve shown
by M/I of the same figure) and a meter-out opening (the curve shown by M/O of the
same figure) are opened. Consequently, the pressure oil flow rate to be supplied
to the hydraulic motor 21 is increased.
The governing equations of this emulation model are shown below.
Abo=fbo(S), Ami=fmi (S),
Abo = fbo (S)
Qbo=Cv Abo√ (2Pp/γ)
Wherein JL: inertial moment of load, P: pressure, Q: flow
rate, K: oil volume elasticity, V: pipe inner capacity, A: area, L: length, Cv:
flow coefficient, γ: oil specific gravity, λ: friction coefficient
of pipe, D: pipe diameter, S: lever manipulated variable, N: reduction ratio of
speed, q: hydraulic motor capacity, c; check valve, r: port relief valve, rp: main
relief valve, pi: pipe part, 1: upstream side, and 2: downstream side.
In the above equations, as the specification of the hydraulic pump
20 that is the hydraulic pressure source, hydraulic pump flow rate Qp
is given to the equation (5).
As the characteristic of the actuator, hydraulic motor capacity q
is given to the equation (2).
As the characteristic of the control valve 24, the relation of each
opening area Abo, Ami, Amo of the bleed-off valve
29, meter-in valve 30, and meter-out valve respectively constituting the control
valve 24 with the lever manipulated variable S is given to the equation (6).
In the emulation model of this embodiment, a numerical integration
method, for example, the Newmark-β method is applied to the system of these
governing equations, whereby time history response operation is carried out.
The operation of the emulation model will be described in reference
to Figs. 5-10.
Fig. 5 shows, as a comparative example, a conventional general control
method for determining a speed target value to the lever manipulated variable by
use of a map 9c to perform a speed feedback control.
In this case, as shown in the operation example of Fig. 6, the lever
is operated stepwise in an intermediate range, the speed target value ωref
changes steeply relative to the lever operation as shown in Fig. 7.
Therefore, the revolving speed ω of the electric motor 6 also
changes steeply to make the responsiveness too sensitive. Consequently, hunting,
swing-back in stopping, or shock is generated to deteriorate the operability.
In contrast to this, in the control method of this embodiment, the
control is performed so as to simulate the dynamic characteristic of the hydraulic
driving device by use of the emulation model.
Accordingly, when the lever is operated stepwise in the intermediate
range, the speed target value ωref draws a waveform as simulates
the delay characteristic peculiar to the hydraulic driving device to the lever operation
as shown in Fig. 8.
Consequently, the speed change of the electric motor 6 to the lever
operation is moderated (refer to ω of the graph) , and the operability can
be improved without causing the hunting, swing-back in stoppage, or shock.
On the other hand, in case of a quick accelerating or quick decelerating
operation, the response delay appears in a conventional model follow-up control
using primary delay, as shown in Fig. 10, similarly to the lever operation in the
intermediate range (refer to L1).
In contrast, in the control method of this embodiment, since the relief
valves 26a, 26b (refer to Fig. 4 (a) ) for keeping the circuit pressure constant
are included in the emulation model, acceleration and deceleration are carried out
at the maximum torque similarly to the case of the hydraulic driving device (refer
to L2) .
According to the control method of this embodiment, thus, the electric
motor 6 mildly responds to a lever operation in the intermediate range, while the
electric motor 6 can be made to rapidly respond to a quick lever operation.
In the emulation model described above, the target rotating speed
ωref is compared with the rotating speed ω outputted from
the encoder 11. However, without being limited to this, toques can be mutually compared
by use of a hydraulic driving system emulation model 9a' shown in Fig. 11.
Namely, the driving torque of the hydraulic actuator with a lever
manipulated variable given is as follows:
τref = τa×N1/N2
The same effect as the above embodiment can be obtained by performing
a feedback control using the control rule of the PID control with the τref
as the torque target value of the electric motor 6. Concretely, a current target
value iref, which is obtained by converting the torque target value τref
to current value is compared with current i determined from the inverter 10a.
A switch or touch panel as the input unit may be connected to the
controller 9, so that the specification of, for example, the control valve 24 in
the emulation model can be properly changed by switching operation of the switch,
an operation on the touch panel, or a change of software.
Such a changeable configuration enables an operator to easily change
the characteristic of the operability according to the operator's taste.
The present invention is useful for a construction machine for driving
a rotational system by an electric motor, and particularly suitable for a construction
machine in which responsiveness equal to a hydraulic driving system is required
for the responsiveness of an actuator to a lever operation.