2008 Sazawa - Robust Fast Tracking Control for Multi-Degrees-of-Freedom Motion System Considering Torque Saturation.pdf
2008 Sazawa - Robust Fast Tracking Control for Multi-Degrees-of-Freedom Motion System Considering Torque Saturation.pdf
2008 Sazawa - Robust Fast Tracking Control for Multi-Degrees-of-Freedom Motion System Considering Torque Saturation.pdf
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<strong>Fast</strong> Continuous Path <strong>Tracking</strong> <strong>Control</strong> <strong>Considering</strong><br />
High Precision and <strong>Torque</strong> <strong>Saturation</strong><br />
Masaki <strong>Sazawa</strong><br />
Nagaoka University <strong>of</strong> Technology<br />
1603-1, Kamitomioka, Nagaoka,<br />
Niigata, 940-2188, JAPAN<br />
Email: sazawa@vos.nagaokaut.ac.jp<br />
Kiyoshi Ohishi<br />
Nagaoka University <strong>of</strong> Technology<br />
1603-1, Kamitomioka, Nagaoka,<br />
Niigata, 940-2188, JAPAN<br />
Email: ohishi@vos.nagaoaut.ac.jp<br />
Abstract—Continuous path tracking control is an important<br />
technology <strong>for</strong> the position control system such as factory<br />
automation field. Particularly, large acceleration and/or deceleration<br />
torque is required <strong>for</strong> continuous path tracking control<br />
at its start position and its goal position. Each AC servo motor<br />
<strong>of</strong> continuous path tracking control has limitation <strong>of</strong> current<br />
and voltage. There<strong>for</strong>e, in controlling a multi-degree-<strong>of</strong>-freedom<br />
continuous path tracking control system, even if only the motor<br />
torque <strong>of</strong> one axis has the current limitation, the actual position<br />
response is not <strong>of</strong>ten equal to the desired trajectory reference.<br />
In fast continuous path tracking control <strong>of</strong> multi-degree-<strong>of</strong>freedom<br />
position control system, the position error sometimes<br />
increases according to the unknown disturbance torque and<br />
inertia variation.<br />
In order to overcome these problems, this paper proposes a<br />
new continuous path tracking control algorithm by considering<br />
both the torque saturation and the coordinated motion. The<br />
proposed method assures the coordinated motion by considering<br />
the torque limitation. The effectiveness <strong>of</strong> the proposed method<br />
is confirmed by the experimental results in this paper.<br />
I. INTRODUCTION<br />
<strong>Fast</strong> continuous path tracking control is demanded <strong>for</strong> the<br />
multi-degrees-<strong>of</strong>-freedom position control system in order to<br />
improve the productivity [1]. Moreover, fast continuous path<br />
tracking control system such as X-Y tables is constructed by<br />
AC servo motor and ball screw. Especially, large acceleration<br />
and/or deceleration torque is necessary <strong>for</strong> fast continuous path<br />
tracking control at its start position and its goal position. As<br />
a result, the actual position response sometimes has the large<br />
overshoot and the oscillated response. Moreover, the position<br />
response <strong>of</strong> each axis cannot coordinate and follow to the<br />
desired path tracking reference [2]–[10].<br />
We have already proposed a new anti-windup algorithm<br />
<strong>for</strong> motor drive control and fast potion control. This control<br />
method realizes the fast and smooth positioning control<br />
without overshoot and the oscillated response [11], [12]. This<br />
paper applies the proposed anti-windup algorithm to the multidegrees-<strong>of</strong>-freedom<br />
position control system such as X-Y table.<br />
In multi-degrees-<strong>of</strong>-freedom position control system, when<br />
the servo motor on Y-axis has torque saturation, the servo<br />
motor on X-axis <strong>of</strong>ten increases the tracking error. In order<br />
to overcome this problem, this paper proposes a new torque<br />
limitation algorithm considering coordinated motion control<br />
<strong>for</strong> robust fast continuous path tracking control system [13].<br />
The proposed method is the on-line real time algorithm, which<br />
assures the coordinated multi-degrees-<strong>of</strong>-freedom motion control<br />
considering the torque saturation.<br />
II. FAST CONTINUOUS PATH TRACKING CONTROL<br />
Fig.1 shows the fast continuous path tracking control system.<br />
The position control system is constructed by the minor<br />
control loop <strong>of</strong> speed PI controller and current PI controller<br />
with each output limitation [6]. In this paper, the limiter <strong>of</strong><br />
the speed controller output is constructed by the proposed<br />
output limitation algorithm based on the priority feedback<br />
compensation <strong>of</strong> proportional output, which is a new antiwindup<br />
algorithm <strong>for</strong> PI controller [11], [12]. Since this<br />
limitation algorithm <strong>of</strong> PI controller output has the robustness<br />
on parameter variation [11], [12], this paper applies the proposed<br />
anti-windup algorithm to the multi-degrees-<strong>of</strong>-freedom<br />
position control system. When the bandwidth <strong>of</strong> position<br />
controller becomes high enough, the transfer function from<br />
the position command θ cmd to the actual position response<br />
θ res can be treated as show in (1).<br />
θ res<br />
θ<br />
ω<br />
ωres αres<br />
= =<br />
cmd cmd<br />
A. Braking Mode Algorithm<br />
≃ 1 (1)<br />
αcmd In order to realize the desired fast continuous path tracking<br />
control, near to the goal position, the maximum torque deceleration<br />
is <strong>of</strong>ten requested. Fig.2 shows the ideal deceleration<br />
response to the target goal position. The fast continuous path<br />
tracking control system decelerates by using the maximum<br />
torque during the proposed decelerating time t d , which is the<br />
time from the braking start time t brake to the braking end time<br />
t end as shown in Fig.2. The moving distance ΔΘ err <strong>for</strong> the<br />
decelerating time t d is defined as (2). The braking start time<br />
t brake is determined by the load torque and the target goal<br />
position. Hence, the moving distance ΔΘ err is treated as the<br />
position error until the target goal position. In this method,<br />
the decelerating speed ω m (t) and the decelerating time t d<br />
are obtained as shown in (3) and (4). The moving distance<br />
ΔΘ err is calculated by using the estimated load torque and<br />
978-1-4244-4649-0/09/$25.00 ©2009 IEEE 3089
α cmd J n<br />
I FF<br />
K tn<br />
ω cmd<br />
i ref d<br />
+<br />
Position P + + ω ref e<br />
+<br />
+<br />
u +<br />
+<br />
+ - <strong>Control</strong>ler<br />
+<br />
ksiTs z-1<br />
i ref<br />
-<br />
- + q<br />
x ~ x +<br />
Speed<br />
- Current + -<br />
ksp<br />
Limiter<br />
+<br />
Limiter<br />
-<br />
-<br />
Δup Δu<br />
+<br />
Δui<br />
Speed <strong>Control</strong>ler<br />
ω res with proposed new anti-windup algorithm<br />
target position<br />
I<br />
ω STOP<br />
STOP =0<br />
Braking Mode<br />
+ - Algorithm<br />
Braking Mode Algorithm<br />
s<br />
θ<br />
cmd<br />
θ<br />
res<br />
+<br />
-<br />
id res<br />
iq res<br />
kcp<br />
kci<br />
s<br />
+<br />
-<br />
1<br />
kcp<br />
Current <strong>Control</strong>ler<br />
with anti-windup algorithm<br />
+<br />
+<br />
kcp<br />
kci<br />
s<br />
1 ΔVd<br />
kcp<br />
ΔVq<br />
Vd<br />
d-q<br />
+<br />
α-β<br />
+ Vq<br />
θre<br />
d-q<br />
t1,<br />
t2<br />
d-q<br />
u,<br />
v,w<br />
iv<br />
iu<br />
p<br />
α-β<br />
t1,<br />
t2<br />
t1<br />
t2<br />
θrm<br />
~<br />
t1<br />
+<br />
-<br />
+ -<br />
~<br />
t2<br />
t1,<br />
t2<br />
Suvw<br />
Inverter<br />
PM<br />
Enc.<br />
Fig. 1.<br />
Continuous path tracking control system with anti-windup algorithm<br />
Current Speed Position<br />
0<br />
ω 0<br />
0<br />
0<br />
~<br />
target position<br />
ΔΘ err<br />
brake point<br />
time[s]<br />
ω m (t)<br />
time[s]<br />
-I MAX<br />
time[s]<br />
Y-Axis<br />
Table<br />
AC Motor<br />
Coupling<br />
X-Axis<br />
Encoder<br />
Ball Screw<br />
Coupling<br />
AC Motor<br />
Encoder<br />
(a) tested X-Y table system<br />
start, goal<br />
(b) path reference<br />
Fig. 3. <strong>System</strong> configuration <strong>of</strong> experimental system<br />
tbrake<br />
td<br />
tend<br />
Fig. 2.<br />
Ideal deceleration & stop response<br />
the maximum torque current I MAX , as shown in (5) [14].<br />
ΔΘ err = ∫ t d<br />
0 ω m(t)dt (2)<br />
ω m (t) =ω 0 − K tnI MAX + ˆT dis<br />
J<br />
t (3)<br />
t d =<br />
2<br />
1 Jω 0<br />
K tn I MAX + ˆT (4)<br />
dis<br />
ΔΘ err = 1 2<br />
Jω 2 0<br />
K tn (I MAX + ˆT dis<br />
K tn<br />
)<br />
B. <strong>System</strong> Configuration and Experimental <strong>System</strong><br />
Fig.3 shows the configuration <strong>of</strong> tested experimental system.<br />
Fig.3(a) shows the tested X-Y table system. TABLE.I is the<br />
specifications <strong>of</strong> tested motor and TABLE.II is the specifications<br />
<strong>of</strong> tested experimental system. In the tested experimental<br />
system, the axis inertia J such as X-axis is 6.21×10 −5 [kgm 2 ].<br />
(5)<br />
As the axis inertia <strong>of</strong> Y-axis is the total inertia including<br />
the weight <strong>of</strong> X-axis, Y-axis inertia becomes 2.5 times value<br />
<strong>of</strong> X-axis inertia. Hence, the tested motion control system<br />
always has the inertia variation. The continuous path tracking<br />
command is shown in the reference <strong>of</strong> Fig.3(b).<br />
Fig.4 shows the experimental results <strong>of</strong> the tested continuous<br />
path tracking control system using the conventional speed<br />
PI controller using integrator with limiter. Fig.4(b) shows the<br />
responses <strong>of</strong> position, speed and current <strong>of</strong> Y-axis on condition<br />
that the driving time <strong>of</strong> path reference is 2 [sec]. In this<br />
condition, the actual path response coincides with the path<br />
reference completely, even if the continuous path tracking<br />
control system has only limiter. However, on condition that<br />
the driving time <strong>of</strong> path reference is 1 [sec], the actual<br />
path response has large tracking error. In multi-degrees-<strong>of</strong>freedom<br />
position control system, when the servo motor on<br />
Y-axis has torque saturation, the servo motor on X-axis <strong>of</strong>ten<br />
increases the tracking error. There<strong>for</strong>e, the multi-degrees-<strong>of</strong>freedom<br />
position control system must be required to have the<br />
coordinated motion considering the torque limitation.<br />
978-1-4244-4649-0/09/$25.00 ©2009 IEEE 3090
TABLE I<br />
SPECIFICATIONS OF TESTED MOTOR<br />
Rated power P [W] 200<br />
Rated voltage v[V] 100<br />
<strong>Torque</strong> constant K t[Nm/A] 0.1597<br />
Actual inertia <strong>of</strong> joint X J x[kgm 2 ] 6.21 × 10 −5<br />
Actual inertia <strong>of</strong> joint Y J y[kgm 2 ] 15.54 × 10 −5<br />
Nominal inertia <strong>of</strong> joint X J xn[kgm 2 ] 6.21 × 10 −5<br />
Nominal inertia <strong>of</strong> joint Y J yn[kgm 2 ] 6.21 × 10 −5<br />
Rated maximum speed ω max[rad/s] 314<br />
Rated current (d-q axis) i max[A] 4<br />
Conversion factor K 0 [rad/m] 100π<br />
Encoder pulse [pulse/rev] 2000<br />
y[mm]<br />
80<br />
60<br />
40<br />
20<br />
0<br />
start, goal<br />
P-reference<br />
P-response(2s)<br />
P-response(1s)<br />
-20<br />
TABLE II<br />
SPECIFICATIONS OF EACH CONTROLLER<br />
Bandwidth <strong>of</strong> current controller ω p[rad/s] 4000<br />
Bandwidth <strong>of</strong> speed controller ω s[rad/s] 600<br />
Bandwidth <strong>of</strong> position controller ω c[rad/s] 150<br />
Current limitation values I limit [A] 4<br />
Speed limitation value ω limit [rad/s] 300<br />
III. TORQUE LIMITATION ALGORITHM FOR<br />
MULTI-DEGREE-OF-FREEDOM SYSTEM<br />
The torque current reference i ref should be divided into the<br />
tracking control current i tra and the disturbance compensation<br />
current i cmp , as shown in (6). The disturbance compensation<br />
current i cmp is estimated by ordinary disturbance observer.<br />
When the fast continuous path tracking control system has<br />
torque saturation, the amplitude <strong>of</strong> i tra should be adjusted<br />
to the maximum tracking control current I traMAX as shown<br />
in (7). Here, I MAX is the maximum torque current, k is the<br />
sampling number.<br />
I tra (k) = I ref (k) − I cmp (k). (6)<br />
⎧<br />
I MAX − I cmp (k)<br />
⎪⎨<br />
when I MAX >I refi<br />
I traMAX (k) =<br />
(7)<br />
−I MAX − I cmp (k)<br />
⎪⎩<br />
when −I MAX
60<br />
40<br />
P-reference<br />
P-response<br />
position[rad]<br />
20<br />
0<br />
-20<br />
θ-cmd<br />
θ-cmd-tilde<br />
θ-res<br />
0 0.5 1 1.5<br />
20<br />
y[mm]<br />
0<br />
Zoom up<br />
speed[rad/s]<br />
200<br />
0<br />
-200<br />
ω-ref<br />
ω-res<br />
-20<br />
0 0.5 1 1.5<br />
-40<br />
iq[A]<br />
5<br />
0<br />
iq-ref<br />
iq-res<br />
Radius error[mm]<br />
0.2<br />
0.1<br />
0<br />
-0.1<br />
-0.2<br />
-60<br />
-150 -100 -50 0 50 100 150<br />
x[mm]<br />
a) path response<br />
0 0.5 1 1.5<br />
Time[s]<br />
b) tracking error<br />
P-reference<br />
P-response<br />
10<br />
-5<br />
0 0.5 1 1.5<br />
Time[s]<br />
a) position, speed and current response <strong>of</strong> X axis<br />
position[rad]<br />
speed[rad/s]<br />
θ-cmd<br />
20<br />
θ-cmd-tilde<br />
θ-res<br />
0<br />
-20<br />
0 0.5 1 1.5<br />
ω-ref<br />
200<br />
ω-res<br />
0<br />
-200<br />
0 0.5 1 1.5<br />
5<br />
5<br />
iq-ref<br />
iq-res<br />
y[mm]<br />
0<br />
iq[A]<br />
0<br />
-5<br />
-5<br />
0 0.5 1 1.5<br />
Time[s]<br />
b) position, speed and current response <strong>of</strong> Y axis<br />
-10<br />
99.4 99.5 99.6 99.7 99.8 99.9 100 100.1 100.2<br />
x[mm]<br />
c) zoom up <strong>of</strong> path response<br />
Fig. 5. Experimental results <strong>of</strong> the tested continuous path tracking control<br />
using conventional torque current limitation algorithm<br />
Ĩ refi (k) =ε min (k)I trai (k)+I cmpi (k) (11)<br />
= Ĩtra i<br />
(k)+I cmpi (k) (12)<br />
The acceleration torque current adjustment ratio ε i is<br />
defined as shown in (10). The acceleration torque current<br />
adjustment ratio ε i shows the content ratio <strong>of</strong> I traMAX to<br />
I trai in each axes. In this torque limitation algorithm, the<br />
fast continuous path tracking control current I trai is adjusted<br />
by using the minimum acceleration torque current adjustment<br />
ratio ε min . When the fast continuous path tracking control<br />
system has no torque saturation, the path tracking control<br />
current I trai should be not adjusted. In this case, ε min<br />
becomes equal to 1. The adjusted current reference Ĩref i<br />
is<br />
the sum <strong>of</strong> the adjusted acceleration torque current and the<br />
disturbance compensation torque current as shown in (12).<br />
Fig.5 shows the experimental results <strong>of</strong> the tested continuous<br />
path tracking control system using this conventional<br />
torque current limitation algorithm. When the continuous path<br />
Fig. 6. Experimental results <strong>of</strong> the tested continuous path tracking control<br />
system using conventional torque current limitation algorithm<br />
tracking control system has torque saturation, the path tracking<br />
error is small in comparison with that <strong>of</strong> Fig.5. The proposed<br />
torque limitation algorithm has the validity on fast continuous<br />
path tracking control. However, in the start position and the<br />
goal position, the path tracking error has just large error as<br />
shown in Fig.5-(b) and Fig.5-(c).<br />
IV. TORQUE LIMITATION ALGORITHM FOR ROBUST<br />
MULTI-DEGREES-OF-FREEDOM FAST POSITION CONTROL<br />
In order to overcome this problem, this paper proposes a<br />
new adjustment path backward torque limitation algorithm.<br />
The new proposed sampling adjusted position command is<br />
determined from the current sampling maximum path tracking<br />
control current I traMAXi . The acceleration command α i (k) is<br />
determined in (13). In this paper, the next sampling adjusted<br />
cmd<br />
position command ˜θ i (k +1) is defined as shown in (14).<br />
The position adjustment ratio γ i (k +1) is defined as shown<br />
in (15). Here, T s is sampling time.<br />
This paper picks up the minimum value γ min (k +1) among<br />
γ i (k +1)(i =1∼ N). The next sampling adjustment time<br />
˜t(k +1) is obtained by the time function <strong>of</strong> position command<br />
f i (t) as shown in (16) and (17). Since the proposed algorithm<br />
calculates the next sampling corrected position command<br />
978-1-4244-4649-0/09/$25.00 ©2009 IEEE 3092
α cmd i<br />
ω cmd i<br />
θ<br />
cmd<br />
i<br />
<strong>Tracking</strong> Adjustment Algorithm <strong>of</strong><br />
<strong>Multi</strong>-<strong>Degrees</strong>-<strong>of</strong>-<strong>Freedom</strong> <strong>Motion</strong> <strong>System</strong><br />
~<br />
I FF i<br />
~<br />
ω cmd i<br />
~<br />
+ + ω ref<br />
i Position P<br />
i<br />
+<br />
+<br />
- <strong>Control</strong>ler<br />
-<br />
Speed<br />
Limiter<br />
i<br />
ω res i<br />
θ<br />
cmd<br />
θ<br />
res<br />
Speed <strong>Control</strong>ler<br />
with proposed new anti-windup algorithm<br />
e<br />
+<br />
+<br />
ksiTs<br />
-<br />
ksp<br />
i ref d i<br />
+<br />
+<br />
z -1 u<br />
i ref<br />
+ q<br />
x ~ i<br />
x +<br />
-<br />
Current<br />
+<br />
-<br />
Limiter<br />
-<br />
Δup Δu<br />
+<br />
Δui<br />
target position<br />
ω STOP =0<br />
+ -<br />
Braking Mode<br />
Algorithm I STOP<br />
Current <strong>Control</strong>ler<br />
with anti-windup algorithm<br />
Inverter<br />
PM<br />
Enc.<br />
^<br />
T dis i<br />
Disturbance<br />
Observer<br />
ω res i<br />
i ref q i<br />
Braking Mode Algorithm<br />
s<br />
Fig. 7.<br />
Proposed continuous path tracking control system considering torque current saturation and coordinated motion<br />
˜θ cmd<br />
i<br />
(k +1) by using ˜t(k +1), ˜θcmd i (k +1) is determined<br />
as shown in (18). Similarly, the corrected speed command<br />
˜ω i<br />
cmd (k +1) is calculated as shown in (19). Here, f ′ (t) is<br />
the time function <strong>of</strong> speed command.<br />
˜θ cmd<br />
i<br />
= θ cmd<br />
i<br />
α i (k) = K tn i<br />
J ni<br />
I traMAXi (k) (13)<br />
(k +1)=θ cmd (k)+T s ω res (k)+ 1 2 T s 2 α i (k)<br />
i<br />
(k)+T s ωi<br />
res (k)+ 1 2 T s<br />
2<br />
γ i (k +1)≡<br />
cmd ˜θ i<br />
θi<br />
cmd<br />
= T sωi<br />
res<br />
i<br />
K tni<br />
J ni<br />
I traMAXi (k) (14)<br />
(k +1)− θi<br />
cmd (k)<br />
(k +1)− θi<br />
cmd (k)<br />
(k)+ 1 2 T s 2 α i (k)<br />
θi<br />
cmd (k +1)− θi<br />
cmd (k)<br />
if I MAX > |I refi |, γ(k +1)=1<br />
˜ω cmd<br />
i (k +1)=<br />
(15)<br />
˜t(k +1)=f −1<br />
i (˜θ i cmd (k + 1)) (16)<br />
≃ t(k)+γ min (k +1)T s (17)<br />
˜θ cmd<br />
i (k +1)=f i (˜t(k + 1)) (18)<br />
⎧<br />
If γ min (k +1)=γ i (k +1)<br />
⎪⎨ f i ′ (˜t(k + 1))<br />
else γ min (k +1)≠ γ i (k +1) (19)<br />
˜θ ⎪⎩ i<br />
cmd (k +1)− θi<br />
cmd (k)<br />
T s<br />
Using (14) and the proposed adjustment path backward<br />
torque limitation algorithm, the next sampling corrected position<br />
command ˜θ i (k +1) is defined as shown in (20). Here,<br />
cmd<br />
Ĩ FFi (k) is the corrected acceleration current reference based<br />
on coordinated motion caused by torque saturation. As the<br />
result, the acceleration current reference ĨFF i<br />
(k) is obtained<br />
as shown in (21).<br />
˜θ i cmd (k +1)<br />
= θ cmd<br />
i<br />
(k)+T s ωi<br />
res (k)+ 1 2 T s<br />
2<br />
K tni<br />
J ni<br />
Ĩ FFi (k) (20)<br />
Ĩ FFi (k) =<br />
2J n i<br />
Ts 2 {f i (t(k)+γ min (k +1)T s )<br />
K tni<br />
− θi<br />
cmd (k) − T s ωi res (k)} (21)<br />
Fig.7 shows the block diagram <strong>of</strong> the proposed fast continuous<br />
path tracking control system considering torque current<br />
saturation and coordinated motion. Fig.8 shows the experimental<br />
results <strong>of</strong> the proposed continuous path tracking control<br />
based on the proposed torque current limitation algorithm.<br />
TABLE III shows the comparison <strong>of</strong> settling time and tracking<br />
error. In fig.9(b), the continuous path tracking control <strong>of</strong> Y-<br />
axis has torque saturation. The proposed method well realizes<br />
the high accuracy path tracking control within radius error<br />
0.02[rad], even if Y-axis acceleration torque is the maximum<br />
torque.<br />
V. CONCLUSION<br />
This paper proposes a new continuous path tracking control<br />
algorithm taking into account both the torque saturation and<br />
the coordinated motion. This paper newly defines the new<br />
position reference adjustment ratio γ by using disturbance<br />
observer, which is the key <strong>for</strong> robust multi-degrees-<strong>of</strong>-freedom<br />
fast position control. The proposed method well realizes the<br />
coordinated motion considering the torque limitation, which<br />
is the on-line real time algorithm. The effectiveness <strong>of</strong> the<br />
proposed method is confirmed by the experimental results.<br />
REFERENCES<br />
[1] K. Sakai, M. Iwasaki, and N. Matsui :“High-speed and high-precision<br />
positioning system by using mode switching control,”(in Japanese), IEEJ<br />
Trans. IA, Vol. 118-D, No. 7/8, pp. 870–876, Jul./Aug. 1998.<br />
978-1-4244-4649-0/09/$25.00 ©2009 IEEE 3093
60<br />
40<br />
P-reference<br />
P-response<br />
position[rad]<br />
20<br />
0<br />
-20<br />
θ-cmd<br />
θ-cmd-tilde<br />
θ-res<br />
0 0.5 1 1.5<br />
20<br />
y[mm]<br />
0<br />
Zoom up<br />
speed[rad/s]<br />
200<br />
0<br />
-200<br />
ω-ref<br />
ω-res<br />
-20<br />
0 0.5 1 1.5<br />
-40<br />
iq[A]<br />
5<br />
0<br />
iq-ref<br />
iq-res<br />
Radius error[mm]<br />
0.2<br />
0.1<br />
0<br />
-0.1<br />
-0.2<br />
-60<br />
-150 -100 -50 0 50 100 150<br />
x[mm]<br />
a) path response<br />
0 0.5 1 1.5<br />
Time[s]<br />
b) tracking error<br />
P-reference<br />
P-response<br />
10<br />
-5<br />
0 0.5 1 1.5<br />
Time[s]<br />
a) position, speed and current response <strong>of</strong> X axis<br />
position[rad]<br />
speed[rad/s]<br />
θ-cmd<br />
20<br />
θ-cmd-tilde<br />
θ-res<br />
0<br />
-20<br />
0 0.5 1 1.5<br />
ω-ref<br />
200<br />
ω-res<br />
0<br />
-200<br />
0 0.5 1 1.5<br />
5<br />
5<br />
iq-ref<br />
iq-res<br />
y[mm]<br />
0<br />
iq[A]<br />
0<br />
-5<br />
-5<br />
0 0.5 1 1.5<br />
Time[s]<br />
b) position, speed and current response <strong>of</strong> Y axis<br />
-10<br />
99.4 99.5 99.6 99.7 99.8 99.9 100 100.1 100.2<br />
x[mm]<br />
c) zoom up <strong>of</strong> path response<br />
Fig. 8. Experimental results <strong>of</strong> proposed continuous path tracking control<br />
based on the proposed torque current limitation algorithm<br />
TABLE III<br />
COMPARISON OF SETTLING TIME AND TRACKING ERROR<br />
settling time path inner error path outer error<br />
only current limiter 1.106s -3.929rad 0.831rad<br />
(-12.51mm) (2.65mm)<br />
conventional torque 1.046s -0.057rad 0.042rad<br />
limitation method (-0.18mm) (0.13mm)<br />
proposed torque 1.041s -0.018rad 0.008rad<br />
limitaion method (0.06mm) (0.03mm)<br />
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consideration algorithm <strong>of</strong> joint torque saturation,” in Proc. IEEE<br />
IES/IECON’98, pp.1812–1817, 1998.<br />
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algorithm <strong>of</strong> joint torque saturation <strong>for</strong> redundant manipulator,”<br />
in Proc. IEEE IES/IECON 2000, pp.2255–2260, 2000.<br />
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based on youla parameterization,” (in Japanese), IEEJ Trans. IA, Vol.121-<br />
D, No. 6, pp. 683–688, Jun. 2001.<br />
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control input,” (in Japanese), SICE, Vol. 30, No. 6, pp. 660–668, Jun.<br />
Fig. 9. Experimental results <strong>of</strong> proposed continuous path tracking control<br />
based on the proposed torque current limitation algorithm<br />
1994.<br />
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[8] K.J.Åstrom, and T.Hagglund:“Automatic Tuning <strong>of</strong> PID <strong>Control</strong>lers,”<br />
Instrument Society <strong>of</strong> America, 1988<br />
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Proc. IEEE IES/ICIT 2006, pp. 866–871, Dec. 2006<br />
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978-1-4244-4649-0/09/$25.00 ©2009 IEEE 3094