The actuators most used today in haptic systems are
direct-current electrical motors. They are easy to install, quiet,
and relatively simple to control. However, their reduction
mechanisms can introduce backlash and high inertia, which are
undesirable in haptic applications. In this brief, we investigate
the use of electropneumatic actuators in a tele operation system.
Compared to the electrical actuators, pneumatic actuators
have higher force-to-mass ratio and can generate larger force
without any reduction mechanism. Moreover, they are inert to
magnetic fields, which is crucial in certain applications such
as robot-assisted surgery under magnetic resonance imaging
guidance [3], [4].
Due to the above advantages, pneumatic actuators have
been used in new applications, such as telerobotics, in recent
years. For instance, Tadano and Kawashima [5] propose a
forceps manipulator for a surgical master–slave system, which
estimates external forces without using any force sensor.
Pneumatic muscle actuators have been also recently used in
the tele operation system [6]. They are compact and have high
power/weight density, but they are difficult to control and
require an accurate experimental characterization.
All of the prior works used proportional servo valves
in pneumatically actuated systems because they allow the
achievement of high performances in various position or force
control tasks. However, they are typically expensive because
they require high-precision manufacturing. Therefore, in this
brief, fast-switching ON/OFF valves are used due to their
advantages in terms of low cost and small size. Thanks to
the breakthroughs in valve technology such as leak reduction,
miniaturized of mechanical elements, and fast electronic components;
the solenoid valves now are faster and more accurate
than the former valves. One of the objectives of this brief is to
show that good transparency in tele operation can be obtained
with these inexpensive components.
The traditional method for controlling a system with a
solenoid valve is pulse-width modulation (PWM) [7]–[9].
A main problem with PWM control is chattering, which is
caused by the high-frequency switching of the valve [10].
Chattering can drastically reduce the lifetime of the
valve and generate noises possibly disturbing for certain
applications.
To overcome the drawbacks of PWM-based control of
solenoid valves, this brief presents a new control method
inspired by the hybrid theory recently developed for asynchronous
and synchronous electrical motor control [11]–[13].
This approach is used in a switching-based hybrid system,
which includes continuous actuators and a discrete controller
with a finite number of states. In the case of alternating
current motor drives, contrary to conventional vector control
such as proportional-integral control in which the inverter model is not taken into account by the controller, hybrid
control considers the state of the inverter a control variable.Therefore, it allows obtaining faster torque dynamics than the
vector-control algorithm. Our contribution in this brief consists
of applying the previously developed hybrid algorithm to
the pneumatic master–slave system actuated by fast-switching
ON/OFF valves. The four-channel (4CH) bilateral tele operation
architecture is used in order to test the efficiency of the
proposed control laws. The reason for this is that the 4CH
method is the most general tele operation control architecture
compared to position error based, direct force reflection, and
shared compliance control methods and it can achieve superior
transparency [14], [15]. Finally, an analysis of the controller
parameters is carried out to achieve satisfactory performance
in terms of tele operation transparency.
For the sake of simplicity, the master and slave actuators
are considered to be identical in this brief. In the experiments,
the master and the slave are one-degree-of-freedom
(1-DOF) pneumatic manipulators. It should be noted that this
brief does not deal with the presence of time delay in the
communication channel of the tele operation system—for time
delay compensation in haptic tele operation, the readers may
refer to [16] and [17]. Such a delay is commonly presented in
remote teleoperation systems, but is generally not significant
in local teleoperation systems.
The structure of this brief is as follows. First, the modeling
of the pneumatic manipulator composed of a cylinder and four
solenoid valves is presented in Section II. Section III describes
the hybrid principle, which is implemented in a 4CH bilateral
control system. Section IV presents experimental results that
validate the proposed theories. Finally, concluding remarks
appear in Section V
The actuators most used today in haptic systems aredirect-current electrical motors. They are easy to install, quiet,and relatively simple to control. However, their reductionmechanisms can introduce backlash and high inertia, which areundesirable in haptic applications. In this brief, we investigatethe use of electropneumatic actuators in a tele operation system.Compared to the electrical actuators, pneumatic actuatorshave higher force-to-mass ratio and can generate larger forcewithout any reduction mechanism. Moreover, they are inert tomagnetic fields, which is crucial in certain applications suchas robot-assisted surgery under magnetic resonance imagingguidance [3], [4].Due to the above advantages, pneumatic actuators havebeen used in new applications, such as telerobotics, in recentyears. For instance, Tadano and Kawashima [5] propose aforceps manipulator for a surgical master–slave system, whichestimates external forces without using any force sensor.Pneumatic muscle actuators have been also recently used inthe tele operation system [6]. They are compact and have highpower/weight density, but they are difficult to control andrequire an accurate experimental characterization.All of the prior works used proportional servo valvesin pneumatically actuated systems because they allow theachievement of high performances in various position or forcecontrol tasks. However, they are typically expensive becausethey require high-precision manufacturing. Therefore, in thisbrief, fast-switching ON/OFF valves are used due to theiradvantages in terms of low cost and small size. Thanks tothe breakthroughs in valve technology such as leak reduction,miniaturized of mechanical elements, and fast electronic components;the solenoid valves now are faster and more accuratethan the former valves. One of the objectives of this brief is toshow that good transparency in tele operation can be obtainedwith these inexpensive components.The traditional method for controlling a system with asolenoid valve is pulse-width modulation (PWM) [7]–[9].A main problem with PWM control is chattering, which iscaused by the high-frequency switching of the valve [10].Chattering can drastically reduce the lifetime of thevalve and generate noises possibly disturbing for certainapplications.To overcome the drawbacks of PWM-based control ofsolenoid valves, this brief presents a new control methodinspired by the hybrid theory recently developed for asynchronousand synchronous electrical motor control [11]–[13].This approach is used in a switching-based hybrid system,which includes continuous actuators and a discrete controllerwith a finite number of states. In the case of alternatingcurrent motor drives, contrary to conventional vector controlsuch as proportional-integral control in which the inverter model is not taken into account by the controller, hybridcontrol considers the state of the inverter a control variable.Therefore, it allows obtaining faster torque dynamics than thevector-control algorithm. Our contribution in this brief consistsof applying the previously developed hybrid algorithm tothe pneumatic master–slave system actuated by fast-switchingON/OFF valves. The four-channel (4CH) bilateral tele operationarchitecture is used in order to test the efficiency of theproposed control laws. The reason for this is that the 4CHmethod is the most general tele operation control architecturecompared to position error based, direct force reflection, andshared compliance control methods and it can achieve superiortransparency [14], [15]. Finally, an analysis of the controllerparameters is carried out to achieve satisfactory performancein terms of tele operation transparency.For the sake of simplicity, the master and slave actuatorsare considered to be identical in this brief. In the experiments,the master and the slave are one-degree-of-freedom(1-DOF) pneumatic manipulators. It should be noted that thisbrief does not deal with the presence of time delay in thecommunication channel of the tele operation system—for timedelay compensation in haptic tele operation, the readers mayrefer to [16] and [17]. Such a delay is commonly presented inremote teleoperation systems, but is generally not significantin local teleoperation systems.The structure of this brief is as follows. First, the modelingof the pneumatic manipulator composed of a cylinder and foursolenoid valves is presented in Section II. Section III describesthe hybrid principle, which is implemented in a 4CH bilateralcontrol system. Section IV presents experimental results thatvalidate the proposed theories. Finally, concluding remarksappear in Section V
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actuators ส่วนใหญ่ใช้วันนี้ในระบบสัมผัสเป็นมอเตอร์ไฟฟ้ากระแสตรง
. พวกเขาจะติดตั้งง่าย , เงียบ ,
และค่อนข้างง่ายที่จะควบคุม อย่างไรก็ตาม กลไกการลด
ของพวกเขาสามารถแนะนำฟันเฟืองและความเฉื่อยสูงซึ่งเป็นที่ไม่พึงประสงค์ในงานสัมผัส
. ในสั้น , เราตรวจสอบ
ใช้ electropneumatic ตัวกระตุ้นในระบบปฏิบัติการเป็น Tele .
เมื่อเทียบกับหัวฉีดไฟฟ้า นิวเมติก ตัวกระตุ้น
มีแรงต่อมวลสูงและสามารถสร้างขนาดใหญ่แรง
โดยไม่ลดกลไก นอกจากนี้ พวกเขาจะเฉื่อย
สนามแม่เหล็ก ซึ่งเป็นสิ่งสำคัญในการเป็นหุ่นยนต์ช่วยผ่าตัดภายใต้
เรโซแนนซ์แม่เหล็กด้านการแนะแนว [ 3 ] บาง [ 4 ] .
เนื่องจากข้อได้เปรียบเหนือลม , actuators มี
ถูกใช้ในงานใหม่ เช่น telerobotics ในล่าสุด
ปี ตัวอย่าง ทาดาโน และ คาวา [ 5 ] เสนอ
คีมแบบราคาประหยัด และระบบต้นแบบสำหรับทาสซึ่ง
ประมาณการแรงภายนอก โดยไม่ต้องใช้แรงใด ๆ เซ็นเซอร์
ตัวกระตุ้นกล้ามเนื้อลมได้รับเมื่อเร็ว ๆ นี้ยังใช้ในงานระบบ Tele
[ 6 ] พวกเขามีขนาดกะทัดรัด และมีความหนาแน่นพลังงาน / น้ำหนักสูง
,แต่พวกเขาจะยากที่จะควบคุม และต้องมีการศึกษาทดลองที่ถูกต้อง
.
ทั้งหมดก่อนงานใช้สัดส่วนใน pneumatically กระตุ้นระบบวาล์ว servo
เพราะพวกเขาอนุญาตให้เรียนสูงสมรรถนะในตำแหน่งต่าง ๆหรือแรงงาน
ควบคุม อย่างไรก็ตาม , พวกเขามักจะแพงเนื่องจากการผลิต
พวกเขาต้องการความเที่ยงตรงสูง ดังนั้น ในนี้
สั้น
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