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A high performance tilting platform driven by hybrid actuator
CIRP Annals - Manufacturing Technology 58 (2009) 363–366
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp
A high performance tilting platform driven by hybrid actuator H. Shinno (2)*, H. Yoshioka, M. Hayashi Precision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Actuator Control Rotary motion
Multi-axis controlled machine tools require a tilting rotary table or a tilting spindle head. In order to realize an ultraprecision multi-axis machine tool, it is an important issue to develop a high performance tilting platform. This paper presents a newly developed hybrid actuator-driven tilting platform. The hybrid actuator is constructed by integrating a pneumatic rotary actuator and a couple of voice coil motors. Performance evaluation results confirm that the platform provides high precision and high torque motions. ß 2009 CIRP.
1. Introduction Demands for simultaneous multi-axis controlled machining have recently increased in the wide range of industries, i.e., automotive, aerospace, consumer product and others. In order to meet such industrial requirements, various types of simultaneous multi-axis controlled machine tools and multi-functional machine tools [1] have been developed to machine the complex shaped optics for an extreme ultraviolet lithography [2], the artificial human joints and human bones [3], the dies and molds [4], etc. In general, such simultaneous multi-axis controlled machine tools have a tilting motion platform such as a tilting rotary table system driven by direct drive motors [5], a trunnion table system equipped with a worm gear, or a tilting rotary spindle head. However, conventional tilting motion platforms cannot fulfill future advanced industrial requirements on such simultaneous multi-axis controlled machine tools due to low rigidity and low motion accuracy. In this study, an innovative tilting motion platform equipped with a hybrid actuator is newly developed for future ultraprecision multi-axis controlled machine tools. The hybrid actuator proposed is successfully composed of pneumatic and electromagnetic actuators. Performance evaluation results confirm that the tilting platform developed provides high resolution, high motion accuracy, high torque motion and high rigidity. 2. Structural configuration of the developed platform Fig. 1 shows the fundamental driving principle of a newly proposed hybrid actuator. The hybrid mechanism was effectively combined with electromagnetic and pneumatic actuators. These actuators are allocated in parallel and have the common driven axis. Two kinds of actuators are characterized by the attributes, as
* Corresponding author. 0007-8506/$ – see front matter ß 2009 CIRP. doi:10.1016/j.cirp.2009.03.093
shown in this figure. The pneumatic actuator can generate high torque without heat generation, while the actuator has disadvantages such as low response and dead band of pressure control in servo valve. In contrast, the electromagnetic actuator provides significant advantages such as quick response, accurate torque control and dead band free, while this actuator has substantial disadvantages such as low torque and heat generation. In consequence, both the actuators could be complementary to each other. The resultant hybrid actuator made it possible to achieve a remarkable performance. A structural concept of the proposed hybrid actuator is shown in Fig. 2. The pneumatic actuator has four air chambers and then generates the resultant driving force by controlling the differential pressure between the opposite chambers. In contrast to the pneumatic actuator, an electromagnetic actuator, a pair of voice coil motors allocated on both sides, can drive the rotor with high accuracy and quick response. In order to achieve accurate torque transfer around the rotary axis, the platform was designed to have a symmetric structure. In order to minimize nonlinear phenomena, noncontact seals were used in the gap between the stator and rotor. Table 1 shows the fundamental design specifications of the tilting platform developed. Fig. 3 shows an actual structural configuration of the overall platform. The tilting and fixed parts in the platform structure are colored in light blue and in green, respectively. The coils in yellow are moving parts. Two precision angular contact ball bearings were used in the rotary axis of the developed platform. Fig. 4 shows the appearance of the overall platform. The outer diameter of the circular tilting platform was 115 mm. 3. Control system for the hybrid actuator Fig. 5 shows a block diagram of the tilting platform motion control system. The motion control system developed consists of the pneumatic and the electromagnetic actuator control systems.
H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
364
Fig. 1. Mutual complementary function of hybrid actuator.
Fig. 3. Structural configuration of the platform. Fig. 2. Structural concept of a hybrid actuator.
The pneumatic actuator was driven by using the servo valve, which control the torque with a PI compensator and pressure transducer outputs. In addition, the electromagnetic actuator was controlled by a PID compensator and an angle encoder output. The torque error of the pneumatic actuator could be estimated by the pressure
Table 1 Specification of the tilting platform. Tilting table system
Dimension (mm) Stroke (8) Moment of inertia (kg m2)
300 200 185 45 9.56 10 3
Rating torque
Pneumatic actuator (N m) Electric actuator (N m)
6.5 1.0
Angle encoder
Resolution (8) Max response velocity (rpm)
1.1 10 24
4
Fig. 4. Appearance of the platform developed.
H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
Fig. 5. Block diagram of control system.
Fig. 6. Stopping characteristics without pressure compensation. Fig. 7. Stopping characteristics with pressure compensation.
Fig. 8. Stepwise response under loading condition.
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H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
transducer outputs and then the estimated torque error could be compensated by the electromagnetic actuator. Furthermore, the outer disturbance in the pneumatic actuator could be compensated by the process expressed in red of the block diagram. The pneumatic actuator generated a large torque at the lower frequency range, while the electromagnetic actuator generated a small torque at the higher frequency range. In consequence, the hybrid actuator provided high torque, accurate control, quick response and low heat generation simultaneously. 4. Performance evaluation of the platform In order to evaluate the performance of the platform developed, the stopping characteristics were investigated. In addition, angular deviation on the platform tilting was evaluated by loading a moment of 1.7 N m. This eccentric load applied here was larger than the maximum driving torque of the voice coil motors. Fig. 6 shows the stopping characteristics without torque compensation with the voice coil motors. As can be seen, a clear position fluctuation of about 0.00158 was observed in the platform rotating angle. This oscillating behavior was caused by the pressure fluctuation in the pneumatic actuator due to the beating of the servo valves. In contrast, Fig. 7 shows the stopping characteristic with the torque compensation. The position fluctuation measured was less than one pulse of sensor resolution and negligibly small. The pressure fluctuation in the pneumatic actuator could be successfully compensated by the voice coil motors. Actual driving characteristics were evaluated under the torque loading condition. Fig. 8(a) shows the loading condition of static moment of 5.1 N m. Fig. 8(b and c) shows the platform response for stepwise positioning of 0.00118 and 0.000118, respectively. In particular, clear stepwise responses of 0.000118 can be observed, as shown in Fig. 8(c). These torque loading experiment results confirmed that the electromagnetic actuator can effectively compensate the position error of the pneumatic actuator.
5. Conclusions This paper presented a newly developed high performance tilting motion platform. In addition, the performance evaluation experiments were performed. As a result, the following conclusions could be drawn: 1. As a hybrid actuator, pneumatic and electromagnetic mechanisms were integrated for realizing a high performance tilting motion platform. 2. The performance evaluation results confirmed that the tilting platform provides high rigidity, high positioning capability and high positioning resolution. 3. The results of tilting motion experiment confirmed that the electromagnetic actuators, a couple of voice coil motors, can successfully compensate a torque error of the pneumatic actuator. Acknowledgements This research project was financially supported by the Japan Society for Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (A) No. 19206017. References [1] Moriwaki T (2008) Multi-functional Machine Tool. Annals of the CIRP 57(2):736– 749. [2] Takino H, Kawai T, Takeuchi Y (2007) 5-axis Control Ultraprecision Machining of Complex Shaped Mirror for Extreme Ultraviolet Lithography System. Annals of the CIRP 56(1):123–126. [3] Mitsuishi M, Warisawa S, Tajima F, Suzuki M, Tanimoto K, Kuramoto K (2003) Development of a 9-axis Machine Tool for Bone Cutting. Annals of the CIRP 52(1):323–328. [4] Altan T, Lilly B, Yen YC (2001) Manufacturing of Dies and Molds. Annals of the CIRP 50(2):405–423. [5] Mori M, Fujishima M, Kashiwara K, Horikawa M (2005) Development and Application of a Direct Drive Motor for Performance of Versatile Machine Tool System. Annals of the CIRP 54(1):337–340.
Contents lists available at ScienceDirect
CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp
A high performance tilting platform driven by hybrid actuator H. Shinno (2)*, H. Yoshioka, M. Hayashi Precision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Actuator Control Rotary motion
Multi-axis controlled machine tools require a tilting rotary table or a tilting spindle head. In order to realize an ultraprecision multi-axis machine tool, it is an important issue to develop a high performance tilting platform. This paper presents a newly developed hybrid actuator-driven tilting platform. The hybrid actuator is constructed by integrating a pneumatic rotary actuator and a couple of voice coil motors. Performance evaluation results confirm that the platform provides high precision and high torque motions. ß 2009 CIRP.
1. Introduction Demands for simultaneous multi-axis controlled machining have recently increased in the wide range of industries, i.e., automotive, aerospace, consumer product and others. In order to meet such industrial requirements, various types of simultaneous multi-axis controlled machine tools and multi-functional machine tools [1] have been developed to machine the complex shaped optics for an extreme ultraviolet lithography [2], the artificial human joints and human bones [3], the dies and molds [4], etc. In general, such simultaneous multi-axis controlled machine tools have a tilting motion platform such as a tilting rotary table system driven by direct drive motors [5], a trunnion table system equipped with a worm gear, or a tilting rotary spindle head. However, conventional tilting motion platforms cannot fulfill future advanced industrial requirements on such simultaneous multi-axis controlled machine tools due to low rigidity and low motion accuracy. In this study, an innovative tilting motion platform equipped with a hybrid actuator is newly developed for future ultraprecision multi-axis controlled machine tools. The hybrid actuator proposed is successfully composed of pneumatic and electromagnetic actuators. Performance evaluation results confirm that the tilting platform developed provides high resolution, high motion accuracy, high torque motion and high rigidity. 2. Structural configuration of the developed platform Fig. 1 shows the fundamental driving principle of a newly proposed hybrid actuator. The hybrid mechanism was effectively combined with electromagnetic and pneumatic actuators. These actuators are allocated in parallel and have the common driven axis. Two kinds of actuators are characterized by the attributes, as
* Corresponding author. 0007-8506/$ – see front matter ß 2009 CIRP. doi:10.1016/j.cirp.2009.03.093
shown in this figure. The pneumatic actuator can generate high torque without heat generation, while the actuator has disadvantages such as low response and dead band of pressure control in servo valve. In contrast, the electromagnetic actuator provides significant advantages such as quick response, accurate torque control and dead band free, while this actuator has substantial disadvantages such as low torque and heat generation. In consequence, both the actuators could be complementary to each other. The resultant hybrid actuator made it possible to achieve a remarkable performance. A structural concept of the proposed hybrid actuator is shown in Fig. 2. The pneumatic actuator has four air chambers and then generates the resultant driving force by controlling the differential pressure between the opposite chambers. In contrast to the pneumatic actuator, an electromagnetic actuator, a pair of voice coil motors allocated on both sides, can drive the rotor with high accuracy and quick response. In order to achieve accurate torque transfer around the rotary axis, the platform was designed to have a symmetric structure. In order to minimize nonlinear phenomena, noncontact seals were used in the gap between the stator and rotor. Table 1 shows the fundamental design specifications of the tilting platform developed. Fig. 3 shows an actual structural configuration of the overall platform. The tilting and fixed parts in the platform structure are colored in light blue and in green, respectively. The coils in yellow are moving parts. Two precision angular contact ball bearings were used in the rotary axis of the developed platform. Fig. 4 shows the appearance of the overall platform. The outer diameter of the circular tilting platform was 115 mm. 3. Control system for the hybrid actuator Fig. 5 shows a block diagram of the tilting platform motion control system. The motion control system developed consists of the pneumatic and the electromagnetic actuator control systems.
H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
364
Fig. 1. Mutual complementary function of hybrid actuator.
Fig. 3. Structural configuration of the platform. Fig. 2. Structural concept of a hybrid actuator.
The pneumatic actuator was driven by using the servo valve, which control the torque with a PI compensator and pressure transducer outputs. In addition, the electromagnetic actuator was controlled by a PID compensator and an angle encoder output. The torque error of the pneumatic actuator could be estimated by the pressure
Table 1 Specification of the tilting platform. Tilting table system
Dimension (mm) Stroke (8) Moment of inertia (kg m2)
300 200 185 45 9.56 10 3
Rating torque
Pneumatic actuator (N m) Electric actuator (N m)
6.5 1.0
Angle encoder
Resolution (8) Max response velocity (rpm)
1.1 10 24
4
Fig. 4. Appearance of the platform developed.
H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
Fig. 5. Block diagram of control system.
Fig. 6. Stopping characteristics without pressure compensation. Fig. 7. Stopping characteristics with pressure compensation.
Fig. 8. Stepwise response under loading condition.
365
366
H. Shinno et al. / CIRP Annals - Manufacturing Technology 58 (2009) 363–366
transducer outputs and then the estimated torque error could be compensated by the electromagnetic actuator. Furthermore, the outer disturbance in the pneumatic actuator could be compensated by the process expressed in red of the block diagram. The pneumatic actuator generated a large torque at the lower frequency range, while the electromagnetic actuator generated a small torque at the higher frequency range. In consequence, the hybrid actuator provided high torque, accurate control, quick response and low heat generation simultaneously. 4. Performance evaluation of the platform In order to evaluate the performance of the platform developed, the stopping characteristics were investigated. In addition, angular deviation on the platform tilting was evaluated by loading a moment of 1.7 N m. This eccentric load applied here was larger than the maximum driving torque of the voice coil motors. Fig. 6 shows the stopping characteristics without torque compensation with the voice coil motors. As can be seen, a clear position fluctuation of about 0.00158 was observed in the platform rotating angle. This oscillating behavior was caused by the pressure fluctuation in the pneumatic actuator due to the beating of the servo valves. In contrast, Fig. 7 shows the stopping characteristic with the torque compensation. The position fluctuation measured was less than one pulse of sensor resolution and negligibly small. The pressure fluctuation in the pneumatic actuator could be successfully compensated by the voice coil motors. Actual driving characteristics were evaluated under the torque loading condition. Fig. 8(a) shows the loading condition of static moment of 5.1 N m. Fig. 8(b and c) shows the platform response for stepwise positioning of 0.00118 and 0.000118, respectively. In particular, clear stepwise responses of 0.000118 can be observed, as shown in Fig. 8(c). These torque loading experiment results confirmed that the electromagnetic actuator can effectively compensate the position error of the pneumatic actuator.
5. Conclusions This paper presented a newly developed high performance tilting motion platform. In addition, the performance evaluation experiments were performed. As a result, the following conclusions could be drawn: 1. As a hybrid actuator, pneumatic and electromagnetic mechanisms were integrated for realizing a high performance tilting motion platform. 2. The performance evaluation results confirmed that the tilting platform provides high rigidity, high positioning capability and high positioning resolution. 3. The results of tilting motion experiment confirmed that the electromagnetic actuators, a couple of voice coil motors, can successfully compensate a torque error of the pneumatic actuator. Acknowledgements This research project was financially supported by the Japan Society for Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (A) No. 19206017. References [1] Moriwaki T (2008) Multi-functional Machine Tool. Annals of the CIRP 57(2):736– 749. [2] Takino H, Kawai T, Takeuchi Y (2007) 5-axis Control Ultraprecision Machining of Complex Shaped Mirror for Extreme Ultraviolet Lithography System. Annals of the CIRP 56(1):123–126. [3] Mitsuishi M, Warisawa S, Tajima F, Suzuki M, Tanimoto K, Kuramoto K (2003) Development of a 9-axis Machine Tool for Bone Cutting. Annals of the CIRP 52(1):323–328. [4] Altan T, Lilly B, Yen YC (2001) Manufacturing of Dies and Molds. Annals of the CIRP 50(2):405–423. [5] Mori M, Fujishima M, Kashiwara K, Horikawa M (2005) Development and Application of a Direct Drive Motor for Performance of Versatile Machine Tool System. Annals of the CIRP 54(1):337–340.