JP3359710B2 - Actuator using an element that converts heat into mechanical force - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator, particularly to a microactuator.

[0002]

2. Description of the Related Art In recent years, attention has been focused on micromachine technology, and medical microrobots and the like are expected. This requires the realization of a microactuator. In this connection, for example, an articulated manipulator using a shape memory alloy is disclosed in Japanese Patent Application Laid-Open No. 63-136014. Shape memory alloy actuators have a large amount of displacement and generated force per unit volume, and are promising as microactuators. This discloses a method of independently performing feedback control of each actuator based on a resistance value characteristic of a shape memory alloy that changes depending on temperature.

[0003]

In such an articulated manipulator, highly accurate control of the actuator is required. Therefore, in addition to the shape memory alloy functioning as an actuator, an electrothermal conversion element for converting supplied electric power to heat and a feedback sensor are required. Fabricating and assembling these minute components individually is a major obstacle to miniaturization.

When high-precision position control is required as in a manipulator, a function for detecting position and stress (load) is desired for a feedback sensor. These two cannot be obtained from only the resistance value of the shape memory alloy. For this reason, another sensor is required. However, mounting the sensor on an electrothermal conversion element that is a drive energy supply device or an element that converts heat into mechanical force is a great obstacle to miniaturization.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an actuator using an element that converts heat into a mechanical force, which is extremely small and capable of highly accurate feedback control based on displacement and stress.

[0006]

According to the present invention, an actuator for converting heat into a mechanical force and an element for generating Joule heat by a supplied electric current to heat the element for converting the heat into a mechanical force. The first electrothermal conversion element and the element that generates Joule heat by the supplied current and heats the element that converts the heat into mechanical force, and at least the gauge factor or the material of the first electrothermal conversion element A second electrothermal conversion element made of a material having one of different temperature coefficients of resistance; and the first and second electrothermal conversion elements can monitor resistance values of the first and second elements. It is configured as follows. The actuator more preferably has a portion for electrical connection from which the resistance value of each of the first and second electrothermal conversion elements can be measured. Another actuator of the present invention is an element that converts heat into mechanical force, a first electrothermal conversion element that generates Joule heat by an applied current, and heats the element that converts the heat into mechanical force. Generating an Joule heat by an electric current supplied thereto, and heating an element for converting the heat into a mechanical force, and at least one of a gauge coefficient or a temperature coefficient of resistance with respect to a material of the first electrothermal conversion element. A second electrothermal conversion element, one of which is made of a different material, wherein the first and second electrothermal conversion elements are configured to monitor a voltage and a current applied to each of the first and second elements. Have been. More preferably, the actuator has a portion for electrical connection that can measure a voltage and a current applied to each of the first and second electrothermal conversion elements.

[0007]

The electrothermal conversion element is made of two types of materials having different gauge factors or different temperature coefficients of resistance.
Therefore, by monitoring the resistance value of each material, temperature and strain can be detected. By knowing these two parameters, the displacement and stress can be obtained from the stress dependence of the temperature-displacement relationship of the element that converts heat into mechanical force. Since the electrothermal conversion element and the two sensors are integrated, the configuration can be made very small.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. First, the configuration of the actuator of the first embodiment will be described with reference to FIGS. FIG. 1 is a top view of the actuator of this embodiment, and FIG.
II-II sectional view of the actuator of FIG. 1, FIG.
1A shows an initial state, and FIG. 1B shows a curved state.

The flat shape memory alloy 1 has been subjected to a two-way shape memory processing of a bent shape in advance. Shape memory alloy 1
Is entirely covered with a polyimide film 2 which is an insulating film. On its main surface, a platinum (Pt) thin film pattern 3 and a titanium (Ti) thin film pattern 4 are provided. A lead wire 6 is connected to the connecting portion 5 between the Pt thin film pattern 3 and the Ti thin film pattern 4, a lead wire 7 is connected to an end of the Pt thin film pattern 3,
A lead wire 8 is connected to an end of the i thin film pattern 4. Leads 7 and 8 are connected to a variable voltage power supply (not shown). Each of the leads 6, 7 and 8 is connected to a potential measuring device (not shown).

When a voltage is applied between the two lead wires 7 and 8, a current flows through the thin film patterns 3 and 4, and Joule heat is generated. Joule heat heats the shape memory alloy 1 via the polyimide film 2. The shape memory alloy 1 changes from the state shown in FIG. 3A to the state shown in FIG. 3B as the temperature rises. At this time, the amount of bending is controlled by adjusting the temperature of the shape memory alloy 1 by adjusting the current flowing through the thin film patterns 3 and 4.

Pt thin film pattern 3 and Ti thin film pattern 4
Is determined by measuring the value of the current flowing through the lead wire 7 (or the lead wire 8) and the potentials of the lead wire 6, the lead wire 7 and the lead wire 8.

In general, the resistance value of a metal thin film changes with temperature and strain. For example, if the resistance value at 300 K and no strain is R, the change ΔR in resistance value with respect to R at temperature T with strain ε is Using the rate K and the temperature coefficient A of the resistance value, it is given by ΔR = R {Kε + A (T−300)}. Here, gauge factor K and temperature coefficient A of resistance value
Is a coefficient depending on the material, and its value differs between platinum and titanium. Therefore, for the Pt thin film pattern 3 and the Ti thin film pattern 4, for example, the resistance value when the strain is 0 at 300K is measured in advance, and the measured resistance value is compared with the strain ε and the temperature T. Can be obtained by calculation. However, since the strain ε and the temperature T calculated here are the values of the thin film patterns 3 and 4, it is necessary to correct them based on calibration data obtained in advance.

The displacement of the actuator is immediately obtained from the calculated strain. The stress is obtained from the displacement and the stress dependency of the temperature-displacement relationship of the shape memory alloy obtained in advance. By performing feedback control of the value of the current flowing through the thin film patterns 3 and 4 based on the displacement and stress obtained in this way, it is possible to control a highly accurate actuator that is suitable for application to a manipulator or the like. Also, since the electrothermal conversion element for heating the shape memory alloy and the two types of sensors are integrally formed in the shape memory alloy, a very small actuator can be obtained.

By incorporating such an actuator into a curved tube, for example, it can function as a manipulator. Such a manipulator can be used for bending of a distal end portion, for example, by disposing it at a curved portion of an endoscope.

Next, a method of manufacturing the actuator according to the first embodiment will be described with reference to FIGS. A polyimide film 102 is formed on the entire surface of the shape memory alloy plate 101 which has been subjected to a shape memory process in advance (FIG. 4). After forming a Pt thin film 103 on the surface (main surface) by a sputtering method,
A semiconductor photoresist 104 is formed thereon by a spin coater (FIG. 5). After exposing a predetermined pattern using a contact aligner or the like, development is performed to form a resist pattern 104 '(FIG. 6). After removing the Pt thin film in a region where the resist pattern 104 'is not formed by using a method such as ion milling to form a Pt pattern 103', the resist pattern 104 'is removed using an organic solvent or the like (FIG. 7). ). A Ti thin film 105 is formed by a sputtering method, and a photoresist 106 for a semiconductor is formed thereon by a spin coater (FIG. 8). After exposing a predetermined pattern using a contact aligner or the like, development is performed to form a resist pattern 106 ′ (FIG. 9). After removing the Ti thin film in the region where the resist pattern 106 'is not formed using a diluted mixed solution of hydrofluoric acid and nitric acid to form a Ti thin film pattern 105', the resist pattern 106 'is formed using an organic solvent.
Is removed (FIG. 10). During this etching, the Pt thin film pattern 103 'is not etched. As a result, the Pt thin film pattern 10 electrically connected at the connection 107
An electric resistance pattern composed of 3 ′ and the Ti thin film pattern 105 ′ is formed. In order to make heat generation of the electric resistance pattern uniform, the Ti thin film pattern 105 ′ is formed thicker than the Pt thin film pattern 103 ′, and the Ti thin film pattern 1 is formed.
The resistance value of 05 ′ and the resistance value of Pt thin film pattern 103 ′ are made equal. As a result, the calorific value per unit area of the two thin film patterns becomes equal, and the shape memory alloy 1 is uniformly heated. Lead wire 108 to connection 107
The lead wire 110 is connected to the end 109 of the Ti thin film pattern 103 ', and the lead wire 112 is connected to the end 111 of the Pt thin film pattern 105' (FIG. 11). Thus, the actuator shown in FIGS. 1 to 3 is completed.

In the above-described embodiment, in order to obtain uniform heat generation, the film thickness is adjusted so that the resistance values of the two types of thin film patterns are equal. However, the layout of the electric resistance pattern is Pt as shown in FIG. This can be dealt with by forming a complicated shape of the thin film pattern 114 and the Ti thin film pattern 115. In this case, since it is not necessary to adjust the film thickness, the manufacture becomes easier.

The structure of the actuator according to the second embodiment of the present invention will be described with reference to FIGS. FIG.
3 is a top view of the actuator of the second embodiment, FIG.
13 is a top view showing a layout of an electric resistance pattern of the actuator of FIG. 13 before providing a shape memory alloy, and FIG. 15 is a cross-sectional view of the structure of FIG. 14 taken along the line XV-XV.

A flexible insulating thin film 2 such as polyimide
Wirings 204, 206, 20 made of aluminum on
8, 210, 212 are provided. An interlayer insulating film 214 made of polyimide is provided thereon. Two electric resistance patterns 218 are formed on the interlayer insulating film 214.
And 232 are provided. The electric resistance pattern 218 includes a Ti thin film pattern 220 and a Pt thin film pattern 222, and both are electrically connected at a connection portion 224. The connection portion 224 is formed by the Pt thin film pattern 228 through an opening 216 provided in the interlayer insulating film 214.
It is connected to the wiring 204. Pt thin film pattern 222
Is connected to the wiring 202 through the opening 216 by a Pt thin film pattern 226. The other end of the Ti thin film pattern 220 is
0 is connected to the wiring 206 through the opening 216.

Similarly, the electric resistance pattern 232 comprises a Ti thin film pattern 234 and a Pt thin film pattern 236,
Both are electrically connected at a connection portion 238.
The connection portion 238 is connected to the wiring 210 via the opening 216 by a Pt thin film pattern 242. The other end of the Pt thin film pattern 236 is
0 is connected to the wiring 208 through the opening 216. The other end of the Ti thin film pattern 234 is connected to the wiring 21 through the opening 216 by the Ti thin film pattern 244.
2 are connected.

A polyimide film 246 is provided on these thin film patterns. The polyimide film 246 and the interlayer insulating film 214 are provided with openings 248 penetrating therethrough and reaching the wiring.
6, 208, 210, 212 lead wires 250, 252, 254, 256, 258, 2
60 are connected respectively.

On the polyimide film 246, at positions corresponding to the upper portions of the electric resistance patterns 218 and 232, respectively.
Plate-shaped shape memory alloys 262 and 264 in which a bent shape is subjected to two-way shape memory processing in advance are attached.

The shape memory alloy 262 is heated by applying a voltage between the lead wire 250 and the lead wire 254 and flowing a current through the electric resistance pattern 218 to generate Joule heat. Cooling is performed by heat dissipation by stopping power supply. Similarly, the shape memory alloy 264 is heated by applying a voltage between the lead wire 256 and the lead wire 258 and flowing a current through the electric resistance pattern 232 to generate Joule heat. Cooling is performed by heat dissipation by stopping power supply.

Since the heating of these two shape memory alloys is performed using separate leads, the two actuators can be driven independently. Further, by measuring the potential of each lead wire during energization, feedback control based on displacement and stress can be independently performed for the two actuators in the same manner as in the first embodiment.

The actuator thus formed is
Since the region other than the shape memory alloy region is constituted by a thin polyimide film and a metal thin film, it is very flexible. For example, it can be made to function as a two-joint manipulator by being incorporated between the curves of an endoscope. In the present embodiment, an example of two joints has been described, but it is needless to say that the same can be realized with three or more joints.

Next, a method of manufacturing the actuator of the second embodiment will be described with reference to FIGS. A silicon nitride film 302, a first polyimide film 303, and an Al thin film 304 are sequentially formed on a silicon substrate 301 by sputtering (FIG. 16). Al is patterned using a photolithography process of a normal semiconductor process, an Al pattern 304 ′ serving as a wiring is formed, a photosensitive second polyimide film 305 is further formed, and a contact formed in the photolithography process is formed thereon. A hole 306 is formed in a predetermined area (FIG. 17). A Pt thin film 306 and a photoresist 307 are sequentially formed by sputtering (FIG. 18). FIG.
A plurality of composite resistor patterns 308 made of Ti and Pt are formed in the same manner as shown in FIG.
9). This is electrically connected to an Al wiring pattern via a contact hole as shown. After the formation of the third polyimide film serving as an insulating film, a shape memory alloy 309 that has been subjected to a predetermined shape memory process is pasted to each composite resistance pattern (FIG. 20). After this,
An articulated manipulator is constructed by selectively removing all of the substrate by etching, cutting out unnecessary portions of the polyimide, and mounting it on a curved tube having an appropriate joint. In this method, since a plurality of actuators incorporating a plurality of sensors are integrally formed without performing an assembling process by photolithography technology, highly accurate control can be performed as an articulated manipulator. This makes it possible to obtain an unprecedented compact and high-precision actuator.

By the way, in the second embodiment, an example of two joints has been described, but it is naturally possible to extend this to three or more joints. However, the method of the second embodiment has a disadvantage that the number of necessary wirings increases as the number of joints increases. In order to avoid this, a method of incorporating a control electronic circuit in each joint by utilizing the fact that the actuator is formed on a semiconductor substrate is conceivable. This method will be described with reference to FIG. Here, a semiconductor electronic circuit region 402 interconnected by a wiring member 401 covered with a flexible material such as polyimide, and FIG.
An articulated manipulator is constituted by a shape memory alloy 403 having an electric heater made of the same Ti thin film and Pt thin film as shown in FIG. Here, the wiring is composed of a power supply line, a ground line, a control signal line, a synchronization signal line, a potential measurement line for a heater, and the like. It has a function of heating and sensing joints at a predetermined timing. The sensed signal is sent to an external controller, which performs feedback control of each actuator to perform a required operation. In this method, the number of wires does not increase even when the number of joints increases. The control electronic circuit was previously formed in a predetermined region of the semiconductor substrate in the description of the manufacturing method of the second embodiment by using a normal integrated circuit manufacturing technique, and the circuit was formed in the step of removing the semiconductor substrate. It is obtained by selectively leaving a region.

[0027]

According to the present invention, it is possible to obtain an actuator that can be minutely controlled with high accuracy.

[Brief description of the drawings]

FIG. 1 is a top view of an actuator according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the actuator of FIG. 1 taken along line II-II.

FIG. 3 is a side view of the actuator of FIG. 1,
(A) shows an initial state before heating, and (B) shows a curved state after heating.

FIG. 4 is a view showing a first step in manufacturing the actuator of the first embodiment shown in FIGS. 1 to 3;

FIG. 5 is a view showing a second step in manufacturing the actuator of the first embodiment.

FIG. 6 is a diagram showing a third step in manufacturing the actuator of the first embodiment.

FIG. 7 is a view showing a fourth step in manufacturing the actuator of the first embodiment.

FIG. 8 is a view showing a fifth step in manufacturing the actuator of the first embodiment.

FIG. 9 is a view showing a sixth step in manufacturing the actuator of the first embodiment.

FIG. 10 is a view showing a seventh step in manufacturing the actuator of the first embodiment.

FIG. 11 is a view showing a final step in manufacturing the actuator of the first embodiment.

FIG. 12 is a diagram showing another electric resistance pattern instead of the electric resistance pattern of FIG. 1;

FIG. 13 is a top view of the actuator according to the second embodiment of the present invention.

14 is a top view of the actuator of FIG. 13 before providing a shape memory alloy, showing a layout of an electric resistance pattern.

15 is a cross-sectional view of the structure of FIG. 14 taken along line XV-XV.

FIG. 16 is a view showing a first step in manufacturing the actuator of the second embodiment shown in FIG. 13;

FIG. 17 is a view showing a second step in manufacturing the actuator of the second embodiment.

FIG. 18 is a view showing a third step in manufacturing the actuator of the second embodiment.

FIG. 19 is a view showing a fourth step in manufacturing the actuator of the second embodiment.

FIG. 20 is a view showing a final step in manufacturing the actuator of the second embodiment.

FIG. 21 is a diagram showing an actuator provided with a control electronic circuit for each joint.

[Explanation of symbols]

1. Shape memory alloy, 2. Polyimide film, 3. Pt thin film pattern, 4. Ti thin film pattern.

Claims (4)

(57) [Claims] 1. An element for converting heat to mechanical force, a first electrothermal conversion element for generating Joule heat by an applied current and heating the element for converting the heat to mechanical force, And heat the element that converts the heat to mechanical force, and at least one of the gauge coefficient or the temperature coefficient of resistance differs from the material of the first electrothermal conversion element. A second electrothermal conversion element made of a material, wherein the first and second electrothermal conversion elements are the first and second electrothermal conversion elements.
An actuator using an element that converts heat into a mechanical force, wherein the actuator is configured to monitor a resistance value of each element. 2. The heat converting device according to claim 1, further comprising an electrical connection portion capable of measuring a resistance value of each of said first and second electrothermal converting elements. Actuator using element. 3. An element for converting heat to a mechanical force, a first electrothermal conversion element for generating Joule heat by an applied current and heating the element for converting the heat to a mechanical force, And heat the element that converts the heat to mechanical force, and at least one of the gauge coefficient or the temperature coefficient of resistance differs from the material of the first electrothermal conversion element. A second electrothermal conversion element made of a material, wherein the first and second electrothermal conversion elements are the first and second electrothermal conversion elements.
An actuator using an element for converting heat into a mechanical force, wherein the actuator is configured to monitor a voltage and a current applied to each element. 4. The heat-to-mechanical machine according to claim 3, further comprising an electric connection portion for measuring a voltage and a current applied to each of the first and second electrothermal conversion elements. Actuator using an element that converts the force into a force.