JPH068943B2 - Transparent screen - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a transmissive screen, and particularly to a two-lens structure having a Fresnel lens and a lenticular lens function which are excellent in optical performance such as a viewing angle and brightness uniformity. The present invention relates to a transmissive screen having a structure suitable for maintaining the optical performance of the transmissive screen without being affected by environmental temperature and humidity.

[Background of the Invention]

A transmissive screen used in a so-called projection television in which three cathode ray tube images of red, blue, and green are magnified and projected by using a magnifying lens, and the brightness is hard to change depending on the screen portion in a wide viewing angle. It has come to be used widely because of its characteristic. For example, as described in detail in JP-A-59-111137, a transmissive screen having excellent optical performance can be obtained by structurally forming a two-sheet structure.

However, there are cases in which a defect due to the two-sheet structure is exhibited. That is, when the two optical element plates that form the transmissive screen are subject to changes in environmental conditions such as temperature or humidity, the two optical element plates differ from the two-contact state in which they are in the designed shape, and the two optical element plates mutually differ. Separation causes image quality deterioration such as out-of-focus, color shift, and image deformation. The above-mentioned publicly known example does not recognize the problem of the image quality deterioration due to the environmental resistance temperature and humidity.

As an attempt to recognize such a problem and attempt to improve it, Japanese Utility Model Publication No. 55-116341 can be cited. However, the technology described in this publication has examined specific problems in actual use. It ’s hard to see the result,
In actual use, it is thought that there are many inadequate points, including ease of use.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks and to maintain excellent optical performance without being affected by environmental temperature and humidity, and moreover, it is easy to use and has a beautiful appearance when the projection television is used for a long period of time. It is to provide an excellent transmissive screen. In addition, it is another object of the present invention to provide a transmissive screen that is most suitable for so-called high-definition video projectors that emphasize optical performance.

[Outline of Invention]

According to the present invention, as described above, the image quality deterioration due to the separation between the two optical element plates constituting the transmissive screen is not affected by the two optical element plates and / or the front and back sides of the respective optical element plates. The present invention has been made paying attention to the occurrence of a warp dimension difference due to a difference in expansion coefficient or the occurrence of sagging, that is, the occurrence of two optical element plates that can move independently of each other.

Here, when the two optical element plates can move independently of each other,
When the environmental temperature and humidity fluctuate, separation between the two element plates is inevitable, but the reason for this is as follows.

That is, when the temperature rises, there is a temperature distribution in the thickness direction of the optical element plates, and the thermal expansion of the surface other than the contact surfaces of the two optical element plates causes the thermal expansion of the contact surfaces of the two optical element plates. It becomes larger than that and warpage occurs due to the so-called bimetal effect. This warp appears in two optical element plates in opposite directions (in this case, the central portion has a biconvex shape with the maximum separation amount). Such defects occur not only when the temperature rises, but also when the temperature drops accompanied by expansion and contraction, or during moisture absorption and dehumidification.

The separation form between the two optical element plates is not necessarily a simple convex or concave shape, but a warp or a difference in size between the two optical element plates causes a defect of separation.

The point of the present invention is that the two optical element plates constituting the transmissive screen are prevented from moving independently of each other, and further, the usability in using the projection television for a long time, the aesthetic appearance, etc. It can be said that it was possible without impairing the above.

Hereinafter, the principle of the present invention will be described with reference to the drawings. First, as a means for preventing the separation of the two optical element plates, a specific example in which the air gap between the mating surfaces of the two element plates is depressurized is shown in FIGS.

FIG. 8 is a sectional view showing the basic concrete example.

In the figure, 1 is a Fresnel lens, 2 is a lenticular lens, and these two optical element plates are used in a superposed manner. At least one of the mating surfaces of the optical element plate is non-planar, and a void 3 is formed therebetween. The ends of the two optical element plates are covered with an airtight holding body 4 that holds the gap 3 airtightly. A part of the airtight retainer 4 is connected to the decompression pump 9 via the communication pipe of the exhaust port component 5, and the opening 10 is formed.
Have. The pressure reducing pump 9 includes a check valve 1 in the cylinder 6.
1 has a piston 7, and the piston 7 is connected to a handle 8. A check valve 12 is provided outside the cylinder 6.

Next, this operating mechanism will be described. The check valve 1 is pulled by pulling the handle 8 of the decompression pump 9 (pulling downward in FIG. 8) while the two optical element plates 1 and 2 are in pressure contact with each other.
1 opens to suck in the air in the void 3 and maintain a reduced pressure. By reducing the pressure of the void 3, the two optical element plates 1 and 2 are
Are brought into close contact with each other. In the case of a 30 to 40 inch transmissive screen for a normal projection television, a decompressed state of 50 mmAq (water column) or more relative to atmospheric pressure, preferably 2
The two optical element plates 1 and 2 are not separated by maintaining the reduced pressure state of 00 mmAq or more.

For example, in the case of a 45-inch projection television, the size of the void 3 is about 0.2 mm on average and its volume is about 100 cm ³ . Therefore, the volume of the decompression pump 9 may be 0.4 cm ³ or more. For example, an inner diameter of 1 cm and a stroke of 1 cm are sufficient.

Next, the constituent materials will be described. Methacrylic resin is usually used for the two optical element plates 1 and 2 because of optical characteristics and other requirements. The airtight retainer 4 has a function of preventing the inflow of air into the voids 3, and may be a methacrylic resin plate of the same type as the optical element plate material or a metal, but if it is made of a material having high rigidity, it will have two pieces. A difference in expansion coefficient occurs as when a temperature difference occurs between the materials 1 and 2, and the so-called bimetal effect may cause the entire screen to be greatly curved. Therefore, it is preferable that the airtight retainer 4 is an elastic body. Moreover, black is preferable because it can prevent deterioration of the optical performance of the screen due to the reflected light from the end of the optical element plate. As an example, an elastic body such as carbon-blended chloroprene rubber or butyl rubber can be used. The airtight retainer 4 is attached to the optical element plates 1 and 2 by adhesion or other means.
Join or adhere to. At that time, a pretreatment agent is used if necessary.

The exhaust port component 5 is composed of an elastic body or a rigid body of the same type as the airtight holding body 4, and is airtightly joined or adhered to the airtight holding body 4.

FIG. 8 shows an example in which the airtight holding member 4 is joined to the end portion of the optical element plate, but the entire circumference of the end portion may be covered with a U-shaped trim as shown in FIG.

In FIG. 9, the same elements as those in FIG. 8 are indicated by the same numbers. In FIG. 9, 4'is a trim strip (elastic body) formed in a U shape. In this case, the pressure reduction is maintained by reducing the pressure of the voids 3 in a closely contacted state without necessarily joining them.

In the case of this example, it is preferable in terms of processing and design that the exhaust port component 5 is provided with a trim end portion at one of the four corners and is provided at the joint portion.

Two specific examples have been shown above, but gas (air, water vapor) may slightly flow in through the optical element plates 1 and 2, the airtight holding member 4, the exhaust port component 5, or through the joint or the close contact portion to reduce the decompression. There is.

In that case, the depressurization (exhaust) operation described above may be repeated. After depressurizing operation, the handle 8 is pushed (upward in FIG. 8) to close the check valve 11 and close the check valve 1.
2 is opened, the gas absorbed in the cylinder 6 is discharged at the time of pressure reduction, the position of the piston 7 is returned to the position at the time of pressure reduction, and the pressure reduction operation can be performed again.

Although FIG. 8 shows a state in which the decompression pumps are always connected, the form in which the decompression pumps are connected only during the decompression operation is preferable in terms of design aesthetics. To achieve this, a check valve is required in the exhaust port component 5. Preferably, the self-closing valve 13, 1 shown in FIG. 10 or FIG.
4 is provided.

10 and 11, the same components as those in FIG. 8 are designated by the same reference numerals. In FIG. 10, 15 is
It is a component having a communication hole 16 and is joined to the exhaust port component 5. Reference numeral 17 denotes an elastic tube made of natural rubber, butyl rubber or the like, which is fitted into the component 15 so as to close the communication hole 16. When a vacuum pump (not shown) is connected and exhausted, a gap is created between the elastic tube 17 and the communication hole 16, and when the exhaust is completed, the elastic tube 17 contracts and closes the connection hole 16.

In FIG. 11 (a), reference numeral 18 denotes a rigid frame, and the poppet valve 19 is configured so that the opening is closed by a spring 20. At the time of exhaust, the poppet valve 19 is pushed up against the spring 20 (upward in FIG. 11) to provide an opening for exhaust. Spring 2 after exhaust
The closed airtightness is maintained by the action of 0.

Here, the poppet valve 19 may be configured as shown in FIG. 11 (b). In this case, since the pressure of the void 3 is lower than the atmospheric pressure, it is automatically closed.

According to this method, it is not necessary to operate the valve each time the depressurizing operation as described in Japanese Utility Model Laid-Open No. 55-116341 is performed, and the usability is improved.

Further, when the reduced pressure is lowered and the reduced pressure is operated as shown in FIG. 12 and the decompression pump is operated, a screen without image deterioration can always be seen.

12, the same structural elements as in FIG. 8 are designated by the same numbers. That is, in addition to the specific example of FIG. 8, a pressure sensor 21 for detecting the pressure in the gap 3, a drive unit 22 for moving the handle 8 forward and backward, and a control unit 23 for controlling the drive unit 22 by the input of the pressure sensor 21 are added. It is configured. The principle of depressurization is the same as in the case of FIG.

When the pressure in the gap 3 detected by the pressure sensor 21 is equal to or higher than the set pressure, the drive unit 22 pulls the handle 8 to reduce the pressure by the signal transmitted from the control unit 23. When the gap 3 is depressurized to the set pressure, the drive unit 22 pushes the handle 8 to return the piston 7 to the position before the depressurizing operation in response to a signal from the control unit 23, and prepares for the next depressurizing operation.

From the above, the principle of the present invention as well as an example of a specific void reducing means used for realizing the present invention can be understood.

Example of Invention

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention. The embodiment shown in the figure is an embodiment in which the decompression pump is driven by using the heat generation energy from the cathode ray tube for projecting an image on the transmissive screen as a power source and exhausted.

In FIG. 1, the same components as in FIG. 8 are indicated by the same numbers. The decompression pump 9 has two cylinders 6a, 6
b, it has two pistons 7a and 7b. The communication pipe sides with the exhaust port component 5 are 6a and 7a, respectively. The pistons 7a and 7b move integrally. Also, cylinder 6b
The gas 25 in the space surrounded by the piston 7b has a sealed structure that prevents inflow or outflow to the other. The decompression pump 9 is arranged close to the cathode ray tube 24 side.

The operation mechanism will be described. The cathode ray tube 24 generates a large amount of heat during use, the temperature around the cathode tube 24 becomes high, and the temperature of the gas 25 also rises. The gas 25 thermally expands and its volume increases, pushing the piston 7b. That is, this is the same operation as when the handle 8 is pulled in FIG. 8, and the pressure is reduced in the space 3.

On the other hand, when the use of the projection television is stopped, the cathode ray tube 24 does not generate heat and the gas 25 falls to room temperature. As a result, the volume of the gas 25 contracts, and the piston 7b
Returns to the same position as before use.

FIG. 2 is a sectional view showing another embodiment in which the heat generated by the cathode ray tube 24 is used efficiently.

In the figure, a transparent liquid 28 is injected into a space whose periphery is closed by a cathode ray tube 24, a projection lens 26, and a radiation fin 27, and heat generated from the cathode ray tube 24 is transmitted to the radiation fin 27 through the transparent liquid 28. It is conducted and then transmitted into the air. As a result, the cathode ray tube 24 is cooled, and damage or the like is prevented. This is a so-called liquid-cooled CRT, which is commonly used in projection televisions to obtain a bright image. At this time, since the heat radiation fins 27 become hot, the pressure reducing pump 9 is inserted in the heat radiation fins 27 to improve the heating efficiency, and the pressure reduction can be maintained unattended and without making noise like an electric vacuum pump. .

For example, in a 45-inch projection TV, gas 25
Since the temperature rise of the gas is about 60 ℃ or more, considering the body expansion of the gas, in order to reduce the pressure to 200 mmAq, the gas 2
The volume of 5 should be about 1.7 cm ³ . Therefore, the decompression pump 9
If the inner diameter of is 1 cm, the total length should be 5 cm. Therefore, it can be sufficiently stored in the radiation fin 27 of the normally used 5 inch to 9 inch cathode ray tube.

In the embodiment shown in FIGS. 1 and 2, the pressure reduction is performed irregularly if the period during which the cathode ray tube 24 is operated is irregular, but the pressure reduction is performed periodically using a timer. You can also do so.

For example, in a 45-inch projection television, the Fresnel lens 1 and the lenticular lens 2 in FIG. 1 are generally made of methacrylic resin. From the gas permeability of methacrylic resin and the size of the screen, the gas permeability per day is about 2.5 cm ³ . Since the void 3 is about 100 cm ³ , about 2% of the volume of the void 3 is permeable to gas. Since it is preferable to reduce the pressure to 200 mmAq, the gas permeation amount is preferably 2% or less.

Therefore, it is necessary to reduce the pressure every day. That is, the cathode ray tube 24 may be activated by a timer every 24 hours, or the heat generating means in place thereof may be activated to reduce the pressure.

Further, it is preferable that the frequency of the depressurizing operation as described above is low, from the viewpoints of electricity consumption, stabilization of optical performance, and the like. For that purpose, it is necessary to reduce the permeation of gas (air, water vapor, etc.) through the optical element. Examples of the gas permeation prevention treatment include vinylidene chloride coating treatment.

FIG. 3 is a graph showing the relationship between the coating film thickness and the gas permeation amount (relative value) when a vinylidene chloride coating is applied to a plastic plate of a methacrylic resin plate.

As can be seen in the figure, the film thickness of vinylden chloride is 0.5
At μm, the amount of gas permeation is reduced to about 1/10 of that of the substrate alone (without vinylidene chloride coating). Further, when the film thickness is 3 μm, it is reduced to about 1/100 of that of the substrate alone.

The treatment method is dipping the substrate in vinylidene chloride emulsion,
It was pulled up at a slow speed, applied to a uniform thickness, dried at room temperature and then baked (about 100 ° C.). For prevention of permeation only, it is sufficient to coat only the mating surface side of each of the two optical elements, but in order to further prevent moisture absorption of the optical element plate, reduce deformation of the optical element plate, and increase the effect, It is desirable to coat the opposite surface, preferably double-sided. Considering the method of forming the coat film, double-sided coating is easy and the effect is great, which is suitable.

Next, an example in which one of the two optical element plates is formed of an adhesive sheet will be described.

As an example of the composition of the adhesive sheet, the base polymer is 100 parts of vinyl chloride resin (PVC) with a degree of polymerization of about 1000, and the plasticizer is most commonly DOP, but has no contact migration property. Add 30 parts or more of polyester or epoxy to prevent the surface of other optical element plates from appearing or swell, and stabilize Ba-Zn or lead to prevent throat deterioration and heat deterioration during processing. 2 parts of agent are used.

By using the optical element plate of such a pressure-sensitive adhesive sheet, it can be easily brought into close contact with other optical element plates, and the degree of close contact can be improved when the pressure is maintained. Considering the optical performance, the Fresnel lens can be made thick (about 3 to 5 mm), but especially in the case of high-definition projection TV, the diffuser plate with the lenticular lens function is 1 mm.
Since it has the following thin wall, it is effective to make it a flexible contact body. In this case, a predetermined amount of diffusing material is blended if necessary.

Next, FIG. 4 shows an embodiment in which a transparent liquid is interposed on the mating surfaces as a method for preventing separation of the two optical element plates.

In FIG. 4, the same components as in FIG. 1 are designated by the same numbers. The embodiment shown in the figure comprises a Fresnel lens 1, a lenticular lens 2, a transparent liquid 30 injected into the gap between the mating surfaces of these two optical element plates, and an outflow prevention member 31 for preventing the outflow of this transparent liquid. Has been done.

The reason why the separation of the two optical element plates 1 and 2 can be prevented in this embodiment will be described.

When the liquid is completely sealed, the volume change of the liquid at a pressure change of 1 kg / cm ² is 0.004 to 0.005%.
For example, to expand the volume of liquid by 1%, 200 kg / cm
A pressure of ² is required. 2 due to changes in environmental temperature and humidity
Even if the optical element plates 1 and 2 are deformed, the deformation force is much smaller than the above pressure, and therefore the volume of the transparent liquid 30 hardly changes. That is, the mating surface side is hardly deformed,
Therefore, it is not separated. The transparent liquid 30 preferably has a high viscosity in consideration of leakage.

However, the following drawbacks are caused by interposing the transparent liquid on the mating surfaces of the two optical element plates 1 and 2 as described above.

That is, as shown in FIG. 5, the relative refractive index of the lenticular lens 2 changes, the focal length changes, and the viewing angle θ changes.

Generally, a cylinder, an ellipse, a sphere, or the like is used as the shape of the lenticular lens 2, but here, a cylindrical lens will be used for description. The following formula holds from the formula of the thin lens.

Here, f is the focal length of the lenticular lens 2, n ₁ is the refractive index of the transparent liquid, n ₂ is the refractive index of the lenticular lens 2,
r is the radius of curvature of the lenticular lens (one surface is a flat surface). Therefore, when n ₁ <n ₁ ′, f <f ′ and the viewing angle θ becomes θ> θ ′.

When the viewing angle θ is small, the range of the observer device that can see the screen well becomes small. That is, the refractive index n of the transparent liquid 30
It is preferable that ₁ is small and the refractive index n ₂ of the lenticular lens ₂ is large. However, water, silicone oil, or the like is used as the transparent liquid 30, but water having a relatively small refractive index is 1.33.

On the other hand, as the lenticular lens 2, other than methacrylic resin, polycarbonate, polystyrene or the like is used, but the refractive index is large and is about 1.6. Therefore, n ₂ / n
₁ is 1.2. Conventionally, the lenticular lens 2 is a methacrylic resin having a refractive index of 1.49, and air is used instead of the transparent liquid to have a refractive index of 1.0, so that n ₂ / n ₁ is 1.49. To obtain the same viewing angle θ, it is necessary to use the same focal length.

That is, in order to obtain the same focal length from the equation (1), the curvature radius r of the lenticular lens may be set to about 2/5. However, the pitch of the conventional lenticular lens 2 is designed to be almost twice the radius r of the lenticular lens. Therefore, the lens pitch must be reduced as the radius of curvature r is reduced. That is, in the case of water and polycarbonate, the lens pitch needs to be 1 / 2.5 or less. If the lens pitch is made fine, it will become difficult in manufacturing. Therefore, in the present invention, it is configured as shown in FIG.

That is, a lens shape is provided on the mating surface side of the Fresnel lens 1 to cause a condensing function, and the radius of curvature r of the lenticular lens is
Even if is large, the focal length is shortened so that it is not necessary to make the lens pitch extremely small. In this embodiment, the radius of curvature r of the lenticular lens 2 and the lens pitch are set to those of the conventional one.
By setting it to about 4/5, we were able to have the same viewing angle as before without problems in manufacturing.

Next, an embodiment using a transparent magnetic material will be described with reference to FIG.

Examples of the transparent magnetic material include orthoferrite and rare earth iron garnet. A magnetic substance dispersion layer 32 is formed by kneading 50 to 70% by volume of a transparent magnetic fine powder on one surface of the optical element plate 1 to form a magnetic substance dispersion layer 32, and N poles and S poles are alternately and continuously magnetized. .

The reason why the addition amount of the fine powder of the transparent magnetic material is 50 to 70% is that if the amount is less than 50%, the desired magnetic force cannot be obtained, and if the amount is more than 70%, it becomes difficult to disperse the fine powder. This is because the reason for processing and the completed magnetic material dispersion layer are so brittle that they cannot be put to practical use.

On the other hand, a soft iron plate 3 with a width of 0.1 mm is provided on one surface of the other optical element plate 2.
3 are arranged in a direction perpendicular to the multi-polarized optical element plate 1 at a pitch that does not interfere with the optical design, and are inserted into a transparent material such as an acrylic resin as a base material and cast or extruded. Produce by molding. By arranging the multi-pole magnetized optical element 1 and the soft iron plate at a right angle, the two optical element plates 1 and 2 can be easily arranged in a desired positional relationship and can be brought into close contact with each other by magnetic force. The reason for using the soft iron plate 33 is
This is because it is a material that is hard to magnetize and facilitates the position setting of the two optical element plates 1 and 2.

If soft iron plates with a width of 0.1 mm and a depth of 1 mm are arranged at a pitch of 1.2 mm, they will occupy 8.3% of the total area, but there is no particular problem in terms of optical performance. Furthermore, as a method of increasing the magnetic force, in order to prevent the surface reflection of the optical element plate, since a black line has been conventionally arranged, in combination with this black line, a magnetic substance is dispersed in the black line part, There is also a method of disposing a magnetic adsorbent.

〔The invention's effect〕

As described above, according to the present invention, the heat generation energy from the cathode ray tube for image projection is used as the drive energy source of the means for maintaining the reduced pressure in the gap between the mating surfaces of the two optical element plates. As a result, it is possible to provide a highly reliable, high-performance transmissive screen that does not separate the two optical element plates even if the environmental temperature and humidity fluctuate, and is easy to use without impairing the aesthetic appearance. There are advantages.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing an essential part of another embodiment of the present invention, and FIG. 3 is a film thickness for showing the effect of gas permeation prevention treatment. FIG. 4 is a cross-sectional view showing a main part of still another embodiment of the present invention, FIG. 5 is an explanatory view showing an optical defect of the embodiment shown in FIG. 4, FIG. 6 is a sectional view showing a main part of still another embodiment of the present invention, FIG. 7 is a perspective view showing a main part of still another embodiment of the present invention, and FIG. 8 is two optical element plates. FIG. 9 is a cross-sectional view showing a concrete example of means for preventing separation between them, FIG. 9 is a cross-sectional view showing the main part of another concrete example, and FIGS. 10 and 11 are other concrete examples using a self-closing valve. 1 is a sectional view showing the main part of FIG.
FIG. 2 is an explanatory diagram showing a specific example in the case of automatically operating the decompression pump. Explanation of reference numerals 1, 2 ... Optical element plate of transmissive screen, 3 ... Air gap, 4, 4 '... Airtight retainer, 5 ... Exhaust port component, 9 ...
… Pump, 13, 14 …… Self-closing valve, 21 …… Pressure sensor, 24 …… Cathode tube, 30 …… Clear liquid, 32 ……
Transparent magnetic material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hironobu Sato Inventor Hironobu Sato 292 Yoshida-cho, Totsuka-ku, Yokohama-shi Kanagawa Electric Appliance Research Institute (72) Inventor Norio Yatsuda 292 Yoshida-cho, Totsuka-ku Yokohama-shi, Kanagawa Inside the Hitachi Home Appliances Research Laboratory (72) Inventor Masao Takagi 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Stock Company Inside the Hitachi Home Appliances Research Laboratory (72) Koji Hirata 292 Yoshida-cho, Totsuka-ku Yokohama-shi, Kanagawa Shikisha Household Appliances Research Laboratory, Hitachi, Ltd. (56) Bibliography Sho 55-116341 (JP, U)

Claims (5)

[Claims] 1. An optical element plate comprising at least two optical element plates, wherein a fluid is sucked from a gap between mating surfaces of the both element plates by a fluid suction means, thereby guiding the gap to a negative pressure so that a space between the optical element plates is formed. In the transmission type screen which is made to be in close contact, the heat generation energy from a cathode ray tube for projecting an image on the transmission type screen is used as a power source of the fluid suction means. 2. The transmissive screen according to claim 1, wherein one or both surfaces of the two optical element plates are subjected to gas permeation treatment. 3. The transmission screen according to claim 1, wherein the diffusion plate having a lenticular lens function, which is one of the two optical element plates, is formed of a flexible and adhesive sheet. A transmissive screen, characterized in that when the air gap on the mating surface with the other optical element plate is decompressed, both diffusion plates are brought into close contact with each other. 4. The transmission screen according to claim 1, wherein a transparent liquid is interposed between the mating surfaces of the two optical element plates to prevent separation of the two optical element plates. And a transmissive screen. 5. The transmission screen according to claim 1, wherein a layer in which a transparent magnetic material is dispersed is formed on the surface of one of the two optical element plates, and soft iron is formed on the other. A transmissive screen characterized by arranging magnetic attraction bodies such as lines.