Patent Description:
Application of flexible display devices is becoming increasingly favored by the market. The flexible display devices have many advantages such as thinness and lightness, flexibility, foldability, and portability. Development of such technology will bring about significant revolution on forms of display, especially on wearable devices, mobile reading display, etc. With development of flexible display technology, flexible screens can be ingeniously swapped between different display dimensions and display regions to adapt to display requirements of different occasions. Meanwhile, storing and carrying the display screens after folding them is more convenient. Compared to traditional screens, advantages of the flexible screens are significant, which not only provide all-new usage effect to users, but also have more compact volumes and lower power consumption. Meanwhile, the screens have flexibility, reducing a risk of screen fracture.

With the development of the flexible displays, various display devices have appeared, for example, foldable display devices, slidable display devices, and rollable display devices, etc. The rollable display devices have a new flexible display manner, because they can omit coil spring assemblies of the display devices which are complicated and have short service life. Therefore, they have huge application value. However, how to ensure the flexible screens and structure thereof while realizing rolling, expanding, and contracting states at same time in current flexible display devices has become a hot spot problem of current researches. When the flexible screens are in a process of rolling, expanding, and contracting, entire flexible display devices are prone to shaking, resulting in the screens to be prone to pulling or squeezing with other assemblies such as a supporting plate, thereby reducing the service life of the flexible screens.

Flexible display devices are known from, for example, <CIT>, <CIT>, and <CIT>.

A purpose of the present disclosure is to provide a flexible display device to solve the technical problem that the shake phenomenon easily occurs on the flexible display devices, and the flexible screens easily to pull or squeeze by other assemblies, thereby reducing the service life of the flexible screens.

A beneficial effect of the present disclosure is to provide the flexible display device to omit the coil spring structures in the prior art. Through the transmission manner of the gear and rack mechanisms coordinating with the guy, smooth transmission of the screens in a stretching process or a contracting process is ensured, while the gear and rack mechanisms can be ensured to operate synchronously in the stretching and contracting processes to prevent the flexible display screens from being pulled or undulated, improving the service life of the flexible display screens, and thereby improving user experience.

The technical solutions and other advantageous effects of the present invention will be apparent with reference to the following accompanying drawings and detailed description of embodiments of the present disclosure.

Components in the drawings are indicated as follows:.

The technical solutions in the embodiments of the present disclosure are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, but are not all embodiments of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts are within the scope of the present disclosure.

In the description of the present disclosure, it is to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" etc. is based on the orientation or positional relationship shown in the accompanying figures, which is merely for the convenience for describing of the present disclosure and for the simplification of the description, and is not intended to indicate or imply that the indicated devices or elements have a specific orientation or is constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present disclosure. Moreover, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical characteristics. Therefore, the characteristics defined by "first" or "second" may include one or more of the described characteristics either explicitly or implicitly. In the description of the present disclosure, the meaning of "a plurality" is two or more unless clearly and specifically defined otherwise.

In the description of the present disclosure, unless specified or limited otherwise, terms "mounted," "connected," "coupled," and the like are used in a broad sense, and may include, for example, fixed connections, detachable connections, or integral connections; may also be mechanical or electrical connections or may be communication between each other; may also be direct connections or indirect connections via intervening structures; may also be inner communications of two elements or may be a relationship of interaction between two elements. For persons skilled in the art in this field, the specific meanings of the above terms in the present disclosure can be understood with specific cases.

The following disclosure provides many different embodiments or examples for implementing the different structures of the present disclosure. In order to simplify the disclosure of the present disclosure, the assemblies and configurations of the specific examples are described below. Of course, they are merely examples and are not intended to limit the present disclosure. In addition, the present disclosure may repeat reference numerals and/or reference numerals in different examples, which are for the purpose of simplicity and clarity, and do not indicate the relationship between the various embodiments and/or arrangements discussed. Moreover, the present disclosure provides embodiments of various specific processes and materials, but one of ordinary skill in the art will recognize the use of other processes and/or the use of other materials.

As illustrated in <FIG>, one embodiment provides a flexible display device, including a transmission assembly <NUM>, rotating shaft assemblies <NUM>, a roller device <NUM>, a first supporting plate <NUM>, a second supporting plate <NUM>, an outer frame <NUM>, and a flexible display screen <NUM>. Furthermore, the first supporting plate <NUM> is dismountably mounted on the outer frame <NUM>, and the outer frame <NUM> is configured to fix the first supporting plate <NUM>. The second supporting plate <NUM> is extendably connected to the first supporting plate <NUM>. Of course, the second supporting plate <NUM> can also be slidably connected to the first supporting plate <NUM>, and it is not limited thereto. The roller device <NUM> is dismountably connected to the second supporting plate <NUM> and is disposed on a lateral edge of the second supporting plate <NUM> away from the first supporting plate <NUM>. One end of the transmission assembly <NUM> is connected to the rotating shaft assemblies <NUM>, and another end is connected to the roller device <NUM>. The rotating shaft assemblies <NUM> are dismountably mounted on the outer frame <NUM>, are disposed under the first supporting plate <NUM>, and are close to a side of the roller device <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively or merged with each other, the transmission assembly <NUM> guides the roller device <NUM> and the rotating shaft assemblies <NUM> to rotate simultaneously.

As illustrated in <FIG>, when the transmission assembly <NUM> is rotating, gaps between the rotating shaft assemblies <NUM> and the roller device <NUM> can gradually increase or gradually reduce. When the gaps between the rotating shaft assemblies <NUM> and the roller device <NUM> gradually increase, that is, the flexible display screen <NUM> is in a relatively expanded state. When the gaps between the rotating shaft assemblies <NUM> and the roller device <NUM> gradually decrease, that is, the flexible display screen <NUM> is in a state merged with each other. The transmission assembly includes a pair of racks <NUM> and a guy <NUM>.

The pair of racks <NUM> are disposed on a bottom surface of the second supporting plate <NUM> in parallel. The rotating shaft assemblies <NUM> are rotatably connected to the racks <NUM>. One end of the guy <NUM> is wound on the rotating shaft assemblies <NUM>, and another end is wound on the roller device <NUM>.

As illustrated in <FIG>, the rotating shaft assemblies <NUM> include a first rotating shaft <NUM>, a second rotating shaft <NUM>, a pair of first gears <NUM>, a pair of second gears <NUM>, a first flange <NUM>, and a first raceway <NUM>.

The first rotating shaft <NUM> and/or the second rotating shaft <NUM> are/is dismountably mounted on a frame body of the outer frame <NUM> and are/is disposed under the first supporting plate <NUM>. The first rotating shaft <NUM> and/or the second rotating shaft <NUM> are/is perpendicular to a length direction of the racks <NUM> in an axial direction. Middle sections of each of the first gears <NUM> are fixed on two ends of the first rotating shaft <NUM>, and teeth of the first gears <NUM> are meshed on the racks <NUM>. Middle sections of each of the second gears <NUM> are fixed on two ends of the second rotating shaft <NUM>, and teeth of the second gears <NUM> are meshed on corresponding teeth of the first gears. A middle section of the first flange <NUM> is fixed on the first rotating shaft <NUM> or the second rotating shaft <NUM>. The first raceway <NUM> is defined on circumference of the first flange <NUM>. An end of the guy <NUM> is wound in the first raceway <NUM>. Furthermore, the middle section of the first flange <NUM> is fixed on the first rotating shaft <NUM>. During operation, when the first rotating shaft <NUM> is rotating, the first rotating shaft <NUM> guides the first gears <NUM> and the first flange <NUM> fixed on the first rotating shaft <NUM> to rotate. In a rotating process, the first gears <NUM> are meshed to the racks <NUM> and guide the second supporting plate <NUM> to move. The guy <NUM> is tightened or loosened in the first raceway <NUM>, thereby making the flexible display screen <NUM> to realize the tightening function or the loosening function.

Preferably, the middle section of the first flange <NUM> is fixed on the second rotating shaft <NUM>. During operation, when the first rotating shaft <NUM> and the second rotating shaft <NUM> are rotating, the first rotating shaft <NUM> guides the first gears <NUM> fixed on the first rotating shaft <NUM> to rotate, the second rotating shaft <NUM> guides the second gears <NUM> and the first flange <NUM> fixed on the second rotating shaft <NUM> to rotate. In a rotating process, the first gears <NUM> are meshed to the second gears <NUM> and the racks <NUM> and guide the second supporting plate <NUM> to move. The guy <NUM> is tightened or loosened in the first raceway <NUM>, thereby making the flexible display screen <NUM> to realize the tightening function or the loosening function. Furthermore, in other embodiments, the first flange <NUM> and the first raceway <NUM> are disposed on two ends of the first rotating shaft <NUM> and/or the second rotating shaft <NUM>, which can make the flexible display screen <NUM> be more smooth during rotation process and prevents the flexible display screens from being pulled or undulated to improve the service life of the flexible display screens. As illustrated in <FIG>, the roller device <NUM> includes a roller tube <NUM>, a roller shaft <NUM>, a pair of end covers <NUM>, a second flange <NUM>, and a second raceway <NUM>.

The roller tube <NUM> is dismountably connected to the second supporting plate <NUM> and is disposed on the lateral edge of the second supporting plate <NUM> away from the first supporting plate <NUM>. The roller shaft <NUM> is disposed in the roller tube <NUM> and is disposed parallel to the first rotating shaft <NUM> relatively. Each of the end covers <NUM> is dismountably connected to two ends of the roller tube <NUM> to close the two ends of the roller tube <NUM>. Each of the end covers <NUM> has a plurality of end cover screw holes <NUM> and a plurality of end cover screws <NUM> being threaded connection with the cover screw holes <NUM>. The end covers <NUM> and the roller tube <NUM> are fixed by the threaded connection manner. A middle section of the second flange <NUM> is fixed on the roller shaft <NUM>, a second raceway <NUM> is defined on circumference of the roller shaft <NUM>, and a second end of the guy <NUM> is wound in the second raceway <NUM>. In other embodiments, the second flange <NUM> and the second raceway <NUM> are disposed on two ends of the roller shaft <NUM>, which can make the flexible display screen <NUM> be more smooth during the transmission process and prevents the flexible display screens from being pulled or undulated to improve the service life of the flexible display screens.

In this embodiment, the roller tube <NUM> has a gap <NUM> defined parallel to the roller shaft <NUM> relatively. The gap <NUM> has two surfaces, a top surface and a bottom surface. A plurality of first screw holes <NUM> are defined on the bottom surface and are in threaded connection with first screws <NUM>. The second supporting plate <NUM> is disposed in the gap <NUM>. Furthermore, second screw holes <NUM> defined relatively to the first screw holes <NUM> are defined on the second supporting plate <NUM>. Please refer to <FIG>, the first screws <NUM> sequentially penetrate the second screw holes <NUM> and the first screw holes <NUM>, thereby making the second supporting plate <NUM> and the roller tube <NUM> in fixed connection.

Radii of the second gears <NUM> are less than radii of the first gears <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively or merged with each other, the racks <NUM> mesh with the first gears <NUM> and guides the second gears <NUM> to rotate. The second gears <NUM> guide the first flange <NUM> in the same shaft, and the first flange <NUM> guides the second flange <NUM> to tighten or release the guys <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are merged with each other, the guy <NUM> and the first flange <NUM> rotate together, and the guy <NUM> in the second raceway <NUM> is released to be wound in the first raceway <NUM> loop by loop. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively, the guy <NUM> and the second flange <NUM> rotate together, and the guy <NUM> in the first raceway <NUM> is released to be wound in the second raceway <NUM> loop by loop.

As illustrated in <FIG>, the radii of the first gears <NUM> are r1, the radii of the second gears <NUM> are r2, a radius of the first flange <NUM> is r3, a radius of the second flange <NUM> is r4, a radius of the roller shaft <NUM> is r5, a stroke of the flexible display device from the relatively merged state to the relatively expanded state is l1. In this embodiment, when l1 is known, according to positional relationships between the first gears <NUM>, second gears <NUM>, the first flange <NUM>, and the second flange <NUM>, it can be understood that:.

In this embodiment, during the stretching or winding processes of the flexible display screen <NUM>, which is the processes of the second supporting plate <NUM> and the first supporting plate <NUM> relatively expanded or merged with each other, a stretching speed or a winding speed of the flexible display screen <NUM> is same as a releasing speed from the second flange <NUM> to the guy <NUM>, making the flexible display screen <NUM> not receive force, and preventing undulating phenomenon from generating on the flexible display screen <NUM>. Furthermore, releasing the guy <NUM> from the second flange <NUM> is due to winding of the first flange <NUM>, and a difference value is a stroke l4, that is l2=l1+l4, therefore, r3/r2+r4/r5=<NUM>. Therefore, when dimensions of each parts and assemblies of the first gears <NUM>, the second gears <NUM>, the first flange <NUM>, the second flange <NUM>, and the roller shaft <NUM> satisfy the above relationships, each parts and assemblies of the flexible display device cannot be pulled or squeezed to the flexible display screen during the process of the second supporting plate <NUM> and the first supporting plate <NUM> expanded relatively or merged with each other.

As illustrated in <FIG>, the first supporting plate <NUM> is a gate-shaped structure, including a first supporting lateral plate <NUM>, first supporting strips <NUM>, and first grooves <NUM>.

The plurality of first supporting strips <NUM> are fixedly connected to the first supporting lateral plate <NUM>. Two adjacent first supporting strips <NUM> and the first supporting lateral plate <NUM> define one first groove <NUM>.

The second supporting plate <NUM> is a gate-shaped structure, including a second supporting lateral plate <NUM>, second supporting strips <NUM>, and second grooves <NUM>.

The plurality of second supporting strips <NUM> are fixedly connected to the second supporting lateral plate <NUM>. Two adjacent second supporting strips <NUM> and the second supporting lateral plate <NUM> define one second groove <NUM>. The second grooves <NUM> close to the two ends of the second supporting plate <NUM> are positioning grooves <NUM>. Other second grooves <NUM> are engagement grooves <NUM>. Gaps of the engagement grooves <NUM> are greater than gaps of the positioning grooves <NUM>. Specifically, the gaps of the positioning grooves <NUM> are less than <NUM>, and are preferably <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The gaps of the engagement grooves <NUM> are greater than or equal to <NUM>. The gaps of the engagement grooves <NUM> range from <NUM> to <NUM>, and a specific value is preferred to be <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively and merged with each other, the second supporting plate <NUM> and the first supporting plate <NUM> will not shake due to excessive friction, thereby not resulting in poor pushing and pulling effects and affecting user experience.

As illustrated in <FIG>, the first supporting strips <NUM> and the second groove <NUM> are meshed with each other. The second supporting strips <NUM> and the first groove <NUM> are meshed with each other. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively, the second supporting plate <NUM> and the first supporting plate <NUM> provide support to make the flexible display screen <NUM> be maximized, so the flexible display screen <NUM> has a maximum display screen. In a situation where the flexible display screen <NUM> receives an external force, a dent phenomenon cannot occur, preventing the flexible display screen <NUM> from deformation.

As illustrated in <FIG>, when the second supporting plate <NUM> and the first supporting plate <NUM> are merged with each other, the second supporting plate <NUM> is contracted into the outer frame <NUM> and is disposed in a staggered manner with the first supporting plate <NUM> to form a smaller flexible display device, which facilitates carrying by users and improves user experience.

As illustrated in <FIG>, the outer frame <NUM> is a square shape configured to fix the first supporting plate <NUM> and the second supporting plate <NUM>. The outer frame includes a first frame body <NUM>, a second frame body <NUM>, a third frame body <NUM>, and a fourth frame body <NUM> which are connected head-to-tail, and a bottom plate <NUM>. The bottom plate <NUM>, the first frame body <NUM>, the second frame body <NUM>, the third frame body <NUM>, and the fourth frame body <NUM> are arranged around to form a hollow cavity.

The first frame body <NUM> is disposed opposite to the second frame body <NUM>. An end of the first frame body <NUM> and an end of the second frame body <NUM> are respectively connected to ends of the third frame body <NUM> perpendicularly. The third frame body <NUM> is disposed opposite to the fourth frame body <NUM>. A connection plate <NUM> is fixed on the third frame body <NUM> and protrudes on an inner lateral wall of the third frame body <NUM>. Furthermore, a top surface 61a of the first frame body, a top surface 62a of the second frame body, a top surface 63a of the third frame body are on a same horizontal plane, and a position of a top surface 64a of the fourth frame body is lower than a position of the top surface 61a of the first frame body. Furthermore, the position of the top surface 64a of the fourth frame body and a top surface of the connection plate <NUM> are on a same horizontal plane. When the first supporting plate <NUM> and the second supporting plate <NUM> are located on the upper surface 64a of the fourth frame and the upper surface of the connecting plate <NUM>, a phenomenon of high and low heights cannot occur, and the flatness of the flexible display device is improved.

The first supporting plate <NUM> and the connection plate <NUM> on the third frame body <NUM> are fixed, and an end of the first supporting strip <NUM> away from the first supporting lateral plate <NUM> is disposed on the top surface of the fourth frame body <NUM>. Specifically, a plurality of third screw holes <NUM> penetrate the connection plate <NUM>, and the third screw holes <NUM> and a plurality of third screws <NUM> are in threaded connection. Fourth screw holes <NUM> are defined on the first supporting lateral plate <NUM> and are relatively disposed with the third screw holes <NUM>. Dimensions of the fourth screw holes <NUM> are same as dimensions of the third screw holes <NUM>. When the third screws <NUM> sequentially penetrate the third screw holes <NUM> and the fourth screw holes <NUM>, the first supporting plate <NUM> and the outer frame <NUM> are connected by screw threads.

Chutes <NUM> are defined on two surfaces of the first frame body <NUM> and the second frame body <NUM> disposed oppositely, and the second supporting strips on the two sides of the second supporting plate <NUM> are slidably disposed in the chutes <NUM> and are disposed on the top surface 64a of the fourth frame body. In this embodiment, the fourth frame body <NUM> has one groove <NUM>, the groove <NUM> concaves on the top surface 64a of the fourth frame body, and the second supporting strips <NUM> are slidably disposed in the grooves <NUM>. Preferably, the groove <NUM> is defined on two ends of the fourth frame body <NUM>, the second supporting strips <NUM> on the two sides of the second supporting plate are slidably disposed in the groove <NUM>. Therefore, when the second supporting plate <NUM> is in the sliding process, the second supporting plate <NUM> cannot shake and is smooth, preventing poor effects of pulling and squeezing generating on the flexible display screen. In this embodiment, bottom surfaces of the first supporting strips <NUM> and bottom surfaces of the second supporting strips <NUM> are tangent to the top surface 64a of the fourth frame body. Furthermore, because the two outermost second supporting strips <NUM> of the second supporting plate <NUM> are slidably disposed in the groove <NUM>, and thicknesses of the two outermost second supporting strips <NUM> of the second supporting plate <NUM> are greater than thicknesses of the other second supporting strips <NUM>, making the two outermost second supporting strips <NUM> of the second supporting plate <NUM> and the other second supporting strips <NUM> remain on a same horizontal plane. Therefore, when the first supporting plate <NUM> and the second supporting plate <NUM> are expanded relatively or merged with each other, that is, when the flexible display screen is in the process of realizing stretching or winding, the second supporting plate <NUM> and the first supporting plate <NUM> will not shake due to excessive friction, making the first supporting plate push and pull smoothly, and each parts and assemblies of the flexible display device cannot be pulled and squeezed to the flexible display screen, improving user experience. Please refer to <FIG>, a via hole <NUM> is defined on the fourth frame body <NUM>, and the guy <NUM> penetrates the via hole <NUM> and is connected to the roller device <NUM>. In this embodiment, fifth screw holes <NUM> and sixth screw holes <NUM> are defined on the first frame body <NUM> and the second frame body <NUM>. Furthermore, two ends of the first rotating shaft <NUM> have first rotating shaft screw holes. Dimensions of the first rotating shaft screw holes are same as dimensions of the fifth screw holes <NUM>. The fifth screws <NUM> sequentially penetrate the fifth screw holes <NUM> and the first rotating shaft screw holes, making the first rotating shaft screw holes <NUM> be fixed between the first frame body <NUM> and the second frame body <NUM>. Two ends of the second rotating shaft <NUM> have second rotating shaft screw holes. Dimensions of the second rotating shaft screw holes are same as dimensions of the sixth screw holes <NUM>. The sixth screws <NUM> sequentially penetrate the sixth screw holes <NUM> and the second rotating shaft screw holes, making the second rotating shaft <NUM> be fixed between the first frame body <NUM> and the second frame body <NUM>.

Please refer to <FIG>, the flexible display screen <NUM> is disposed on the first supporting plate <NUM> and the second supporting plate <NUM> in the chutes, a side of the flexible display screen <NUM> is fixed on the third frame body, and another side of the flexible display screen <NUM> is wound on the roller device <NUM>.

As illustrated in <FIG>, the flexible display screen <NUM> has a display surface <NUM> and a sleeve <NUM>. The display surface <NUM> and the top surface of the first frame body is on the same horizontal plane, or a position of the display surface <NUM> is lower than the top surface of the first frame body. The display surface <NUM> is in fixed connection with the sleeve <NUM>. An inner lateral wall of the sleeve <NUM> is tangent to an outer lateral wall of the roller shaft <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are merged with each other, the sleeve <NUM> and the roller shaft <NUM> rotate simultaneously, the display surface <NUM> is wound and is stored in the roller tube <NUM>. When the second supporting plate <NUM> and the first supporting plate <NUM> are expanded relatively, the sleeve <NUM> and the roller shaft <NUM> rotate simultaneously, the display surface <NUM> is stretched, and the display surface <NUM> stored in the roller shaft <NUM> is stretched outside. The small display surface <NUM> gradually becomes the big display surface <NUM>, making the display device have a larger screen.

Compared to the prior art, the embodiments omit the coil spring structures in the prior art. Through the transmission manner of the gear and rack mechanisms coordinating with the guy, smooth transmission of the screens in a stretching process or a contracting process is ensured, while the gear and rack mechanisms can be ensured to operate synchronously in the stretching process and contracting processes to prevent the flexible display screens from being pulled or undulated, improving the service life of the flexible display screens, and thereby improving user experience.

Claim 1:
A flexible display device, comprising:
an outer frame (<NUM>);
a first supporting plate (<NUM>) mounted on the outer frame (<NUM>);
a second supporting plate (<NUM>) extendably connected to the first supporting plate (<NUM>);
a roller device (<NUM>) connected to the second supporting plate (<NUM>) and disposed on a lateral edge of the second supporting plate (<NUM>) away from the first supporting plate (<NUM>);
rotating shaft assemblies (<NUM>) mounted on the outer frame (<NUM>); and
a transmission assembly (<NUM>), wherein one end of the transmission assembly (<NUM>) is connected to the rotating shaft assemblies (<NUM>), and another end of the transmission assembly (<NUM>) is connected to the roller device (<NUM>),
wherein when the second supporting plate (<NUM>) and the first supporting plate (<NUM>) are expanded relatively or merged with each other, the transmission assembly (<NUM>) guides the roller device (<NUM>) and the rotating shaft assemblies (<NUM>) to rotate simultaneously;
wherein the transmission assembly (<NUM>) comprises:
a pair of racks (<NUM>) disposed on a bottom surface of the second supporting plate (<NUM>) in parallel, wherein the rotating shaft assemblies (<NUM>) are rotatably connected to the racks (<NUM>); and
a guy (<NUM>), wherein one end of the guy (<NUM>) is wound on the rotating shaft assemblies (<NUM>), and another end of the guy (<NUM>) is wound on the roller device (<NUM>).