Patent Description:
Hitherto, there has been known a printing unit that performs printing on a heat sensitive sheet (see, for example, <CIT>). This printing unit is configured to perform printing by heating a printing surface of a recording sheet with heating elements of a thermal head to develop a color on the printing surface while feeding the recording sheet through rotation of a platen roller under a state in which the recording sheet is nipped between the platen roller and the thermal head.

The related-art printing unit described above includes a thermal head, a support plate, a platen roller, a frame, and an elastic member. The thermal head is fixed to the support plate. The frame supports the platen roller and the support plate. The elastic member is arranged in a gap between the support plate and the frame, and presses the support plate to the platen roller side. The elastic member applies a predetermined head pressing force between the platen roller and the thermal head.

However, in the related-art printing unit described above, there is the gap between the support plate and the frame, and hence the support plate may bend. Thus, when an impact is given to the printing unit at the time of, for example, falling, the support plate bends and the thermal head is distorted, which may cause breakage of the thermal head.

Accordingly, the present invention provides a printing unit having excellent impact resistance, and a portable terminal including the printing unit.

<CIT> discloses a printing unit that includes a platen roller configured to convey a recording sheet, a thermal head configured to perform printing on the recording sheet through press contact with an outer peripheral surface of the platen roller, a motor configured to rotate the platen roller about a predetermined axis, and a frame configured to support the platen roller in a rotatable manner, and allow the motor to be fixed to the frame with an adhesive.

According to the present invention, there is provided a printing unit as defined in claim <NUM>.

According to the present invention, there is provided a portable terminal that includes the above printing unit.

Now, an embodiment of the present invention is described by way of example only with reference to the drawings. In the following description, components having the same or similar function are denoted by the same reference symbols. In some cases, overlapping description of the components is omitted.

<FIG> is a perspective view for illustrating a portable terminal according to at least one embodiment of the present invention.

As illustrated in <FIG>, a portable terminal <NUM> is capable of performing printing on a recording sheet P. The recording sheet P is a heat sensitive sheet that develops a color when heat is applied thereto, and is used suitably for printing a variety of labels, receipts, and tickets. The recording sheet P is set in the portable terminal <NUM> in a state of a roll sheet R obtained by rolling the recording sheet P so as to have a hollow hole, and printing is performed on a part drawn from the roll sheet R.

The portable terminal <NUM> includes a casing <NUM>, a display unit <NUM>, a control unit <NUM>, and a printing unit <NUM>.

The casing <NUM> formed into a hollow box-shape is made of a metal material or plastic such as ABS or a composite material of ABS and polycarbonate. The casing <NUM> includes a main body portion <NUM> having a rectangular parallelepiped shape, and a roll sheet receiving portion <NUM> formed at one end portion of the main body portion <NUM> in a longitudinal direction thereof so as to be bent toward one side of a thickness direction of the main body portion <NUM>. The printing unit <NUM> is received at the one end portion of the main body portion <NUM> in the longitudinal direction. A discharge port 3a is formed in one end surface of the main body portion <NUM> in the longitudinal direction. The discharge port 3a is configured to discharge the recording sheet P printed by passing through the printing unit <NUM>. The display unit <NUM> is arranged on a main surface of the main body portion <NUM>, which faces the other side in the thickness direction. The display unit <NUM> is, for example, a liquid crystal panel. The display unit <NUM> is connected to the control unit <NUM>, and is configured to display various kinds of information. The roll sheet receiving portion <NUM> is configured to receive the roll sheet R. The printing unit <NUM> is a so-called thermal printer.

<FIG> is a perspective view for illustrating a printing unit according to the embodiment. <FIG> is an exploded perspective view for illustrating the printing unit according to the embodiment.

As illustrated in <FIG> and <FIG>, the printing unit <NUM> includes a platen roller <NUM>, a thermal head <NUM>, a head support plate <NUM> (support plate), a main body frame <NUM> (frame), urging members <NUM>, a motor <NUM>, a first reduction gear <NUM>, and a second reduction gear <NUM>. The platen roller <NUM> conveys the recording sheet P. The thermal head <NUM> performs printing on the recording sheet P through press contact with an outer peripheral surface of the platen roller <NUM>. The head support plate <NUM> is arranged on a side opposite to the platen roller <NUM> across the thermal head <NUM>, and supports the thermal head <NUM>. The main body frame <NUM> includes a rear plate portion <NUM> arranged on a side opposite to the platen roller <NUM> across the head support plate <NUM>, and supports the platen roller <NUM> and the head support plate <NUM>. The urging members <NUM> urge the head support plate <NUM>. The motor <NUM> rotates the platen roller <NUM> about a rotation axis O. The first reduction gear <NUM> and the second reduction gear <NUM> reduce a driving force of the motor <NUM>, and transmit the driving force to a driven gear <NUM> fixed to the platen roller <NUM>.

As illustrated in <FIG>, the printing unit <NUM> is configured to convey the recording sheet P passing between the platen roller <NUM> and the thermal head <NUM> in a direction indicated by an arrow A. Mainly in the description for the printing unit <NUM> below, a direction along the arrow A is defined as a vertical direction L1, and the direction indicated by the arrow A is defined as an upper side. Further, a direction which is orthogonal to the vertical direction L1 and matches an axial direction of the platen roller <NUM> is defined as a horizontal direction L2. In addition, a direction orthogonal to the vertical direction L1 and the horizontal direction L2 is defined as a fore-and-aft direction L3, and the platen roller <NUM> side with respect to the thermal head <NUM> in the fore-and-aft direction L3 is defined as a front side.

<FIG> is a perspective view for illustrating part of components of the printing unit according to the embodiment. <FIG> is a view for illustrating the printing unit according to the embodiment when viewed from above.

As illustrated in <FIG>, the main body frame <NUM> is formed into a U-shape opened toward the front side when viewed in the vertical direction L1. Specifically, the main body frame <NUM> includes a rear plate portion <NUM> extending in the horizontal direction L2, a first side wall portion <NUM> formed upright from one (left) end portion of the rear plate portion <NUM> in the horizontal direction L2 toward the front side, a second side wall portion <NUM> formed upright from another (right) end portion of the rear plate portion <NUM> in the horizontal direction L2 toward the front side, and a sheet guide portion <NUM> formed between the first side wall portion <NUM> and the second side wall portion <NUM>. The rear plate portion <NUM>, the first side wall portion <NUM>, the second side wall portion <NUM>, and the sheet guide portion <NUM> are integrally formed of, for example, a polycarbonate resin containing glass fibers.

The rear plate portion <NUM> is formed into a plate shape having a thickness in the fore-and-aft direction L3. The first side wall portion <NUM> is formed into a plate shape having a thickness in the horizontal direction L2. A portion of an upper edge of the first side wall portion <NUM> is cut downward to form a first roller insertion groove 14A. The second side wall portion <NUM> is formed into a plate shape having a thickness in the horizontal direction L2. A portion of an upper edge of the second side wall portion <NUM> is cut downward to form a second roller insertion groove 14B. The first roller insertion groove 14A and the second roller insertion groove 14B are formed so as to match each other when viewed in the horizontal direction L2. The platen roller <NUM> is removably inserted into the first roller insertion groove 14A and the second roller insertion groove 14B.

<FIG> is a view for illustrating the printing unit according to the embodiment when viewed from a left side thereof.

As illustrated in <FIG> and <FIG>, a hole portion 12a is formed in the first side wall portion <NUM>. A hole portion 13a is formed in the second side wall portion <NUM>. The hole portions 12a and 13a are formed so as to match each other when viewed in the horizontal direction L2. The hole portions 12a and 13a are each formed into a rectangular shape having a pair of sides extending in the fore-and-aft direction L3 and the remaining pair of sides extending in the vertical direction L1 when viewed in the horizontal direction L2.

As illustrated in <FIG> and <FIG>, the sheet guide portion <NUM> is formed into a column shape extending along the horizontal direction L2. A left end portion of the sheet guide portion <NUM> is connected to an inner surface of the first side wall portion <NUM>. A right end portion of the sheet guide portion <NUM> is connected to an inner surface of the second side wall portion <NUM>.

As illustrated in <FIG>, a gearbox portion <NUM> is formed on an outer side of the second side wall portion <NUM>. The gearbox portion <NUM> includes a peripheral wall portion <NUM> formed to extend upright from a peripheral edge of the second side wall portion <NUM> toward the outer side in the horizontal direction L2. That is, the gearbox portion <NUM> is formed of the second side wall portion <NUM> and the peripheral wall portion <NUM>, and is opened toward the outer side in the horizontal direction L2. The peripheral wall portion <NUM> is opened upward when viewed in the horizontal direction L2. The peripheral wall portion <NUM> includes a pair of locking recessed portions <NUM> formed so as to be recessed downward. The pair of locking recessed portions <NUM> are formed on both front and rear sides of an upper opening of the peripheral wall portion <NUM>, respectively. A gear cover <NUM> is engaged with the pair of locking recessed portions <NUM>. The gear cover <NUM> covers an inner side of the gearbox portion <NUM> from an outer side thereof in the horizontal direction L2. The first reduction gear <NUM> and the second reduction gear <NUM> which mesh with each other are assembled inside the gearbox portion <NUM> so as to be rotatable.

The motor <NUM> generates torque about an output axis Q. The motor <NUM> is arranged so that the output axis Q is parallel to the rotation axis O of the platen roller <NUM> (see <FIG>). The motor <NUM> is arranged on a side opposite to the platen roller <NUM> across the sheet guide portion <NUM> and below the rear plate portion <NUM>. The motor <NUM> is fixed to an inner surface of the second side wall portion <NUM> in the horizontal direction L2. An output shaft <NUM> of the motor <NUM> passes through the second side wall portion <NUM>. The output shaft <NUM> meshes with the first reduction gear <NUM> inside the gearbox portion <NUM>. A flexible printed board <NUM> is connected to the motor <NUM>. The motor <NUM> is electrically connected to the control unit <NUM> (see <FIG>) via the flexible printed board <NUM>. The motor <NUM> is configured to be driven based on a signal from the control unit <NUM>.

The thermal head <NUM> is configured to perform printing on the recording sheet P (see <FIG>). The thermal head <NUM> is arranged in front of the rear plate portion <NUM>. The thermal head <NUM> is formed into a rectangular shape having its longitudinal direction defined as the horizontal direction L2 when viewed in the fore-and-aft direction L3. The thermal head <NUM> is arranged under a state in which a thickness direction of the thermal head <NUM> matches the fore-and-aft direction L3. A head surface 40a of the thermal head <NUM> faces a side opposite to the rear plate portion <NUM> (front side). On the head surface 40a of the thermal head <NUM>, a large number of heating elements <NUM> are arrayed in the horizontal direction L2.

The head surface 40a is opposed to a printing surface of the recording sheet P, and the recording sheet P can be nipped between the head surface 40a and the outer peripheral surface of the platen roller <NUM>. The thermal head <NUM> is connected to the control unit <NUM> (see <FIG>) through intermediation of the flexible printed board <NUM>. A driver IC (not shown) mounted on the thermal head <NUM> is configured to control heat generation of the heating elements <NUM> based on the signal from the control unit <NUM>. Through the control of the heat generation of the heating elements <NUM>, the thermal head <NUM> prints, for example, various kinds of letters and figures on the printing surface of the recording sheet P. The thermal head <NUM> is fixed to the head support plate <NUM> by being bonded onto a front surface of the head support plate <NUM> with use of, for example, a double-sided tape.

The head support plate <NUM> is arranged in front of the rear plate portion <NUM> and behind the sheet guide portion <NUM>. The head support plate <NUM> is arranged between the first side wall portion <NUM> and the second side wall portion <NUM>. The head support plate <NUM> is made of a metal material. The head support plate <NUM> is a plate-like member having its longitudinal direction defined as the horizontal direction L2. The head support plate <NUM> is arranged under a state in which a thickness direction of the head support plate <NUM> matches the fore-and-aft direction L3. The head support plate <NUM> extends in the horizontal direction L2 and the vertical direction L1 so as to have a constant thickness over an entire region of the head support plate <NUM> excluding protruding portions <NUM> to be described later. The thermal head <NUM> is fixed to the front surface of the head support plate <NUM>. An intermediate position of the thermal head <NUM> in the horizontal direction L2 matches an intermediate position of the head support plate <NUM> in the horizontal direction L2.

<FIG> is a plan view for illustrating the head support plate in the embodiment.

As illustrated in <FIG>, the head support plate <NUM> includes a fixed portion <NUM> and a pair of stoppers <NUM>.

The fixed portion <NUM> is formed at a lower portion of the head support plate <NUM>. The fixed portion <NUM> is located at a center portion of the head support plate <NUM> in the horizontal direction L2, and protrudes downward. The fixed portion <NUM> is sandwiched between the rear plate portion <NUM> and the sheet guide portion <NUM> of the main body frame <NUM>, and thus displacement of the fixed portion <NUM> in the fore-and-aft direction L3 with respect to the main body frame <NUM> is substantially regulated. The head support plate <NUM> is pivotable about the fixed portion <NUM> so that an upper portion of the head support plate <NUM> is moved in the fore-and-aft direction.

As illustrated in <FIG> and <FIG>, the pair of stoppers <NUM> are formed at an upper end portion of the head support plate <NUM>. Each of the pair of stoppers <NUM> protrudes outward in the horizontal direction L2 so as to have a substantially constant width when viewed in the fore-and-aft direction L3. The stoppers <NUM> are inserted into the hole portions 12a and 13a of the main body frame <NUM>, respectively. The stopper <NUM> is inserted with a gap in the fore-and-aft direction L3 with respect to an inner wall surface of a corresponding one of the hole portions 12a and 13a. The stoppers <NUM> are movable in the fore-and-aft direction L3 inside the hole portions 12a and 13a, respectively, along with pivot of the head support plate <NUM>, and may be brought into contact with the inner wall surfaces of the hole portions 12a and 13a, respectively. Through the contact of the stoppers <NUM> with the inner wall surfaces of the hole portions 12a and 13a, the pivot amount of the head support plate <NUM> is regulated. A rear gap G (see <FIG>) between the stopper <NUM> and the inner wall surface of the hole portion 12a or the inner wall surface of the hole portion 13a is set to have a size capable of preventing a portion of the head support plate <NUM> other than the fixed portion <NUM> and the stoppers <NUM> from being brought into contact with the main body frame <NUM> even when the stopper <NUM> is advanced and brought into contact with the inner wall surface of the hole portion 12a or the inner wall surface of the hole portion 13a.

As illustrated in <FIG>, the platen roller <NUM> is supported by the main body frame <NUM> so as to be rotatable about the rotation axis O. The platen roller <NUM> is arranged so as to be opposed to the thermal head <NUM> under a state in which the rotation axis O matches the horizontal direction L2. The platen roller <NUM> is rotated about the rotation axis O under a state in which the recording sheet P is nipped between the platen roller <NUM> and the thermal head <NUM>, to thereby convey the recording sheet P in the direction indicated by the arrow A.

As illustrated in <FIG>, the platen roller <NUM> includes a roller shaft <NUM>, a roller main body <NUM> mounted on the roller shaft <NUM>, and a pair of bearings <NUM> mounted at both ends of the roller shaft <NUM>. The roller shaft <NUM> is formed slightly longer than the separation distance between the first side wall portion <NUM> and the second side wall portion <NUM> of the main body frame <NUM>. The roller main body <NUM> is made of, for example, rubber, and is arranged along the horizontal direction L2 uniformly over the entire region excluding portions corresponding to both the ends of the roller shaft <NUM>.

As illustrated in <FIG> and <FIG>, the pair of bearings <NUM> of the platen roller <NUM> are inserted into the first roller insertion groove 14A and the second roller insertion groove 14B of the main body frame <NUM>, respectively. The bearings <NUM> are held in the first roller insertion groove 14A and the second roller insertion groove 14B by locking springs <NUM> supported on the main body frame <NUM>. With this configuration, the platen roller <NUM> is held so as to be rotatable relative to the main body frame <NUM>. Further, when the locking springs <NUM> are elastically deformed in order to insert and remove the bearings <NUM> into and from the first roller insertion groove 14A and the second roller insertion groove 14B, the platen roller <NUM> is mountable to and removable from the main body frame <NUM>. Under a state in which the platen roller <NUM> is inserted into the first roller insertion groove 14A and the second roller insertion groove 14B, the platen roller <NUM> is arranged so that an outer peripheral surface of the roller main body <NUM> is brought into contact with the head surface 40a of the thermal head <NUM> while nipping the recording sheet P drawn out from the roll sheet R (see <FIG>) between the platen roller <NUM> and the thermal head <NUM>.

As illustrated in <FIG>, the driven gear <NUM> is fixed on another (right) end portion of the platen roller <NUM> in the horizontal direction L2. The driven gear <NUM> is assembled to an upper part of the gearbox portion <NUM> when the platen roller <NUM> is held on the first side wall portion <NUM> and the second side wall portion <NUM>. The driven gear <NUM> meshes with the second reduction gear <NUM>. With this, a rotational driving force from the motor <NUM> is transmitted to the driven gear <NUM> via the first reduction gear <NUM> and the second reduction gear <NUM>. The platen roller <NUM> is rotated under a state of being held on the first side wall portion <NUM> and the second side wall portion <NUM>, thereby being capable of conveying the recording sheet P (see <FIG>).

<FIG> is a view for illustrating the printing unit according to the embodiment when viewed from an upper rear side thereof.

As illustrated in <FIG> and <FIG>, each of the urging members <NUM> is arranged between the head support plate <NUM> and the rear plate portion <NUM>. The urging member <NUM> urges the head support plate <NUM> and the rear plate portion <NUM> in a direction of separating the head support plate <NUM> and the rear plate portion <NUM> away from each other. The urging member <NUM> presses the head support plate <NUM> to the platen roller <NUM> side. The urging member <NUM> is a helical compression spring that is extended and compressed in the fore-and-aft direction L3. Specifically, the urging member <NUM> is a conical spring having a diameter decreasing from the front side to the rear side. A rear end portion of the urging member <NUM> is held in abutment against a front surface 11a of the rear plate portion <NUM>. A front end portion of the urging member <NUM> is held in abutment against a surface (rear surface) of the head support plate <NUM> facing the rear plate portion <NUM> side. The urging members <NUM> are arranged in a bilaterally symmetric manner with respect to the intermediate position of the head support plate <NUM> in the horizontal direction L2. Three urging members <NUM> are arrayed at equal intervals in the horizontal direction L2.

As illustrated in <FIG> and <FIG>, the protruding portions <NUM> are formed on the rear surface of the head support plate <NUM>. Each of the protruding portions <NUM> is formed into a columnar shape, and protrudes from the head support plate <NUM> to the rear plate portion <NUM> side. The protruding portions <NUM> have the same height. The protruding portions <NUM> are arranged so as to overlap the rear plate portion <NUM> when viewed in a thickness direction (fore-and-aft direction) of the head support plate <NUM>. A pair of the protruding portions <NUM> is provided for each of the urging members <NUM>. The pair of the protruding portions <NUM> are provided apart from each other with an interval in the horizontal direction L2. The interval between the pair of the protruding portions <NUM> is smaller than a width of the front end portion of the urging member <NUM> in the horizontal direction L2. The pair of the protruding portions <NUM> can be brought into contact with the front end portion of the urging member <NUM> from the upper side. The pair of the protruding portions <NUM> are brought into contact with the front end portion of the urging member <NUM> so as to regulate upward movement of the urging member <NUM>, to thereby position the urging member <NUM>. In the following description, among the protruding portions <NUM>, each of a pair of the protruding portions <NUM> corresponding to the center urging member <NUM> is referred to as a center protruding portion 85A in some cases. The center urging member <NUM> is, among all the urging members <NUM>, one urging member <NUM> other than the urging members <NUM> arranged at both ends in the horizontal direction L2, in other words, among all the urging members <NUM>, the urging member <NUM> arranged in the middle as counted from the urging members <NUM> arranged at the both ends in the horizontal direction L2.

<FIG> is an enlarged view for illustrating a portion IX of <FIG>.

As illustrated in <FIG>, <FIG>, and <FIG>, the rear plate portion <NUM> includes holding portions <NUM> and recessed portions <NUM>. The holding portions <NUM> hold the urging members <NUM> therein. The recessed portions <NUM> are formed to prevent contact between the rear plate portion <NUM> and the protruding portions <NUM>.

Each holding portion <NUM> is opened in the front surface 11a of the rear plate portion <NUM> and formed into a recessed shape recessed to the rear side. The holding portion <NUM> extends in the vertical direction L1, and is opened in an upper end surface of the rear plate portion <NUM>. The number of the holding portions <NUM> is the same as the number of the urging members <NUM> (three in this embodiment). The rear end portion of the urging member <NUM> is arranged in the holding portion <NUM>. The holding portion <NUM> allows entry of the rear end portion of the urging member <NUM> from the upper side, and regulates displacement of the rear end portion of the urging member <NUM> in the horizontal direction L2.

The recessed portions <NUM> are formed in portions of the rear plate portion <NUM> that are opposed to the protruding portions <NUM> of the head support plate <NUM> in the fore-and-aft direction L3 in a one-to-one relationship, respectively. The recessed portions <NUM> are opened in the front surface 11a of the rear plate portion <NUM> and recessed to the rear side. The recessed portions <NUM> are each opened continuously in a range from the front surface 11a to the upper end surface of the rear plate portion <NUM>. The recessed portions <NUM> are formed in the rear plate portion <NUM> so as to include entire portions overlapping the protruding portions <NUM> when viewed in the fore-and-aft direction L3. With this configuration, the recessed portions <NUM> prevent the protruding portions <NUM> from being brought into contact with the rear plate portion <NUM> when the protruding portions <NUM> are displaced to the rear side.

One recessed portion <NUM> is formed at each side adjacent position of the holding portion <NUM> in the horizontal direction L2. The recessed portion <NUM>, which receives the center protruding portion 85A, has a smaller dimension in the vertical direction than a dimension of the holding portion <NUM>, which holds the center urging member <NUM> therein, in the vertical direction. Each of the recessed portions <NUM> communicates with the holding portion <NUM>. In the upper end surface of the rear plate portion <NUM>, openings of the recessed portions <NUM> are continuous with an opening of the holding portion <NUM>. Opening edges of the recessed portions <NUM> and an opening edge of the holding portion <NUM> in the upper end surface of the rear plate portion <NUM> are chamfered. The recessed portions <NUM> are formed so as to be shallower than the holding portion <NUM> to which the recessed portions <NUM> are adjacent. The recessed portions <NUM> each have a depth larger than a height of the protruding portion <NUM>. As illustrated in <FIG>, a depth D of the recessed portion <NUM> is a depth determined with reference to the front surface 11a of the rear plate portion <NUM>. A height H of the protruding portion <NUM> is a height determined with reference to the rear surface of the head support plate <NUM>.

Operations of the above-mentioned printing unit <NUM> are described.

When an impact is given to the printing unit <NUM> at the time of, for example, falling, inertia acts on the head support plate <NUM>, and thus the head support plate <NUM> is brought to be momentarily displaced with respect to the main body frame <NUM>. Depending on an orientation of the falling, the head support plate <NUM> is displaced with respect to the main body frame <NUM> so as to reduce the gaps between the stoppers <NUM> of the head support plate <NUM> and the inner wall surfaces of the hole portions 12a and 13a of the main body frame <NUM>. Further, under a state in which displacement of the stoppers <NUM> with respect to the main body frame <NUM> is regulated, both ends of the head support plate <NUM> in the horizontal direction L2 substantially serve as fixed ends, and thus the head support plate <NUM> bends. In this case, a displacement amount at a center portion of the head support plate <NUM> in the horizontal direction L2 may be maximum. In particular, the head support plate <NUM> is formed into a plate-like shape having a thickness in the fore-and-aft direction L3, and hence the head support plate <NUM> easily bends in the fore-and-aft direction L3.

The recessed portions <NUM> are formed in portions of the rear plate portion <NUM> of the main body frame <NUM> that are opposed to the protruding portions <NUM> of the head support plate <NUM> in the fore-and-aft direction L3, respectively. With this configuration, even when the head support plate <NUM> is displaced to the rear plate portion <NUM> side along the fore-and-aft direction L3, the recessed portions <NUM> receive the protruding portions <NUM>, thereby being capable of preventing the protruding portions <NUM> from being brought into contact with the rear plate portion <NUM>.

When the head support plate <NUM> bends so that the protruding portions <NUM> enter the recessed portions <NUM>, under a state in which the protruding portions <NUM> are held in non-contact with the rear plate portion <NUM>, the head support plate <NUM> is brought into contact with portions of the rear plate portion <NUM> outside the recessed portions <NUM>. At this time, the head support plate <NUM> is brought into surface contact with flat portions in vicinities of the openings of the recessed portions <NUM> in the front surface 11a of the rear plate portion <NUM>.

Here, if the head support plate is displaced due to an impact given to the printing unit, and thus the protruding portions are brought into contact with the rear plate portion, inertia acts on the head support plate continuously even after the protruding portions are brought into contact with the rear plate portion. In this case, displacement of the protruding portions is regulated by the rear plate portion, and hence the head support plate may be deformed so as to bend with a larger curvature as compared to a case in which the protruding portions are not brought into contact with the rear plate portion. According to this embodiment, the protruding portions <NUM> can be prevented from being brought into contact with the rear plate portion <NUM>, and hence even when an impact is given to the printing unit <NUM>, the head support plate <NUM> can be prevented from bending with a relatively large curvature. Accordingly, excessive distortion can be prevented from occurring in the thermal head <NUM> supported by the head support plate <NUM> and causing breakage of the thermal head <NUM>. Thus, the printing unit <NUM> having excellent impact resistance can be provided.

Further, in this embodiment, the recessed portions <NUM> are formed in the portions opposed to the protruding portions <NUM> (center protruding portions 85A) that correspond to, among all the urging members <NUM>, one urging member <NUM> other than the urging members <NUM> arranged at the both ends in the horizontal direction L2. When the head support plate <NUM> bends so that the center portion of the head support plate <NUM> in the horizontal direction L2 approaches the rear plate portion <NUM>, the protruding portions <NUM> closer to the center portion of the head support plate <NUM> have larger displacement amounts. According to this embodiment, even when the head support plate <NUM> bends so that the center portion of the head support plate <NUM> in the horizontal direction L2 approaches the rear plate portion <NUM>, the recessed portions <NUM> receive, among all the protruding portions <NUM>, the protruding portions <NUM> having relatively large displacement amounts. Thus, the protruding portions <NUM> can be more reliably prevented from being brought into contact with the rear plate portion <NUM>.

Moreover, in this embodiment, the recessed portions <NUM> are formed in the portions opposed to the protruding portions <NUM> (center protruding portions 85A) that correspond to, among all the urging members <NUM>, the urging member <NUM> arranged in the middle as counted from the urging members <NUM> arranged at the both ends in the horizontal direction L2. With this configuration, even when the head support plate <NUM> bends so that the center portion of the head support plate <NUM> in the horizontal direction L2 approaches the rear plate portion <NUM>, the recessed portions <NUM> receive, among all the protruding portions <NUM>, the protruding portions <NUM> having the largest displacement amounts. Thus, the protruding portions <NUM> can be more reliably prevented from being brought into contact with the rear plate portion <NUM>.

In addition, the recessed portions <NUM> have depths larger than the heights of the protruding portions <NUM>, thereby being capable of preventing the protruding portions <NUM> from being brought into contact with bottom surfaces of the recessed portions <NUM>.

When the head support plate <NUM> bends so that the protruding portions <NUM> enter the recessed portions <NUM>, under a state in which the protruding portions <NUM> are held in non-contact with the rear plate portion <NUM>, the head support plate <NUM> is brought into contact with the portions of the rear plate portion <NUM> outside the recessed portions <NUM>. Thus, as compared to a case in which the protruding portions are brought into contact with the rear plate portion, a reaction force is applied to a wider range of the head support plate <NUM> when the head support plate <NUM> is brought into contact with the rear plate portion <NUM>, thereby being capable of preventing an excessive external force from being applied to a relatively narrow range of the thermal head <NUM>. Accordingly, occurrence of stress concentration on the thermal head <NUM> is avoided, thereby being capable of more effectively preventing breakage of the thermal head <NUM>.

The portable terminal <NUM> according to this embodiment includes the printing unit <NUM> described above, and hence can be provided as a portable terminal having high durability.

The present invention is not limited to the embodiment described above with reference to the drawings, and various modification examples may be employed within the technical scope of the present invention as defined by the claims.

For example, in the embodiment described above, the plurality of urging members <NUM> are provided on the printing unit <NUM>, and the protruding portions <NUM> are provided for each of the urging members <NUM>. Further, the recessed portions <NUM> are formed in the portions of the rear plate portion <NUM> opposed to the protruding portions <NUM>, respectively. However, the present invention is not limited to this configuration. For example, only one urging member may be provided. Further, the recessed portions may be formed only in portions of the rear plate portion that are opposed to part of the protruding portions. In this case, it is desired that the part of the protruding portions include a protruding portion that regulates displacement of, among all the urging members, the urging member other than the urging members arranged at the both ends in the horizontal direction. That is, it is desired that the recessed portion be formed in a portion opposed to the protruding portion that corresponds at least to the urging member other than the urging members arranged at the both ends. In addition, when a plural number of and an odd number of urging members are provided, it is further desired that the part of the protruding portions include a protruding portion that regulates displacement of, among all the urging members, the urging member arranged in the middle as counted from the urging members arranged at the both ends in the horizontal direction. That is, it is further desired that the recessed portion be formed in a portion opposed to the protruding portion that corresponds at least to the center urging member. For example, the recessed portion may be formed only in a portion opposed to the center protruding portion 85A.

Claim 1:
A printing unit (<NUM>), comprising:
a platen roller (<NUM>), which extends in an axial direction, and is configured to convey a recording sheet (P);
a thermal head (<NUM>) configured to perform printing on the recording sheet (P) through press contact with an outer peripheral surface of the platen roller (<NUM>);
a support plate (<NUM>), which is arranged on a side opposite to the platen roller (<NUM>) across the thermal head (<NUM>), and is configured to support the thermal head (<NUM>);
a frame (<NUM>), which includes a rear plate portion (<NUM>) arranged on a side opposite to the platen roller (<NUM>) across the support plate (<NUM>), and is configured to support both ends of the support plate (<NUM>) in the axial direction;
at least one urging member (<NUM>), which is arranged between the rear plate portion (<NUM>) and the support plate (<NUM>), and is configured to press the support plate (<NUM>) to the platen roller (<NUM>) side; and
a protruding portion (<NUM>), which is formed on the support plate (<NUM>) to protrude from the support plate (<NUM>) to the rear plate portion side, and is configured to regulate displacement of a predetermined urging member (<NUM>) of the at least one urging member (<NUM>),
wherein a recessed portion (<NUM>) is formed in a portion of the rear plate portion (<NUM>) opposed to the protruding portion (<NUM>) in a thickness direction of the support plate (<NUM>),
wherein the recessed portion (<NUM>) has a depth larger than a height of the protruding portion (<NUM>), and
characterized in that the recessed portion (<NUM>) is configured to accommodate the protruding portion (<NUM>) in a state in which the protruding portion (<NUM>) is held in non-contact with the rear plate portion (<NUM>), in a case that the support plate (<NUM>) bends due to an impact on the printing unit (<NUM>) so that the support plate (<NUM>) is brought into contact with a portion of the rear plate portion (<NUM>) outside the recessed portion (<NUM>).