JPH07117315A - Cooling device for thermal head of printer apparatus - Google Patents

Abstract

PURPOSE:To cool a thermal head in a balanced state without locally accumulating heat and without making a cooling fan large in size. CONSTITUTION:A radiator fin 30 having many fin parts 30a extended in a widthwise direction of a printing medium 13 is attached to a thermal head 10 and moreover, a duct 32 is provided to guide a cooling wind K outside a printer apparatus which is sent by a cooling fan 36 to a central part of the radiator fin 30. The cooling wind K not yet heated and guided by the duct 32 intensively cools, through the radiator fin 30, a central part of the thermal head 10 where heat is generated most when printing is performed. Then, the cooling wind moves along the fin parts 30a of the radiator fin 30 to both ends of the thermal head 10 to cool the both ends.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head cooling device for cooling a thermal head of a color printer, for example.

[0002]

2. Description of the Related Art FIG. 9 is a perspective view around a thermal head of a printer apparatus disclosed in, for example, Japanese Utility Model Laid-Open No. 63-37243. In the figure, reference numeral 1 is a thermal head in which heating element groups are arranged in parallel in the longitudinal direction, and 2 is a heat radiation fin attached to the back surface of the thermal head 1. A large number of fin portions 2a of the heat radiating fins 2 are arranged in a direction orthogonal to the longitudinal direction of the thermal head 1, and correspond to the heat storage distribution of the thermal head 1 in a dense state at the central portion in the longitudinal direction of the thermal head 1. That is, it is provided so that the heat dissipation area of the central portion in the longitudinal direction becomes a large area. Reference numeral 3 is a cooling fan that sends cooling air toward the fin portion 2a of the heat radiation fin 2, and reference numeral 4 is a thermal head cooling device including the heat radiation fin 2 and the cooling fan 3.

Next, the operation of the thermal head cooling device 4 will be described. When printing, thermal head 1
Is supplied with electric power to form a desired heat generation pattern in the longitudinal direction thereof, and the heat generation pattern is brought into contact with a printing medium (not shown), thereby recording paper (not shown). ) A print is made on top. In this case, the heat generation pattern portion of the thermal head 1 is heated. However, if the temperature of the portion other than the heat generation pattern portion of the thermal head 1 rises, bleeding or the like will occur in the printing and defective printing will occur. Therefore, it becomes necessary to cool the thermal head 1.

On the other hand, the printing density in the width direction of the recording paper is
In general, since the central portion is higher than both end portions, the heat generation amount of the thermal head 1 is larger on the central portion side than on both end portions. Further, when printing is performed on, for example, A4 size recording paper using a printer device capable of printing up to A3 size recording paper, the amount of heat generated in the central portion of the thermal head 1 similarly increases. Under such circumstances, it is necessary to increase the cooling amount of the central portion of the thermal head 1 rather than both end portions thereof.

That is, the heat generated by the thermal head 1 is transferred to the heat radiation fin 2 side, but since cooling air is sent to the heat radiation fin 2 from the cooling fan 3, it is transferred from the thermal head 1 accumulated in the heat radiation fin 2. The generated heat is dissipated into the atmosphere. Therefore, the thermal head 1 is cooled via the radiation fins 2. In this case, since the installation density of the fin portions 2a in the central portion of the radiation fin 2 in the longitudinal direction is larger than that of the other portions and the heat radiation area is large, the amount of heat radiation in the central portion of the radiation fin 2 becomes larger than that in the other portions. The thermal head 1 is maintained at a uniform temperature along its longitudinal direction.

FIG. 10 is a perspective view around a thermal head cooling device described in, for example, Japanese Patent Laid-Open No. 173669/1993. In the figure, 5 is a thermal head, 6 is a radiating fin attached to the back surface of the thermal head 5, 7 is a cooling fan that sucks air from the central portion side of the radiating fin 6 through a duct 8, and 9 is the radiating fin 6 and cooling. The thermal head cooling device includes a fan 7, a duct 8 and the like.

Next, the operation of the thermal head cooling device 9 will be described. With the operation of the cooling fan 7,
The cooling air K sucked from both ends of the radiation fins 6 cools the radiation fins 6 while passing through the radiation fins 6 and is collected on the duct 8 side. Then, the cooling air K that has sucked the heat transferred from the thermal head 5 via the radiation fins 6 is discharged to the outside via the cooling fan 7, and the thermal head 5
Is cooled.

[0008]

In the conventional thermal head cooling device 4 shown in FIG. 9, the heat dissipating fins 2 having a high disposition density of the fin portions 2a at the central portion in the longitudinal direction are arranged.
Since the cooling fan 3 that blows the air inside the printer device to the radiating fins 2 is provided, the air heated by another heat source inside the device is used as the cooling air, and the cooling effect is reduced, and the fin portion is reduced. Even if the arrangement density of 2a is changed, the cooling performance of the central portion in the longitudinal direction cannot catch up with the heat storage amount. As a result, there is a problem that the cooling amount of the central portion of the thermal head 1 is insufficient and heat is accumulated in the central portion of the thermal head 1. In particular, such a thermal head cooling device 4 is used for a color printer device that generates a large amount of heat.
If the above is used, a large thermal gradient is generated in the longitudinal direction of the thermal head 1, and uneven density occurs during printing along the longitudinal direction of the thermal head 1.

Further, in this thermal head cooling device 4, since it is necessary to cool the entire radiation fin 2 by the cooling fan 3 at once, there is a problem that the cooling fan 3 becomes large.

Further, the conventional thermal head cooling device 4 shown in FIG. 10 sucks cooling air from both ends of the cooling fin 6 and discharges it from the central portion of the cooling fin 6 to the outside through the duct 7. Therefore, the cooling air blown to the central portion of the cooling fins 6 that should exhibit the most cooling capacity is
The cooling fin 6 is sent from both ends of the cooling fin 6 while being cooled, and the temperature thereof rises.
There was a problem that the central part of the could not be cooled sufficiently.

The present invention has been made in order to solve the above problems, and is capable of cooling the thermal head in a well-balanced manner without causing local heat accumulation and at the same time without increasing the size of the cooling fan. An object is to provide a cooling device.

[0012]

SUMMARY OF THE INVENTION A first invention of the present invention is a thermal head cooling device for applying heat to a printing medium for printing, which is attached to the thermal head to cool the thermal head. Radiating fins whose fins extend in the width direction of the printing medium, a duct for guiding cooling air to the central portion of the radiating fins in the width direction of the printing medium, and a cooling air external to the printer for this duct. And a cooling fan for feeding.

According to a second aspect of the present invention, in the cooling air introduction portion to the heat radiation fin of the duct, the air volume of the cooling air flowing toward each end side of the heat radiation fin along the fin portion is adjusted, The variable wind direction adjusting means for adjusting the variation of the cooling amount of the radiation fin along the printing medium is provided.

In a third aspect of the present invention, a plurality of cooling fans are provided, temperature detecting means for detecting the temperature of the radiation fins is provided, and all or one of the cooling fans is provided based on a signal from the temperature detecting means. That is, a control means for ON / OFF controlling the unit is provided.

[0015]

According to the first aspect of the present invention, the cooling fan blows unheated cooling air outside the printer through the duct to the central portion of the heat radiating fin. The central part of the thermal head, which generates the most heat, is intensively cooled. Next, the cooling air is moved to both ends of the heat radiating fins along the fins of the heat radiating fins extending in the width direction of the print medium, and is passed through the heat radiating fins to the print medium of the thermal head. Cool both ends along the line. In this case, the temperature of the cooling air rises slightly and the air volume also decreases, but since the amount of heat generated on both end sides of the thermal head is less than that on the center side, cooling of both end sides of the thermal head is also sufficient. It

According to a second aspect of the present invention, in the case of the first aspect, the cooling air introduced from the duct to the central portion of the radiation fin moves to both ends of the radiation fin along the fin portion of the radiation fin. In this case, the variable air flow rate adjusting means can adjust the air flow rate of the cooling air to the respective end portions of the radiating fins. As a result, it is possible to eliminate variations in the cooling amount of the radiation fin along the printing medium.

In a third invention of the present invention, in the case of the first or second invention, all or some of the plurality of cooling fans are turned on / off depending on whether the temperature of the radiation fins is high or low.
F control is performed. For example, if the temperature of the heat radiation fins is higher than that due to continuous use of the thermal head, etc., the control means actuates all the cooling fans based on the signal from the temperature detection means to increase the amount of cooling air. Further, for example, when the thermal head is not continuously used and the temperature of the radiation fin is low, the control means stops the operation of a part of the cooling fan based on the signal from the temperature detection means to reduce the air volume of the cooling air. Furthermore, if the temperature of the radiation fins has not risen, the control means stops the operation of all the cooling fans to stop the blowing of the cooling air.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. Example 1. FIG. 1 is a perspective view of a thermal printer including a thermal head cooling device according to an embodiment of the first invention of the present invention.
FIG. 2 is a sectional view taken along the line II-II of FIG.

In the figure, 10 is a thermal head in which heating element groups are arranged in parallel in the longitudinal direction, 11 is a thermal head cooling device arranged on the back side of the thermal head 10 for cooling the thermal head 10, 12 is a platen roller arranged on the front side of the thermal head 10,
An ink sheet 13 is arranged between the platen roller 12 and the thermal head 10 and is a printing medium that is sequentially wound from the supply reel 13A side to the take-up reel 13B side during printing. On the ink sheet 13, cyan, magenta, and yellow colors are sequentially and repeatedly formed in the longitudinal direction.

Reference numeral 14 is a recording paper which is arranged between the ink sheet 13 and the platen roller 12 and which prints while being moved in the direction of arrow A1. The thermal head 10
Longitudinal length L of ink sheet 13 and recording paper 14
Is almost equal to the width length of the. One end of 15 is a thermal head 10 or a thermal head cooling device 11
Is attached to both ends of the pressure shaft 16 on the other end side.
A pair of head side supports rotatably supported on the
Reference numeral 17 is a top plate of the printer device, and 18 is a rear cover of the printer device.

Next, the detailed structure of the thermal head cooling device 11 will be described. In the figure, 30 is attached to the back side of the thermal head 10 over the entire length L of the thermal head 10 in the longitudinal direction, and a large number of fin portions 30 a standing upward are provided in the longitudinal direction of the thermal head 10, that is, the ink sheet 13. A heat radiation fin for cooling the thermal head 10 extending in the width direction. One end of the head side support 15 is attached via a screw to both ends in the longitudinal direction along the fin portion 30a of the heat radiation fin 30. 31 is a radiation fin 3
It is a fin cover that covers the upper part of the zero fin portion 30a.
The fin cover 31 covers the entire upper portion of the fin portion 30a except for both ends of the heat radiation fin 30, and has a rectangular opening 31a of a certain size in the central portion of the heat radiation fin 30.

A rear end 32 of the fin 32 is arranged near the rear cover 18, and a front end thereof is arranged above the fin cover 31, so that the cooling air K outside the printer can be directed to the opening 3 of the fin cover 31.
It is a duct that is fed into the radiation fin 30 side via 1a. At the rear end of the duct 32, the opening 3 is provided at a position facing the air intake holes 18a provided in the rear cover 18.
2a is formed, and an opening 32b is formed on the lower surface of the front side of the duct 32 at a position facing the opening 31a of the fin cover 31. The lower rear end of the duct 32 is fixed to the pressure shaft 16. 33 is the opening 32b of the duct 32 and the fin cover 3
It is a sponge cylinder that connects the first opening 31a.

Reference numeral 34 is a head spring mounted between the heat radiation fin 30 and the inner surface of the duct 32 through the openings 31a and 32b. This head spring 34
Is transmitted by the pressure shaft 16 in the direction of arrow B1 in FIG.
It has a function of pressing the thermal head 10 toward the platen roller 12 side. Reference numeral 35 is a U-shaped hook whose lower part is attached to the outer side of the radiation fin 30, and whose upper part is engaged with the front end of the duct 32. The hook 35 has a function of rotating the radiating fin 30, the thermal head 10 and the like via the duct 32 in the direction of the arrow B2 as the pressure shaft 16 rotates in the direction of the arrow B2. A cooling fan 36 is attached to one side of the opening 32a of the duct 32 and sends air outside the printer device as cooling air to the duct 32 through the air intake hole 18a of the rear cover 18.

Next, the operation of the printer device will be described focusing on the operation of the thermal head cooling device 11. With the start of the printing operation, the electric power of the heating element group of the thermal head 10 is supplied, and a heating pattern is formed in the longitudinal direction. Then, when the heat generation pattern comes into contact with the ink sheet 13, the ink of the ink sheet 13 is melted or sublimated and moved onto the recording paper 4, and an image is printed on the recording paper 14. In this case, the recording sheet 14 moves in the direction of arrow A1 while the ink sheet 13 is wound up on the take-up reel 13B side, and, for example, a cyan image is printed on the entire recording sheet 14. When the printing of the cyan image is completed and the printing operation is stopped, the recording paper 14 is moved to the predetermined position by the arrow A.
It is transported in two directions. Subsequently, a magenta image is similarly printed on the cyan image on the recording paper 14 through the magenta ink sheet 13. Similarly, a yellow image is printed on the cyan image and the magenta image on the recording paper 14 via the yellow ink sheet 13, and a full color image is printed on the recording paper 14.

On the recording paper 14, cyan, magenta,
If three yellow images are formed in succession, the temperature of the thermal head 10 rises rapidly. In this case, the temperature along the longitudinal direction of the thermal head 10 has a mountain shape having a high central portion, as shown in FIG. Then, when the printing operation is started, the cooling fan 36 of the thermal head cooling device 11 is operated, and the unheated air outside the printer device is introduced into the duct 32 as the cooling air K by the cooling fan 36. The cooling air K is guided to the central portion in the longitudinal direction of the radiation fin 30 through the duct 32, the sponge cylinder 33, and the opening 31a of the fin cover 31, and then radiates heat along the fin portion 30a below the fin cover 31. It is guided to both ends of the fin 30. Then, this cooling air K finally reaches the fin cover 31.
From the both ends of the heat dissipation fin 30 without the heat dissipation fin 30
Diffused to the outside.

As described above, in the thermal head cooling device 11, first, the cooling air K having a low temperature outside the printer device is provided.
Is intensively applied to the central portion in the longitudinal direction of the radiating fins 30 having a high temperature, and the radiating fins 30 in this portion are intensively cooled, so that the temperature rise in the central portion in the longitudinal direction of the thermal head 10 is sufficiently suppressed. To be Further, the cooling air K whose temperature has risen due to heat absorption from the heat radiation fins 30 is divided into two, one of which is guided to the one end side of the heat radiation fins 30 and the other is guided to the other end side of the heat radiation fins 30. The cooling air K also sufficiently cools both end portions in the longitudinal direction of the radiating fins 30 where the temperature rises relatively little.

Therefore, as shown in FIG. 3 (b), the temperature along the longitudinal direction of the radiation fin 30 becomes substantially uniform, and the thermal head cooling device 11 causes the thermal head 10 to be localized over the longitudinal direction. It is cooled in a well-balanced manner without generating a lot of heat. Therefore,
In this printer device, it is not necessary to stop printing during printing to cool the thermal head, and printing can be performed continuously. Further, in the thermal head cooling device 11, since it is not necessary to cool the entire radiation fin 30 at once, the cooling fan 36 does not become large.

When the ink sheet 13 is replaced, the pressure shaft 16 is rotated in the direction of the arrow B2 so that the heat radiation fin 30 and the thermal head 10 are connected to the pressure shaft 16 via the duct 32 and the hook 35. It suffices to rotate them to the center and separate them from the platen roller 12.

Example 2. FIG. 4 is a perspective view around the fin cover of the thermal head cooling device according to the second embodiment of the present invention, and FIG. 5 is a sectional view around the fin cover of the thermal head cooling device.

In the figure, reference numeral 37 denotes an airflow direction adjusting plate as a V-shaped variable airflow direction adjusting means provided in an opening 31a of a fin cover 31 which is a cooling air introducing portion for the radiation fins 30 of the duct 32. is there. The wind direction adjusting plate 37 adjusts the amount of the cooling air K guided from the opening 32b of the duct 32 to the opening 31a of the fin cover 31 to each end side of the heat radiating fin 30 to increase the length of the heat radiating fin 30. It adjusts the variation of the cooling amount along the direction. The wind direction adjusting plate 37 has the same number of air holes 37a on the left and right around the ridgeline of the V-shape, and pin portions 37b provided at the four corners are located on both outer sides of the heat radiation fin 30. The heat radiation fin 30 is positioned and supported by engaging with the adjustment hole 38 of the fin portion 30a.

In this case, the wind direction adjusting plate 37 is 0.5 to 0.
It consists of a thin copper plate of about 7 mm bent in a slightly V shape, and it is attached to the heat radiation fin 30 under the condition of elastic force with a large bending angle.
It is attached to the radiation fin 30 without rattling. The other structure of the thermal head cooling device 11 of the second embodiment is the same as that of the thermal head cooling device 11 of the first embodiment.

Next, the operation of the wind direction adjusting plate 37 will be described with reference to FIG.
Will be described with reference to. FIG. 6 is a view showing various ways of attaching the wind direction adjusting plate 37 to the heat radiation fins 30. For example, if the temperature of the cooling air K discharged from the one end C1 side (see FIG. 5) of the heat radiation fin 30 is higher than the temperature of the cooling air K discharged from the other end C2 side, one end C of the heat radiation fin 30 is generated.
It is considered that the cooling amount on the 1 side is insufficient. in this case,
The airflow direction adjusting plate 37 is positioned in the state shown by (a) in FIG. 6A, and the amount of the cooling air K to the one end C1 side of the heat radiation fin 30 is increased. In this case, the wind direction adjusting plate 37 may be positioned in the states indicated by B, C and D in FIG.

In addition, for example, one end C1 of the radiation fin 30
If the temperature of the cooling air K discharged from the other side is lower than the temperature of the cooling air K discharged from the other end C2 side, conversely, it is considered that the cooling amount on the other end C2 side of the radiation fin 30 is insufficient. . In this case, the airflow direction adjusting plate 37 is positioned in the state shown by (e) in FIG. 6A, and the amount of the cooling air K to the other end C2 side of the radiation fin 30 is increased. In this case, the wind direction adjusting plate 37 may be positioned in the state shown in F of FIG. 6B or G of FIG. 6C. In addition, as shown in FIGS. 6A, 6B, and 6C, the wind direction adjusting plate 37 can be positioned in various states.
Thus, the variation in the cooling performance along the longitudinal direction of the radiation fin 30 is finely adjusted.

On the other hand, regardless of the position of the wind direction adjusting plate 37, since a plurality of air holes 37a are formed in this air direction adjusting plate 37, the cooling air K from the duct 32 passes through these air holes 37a. A certain amount is introduced to the central portion side of the radiation fin 30, and the central portion of the radiation fin 30 is cooled intensively. Therefore, also in the thermal head cooling device 11 of the second embodiment, the same effect as that of the thermal head cooling device 11 of the first embodiment can be obtained.

Example 3. FIG. 7 is a perspective view of the periphery of the thermal head cooling device of a color printer device including a thermal head cooling device according to an embodiment of the third invention of the present invention, and FIG. 8 is a thermal head cooling device of the printer device. FIG.

In the figure, 40 is a thermistor as a temperature detecting means for detecting the temperature of the radiation fin 30, and 41 is a controller as a controlling means for controlling the cooling fan 36 based on a signal from the thermistor 40. Further, the thermal head cooling device 11 is provided with a plurality of (for example, two) cooling fans 36A and 36B as the cooling fans 36. The other structure of the thermal head cooling device 11 of the third embodiment is the same as that of the thermal head cooling device 11 of the first embodiment.

That is, if the thermal head 10 is continuously used and the temperature of the radiation fin 30 is high, the thermistor 4
Based on the signal from 0, the controller 41 simultaneously operates the two cooling fans 36A and 36B. Therefore, the flow rate of the cooling air K introduced to the radiating fin 30 side increases, and the thermal head 10 is effectively cooled. Further, in printing, when only a part of the thermal head 10 is used, when the thermal head 10 is not used continuously, or the like, when the temperature of the heat radiation fin 30 is maintained below a certain value, the thermistor 40 is used. Based on the signal of, the controller 41 operates, for example, only one cooling fan 36A,
The other cooling fan 36B is stopped. As a result, it is possible to reduce noise and save power by the cooling fan 36. Further, if the printing work is not performed for a certain period of time and the temperature of the radiation fins 30 hardly rises,
The controller 41 stops both of the two cooling fans 36A and 36B.

The thermal head cooling device 11 of the second embodiment may be provided with a plurality of cooling fans 36A and 36B, and the cooling fans 36A and 36B may be controlled by the thermistor 40 and the controller 41.

[0039]

Since the present invention is constituted as described above, it has the following effects.

According to the first aspect of the present invention, in a thermal head cooling device for applying heat to a printing medium to perform printing, a large number of fin portions are attached to the thermal head to cool the thermal head. A radiating fin extending in the width direction of the printing medium, a duct for guiding cooling air to the central portion of the radiating fin in the width direction of the printing medium, and a cooling fan for sending cooling air outside the printer to this duct. The thermal head can be cooled in a well-balanced manner without locally storing heat in the longitudinal direction. Further, in this case, since it is not necessary to cool the radiation fins at once, the cooling fan does not become large.

According to the second aspect of the present invention, in the cooling air introducing portion to the heat radiation fin of the duct, the air volume of the cooling air flowing toward each end side of the fin portion of the heat radiation fin is adjusted along the fin portion. Since the variable wind direction adjusting means for adjusting the variation of the cooling amount of the heat radiation fin along the printing medium is provided, in the case of the first invention, both ends of the heat radiation fin are cooled in a well-balanced manner, and the thermal head Is maintained at a more uniform temperature along its length.

According to the third aspect of the present invention, a plurality of cooling fans are provided, temperature detecting means for detecting the temperature of the radiating fins is provided, and all the cooling fans are detected based on a signal from the temperature detecting means. Or some of them are ON / OF
Since the control means for controlling the F is provided, in the case of the first and second inventions, a required amount of cooling air can be supplied to the heat radiating fins according to the temperature of the heat radiating fins, thereby reducing noise and energy saving related to the cooling fan. To be achieved.

[Brief description of drawings]

FIG. 1 is a perspective view around a thermal head cooling device of a printer device including a thermal head cooling device according to a first embodiment of the present invention.

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

FIG. 3A is a graph showing a temperature change along a longitudinal direction of a thermal head, and FIG. 3B is a graph showing a temperature change along a longitudinal direction of a heat radiation fin.

FIG. 4 is a perspective view around the fin cover of the thermal head cooling device according to the second embodiment of the present invention.

5 is a cross-sectional view around the fin cover of the thermal head cooling device of FIG.

FIG. 6 is a view showing the arrangement of airflow direction adjusting plates of the thermal head cooling device of FIG. (A), (b), (c) show various arrangements of the airflow direction adjusting plate.

FIG. 7 is a perspective view around a thermal head cooling device of a printer device including a thermal head cooling device according to a third embodiment of the present invention.

8 is a sectional view taken along the line VIII-VIII in FIG.

FIG. 9 is an explanatory diagram of a first conventional thermal head cooling device.

FIG. 10 is an explanatory diagram of a second conventional thermal head cooling device.

[Explanation of symbols]

 10 Thermal Head 11 Thermal Head Cooling Device 13 Ink Sheet (Printing Medium) 30 Radiating Fin 30a Fin Section 32 Duct 36 Cooling Fan 36 Cooling Fan 36B Cooling Fan 37 Wind Direction Adjusting Plate (Variable Air Direction Adjusting Means) 40 Thermistor (Temperature Detecting Means) 41 controller (control means)

Claims (3)

[Claims] 1. A cooling device for a thermal head, which applies heat to a printing medium to perform printing, wherein a plurality of fins are attached to the thermal head to cool the thermal head, and a large number of fins extend in the width direction of the printing medium. The heat radiation fins, a duct for guiding cooling air to the widthwise central portion of the printing medium of the heat radiation fins, and a cooling fan for sending cooling air outside the printer to the ducts. And a thermal head cooling device. 2. The cooling air introduction portion for the radiation fins of the duct adjusts the amount of the cooling air flowing toward each end side of the radiation fins along the fin portion so as to follow the printing medium of the radiation fins. 2. The thermal head cooling device according to claim 1, further comprising variable wind direction adjusting means for adjusting the variation of the cooling amount. 3. A plurality of cooling fans are provided, temperature detecting means for detecting the temperature of the heat radiation fins is provided, and all or part of the cooling fan is ON / OFF controlled based on a signal from the temperature detecting means. 3. The thermal head cooling device according to claim 1, further comprising control means for controlling the thermal head.