Thermal management in optical scanning apparatuses

FIELD OF THE INVENTION

The present invention relates to an optical scanning apparatus for reading information from an optical disc, the apparatus comprising communication means for receiving instructions from and sending information to an internal or external host. The invention also relates to a method for handling communication between an optical scanning apparatus and an internal or external host, the communication corresponding to the optical scanning apparatus receiving instructions from and/or sending information to the host.

BACKGROUND OF THE INVENTION As it is commonly known, an optical disc comprises at least one track, either in the form of a continuous spiral or in the form of multiple concentric circles, of storage space where information may be stored. Optical discs may be read-only type, where information is recorded during manufacture, which data can only be read by a user. The optical storage disc may also be of a writable type, where information may be stored by a user. Typical examples of optical discs are, for instance, CD, DVD or high density discs such as HD-DVD or Blu-Ray (BD) discs. For writing information onto or for reading information from the optical disc, an optical scanning apparatus comprises, on the one hand, rotating means for receiving and rotating an optical disc, and on the other hand optical means for scanning the storage track with an optical beam. With increasing the information density on the optical disc and with increasing the data transfer rate reading from/ recording onto the optical disc, problem may appear with respect to the temperature inside the optical scanning apparatus. Apart from the design of the optical scanning apparatus and cooling efficiency of its casing, the temperature rise depends, inter alia, on the rotational speed of the optical disc, on the angular acceleration and on the duration of such operations. It is further known that if a laser temperature rises too high, optical scanning apparatus failure may take place because of a high laser temperature and/or of a high motor core temperature of the turntable motor (TTM). The laser temperature should stay below a temperature specified by the manufacturer; usually, this temperature is

75 ⁰ C in the case of a DVD laser of a CD laser and only 70 ⁰ C in the case blue lasers used for reading/recording high density discs such as HD-DVD or Blu-Ray (BD) discs.

PCT Patent application no WO 2004/064059 describes an optical scanning apparatus wherein, when the temperature reaches a threshold value, the optical disc is rotated at a constant rotational velocity for a period, thereby providing further cooling. Thus, the cooling of the laser after writing/reading operation is improved, so that it takes longer for the laser to reach a critical temperature. Said method has the disadvantage that it is requires cooling periods after executing an operation. Therefore, it is desirable to improve the ability of an optical scanning apparatus to handling prolonged operations, preferably at higher rotational speeds.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an optical scanning apparatus with improved ability to handle prolonged operations. The object of the invention is reached by a method according to claim 1. This is based on the insight that an internal or external host normally attempts to optimize the data transfer process in advance, in view of expected future user actions. Therefore the host may issue a number of predetermined instructions intended for optimizing future data transfer. Executing such instructions leads to an improved data transfer efficiency at the expense of an increase in the amount of dissipated power, while non-execution of such instructions may impact the data transfer rate but does not lead to a malfunction or failure of the optical scanning apparatus. Examples of such instructions are seek commands, which correspond to positioning reading means such that information stored on a given address may be read, or may request positioning on a next writable address to optimize a recording process. For example, it noted that seek instructions can only increase the performance of the apparatus so that so that a subsequent read instruction completes faster as the seek part has already been performed itself. Therefore, when the optical scanning apparatus is enabled to decide, when receiving a predetermined instruction for executing an associated action, to send information indicating successful execution of the associated action without executing the associated action, this leads to a reduced power dissipation, implying an improved ability to handle prolonged operations without reaching thermal overload. Sending information indicating successful execution allows indicating to the host that the optical scanning apparatus is functioning normally.

In an advantageous embodiment, the predetermined instruction corresponds to a seek instruction, hence the associated action corresponding to positioning the reading

means to enabling reading information from a predetermined address. It is known that execution a seek instruction consumes a large amount of power when compared with normal recording and/or reading, which does not include high-speed movement of the positioning means and/or acceleration. Accordingly if a large number of seeks are performed over an extended period of time the temperature of the drive becomes very high. As a seek command is only intended to optimize future data transfer, not executing such a seek command has the advantage of significantly reducing the power dissipation.

It is advantageous that the optical scanning apparatus further comprises temperature measurement means for measuring a temperature inside the optical scanning apparatus, the decision means are enabled to sending information indicating successful execution of the associated action without executing the associated action, if a measured temperature exceeds a first threshold temperature. If the temperature is below a certain threshold temperature, the optical scanning apparatus may allow increased power dissipation without risk of operation failure. In such cases when the temperature and the risk of thermal failure is low, the operation of the optical scanning apparatus should be optimized for high data transfer rate, and when the temperature exceeds a first threshold, the optical scanning apparatus should be optimized for avoiding the risk of thermal failure.

In an advantageous embodiment, the optical scanning apparatus is further enabled to delaying sending the information indicating successful execution of the associated action for a period of time. A host expects that a predetermined instruction, such as a seek instruction, requires some amount of time before successfully executed, therefore waits for a period of time for a reply indicating successful completion. Delaying sending the information indicating successful execution allows the optical scanning apparatus to further reduce the temperature. In an advantageous embodiment, the optical scanning apparatus is further enabled to entering a temperature management mode when reaching a second threshold temperature, the temperature management mode comprising controlling a rotational speed and/or a rotational acceleration of the optical disc. This allows further mitigating the risk of operational failure. The invention also relates to a method for handling communication between an optical scanning apparatus and an internal or external host, the communication corresponding to the optical scanning apparatus receiving instructions from and/or sending information to the host.

These and other aspects of the invention are apparent from and will be explained with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

Fig. 1 illustrates schematically a known optical disc; Fig. 2 illustrated schematically an optical scanning apparatus wherein the invention is practiced; Fig. 3 illustrates by means of a flow diagram a method of communicating between an optical scanning apparatus and a host according to the invention;

Fig. 4 illustrates by means of a flow diagram a method of temperature management according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. Ia illustrates schematically an optical disc 11 having a track 12 and a central hole 10. The track 12, being the position of the series of (to be) recorded marks representing information, is arranged in accordance with a single spiral pattern constituting substantially parallel tracks on an information layer. The optical disc may comprise one or more information layers of a recordable type. Known examples of recordable optical discs are CD-RW, or DVD+/-RW, DVD-RAM or BD-RE for the rewritable type and CD-R, DVD+/-R or BD-R for the write once type. For example, further details about the physical structure and addressing information for DVD+/-RW optical discs can be found in references ECMA-337 and ECMA-338, respectively. The information is represented on the information layer by recording optically detectable marks along the track, e.g. crystalline or amorphous marks in phase change material. The track 12 on the optical disc is indicated by a pre- embossed track structure provided during manufacture of the blank optical disc. The track structure is constituted, for example, by a pregroove, which enables a read/write head to follow the track during scanning. The track structure comprises a periodical known in the art as wobble, so that information, modulation of said periodical variation being used for encoding further information such as physical addresses for indication the location of stored units of information. The position information may include specific synchronizing marks for locating the start of such information blocks.

The optical disc 11 is intended for carrying user information according to a standardized format, to be playable on standardized playback devices. The recording format includes the way information is recorded, encoded and logically mapped onto the recording space provided by the track 12 and it will be described with reference to Fig Ib. The recordable space is usually subdivided into a lead-in area, a data zone for recording user data and a lead-out area and it is addressable by means of sequentially numbered units known as physical sectors. The lead-in area usually comprises an area 13 wherein basic disc management information is stored and a disc description area 14 wherein the information how to physically access the data zone is provided. For example, said disc management information corresponds to the table of contents in CD systems or the formatting disc control blocks in DVD systems. Further, at logical level, the user data in the data zone is arranged according to a file system comprising file management information, such as ISO 9660 used in CD systems (available as ECMA-119) or UDF used in DVD systems (available as ECMA 167). Such file management information is mapped on a predefined location 15 on the optical disc 11, usually in or directly after the lead-in area. The user information may be further arranged according to an application format, for example comprising a predefined structure of files and directories.

Fig. 2 illustrates schematically an optical scanning apparatus 1 for reading and/or writing information on an optical disc 11.The optical scanning apparatus is provided with a drive unit 16 for rotating the optical disc 11, a head 18, a positioning unit 21 for coarsely positioning the head 18 in the radial direction on the track, and a control unit 17. The head 18 comprises an optical system of a known type for generating a radiation beam 20 guided through optical elements focused to a radiation spot 19 on a track of the information layer of the optical disc. The radiation beam 20 is generated by a radiation source, e.g. a laser diode. The head further comprises (not shown) a focusing actuator for moving the focus of the radiation beam 20 along the optical axis of said beam and a tracking actuator for fine positioning of the radiation spot 19 in a radial direction on the center of the track. The tracking actuator may comprise coils for radially moving an optical element or may alternatively be arranged for changing the angle of a reflecting element. For reading information, the radiation reflected by the information layer is detected by a detector of a usual type, e.g. a four-quadrant diode, in the head 18 for generating a read signal and further detector signals, such as a tracking error and a focusing error signal for controlling said tracking and focusing actuators.

Optionally, recording means comprise the drive unit 16 for rotating the optical disc 11, the head 18, the positioning unit 21 for coarsely positioning the head 18 in the radial direction on the track, and the control unit 17. For recording information the radiation beam 20 is controlled to create optically detectable marks in the recording layer. For this purpose, the optical scanning apparatus comprises write processing means for processing input information to generate a write signal to drive the head 18, which write processing means comprise an input unit 23, and data processing means comprising a formatter 24 and a modulator 25.

The control unit 17 controls the recording and retrieving of information and may be arranged for receiving commands from a host 30. The host may be external, for example in the case the optical scanning apparatus is connected to a host computer or internal, for example when the optical scanning apparatus forms an internal unit to a larger apparatus, such as set top box (STB) or a video player/recorder. The communication with the host 30, may take place via known communication interfaces such as IDE or USB. To this end, the control unit 17 may comprise control circuitry, for example a microprocessor, a program memory and control gates, for performing the procedures described below. The control unit 17 is connected via control lines 22, e.g. a system bus, to said input unit 23, formatter 24 and modulator 25, to the drive unit 16, and to the positioning unit 21. The control unit 17 comprises control circuitry, for example a microprocessor, a program memory and control gates, for performing the procedures and functions according to the invention as described below. The control unit 17 may also be implemented as a state machine in logic circuits.

The input unit 23 receives and pre-processes the user information. For example, when processing audio-video information, the input unit 23, may comprise of compression means for input signals such as analog audio and/or video, or digital uncompressed audio/video. Suitable compression means are described for audio in WO 98/16014-A1 (PHN 16452), and for video in the MPEG2 standard. The input signal may alternatively be already encoded. The output of the input unit 23 is passed to the formatter 24 for adding control data and formatting the data according to a recording format, e.g. by adding error correction codes (ECC) and/or interleaving. For computer applications units of information may be interfaced to the formatter 24 directly. The formatted data from the output of the formatter 24 is passed to the modulation unit 25, which comprises for example a channel coder, for generating a modulated signal, which drives the head 22. Further the modulation unit 25 comprises synchronizing means for including synchronizing patterns in

the modulated signal. The formatted units presented to the input of the modulation unit 25 comprise address information and are written to corresponding addressable locations on the optical disc under the control of control unit 17. The control unit 17 is arranged for recording and retrieving position data indicative of the position of the recorded information volumes. During the recording operation, marks representing the information are formed on the optical disc 11. The marks may be in any optically readable form, e.g. in the form of areas with a reflection coefficient different from their surroundings, obtained when recording in materials such as dye, alloy or phase change material, or in the form of areas with a direction of magnetization different from their surroundings, obtained when recording in magneto-optical material. Writing and reading of information for recording on optical disks and usable formatting, error correcting and channel coding rules are well-known in the art, e.g. from the CD system.

For reading the radiation, the read signal is processed by a read processing unit comprising a demodulator 26, a de-formatter 27 and an output unit 28 for outputting the information. The functioning of the demodulator 26, the de-formatter 27 and the output unit 28 are controlled by the controller 17. Hence, retrieving means for reading information include the drive unit 16, the head 18, the positioning unit 21 and the read processing unit.

The control unit 17 is further adapted, for example by means of suitable firmware, for implementing the method of communicating between an optical scanning apparatus and a host according to the invention, as described with reference to Fig. 3.

Fig. 3 illustrates by means of a flow diagram a method of communicating between an optical scanning apparatus and a host according to the invention;

In step 31 (INSTR), the control unit 17 of the optical scanning apparatus 1 receives an instruction from the host 30. In step 32 (CHK) it is checked whether the instruction corresponds to a predetermined instruction that are to be simulated instead of being executed. In an embodiment, a list such instructions is maintained in a memory of the control unit 13, and preferably it comprises at least instructions of the seek type.

It is noted that seek instruction are intended to increase the performance of the optical scanning apparatus 1. If the host expects that the next operation would correspond to reading information starting from a given address X, preferably the head 18 is pre-positioned along the track of the optical disc 11, by means of the seek instruction, such that reading information from the given address X is directly for reading from position x. The execution of the seek instruction enables that a subsequent read instruction, if correctly anticipated by the host 30, to complete faster. Some applications running on the host may send several seek

instructions to the optical scanning apparatus 1 before actually accessing (i.e. requesting information to be read or recorded) the. Because execution a seek instruction usually comprises a sledge movement and an actuator movement, this dissipates a lost of heat inside the optical scanning apparatus 1. When combining this behavior with an insufficient cooling, and/or a higher room temperature, the optical scanning apparatus 1 may heat up beyond a critical temperature. Normally when the temperature of the optical scanning apparatus 1 increases beyond a critical temperature, the optical scanning apparatus 1 sends to the host 30 some error code and this may cause the application running on the host 30 to fail.

If the received instruction is not of a type to be simulated (for example, a read or write instruction, which need to be executed), in step 33 (EXEC), a corresponding action associated with the received instruction is performed. Optionally, the execution of the instruction is succeeded by sending an appropriate reply to the host 30 indicating the outcome of the execution in step 34 (REPL).

If the received instruction is a type to be simulated (for example, a seek instruction), in step 33 (EXEC), a corresponding action associated with the received instruction is not performed. This prevents unnecessary sledge and actuator movements, as the optical scanning apparatus 1 performs only the strictly necessary actions (for example for read or write requests) and allow the optical scanning apparatus 1 to cool down. Optionally, in step 35 (DELAY) a delay is introduced. A host expects that a predetermined instruction, such as a seek instruction, requires some amount of time before successfully executed, therefore waits for a period of time for a reply indicating successful completion. Delaying sending the information indicating successful execution allows the optical scanning apparatus 1 to further reduce the temperature. In step 36 (REPL), a reply is sent to the host 30 indicating the successful execution of the instruction. After a reply has been sent to the host 30 in either step 34 or step 36, in step 37 (LSN) the optical scanning apparatus 1 is ready to listen to the host 30 for a new instruction.

Fig. 4 illustrates by means of a flow diagram a method of temperature management according to the invention.

In step 31 (TEMP) the optical scanning apparatus 1 monitors the internal temperature inside the apparatus. It is noted that it is known for optical scanning apparatuses to monitored continuously the internal temperature may be to insure the apparatus is not used in conditions that could damage any of its components, and means for such temperature measurement and monitoring are known and were not illustrated in Fig. 2. The internal temperature is in general influence by several parameters, including the design of the

enclosure, mode of usage (for example recording of several discs leads to higher operational temperatures) and ambient temperature.

After a temperature measurement, the measured value is compared against a first threshold value (Tl) in step 42 (?T1). If the measured temperature is below the first threshold value, the drive operates in step 43 (NORM) in the normal mode, that is all instructions received from host are executed normally.

If the measured temperature is above the first threshold value, in step 44 (?T2) the measured temperature is compared against a second threshold value. If the temperature is found below the second threshold value, the optical scanning apparatus 1 enter the simulation mode in step 45 (SIM MODE). This mode corresponds to handling communications with the host 30 according to the method described with reference to Fig. 3. Basically, this corresponds to the following: when the measured temperature goes above the first threshold value, several types of instructions such as seek instructions are not executed anymore, but successful completion is simulated. If in step 44 the temperature is found above a second threshold temperature, then in step 46 (TM MODE) the optical scanning apparatus enters in a thermal management mode. This mode preferably corresponds to that described in PCT Patent application no WO 2004/064059, to be inserted herein by reference.

With respect to hardware implementation of the above-described methods, it is further noted that the optical scanning apparatus 1 may be provided with decision means 29 for controlling the communication between the optical scanning apparatus and the host as described with reference to fig 3, i.e. for to send information indicating successful execution of an action associated with the predetermined instruction without executing said action when receiving said instruction. Further means 29a may be provided for taking such decision based on the measured temperature. In an alternative embodiment such decision means 29 and means 29a may be incorporated in the control unit 17 by means of suitable firmware. It should be noted that the above-mentioned embodiments are meant to illustrate rather than limit the invention. And that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verbs "comprise" and "include" and their conjugations do not exclude the presence of elements or steps other than those stated in a claim. The article "a" or an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements and/or by means of

a suitable programmed processor. A computer program may be stored/distributed on a suitable medium, such as optical storage or supplied together with hardware parts, but may also be distributed in other forms, such as being distributed via the Internet or wired or wireless telecommunication systems. In a system/device/apparatus claim enumerating several means, several of these means may be embodied by one and the same item of hardware or software. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.