One known method of producing expanded (puffed) cakes or crackers from starchy granular material such as a rice, involves introducing the starchy rice material into a baking mold comprising an upper and lower mold plate. A cavity is defined between the mold plates, which are disposed opposite to each other.

At least one of the upper or lower mold plates is capable of moving relative to the other plate so that the baking mold can operate between a charging stage in which material is introduced into to the baking cavity prior to the baking cycle; an operative stage in which the volume of the baking cavity is alterable during the baking cycle; and a discharging stage in which the cake or cracker is discharged from the chamber after the baking cycle.

During the baking cycle, the starchy granular material is subjected to a compressive step in which a compressive force is applied to said starchy granular material while being subjected to heat in a hermetic environment, and an expansion step in which the compressive force is released from said starchy granular material and the environment is no longer hermetic, to thereby cause the starchy granular material to expand to form a cake or cracker having a substantially self-sustaining structure ; Following the compressive step, at a pre-set point in the baking cycle, movement by one mold, away from the other mold removes the compressive force. The chamber is no longer airtight and the reduction in pressure within the mold causes the heated granular cereal material, which by this stage has been reduced to a gelatinous state, to expand and thereby form a cake or cracker having a unitary, self-sustaining structure. The cake or cracker is subsequently discharged from the mold cavity.

Movement of the upper and/or lower plate to produce cakes or crackers as described above requires the employment of a drive mechanism US-A-4328741 and BE-A-902360 disclose a drive mechanism that employs pneumatic drivers to drive a lower mold held on a drive punch towards the upper mold. Control using pneumatic drivers can be problematic due to deviations in the quantity of air fed from a compressor to an air cylinder which will affect movement of the drive punch, possibly resulting in a non-uniform cracker. Furthermore, air compressors can be noisy and may require a high level of maintenance and a large duty of energy to operate.

An alternative form of drive mechanism is taught in GB-A-2165437, which employs highly engineered rotary cam plates to drive the lower mold plate in an apparatus for the production of puffed cereal cakes and crackers. The cam plate is rotated at substantially constant speed by a drive motor, and the profiled rim of the cam plate abuts against a drive punch to directly drive the lower mold plate. These rotary cam plates can be mechanically complex and require a high degree of precision in order to position the lower mold relative to the upper mold at particular points within the baking cycle. This is particularly the case when a high degree of precision is required in releasing the lower mold from the upper mold for expansion of the rice cake material. The cam suffers from serious problems of wear due to the high forces being applied directly to the mold punch, and the apparatus is noisy in use.

EP-A-0359740 discloses yet another drive mechanism which implements a hydraulic ram to move the lower mold relative to the upper mold. A problem with hydraulic rams is that the position of the ram will depend upon the viscosity (and hence the temperature) of the oil, thereby making control difficult. For example, if the alignment of the lower mold relative to the upper mold is calibrated when the temperature of the oil is elevated and therefore the viscosity low, the alignment of'cold start'drive shaft will be different at start-up of the drive mechanism due to the lower temperature of the oil and hence higher viscosity.

It is an object of the invention to provide a baking apparatus which overcomes at least some of the problems of the prior art.

In first embodiment, the present invention provides an apparatus for producing an expanded starchy cake or cracker from a starchy granular material according to a method in which said material undergoes a baking cycle comprising a compressive step in which a compressive force is applied to said starchy granular material while being subjected to heat, and an expansion step in which the compressive force is released from said starchy granular material to thereby cause it to expand to form said cake or cracker having a substantially self-sustaining structure, said apparatus comprising: a mold defining at least one cake or cracker-forming chamber for containing starchy granular material therein, said mold having at least one movable mold element to alternate the chamber between: a charging stage in which the starchy granular material is introduced to the cake or cracker-forming chamber prior to the baking cycle; an operative stage in which the volume of said chamber is alterable during said baking cycle for subjecting said starchy granular material to said compressive step followed by said expansion step ; and a discharging stage in which the cake or cracker is discharged from the chamber after said baking cycle ; a heating element for heating said starchy granular material within said chamber during said baking cycle; a drive mechanism coupled to said moveable mold element a servo motor coupled to said drive mechanism to operatively actuate said drive mechanism for movement of said moveable mold element and a controller to control said servo motor to move said moveable mold element so that said starchy granular material is subjected to said compressive step and said expansion step during desired time periods of said baking cycle.

The drive mechanism for movement of the moveable mold element is operatively actuated by the servo motor through a suitable coupling and under the control of the controller. The term"operatively actuated"signifies that the controller is adapted or programmed to operate the servo motor for programmable periods of time and/or at varying angular speeds and directions and/or for programmable total angles of rotation at the different stages of the process, and especially at different parts of the operative stage. The position of the movable mold element is a function of the total angular movement of the servo motor shaft

relative to a reference position. The servo motors and controllers used in the present invention are clearly distinct from the drive motors of the kind used in GB-A-2165437, which are adapted to drive a cam plate at constant angular velocity at least throughout the stages of the cereal cake production process.

The use of a servo motor to drive the mold punch in a puffed starchy cereal cake manufacturing machine is new, and provides advantages including improved control over manufacturing parameters such as cake dimensions, and increased manufacturing speed.

The difficulties associated with pneumatically or hydraulically driven equipment can be avoided, as can the drawbacks of the machined cam plate described in GB-A-2165437.

Servo motors have not hitherto been used in this application, in part because it is not possible to control the process with sufficient precision by the use of limit switches to regulate the position of the movable molding element. Instead, the present inventors have found that the servo motor can be regulated to carry out the process in an accurate and repeatable fashion, either by operating the servo according to a predetermined program, and/or by using feedback from one or more signals generated by the servo.

In certain embodiments of the present invention the servo is pre-programmed to carry out a predetermined operating cycle. In these embodiments the controller controls the position of the servo, typically by sending control pulses to the servo (e. g. 4086 pulses for one complete rotation of the servo shaft) in accordance with a predetermined program. This provides a high degree of reproducibility without a need for limit switches or other sensors to control the position of the mold punch. Of course, such equipment must be reprogrammed to optimise the process for each product and cannot ideally accommodate variations in the amount of feed material supplied to the mold.

In order to achieve the desired control over the process, the angular position of the servo motor drive shaft is preferably controllable to +/-10°, more preferably +/-1 °.

In certain embodiments, a sensor is associated with said servo motor, the sensor being adapted to monitor an operating variable of said servo motor to thereby produce a signal representative of said operating variable. In such cases the controller may include a

feedback control loop to generate the control response for controlling the operating variable of the servo motor during the baking cycle.

For example, the operating variable may be the speed of the servo motor shaft. This parameter can be integrated in the controller to give the exact position of the mold punch.

In certain embodiments, the operating variable can include the torque of the servo motor shaft, since this allows the optimum pressure to be applied to the product during the compression step, and/or allows expansion to be initiated when the pressure reaches a predetermined level.

The drive mechanism converts the rotary motion of the servo shaft into a linear motion of the movable mold element. Preferably, the drive mechanism permits high precision control of the position of the movable mold element. For example, preferably, the drive mechanism is adapted to convert one complete revolution of the servo drive shaft into a linear movement of the movable mold element of from 1 to 500 micrometers, more preferably from 4 to 100 micrometers. Preferably, the linear position of the movable mold element is controllable to +/-0. 1mm or less, more preferably to +/-20, im or less, and most preferably to +/-10m or less.

Preferably, the drive mechanism comprises a drive shaft coupled to said at least one movable mold element and an eccentric coupling between the drive shaft and the servo motor. The eccentric coupling may for example be a rotary plate driven by the servo motor (optionally via a step-down gear) and eccentrically coupled to the drive shaft, whereby in use, the servo motor drives said rotary plate and said rotary plate actuates the drive shaft to move the movable mold element. More preferably, the drive mechanism further comprises a gear mechanism to step down the rotary speed imparted to the coupling by the servo motor.

The drive shaft may drive the movable mold element directly. However, preferably the movable mold element is driven through a linkage as described for example in W088/06425 or EP-A-0359740. The linkage comprises a two-arm joint hinged together at on end, the unhinged end of one arm being swingably connected to the movable mold element and the unhinged end of the other arm being swingably connected to a fixed shaft

of the apparatus to be rotatable thereabout. The linkage is then driven by the drive shaft extending from the region where the two arms are hinged together.

It will be appreciated that, for the purpose of start-up, the apparatus preferably further comprises a limit stop or limit switch at a predetermined limit position of the movable mold element, usually a limiting open position of the mold. During start-up, the servo moves the movable mold element until this limit position is reached, thereby providing the necessary reference position for the start of the program.

It is a particular advantage of the present invention that the precise control provided by the servo mechanism enables thinner cereal cakes to be made in a controlled and reproducible fashion. In preferred embodiments, the apparatus is configured and programmed such that the height of the mold cavity during the compression step of the operating stage is from 0.01 to 2mm, preferably from about 0.1 to about lmm, for the production of very thin cakes.

In a second aspect, the present invention provides a method of making an expanded self sustaining starchy cake or cracker, the method comprising: providing a cake or cracker baking apparatus according to the first aspect of the invention ; in a charging stage, opening the cake or cracker forming chamber, and charging a starchy granular material into the cake or cracker-forming chamber ; in an operative stage, operating said servo motor and heating element so as to subject said starchy granular material to compression and heating, followed by rapid expansion ; and in a discharging stage, opening the cake or cracker forming chamber to allow the cake or cracker to be discharged from the chamber.

Preferably, the method according to this aspect of the invention further comprises a step of initiating the apparatus by operating the servo motor to move the movable mold element to a predetermined limit position. This position may be a limit stop or switch as described above.

It is a particular advantage of the present invention that the precise control provided by the servo mechanism enables the duration of the operative stage to be reduced below the current 11-16 seconds conventional for cereal cakes. In the methods of the present invention, the duration of the operative stage is preferably less than about 10 seconds, and more preferably from about 2 to about 7 seconds.

As already noted, it is a further particular advantage of the present invention that the precise control provided by the servo mechanism enables thinner cereal cakes to be made in a controlled and reproducible fashion. For example, the process is preferably adapted to produce puffed cereal cakes having a mean thickness of from about 1 to about 5mm, and/or preferably a density per unit area of from about 0.01 to about 0. 05g/cm2.

An embodiment of the invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a schematic illustration of a cereal cake baking apparatus according to the invention ; Referring to Fig. 1, there is shown a schematic illustration of a cereal cake baking apparatus 10 in side elevation. The cereal cake baking apparatus 10 includes a mold 12, a drive mechanism 16, and a servo motor 18.

The mold 12 consists of an upper mold plate 20 and a lower mold plate 22. The upper mold plate 20 has an array of cylindrical mold punches 24 projecting from its surface that are received in corresponding mold cavities of the lower mold plate 22. In this way a single movable mold element can drive the production of a plurality of smaller cereal cakes.

The rice cake baking apparatus 10 shown in Fig. 1 is shown in its charging stage. The method of charging the mold 12 is known to those skilled in the art and will not be disclosed here in detail.

The upper mold plate 20 is mounted on a support 23 that is fixed to the frame of the apparatus. The lower mold plate 22 sits on a punch shaft 32 which extends through a guide

frame 26 which is connected to a fixed support 21. The guide frame 26 is used to guide the punch shaft 26 as the lower mold plate 22 travels relative to the upper mold plate 20 in the direction of arrow 40. The punch shaft is supported on a linkage, which comprises a two arms 27,28 linked together by a hinge or pivot 25, the unhinged end of one arm 27 being swingably connected to the end of the punch shaft and the unhinged end of the other arm 28 being swingably connected to a shaft fixed to the lower frame 24 of the apparatus.

The drive mechanism 16 further comprises a drive shaft 34 linked at one end to the hinge 25. The other end of the drive shaft 34 is eccentrically fastened to a rotary plate 36, so that the eccentric motion of the rotary plate 36 will raise and lower the punch shaft 32 as the drive shaft 34 moves linearly.

The servo motor 18 drives the rotary plate 36 via a gearbox (not shown) which regulates the speed of the rotary plate. In the present embodiment, the gear ratio of the box is 1: 45.16 in order to decrease the speed of rotation of the rotary plate relative to the servo and thereby offer great control over the movement of the lower mold plate 22 relative to the upper mold plate 20 during the baking cycle. In this embodiment, the servo motor is controlled by electric pulses from the control circuit; 4086 pulses result in one complete rotation of the servo motor. In conjunction with the step-down effect of the gearbox and the lever arm arrangement of the drive mechanism, this gives exceptional control over the vertical movement of the mold plate. The vertical movement of the mold plate is controllable to within +/-5, um.

A speed sensor (not shown) is located adjacent to the servo motor shaft to monitor the speed of the servo motor 18. Typically, the maximum speed of the servo motor 18 is 2000 rpm, although the usual speed for production of rice cakes is 1200 rpm. The sensor transmits a signal to an amplifier which sends an amplified speed signal to the controller via a signal transmission line. A torque sensor may likewise be operatively associated with the servo motor.

A baking cycle for baking an expanded rice cake will now be described. Parboiled rice kernels having a moisture content of about 12% by weight are charged into the baking chambers by methods known in the art. In order to achieve a very thin final product, the

kernels are charged at an area density of only about 0. 03g/cm2. At the beginning of the baking cycle the compressive step for the baking cycle is initiated in which the servo motor 18, controlled by the controller, drives the rotary cam plate 36 to raise the punch shaft 32 toward the upper mold plate 20. The final position of the punch shaft may determined by a sending predetermined number of pulses sent to the servo (this assumes that the optimum position for this particular process and cake thickness has been predetermined, and that the apparatus has been initiated by locating a stop element beforehand). Alternatively, the feedback from the torque sensor can be used to stop the compression at a predetermined optimum initial pressure in the molds.

Heating elements 29 are located in the mold plates 20 and 22 to provide a heat source for baking the granular rice material. The combination of heat and pressure renders the rice gelatinous and plastic. The grains flow together to form a bonded mass.

After a predetermined period of time, the expansion step is initiated and the lower plate 22 is released from the upper plate 20 by lowering the punch shaft 32 rapidly, and the pressure within the chamber is reduced. The gelatinous rice material undergoes expansion due to the pressure reduction within the baking chambers and the release of gases emitted during the baking process. The expansion causes the gelatinous material to rapidly cool and form a rice cake or cracker having a self-sustaining structure.

After expansion is completed, the molds are opened and the rice cakes or crackers are ejected from the mold 12 by methods known in the art.

As the speed of the servo motor can be adjusted for each baking cycle time period, it is possible to achieve a desired pressure change profile within the chambers and therefore control the expansion rate of the rice cake or cracker. Controlling the power output of the servo motor also allows the operator of the baking apparatus to achieve a relatively constant pressure during the compressive step of the baking cycle and the controlled expansion rate of the resulting cake or cracker results in a uniform finished product.

Control over the speed of the servo motor leads to other advantages such as accuracy in movement of the lower mold plate relative to the upper mold plate. The improved control

over the speed of the servo motor 18 also results in the average baking cycle time of the rice cakes being reduced from an average cycle time of 11 sec with the known prior art to 6 sec, thereby increasing the throughput of the baking apparatus. Furthermore, because the controller is used to alter the speed of the servomotor 18, it is not necessary to have a finely engineered rotary cam plate in order to gain the desired pressure reduction profile within the chamber as the controller can be tuned empirically.

Additionally, different granular products such as corn, wheat, barley, cereals, oats, soya bean and other cereals will require different pressure reduction profiles during the baking cycle than the profile for rice. Changing the variables within the controller however can easily alter the operation of the baking rice apparatus and therefore the baking apparatus can be adapted for different starchy granular materials.

The control system of the above described embodiment provides better control over the dimensions and expansion rate of the starchy granular material in the cake or cracker baking process in comparison to using a hydraulic or pneumatic drive or a highly engineered cam plate. Additionally, better control over the servo drive results in an improvement in the accuracy of the baking apparatus at start-up, hence better'cold start' reproducibility for the cake or cracker product.

The above embodiment has been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.