Method of controlling a woodchipper apparatus

Abstract

A method of controlling a woodchipper apparatus, the apparatus having a powertrain to provide torque to a rotor disc having blades, an infeed mechanism adapted to feed or prevent feed of material to t

Description

Field of the inventive concept The present inventive concept relates to the field of woodchipper apparatus. Background to the invention A woodchipper generally has a powertrain providing torque to a rotor disc that is fitted with blades. The rotor is generally spun at very high speed and the material to be chipped is fed onto the rotor using hydraulically powered rollers. The torque requirement due to the cutting of the wood by the rotor while chipping is generally significantly more than that which the powertrain can provide; it would be inefficient to match the powertrain torque rotor to the torque requirement. This is true whether the powertrain is an internal combustion engine, power take-off (PTO), hybrid or electric motor. Therefore, when the material (e.g. wood) is fed into the rotor and the rotor speed decays, the infeed of material must be paused to allow the rotor speed to recover. A woodchipper can be operated so that if the rotational speed of the rotor drops below a predetermined low level the apparatus is adapted to prevent insertion of material while the powertrain increases the rotational speed of the rotor to above the said pre-determined low level. The period when the apparatus prevents insertion of material is referred to as the no stress window. When the rotor speed has accelerated to a pre-determined high level at which chipping can recommence, infeed can be restarted. The process will continue to cycle through these conditions until the material has been processed. An issue with the above approach is that it does not allow for differences in load conditions coming from the variety of size, species of wood (hardwood / softwood), moisture content etc. of the wood being processed. This results in the no stress settings applied to a machine, must be suitable for the full range of material types and sizes. Indeed, these settings may have to be very inefficient for certain types of wood, just to ensure that the machine can process a difficult material (e.g., wet conifer). Therefore an aim of the present inventive concept is to provide a more efficient woodchipper apparatus by providing a method of controlling a woodchipper apparatus. Summary of the inventive concept A method of controlling a woodchipper apparatus, the apparatus having a powertrain adapted to provide torque to a rotor disc having blades, the apparatus further having an infeed mechanism adapted to feed material to the rotor disc or to prevent the feed of material to the rotor disc, the method comprising the steps of: - at regular intervals taking samples of a rotational speed of the rotor disc and storing the samples in a data storage means; - from the samples of the instant rotational speed stored in the data storage means, at regular intervals calculating a current mean rotational speed of the rotor disc and storing the values thereof in the data storage means; - calculating from the values of the mean rotational speed of the rotor disc a rate of change of rotational speed of the rotor disc; - storing the rate of change of rotational speed of the rotor disc in a data storage means; - comparing the rate of change of rotational speed of the rotor disc with reference values stored in a data storage means to set a mode of operation of the woodchipper apparatus; and - setting the infeed mechanism to feed or prevent the feed of material to the rotor disc according to the mode of operation and the rotational speed of the rotor disc. The or each mode of operation may include a low rotational speed and a high rotational speed. If the rotational speed of the rotor disc is at or below the low rotational speed then the infeed mechanism will be set to prevent the feed of material to the rotor disc. If the rotational speed of the rotor disc is at or above the high rotational speed then the infeed mechanism will be set to feed material to the rotor disc. The applicant has developed a method of using the rate of change of rotational speed of the rotor disc to estimate the size of material such as wood being fed to the woodchipper. When material is fed to the rotor disc, the rotor disc tends to have a negative rate of change of rotational speed - i.e. it decelerates - due to the powertrain generally not being able to provide sufficient torque as described above. In broad terms, a relatively high deceleration rate indicates large wood being fed to the rotor disc, a relatively low deceleration rate indicates small wood or brash being fed to the rotor disc and an deceleration rate between high and low indicates medium wood being fed to the woodchipper. The efficiency of woodchipping varies across the variety of wood being fed, and the no stress settings can influence the overall efficiency of woodchipping. Thus, the efficiency of the woodchipper can be improved by having no stress settings which are set according to the load or stress conditionsof wood being fed to the rotor disc. No stress settings include - as described above - a low rotational speed of the rotor disc, at or below which the infeed mechanism is set to prevent the feed of material to the rotor disc, and a high rotational speed of the rotor disc, at or above which the infeed mechanism is set to feed material to the rotor disc. In general for large wood a smaller difference between the low rotational speed and the high rotational speed leads to more efficient chipping; for small wood or brash a larger difference between the low rotational speed and the high rotational speed leads to more efficient chipping; for medium wood a difference between the low and high rotational speeds should be between that for the large wood and small wood differences. Thus, for large wood the no stress settings would lead to more frequent switches between the infeed mechanism feeding material to the rotor disc and the infeed mechanism preventing the feed of material to the rotor disc. Conversely, for small wood the no stress settings would lead to less frequent switches between the infeed mechanism feeding material to the rotor disc and the infeed mechanism preventing the feed of material to the rotor disc. Testing has shown that larger material is processed more quickly if a smaller window (smaller gap between high rotational speed and low rotational speed is used; this will result in more no stress events however keeping inertia in the rotor disc for large material reduces the process time. Alongside this, testing has also shown that smaller material is processed more quickly if a larger window (larger gap between high rotational speed and low rotational speed) is used; the longer window allows the engine torque to provide extra applied cutting torque and possibly avoid the infeed stopping for a particular batch of material. While these large and small conditions see an improvement in tailoring the no stress settings, there is still an area between these extremes of large and small where a more standard window is more efficient. Importantly, the present method provides for the detection of the type of wood being fed into the woodchipper so that the no stress settings can be varied in real time. Initially, it was thought that a human machine interface (HMI) could be used so that a user could select the no stress settings before feeding material to the woodchipper. However, this was found to be insufficient and led to inefficiencies. The method may comprise calculating the mean rotational speed of the rotor disc by taking the mean of a plurality of samples and storing the mean value ("rotor speed averaged") and regularly updating the mean value as stored in the data storage means. The number of samples may be ten. The rate of change of rotational speed of the rotor disc may be calculated by deriving the mean value of the of the mean rotational speed and regularly updating the value as stored in the data storage means - ("Deceleration Average Stored"). There may be at least three modes of operation: Currently 3 different No-Stress modes have been provided (however this could increase to many more depending on further testing) these may be termed: 1) Large wood mode 2) Medium wood mode 3) Small / brash wood mode. More modes could be provided. The Deceleration Average Stored is used within the software to decide which no stress settings to apply. Exemplary settings may be as follows: - If Deceleration Average Stored >"Value X” -> Large wood mode If "Value X” >Deceleration Average Stored >"Value Y” -> Medium wood mode If Deceleration Average Stored <"Value Y” -> Small / brash wood mode The method may start with the method of operation in large wood mode and will adjust as the stored values are updated. The present method can be applied to all powertrain types, especially those set out above. However, the increase in efficiency provided by this method is especially important to efficient use of low and zero emission powertrains in a woodchipper apparatus. This is important given the push to reduce carbon emissions to reduce consequent environmental damage. The present method is especially effective in the control of woodchipper apparatus having a hybrid (petrolelectric) powertrain. Detailed description of the inventive concept The present inventive concept will now be described in further detail, with reference to the accompany drawing(s), in which: Figure 1 shows an representation as a flow chart of part of an exemplary control method of the present inventive concept. In Figure 1, it can be seen that the Rotor Speed Averaged is sampled from the rotor speed, and from the Rotor Speed Averaged a Rotor Deceleration Rate is calculated (for example by derivation). An average, Rotor Deceleration Averaged, is calculated from the Rotor Deceleration Rate. In turn, this information is passed to the no stress mode selector which in turn controls the infeed mechanism to run a no stress mode according to whether the material detected is large wood, medium wood or small / brash wood.

Claims

27 08 251. A method of controlling a woodchipper apparatus, the apparatus having a powertrain adapted to provide torque to a rotor disc having blades, the apparatus further having an infeed mechanism adapted to feed material to the rotor disc or to prevent the feed of material to the rotor disc, the method comprising the steps of:- at regular intervals taking samples of a rotational speed of the rotor disc and storing the samples in a data storage means;- from the samples of the instant rotational speed stored in the data storage means, at regular intervals calculating a current mean rotational speed of the rotor disc and storing the values thereof in the data storage means;- calculating from the values of the mean rotational speed of the rotor disc a rate of change of rotational speed of the rotor disc;- storing the rate of change of rotational speed of the rotor disc in a data storage means;- comparing the rate of change of rotational speed of the rotor disc with reference values stored in a data storage means to set a mode of operation of the woodchipper apparatus; the steps effecting a detection of the type of wood being fed into the woodchipper;- varying in real time a mode of operation according to the type of wood detected as being fed into the woodchipper, the mode of operation comprising at least no stress settings; and- setting the infeed mechanism to feed or prevent the feed of material to the rotor disc according to the mode of operation and the rotational speed of the rotor disc.

2. A method according to claim 1, wherein the or each mode of operation includes a low rotational speed and a high rotational speed.

3. A method according to claim 1 or claim 2, comprising calculating the mean rotational speed of the rotor disc by taking the mean of a plurality of samples and storing the mean value and regularly updating the mean value as stored in the data storage means.

4. A method according to claim 3, wherein the number of samples is ten.

5. A method according to any preceding claim, in which the mode of operation depends on the detection of large wood, medium wood or small / brash wood.

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