Abstract:
This invention relates to a height measurement apparatus for determining volume/density of wood chips on a conveyor. Such structures of this type, generally, employ the use of contacts that ride on top of the pile of wood chips in order to more accurately measure the volume and density of the wood chips.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a height measurement apparatus for determining volume/density of wood chips on a conveyor. Such structures of this type, generally, employ the use of contacts that ride on top of the pile of wood chips in order to more accurately measure the volume and density of the wood chips. 
     2. Description of the Related Art 
     A conventional paper mill approach to measuring chip moisture relies on accurate, but slow, oven-drying of random belt grab samples of chips. Typically, chip moistures are measured several times throughout a day. This daily data becomes a part of monthly moisture averages that guides the paper mill digesting process. Consequently, this approach creates varying minimums and maximums throughout the year. Also, different wood species, different historical moisture and different sizes of chips available from chippers will alter the volume or density of a given chip pile. It is important to be able to accurately assess the chip moisture going into the digester, whether it a continuous or batch digester, of a paper mill because this affects the amount of chemicals that go into the digester and the operating conditions of the digester. 
     It is known to employ devices to correct flows of various items for moisture. Exemplary of such prior art is U.S. Pat. No. 3,186,596 (&#39;596) to C. O. Badgett, entitled “Concrete Batch Blending Control System”. While the &#39;596 reference teaches how to correct a flow for moisture, it is not concerned with chip moisture for digesting. Also, it must be pointed out a similar negative result occurs for cement when moisture is unknown, namely the resulting product (concrete) quality can be poor. Finally, the &#39;596 reference does not consider any impact of volume when measuring moisture. 
     It is also known to employ various devices for feeding wood chips into a digester. Exemplary of such prior art is U.S. Pat. No. 5,266,159 (&#39;159) to B. Greenwood et al., entitled “Mass Flow Measurement, Preferably for Controlling Chip Feed to a Digester.” While the &#39;159 reference involves feeding a continuous digester with chips from a conveyor belt and controlling chip density, it recommends determining chip density in a free-fall of the chips. However, the &#39;159 reference does not teach that volume of chips is important for density nor does it present a chip volume-determining method. 
     Several other references mention that both density and volume can be important when filling a container. Exemplary of such prior art are U.S. Pat. No. 4,582,992 (&#39;992) to T. L. Atwell et al., entitled “Self-Contained, On-Line, Real-Time Bulk Material Analyzer,” U.S. Pat. No. 3,822,032 (&#39;032) to R. W. Vergobbi, entitled “Apparatus For Filling Containers Including Means Responsive to Both the Weight and the Height of the Material Dispensed,” and U.S. Pat. No. 4,520,883 (&#39;883) to M. Fukuda, entitled “Combinatorial Weighing Method and Apparatus With Volume.” While these references mention both volume and density, the &#39;292 reference uses gamma and neutron detectors to determine the “elemental content” of a bulk material in a chute based on the prompt gamma ray neutron activation analysis method. Similarly, the &#39;032 reference employs a hopper that holds a preset allowable weight limit and a filling volume or height for a container. Finally, the &#39;833 reference uses a consumer-product filling machine having a preset allowable weight limit and a filling volume or height for a container. 
     It is also known to employ a nuclear source for use in chip moisture measurement. Moisture is measured by such neutron devices by determining the hydrogen content of both the wood chip material and the conveyor belt, subtracting the hydrogen content of the belt and surroundings, and distinguishing between higher hydrogen contents due to more chip moisture or more chips in the pile. Exemplary of such prior art are U.S. Pat. No. 3,748,473 (&#39;473) to Y. M. Chen, entitled “Gauge for Determining the Percentage by Weight of Moisture Contained in a Bulk Material Transported on a Moving Conveyor,” U.S. Pat. No. 3,761,712 (&#39;712) to P. L. Listerman, entitled “Gauge for Determining the Percentage by Weight of Moisture Contained in a Bulk Material Transported on a Moving Conveyor,” and U.S. Pat. No. 3,794,843 (&#39;843) to Y. M. Chen, entitled “Gauge for Determining the Percentage by Weight of Moisture Contained in a Bulk Material Transported on a Moving Conveyor.” While the &#39;473, &#39;712, and &#39;843 references employ a nuclear source for chip moisture measurement, the percent moisture is determined as the ratio of weight of water over total water. The weight of water is estimated by sensing slowed neutrons. The total weight is similarly determined by sensing the result of impacts of an object by gamma rays. The specifics of signal collection during the set of testing intervals is defined in the &#39;712 reference. The special case of determining percent moisture for very high moisture levels and/or high levels of iron or sodium chloride is set forth in the &#39;843 reference. However, none of these references consider correcting the radiation measurements for the volume of material being measured. Also, none of these references measure the volume or height. 
     It is also known to employ a chip moisture meter to measure chip volume on a conveyor. See, for example, FIG.  1 . As shown in FIG. 1, the wood chips are transported down a conveyor. As the chips are transported down the conveyor, they are rearranged on the belt so as to have a Gaussian distribution cross-section of bulk material including a maximum height. An ultrasonic beam is used in the height sensor. While this device can accurately measure the height of the pile, it cannot accurately measure the density of the pile because the volume it estimates is not necessarily accurate. Also, this prior art device requires frequent re-calibration since chip distribution can vary with height. 
     It is apparent from the above that there exists a need in the art for an accurate height measurement system which is capable of measuring the volume and density of wood chips on a conveyor. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure. 
     SUMMARY OF THE INVENTION 
     Generally speaking, this invention fulfills these needs by providing a height measurement apparatus for determining the volume/density of a pile of wood chips on a conveyor, comprising a plurality of wood chip pile contact means in contact at one end to the wood chip pile, an arm means rigidly attached at the other end of each of the contact means, an angle measurement means located a predetermined distance away from the arm means for measuring an angle of movement of each of the arm means, a bracket means operatively connected to the arm means and the angle measurement means and extending substantially across a cross-section of the wood chip pile, and a wood chip pile weight measuring means operatively connected to the wood chip pile conveyor and the angle measurement means. 
     In certain preferred embodiments, the angle measurement means includes a potentiometer. Also, the wood chip pile contact means are constructed of spring steel. Finally, an inertial dampener is attached to the other end of the arm to act as a counter-balance while the wood chip contact means contact the changing wood chip pile surface. 
     In another further preferred embodiment, the volume/density of a wood chip pile can be accurately determined even if the wood chip pile is not uniformly constructed, i.e., in a Gaussian distribution. 
     The preferred measurement device, according to this invention, offers the following advantages: ease of assembly and repair; good stability; good durability; excellent economy; excellent height measurement; excellent volume measurement; and excellent density measurement. In fact, in many of the preferred embodiments, these factors of economy, height measurement, volume, and density measurement are optimized to the extent that is considerably higher than heretofore achieved in prior, known measurement devices. 
     The above and other features of the present invention, which will become more apparent as the description proceeds, are best understood by considering the following detailed description in conjunction with the accompanying drawings, wherein like characters represent like parts throughout the several views and in which: 
    
    
     A BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a chip moisture measurement system, according to the prior art; 
     FIG. 2 is an isometric view of a height measurement system for volume/density determination of wood chips on a conveyor, according to the present invention; 
     FIG. 3 is a side view of the height measurement system for volume/density determination of wood chips on a conveyor; and 
     FIG. 4 is a front view of the height measurement device for volume/density determination of wood chips on a conveyor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As discussed earlier, FIG. 1 is a schematic illustration of a chip moisture measurement device, according to the prior art. This device is manufactured by Acrowood of Everett, Wash. 
     With reference to FIG. 2, there is illustrated an advantageous environment for use of the concepts of this invention. In particular, height measurement apparatus  2  for the determination of volume/density of wood chips on a conveyor  100  (FIG. 4) is illustrated. In particular, apparatus  2  includes, in part, conventional brackets  4  and  6 , brackets  8 , conventional pivot pin  10 , arm  12 , pile contact  14 , movement sensor  16 , control mechanism  18 , and inertial dampener  20 . 
     Preferably, brackets  4 ,  6 , and  8  are constructed of any suitable, durable ferro-magnetic material because such ferro-magnetic materials are readily distinguishably from wood chips by a conventional magnetic scavenger. Pivot pin  10 , preferably, is constructed of any suitable, durable ferro-magnetic material and is placed within bracket  8  to allow arm  12  to freely pivot. Arm  12 , preferably, is constructed of any suitable, durable ferro-magnetic material. Contact  14 , preferably, is constructed of spring steel. Sensor  16 , preferably, is a potentiometer which is capable of measuring the angle of movement of arm  12 . Inertial dampener  20  is rigidly attached to the other end of arm  12  in order to keep contact  14  against the changing pile of wood chips moving along the conveyor (FIGS. 3 and 4) at the point of measurement. 
     Finally, a conventional control system  18  is electrically connected to sensor  16 . The angle of movement of arm  12  is read by sensor  16  and this information is fed back to control mechanism  18 . This information is then conventionally manipulated in control mechanism  18  to provide the operator with information regarding the height of the moving wood pile, the volume of the wood pile, and the density of the wood pile, which will be discussed later. 
     As shown in FIG. 3, contact  14  is able to ride along the top of pile  50  of wood chips. Wood chips are moving along the direction of arrow A. The inertial dampener  20  counteracts the rapid, bouncing movement of contacts  14  up and down so as to keep contacts  14  substantially in contact with the top of wood pile  50 . Dampener  20  must be constructed so as to retain its center of gravity substantially over pivot pin  10 . Dampener  20  includes, in part, extension  22  and weight  24 . Preferably, dampener  20 , extension  22  and weight  24  are constructed of any suitable, durable ferro-magnetic material. Extension  22  is rigidly connected to dampener  20  by conventional techniques. Weight  24  is rigidly connected to extension  22  by conventional techniques. 
     As shown in FIG. 4, a conventional conveyor  100  includes rollers  102  and a weight measurement device  104  which is located beneath wood chip pile  50 . Also, inertial dampener  20  can be seen in FIG. 4. A plurality of height measurement apparatus  2  are located along the cross-section of wood chip pile  50  in order to provide an accurate determination of the volume of wood chip pile  50 . In this manner, any deviation across the cross-section of wood chip pile  50  will be accounted for by the plurality of height measurement apparatus  2 . 
     In order to determine the density of wood chip pile  50  having a non-gaussian distribution, knowledge of the cross sectional area leads to an accurate estimate of the volume flow, Q. 
     
       
           Q=Av,   (Eq. 1) 
       
     
     Where A is the cross sectional area being determined and v is the speed of the belt, which are readily known. 
     Since the weight flow, W is already measured by weight measurement device  104 , the density (ρ) of the wood chips may be determined, according to Equation 2: 
     
       
         ρ= W/Q   (Eq. 2) 
       
     
     After the density has been determined, a conventional moisture measuring device, such as the one previously discussed with respect to the nuclear source used with chip moisture measurement, can be provided with the accurate determination of the volume/density of the wood chips in order to more accurately determine the moisture of those wood chips. Ideally, this would then result in a more efficient use of the chemicals added into the digester and a more efficient use of the digester. 
     As further proof of the efficacy of the present invention, the following Example is presented. 
     EXAMPLE 
     The apparent moisture value of chips by the neutron meter is composed of several factors: 
     (1) The actual moisture level in chips, indicated by the H-atoms of water; 
     (2) The base level for an empty conveyor belt with no chips on the belt; and 
     (3) The volume/density of the chip pile on the traveling belt. 
     The first correction, for base level, overcomes changes in positioning of contacts  14 , conveyor belt area differences, changes in belt speed between times of measurement, etc. 
     The second correction, for volume/density, is also critical. The chip moisture meter cannot distinguish from the neutron reading whether the neutron reading is higher because chips are more moist, piled higher, or there are denser chips in the same volume. All these increase neutron measurement value, and hence the “apparent” moisture. 
     The most difficult job is measuring the volume on the fast belt. In the present invention this is done by averaging the cross-sectional height from three point measurements by apparatus  2  of chip pile  50  height on the belt  100 . However, the top of the chip pile  50  on a belt  100  may develop undulations from chips being added and then slipping back down an upward-traveling belt  100 . Therefore, an inertial counterweight dampener  20  is added to overcome the “bounce” of volume-measuring contacts  14  when they pass over undulation bumps. Without this correction, contacts  14  alone will give an inflated estimate of chip volume due to contacts bounce, and an overcorrection of moisture value for chips will be made using chip volume. 
     The data below compare measurements by: (1) undampenered “contacts only” pile meter for  15  digester batches=“o” vs. (2) dampened pile meter for 15 other digester batches=“d”. 
     The table shows that the addition of an inertial dampener to contacts  14 , which hold contacts  14  to the pile surface despite constant undulations, reduced apparent net pile height by over 5%. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 
               
               
                   
               
               
                   
                   
                   
                 Base 
                 True 
                   
               
               
                   
                   
                 Apparent 
                 Height 
                 Chip 
                 % correc- 
               
               
                 Equipment 
                 Ave. Flow 
                 Average 
                 when 
                 Pile 
                 tion by 
               
               
                 Used 
                 Rate of 
                 Pile 
                 Belt 
                 Height 
                 dampener, 
               
               
                 to Measure 
                 Chips on 
                 Height = 
                 is Emp- 
                 (C = 
                 (Co-Cd)/ 
               
               
                 Chip Volume 
                 Conveyor 
                 A 
                 ty = B 
                 A − B) 
                 Co × 100% 
               
               
                   
               
             
             
               
                 Pile meter 
                 526.7 
                 8.69 
                 6.26 
                 2.43 
                 control 
               
               
                 with contacts 
                 (range 
                 (range 
                 (range 
               
               
                 only (o) 
                 483-563) 
                 8.32- 
                 6.23- 
               
               
                   
                   
                 9.02) 
                 6.28) 
               
               
                 Pile meter-- 
                 510.9 
                 8.84 
                 6.56 
                 2.28 
                 6.2% 
               
               
                 contacts plus 
                 (range 
                 (range 
                 (range 
               
               
                 dampeners (d) 
                 468-533) 
                 8.40- 
                 6.46- 
               
               
                   
                   
                 9.05) 
                 6.68) 
               
               
                   
               
             
          
         
       
     
     Once given the above disclosure, many other features, modifications or improvements such as volume measurement of other materials than wood chips will become apparent to the skilled artisan. Such features, modifications or improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.