The present invention relates generally to grinding machines for grinding wood and construction waste materials. More particularly, the present invention relates to a feed control system for grinding machines known as horizontal grinders.
Horizontal grinders have recently been developed for grinding a wide variety of materials including green wood waste and construction demolition. These machines include a feed system that is adapted to feed the wide variety of materials to a grinding unit which is adapted to effectively grind the materials and includes a feed conveyor and a feed roller. The grinding unit typically includes a grinding drum, which is rotated and includes hammers or blocks, and screens that hold material such that it will be forced into contact with the grinding drum until ground to a certain size.
The productivity of the grinding machines is related to the ability to control the feed system to deliver the material to the grinding drum at a rate equal to the capacity to grind. If the material is not delivered to the drum fast enough, the rate of grinding will be less than the potential. If the material is delivered too fast the material can become trapped between the grinding drum and the screens thereby increasing the risk of plugging. During normal grinding, the load on the grinding drum will typically increase in proportion to the rate at which material is being ground. When plugging begins, the load increases at a faster rate, and may reach an overload state. For grinders powered by diesel engines, the grinding unit may become plugged to the point the grinding drum will stop rotating, with material trapped between the grinding drum and the screens. This condition is undesirable, as it is difficult and time consuming to remedy. For grinders powered by electric motors the amperage draw may increase sharply, possibly damaging the motor or transmission components, or causing excessive power costs related to these spikes in electrical demand.
The overload condition can develop quickly. The feed systems are typically operated at a speed just below where the operator believes the machine may plug, in order to maximize productivity. Thus it can be difficult for an operator to control the feed system to avoid plugging. Systems have been developed to monitor for this overload condition, and subsequently automatically control the feed system. One such system is disclosed in U.S. Pat. No. 5,881,959, which describes a system that monitors for an overload condition of the grinding drum or of the feed system. If such a condition is detected, the feed system is stopped and can be reversed to correct the overload condition.
The present invention provides a control system for a grinder to automatically control the elements of the feed system to maximize productivity of the grinding machine. The productivity of the grinding machine can be estimated by measuring the load condition, the amount of power that is being utilized. If very little power is being utilized, the productivity is known to be low. If the amount of power being utilized is approaching the maximum available, then the productivity will be close to maximum.
In one embodiment the speed of the feed conveyor is controlled in order to achieve a desired load condition. In another embodiment the speed of the feed roller is controlled to achieve a desired load condition. In a third embodiment the speed of both the feed rollers and the feed conveyor are controlled, independently, to achieve a desired load condition.
a is a schematic illustrating the mechanical drive to the grinding unit, the hydraulic system for driving the feed system and the electrical control system for a system utilizing hydrostatic drive system for the feed system;
a is a characteristic maximum torque and maximum power curve for a diesel engine of a second model of a Horizontal grinder;
a–6h are control curves, for control of the signal to the pulse width modulated solenoids of
a is a characteristic power and efficiency curve for a motor of a first model of a horizontal grinder;
b is a characteristic power and efficiency curve for a motor of a first model of a horizontal grinder; and
a–8h are control curves, for control of the signal to the pulse width modulated solenoids of
Referring now to the drawings wherein like reference numerals designate identical or corresponding parts throughout the several views, a horizontal grinder 100 is illustrated in
Many horizontal grinders are configured for mobile applications where the grinder is moved from one processing location to another. In the mobile configuration, the ground support 150 typically includes an axle 152 and wheels 154. Track units, either freely rotating tracks or powered tracks replace the wheels in some models of horizontal grinders.
In other configurations the machines are set-up for stationary applications, such as for use in a paper mill or land-fill, where the material can be delivered to the machine. In this configuration the wheels may be omitted, with the frame fixedly secured to a foundation. The ground support is not an element of the current invention.
The frame 140 is supported by the ground support 150 and includes side rails 142 and can include a hitch point 144. The hitch point 144 is adapted to cooperate with a towing vehicle, and may come any a variety of configurations. Typically the opposite end of the frame 140 is adapted to support discharge conveyor 130.
Discharge conveyor 130 is adapted to accept ground material from the grinding unit 110 and transport it to a location as desired by the operator. This may include transportation to a further processing machine such as a trommel screen, or to a truck for transport, or to simply elevate the material to be dropped to create a pile.
The current invention involves the interaction of the grinding unit 110, feed system 120, and prime mover 102. The prime mover 102 is preferably mounted to the frame 140 and for mobile applications, preferably includes a diesel engine. Alternatively, the prime mover may be an electric motor. In either case the prime mover provides power to the grinding unit 110 and to the feed system 120.
In alternative embodiments, the feed roller can be replaced with other types of feed conveyors such as chain conveyors, belt conveyors or other structures. Also, while feed conveyor 122 is shown as a chain conveyor, other types of conveyors such as rollers, belt conveyors or other structures could also be used.
The grinding unit 110 is illustrated in
The feed system 120 delivers material to be ground to the grinding unit 110. The interaction of the feed roller 124 and the feed conveyor 122 are effective in feeding a variety of materials to the cutting unit 110: the speed of the outer surface of the feed roller 124 as compared to the speed of the feed conveyor 122 affects the way material is fed. Preferably, the speed of feed roller 124 is controlled to be slightly faster than the speed of feed conveyor 122. This speed difference provides a more consistent feeding, and tends to reduce the potential for fluctuations in feed rate or plugging of the feed system.
One embodiment of the hydraulic and electric control systems are illustrated schematically in
Pulse width solenoids 188 and 189 control the hydraulic fluid output from valve 168. Only one of these solenoids is energized at any one time. If solenoid 188 is energized the hydraulic fluid will be delivered to motor 164 such that it rotates in a first direction. If solenoid 189 is energized, the motor 164 will rotate in the opposite direction.
Solenoids 188 and 189 and the associated valving are designed to respond to an electrical signal, typically in the form of a square wave fluctuating between an energized state at a set voltage and a deenergized state, with a certain frequency and duty cycle. The duty cycle is defined by looking at an individual period, with time duration equal to the inverse of the frequency. The duty cycle is the % of time of each period that the signal is energized. Thus if the duty cycle is 40%, then for 40% of each time period the signal will be energized and for 60% it will be deenergized. The controller 200 supplies this electrical signal: for solenoid 188 through electrical conductor 175 and for solenoid 189 through electrical conductor 174.
The result of supplying one of the solenoids 188 or 189 with a specific duty cycle will be that a controlled pilot pressure will be delivered to a main spool within valve 168 causing it to shift in a certain direction compressing a spring and thus shifting a set distance. The design of the main spool is such that this shift will result in hydraulic fluid being directed to motor 164 in a set direction, and with a controlled flow rate. This controlled flow rate will result in a set speed of rotation for the motor. If the duty cycle is 100% then the spool will be shifted fully, resulting in maximum flow rate, and maximum motor speed of rotation. If the duty cycle is less than 100%, then the flow rate will be reduced.
Control module 200 is adapted to provide the electrical signals to solenoids 186, 187, 188, and 189 with electrical conductors 174, 175, 176 and 177 to control the direction and speed of the feed system 120.
An alternative embodiment of the hydraulic and electric control systems is illustrated schematically in
The control module 200 is thus able to control the direction of rotation, and the speed of rotation of the feed roller 124 and of the feed conveyor 122 with its outputs. The inputs to controller 200 include a load signal from the prime mover 102 through electrical conductor 192, and a communication signal from operator controls 190 through communication link 194.
The load signal can be any of a number of signals including a speed signal if the prime mover is a diesel engine, or a measure of amperage draw if the prime mover is a motor. Other techniques of measuring load, particularly for a diesel engine are disclosed in U.S. Pat. No. 5,588,474 U.S. Pat. No. 5,845,689 and U.S. Pat. No. 6,014,996 which are herein incorporated by reference in their entireties.
For the embodiment illustrated in
The overall performance of the machine is determined by the capability of the feed system 120 to deliver material to the cutting unit 110. The normal goal is to maximize productivity. It can be assumed that maximum productivity occurs at the time that the prime mover is delivering maximum power.
The prime mover (102) of a horizontal grinder constructed for mobile applications will typically be a diesel engine. Each model of such diesel engine will typically have known performance characteristics. One measurement of a diesel engine's performance characteristic is its torque curve;
When the prime mover comprises an internal combustion engine, there is a preferred operating range, which corresponds to engine speed between (120) and (122). In this manner the speed of the engine, or any parameter directly correlating to the speed of the engine, can be monitored to approximate loading: if the engine speed is below high idle (120) and above the maximum torque speed 122, the loading is approximately maximized. In this preferred embodiment illustrated in
a–6h illustrate static state control curves used by controller 200 to determine the duty cycle of electrical signals (i.e., pulse width modulated signals) provided to one of the solenoids of valves 168 and 166. It is preferred for the operator to select different control curves or to vary the settings of the control curves in accordance with the type of material being processed. For example, in one embodiment, the operator can set the ‘Duty Cycle’ and ‘Autofeed Droop’ at a variety of settings. In the embodiment of
The static state control curves illustrate how the duty cycle, as described previously, supplied to a solenoid 186, 187, 188 or 189 is varied in response to variations in the engine speed, if the loading is such that the engine speed variations are relatively stable, if the speed is not changing quickly. The dynamic response of the control algorithm will be defined by the type of control technique selected. An example of a predictive technique is disclosed in U.S. patent application Ser. No. 10/001,509, which is hereby incorporated by reference in its entirety. The operator is preferably able to adjust the ‘Duty Cycle’ which affects the maximum duty cycle applied to a solenoid, and the ‘Autofeed Droop’ the engine rpm where the duty cycle is set to zero, effectively stopping the feed system.
A preferred embodiment, defined by the settings which have been determined to be the most versatile, is illustrated in
The feed system will be reversed, as illustrated in
The ‘Duty Cycle’ and the ‘Autofeed Droop’ can be adjusted by an operator so that they can be tailored to the specific type of material, and to a specific engine's characteristics. The ‘Duty Cycle’ can be set for the feed roller independent of the feed conveyor, allowing the two feed elements to be operated at a variety of speeds. The ‘Autofeed Droop’ is the same for both the feed roller and the feed conveyor control curves.
The curves provide a stepped function. It has been found that this stepped function provides more reliable performance of the pulse width modulated valves, also known as proportional control valves, and is particular to use with proportional control valves. The characteristic of pulse width modulated valves is such that there is inherent hystersis, resulting in a difficulty to consistently make small corrections. It has been found that this stepped function gives adequate speed control. The stepped function illustrated is a static curve, defining the appropriate duty cycle applicable to a specific static loading condition. The actual algorithm used to implement this function may cause the duty cycle applied to the solenoid driving the feed conveyor, for the curve illustrated in
If the controller were being utilized to control the hydraulic system of
If the prime mover of
a–8h illustrate static control curves provided by controller 200 for a configuration of the horizontal grinder 100 with prime mover 102 comprising an electric motor, and proportional valves controlling the feed system, as illustrated in
The feed system will be reversed whenever the loading exceeds the ‘Autofeed Droop’ plus 12.5%, or 112% if the ‘Autofeed Droop’ is set at 100%. This reversal may occur for a predetermined time period, or may be maintained until the loading condition drops such that the load is below the ‘Autofeed Droop’ setting.
The operator is able to control the settings of the ‘Autofeed Droop’ and ‘Duty Cycle’ in order to tailor the machine's operating characteristics as may be necessary for the different type of products that are being ground.
With the system herein described the horizontal grinder's feed system is operated in a manner to enable the operator to maximize the productivity of the horizontal grinder.
The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.
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Number | Date | Country | |
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20040112999 A1 | Jun 2004 | US |