Abstract:
The present invention provides a forward motion speed control system for a self-propelled concrete saw, a self-propelled concrete saw equipped with a forward motion speed control system and a method of controlling the forward motion speed of a concrete saw during a cutting or scoring operation. In one preferred embodiment of the invention, the forward motion speed control system senses and monitors the speed of a power plant transmitting rotational energy to a saw blade and adjusts the forward motion speed of the self-propelled concrete saw to maximize the forward motion speed of the self-propelled concrete saw while maintaining the speed of the power plant in a peak operational range.

Description:
This application is a continuation of application Ser. No. 11/307,742 filed Feb. 20, 2006 which is incorporated by reference herein in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a saw for cutting concrete, asphalt, and other hard, flat surfaces and, more particularly, to a self-propelled concrete saw equipped with a forward motion speed control system. 
   2. Description of Related Art 
   Large, horizontal slabs of concrete are frequently poured during the construction of buildings, bridges, roads, runways and the like. Once poured, such slabs must often be cut or scored using a concrete saw for various reasons such as, for example, to form expansion joints, to allow for foundation shifting, to create stress cracks along which the slab will split and/or to create high friction surfaces such as for bridge decks and airport runways. In most large-scale applications, a self-propelled concrete saw is used to cut or score the slab. Self-propelled concrete saws are also used to cut or score asphalt, stone and other hard surfaces. 
   Most self-propelled concrete saws are equipped with a power plant (e.g., an internal combustion engine or electric motor) and a drive system that is configured to rotate a diamond impregnated saw blade during the cutting and/or scoring operation. The power plant is usually configured to produce maximum horsepower in a peak operational range, which is usually expressed in terms of a range of revolutions per minute (“RPM”). In this peak operational range, the power plant can generate maximum torque, and thus the work the saw blade can accomplish is also maximized. Internal combustion engines, in particular, are usually designed to provide maximum engine cooling in this peak operational range. 
   Diamond impregnated saw blades are extremely durable, but they do wear out over time. Studies have shown that the service life of a diamond impregnated saw blade is maximized when the blade is rotated at a rate within a specified range of optimal angular velocities and when the torque loading on the blade is held within a specified range. Excessive angular velocities or torque loadings can result in premature wearing, while insufficient angular velocities or torque loadings can cause the cutting surfaces of the saw blade to become polished, which severely diminishes the cutting efficiency of the saw blade. 
   Generally speaking, torque loading on a saw blade mounted on a self-propelled concrete saw is a function of the depth of cut, the rotational energy being transmitted to the saw blade by the power plant, and the forward motion speed of the concrete saw. The depth of the cut is usually application specific, and thus cannot be varied to optimize the speed of the cutting or scoring operation and/or the service life of the saw blade. The power plant is configured to operate in a peak range or band of optimal RPM&#39;s, and thus it is generally not advantageous to attempt to adjust the rotational speed of the power plant to optimize the speed of the cutting or scoring operation and/or the service life of the saw blade. 
   In most conventional self-propelled concrete saws, the forward motion speed of the concrete saw is set at a constant predetermined speed, or is manually controlled by the operator of the concrete saw, who walks behind the saw making adjustments in response to perceived changes in the performance of the concrete saw. In either instance, an operator must manually select and control the forward motion speed of the self-propelled concrete saw in response to perceived torque loading on the saw blade in order to attempt to maintain the angular velocity of the blade and the torque loading on the blade within their optimal ranges. This requires a high level of operator skill and creates a risk that the operator will select a forward travel speed that will damage the blades. 
   SUMMARY OF THE INVENTION 
   The present invention provides a forward motion speed control system for a self-propelled concrete saw, a self-propelled concrete saw equipped with a forward motion speed control system and a method of controlling the forward motion speed of a concrete saw during a cutting or scoring operation. In one preferred embodiment of the invention, the forward motion speed control system senses and monitors the rotational speed of the saw blade and/or speed of a power plant transmitting rotational energy to a saw blade and adjusts the forward motion speed of the self-propelled concrete saw to maximize the forward motion speed of the self-propelled concrete saw while maintaining the rotational speed of the saw blade and/or the power plant in a peak operational range. 
   The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a self-propelled concrete saw according to the invention. 
       FIG. 2  is a block diagram of a control system according to one embodiment of the invention. 
       FIG. 3  is a flow chart illustrating a method of the invention for controlling the forward motion speed of a concrete saw during a cutting or scoring operation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a self-propelled concrete saw  10  comprises a diamond impregnated saw blade  20 , a power plant (illustrated as an internal combustion engine)  30  and an associated drive system for providing rotational energy to the saw blade  20 , a frame  40  for supporting the power plant  30 , and a set of front wheels  50  and rear wheels  60  connected to the frame. In the schematically illustrated self-propelled concrete saw  10 , the rear wheels  60  are driven in a conventional manner using a prime mover  70 , typically a hydraulic drive system such as that shown in U.S. Pat. No. 5,810,448 which is incorporated herein by reference in its entirety. The forward motion speed of the self-propelled concrete saw  10  during a cutting or scoring operation is controlled by a control system  80 . It will be appreciated that power plant  30  may comprise any one of a variety of power sources other than an internal combustion motor, such as, for example, a diesel motor or an electric motor. 
   In operation, the saw blade  20  preferably rotates in a direction that is the same as the rotation of the front wheels  50  as the self-propelled concrete saw  10  moves in a forward direction. The saw blade  20  thus naturally attempts to “climb out” of the cut as the cutting or scoring operation proceeds. This climbing out can be discernible as a decrease in the load on the saw blade  20 , which will cause the RPM&#39;s of the internal combustion engine  30  to increase. 
   It will be appreciated that the saw blade  20  can alternatively be rotated in a direction opposite that of the rotation of the front wheels  50  as the self-propelled concrete saw  10  moves in a forward direction. This is disadvantageous in some applications, however, as it can result in chipping of the surface of the concrete being cut or scored adjacent to the cut. 
   As noted, the self-propelled concrete saw  10  schematically illustrated in  FIG. 1  is equipped with a control system  80  in accordance with the invention. The control system  80  generates an output signal to the prime mover  70  to control the forward motion speed of the self-propelled concrete saw  10  in response to a first operational parameter that correlates to the rotational speed of the saw blade  20  during the cutting or scoring operation. 
   The control system  80  includes a controller  90  and a memory device  100  for storing both data and software used in conjunction with the controller  90 . The control system  80  further comprises a first sensor  110  that measures a first operational parameter of the self-propelled concrete saw  10 , and then provides a first output signal representative of a rotational speed value for the saw blade  20  to the controller  90 . Because the rotational speed (usually measured in terms of RPM&#39;s) of the power plant  30  providing rotational energy to saw blade  20  generally correlates to the rotational speed of the saw blade  20 , the first sensor  110  is preferably an electronic load control module or a tachometer mounted on the internal combustion engine  30 . Alternatively, the first sensor  110  can be a digital RPM sensor for measuring the actual rotational speed of the saw blade  20 . 
   Preferably, the controller  90  also receives input from a second sensor  120  that measures a second operational parameter of the self-propelled concrete saw  10  that correlates to the cutting depth of the saw blade  20 . Data can also be provided to the controller  90  by a rotary transducer  130  mounted on one of the front wheels  50  of the self-propelled concrete saw. The output of the rotary transducer  130  can be used to determine the actual forward motion speed of the self-propelled concrete saw during the cutting or scoring operation. 
   The controller  90  can also include a user input/output (“I/O”) interface  140  combining an interface such as a display screen with user controls such as an alphanumeric keyboard or keypad that can be manipulated by the user. The I/O interface enables input of operational data for use by the controller  90 . 
   A number of mechanisms can be used to set or alter the forward motion speed of the self-propelled concrete saw  10 . In one embodiment, the rear wheels  60  of the self-propelled concrete saw  10  are driven by a prime mover  70 , which preferably comprises a hydraulic motor. The hydraulic flow can be altered using a swash plate, which is controllable via an electric signal. The magnitude of the flow generated by the swash plate determines the speed at which the self-propelled concrete saw  10  moves in a forward direction. Therefore, the controller  90  can control the forward motion speed of the self-propelled concrete saw  10  by providing a first controller output signal  150  to the prime mover  70  to ensure the swash plate provides the required hydraulic flow. 
   The control system  80  according to the invention can be configured with the objective of maximizing the rate at which the self-propelled concrete saw  10  is propelled in a forward motion as the saw blade cuts or scores a slab of concrete or other hard surface without exceeding the load limits on the saw blade. In doing so, the controller  90  can use the I/O interface  140  to prompt the operator for control parameters. For example, the control system  80  can prompt the operator to enter a maximum allowable forward travel speed for the particular cutting or scoring operation, maximum and minimum rotational speed values for the particular saw blade, and the depth of the cut. The maximum allowable forward travel speed is typically chosen in view of operator safety. Maximum and minimum rotational speed values are chosen to ensure that the saw blade does not wear too rapidly or become polished. The depth of the cut is typically determined in view of the particular cutting or scoring operation. The operator&#39;s input in response to prompts can be provided to the controller  90  through the I/O interface  140 . Alternatively, the controller  90  can be pre-programmed with default values. The values entered by the operator, or the default values, are then used by the controller  90  to control the forward motion speed of the self-propelled concrete saw  10  in response to signals received from the first sensor  110  sensor and, optionally, from the second sensor  120  and the rotary transducer  130 . 
   A flowchart illustrating a process for generating control signals in response to inputs from a first sensor  110  (e.g., an electronic control module, tachometer or digital RPM sensor), a second sensor  120  (e.g., cutting depth gauge) and a rotary transducer  130  in accordance with the present invention is illustrated in  FIG. 3 . The process  160  is a closed-loop process that operates continuously during the cutting or scoring operation. The process  160  comprises determining ( 170 ) the forward motion speed of the self-propelled concrete saw using inputs received from the rotary transducer  130 . Once the forward motion speed is determined, it is compared ( 180 ) to a predetermined maximum allowable forward motion speed (e.g., entered by the operator or set as a default). If the forward motion speed of the self-propelled concrete saw  10  exceeds the predetermined maximum allowable speed, then the controller  90  sends an output signal  150  to the prime mover  70  to reduce ( 190 ) the forward motion speed of the self-propelled concrete saw  10 . 
   If the forward motion speed of the self-propelled concrete saw  10  is determined to be below the predetermined maximum allowable speed, then a first operational parameter of the concrete saw that correlates to the rotational speed of the saw blade is measured ( 200 ) by a first sensor  110 , which transmits a first output signal to the controller  90  representative of a rotational speed value for the saw blade  20 . The controller  90  compares ( 210 ) the rotational speed value received from the first controller  110  with the predetermined maximum rotational speed value. If the rotational speed value for the saw blade is greater than or equal to the predetermined maximum rotational speed value, the controller  90  sends an output signal  150  to the prime mover  70  to increase ( 220 ) the forward motion speed of the self-propelled concrete saw  10 . 
   If the rotational speed value for the saw blade does not exceed the predetermined maximum rotational speed value, the controller  90  compares ( 230 ) the rotational speed value for the saw blade received from the first controller  110  with the predetermined minimum rotational speed value. If the rotational speed value for the saw blade is less than or equal to a predetermined minimum rotational speed value, the controller  90  sends an output signal  150  to the prime mover  70  to decrease ( 240 ) the forward motion speed of the self-propelled concrete saw  10 . 
   If the rotational speed value for the saw blade does not exceed the predetermined maximum rotational speed value and is not below the predetermined minimum rotational speed value, the depth of the cut is measured ( 250 ) by the second sensor  120 , which transmits a second sensor output signal to the controller  90  representative of the depth of the cut. If the depth of the cut is less than a predetermined cutting depth, the controller  90  sends an output signal  150  to the prime mover to decrease ( 270 ) the forward motion speed of the self-propelled concrete saw  10 . If the depth of the cut is not less than the predetermined cutting depth, the controller  90  sends an output signal  150  to the prime mover to maintain ( 280 ) the forward motion speed of the self-propelled concrete saw  10 . 
   It will be appreciated that the operator of the self-propelled concrete saw  10  can manually override the output signal  150  produced by the controller  90  in response to conditions perceived by the operator (e.g., the end point for cutting or safety concerns). Furthermore, the operator can make changes to the predetermined values used in the process  160  as needed, such as after a different size or configuration of saw blade  20  has been installed on the self-propelled concrete saw  10 . 
   The control system  80  in accordance with the present invention causes a self-propelled concrete saw  10  to operate at the safest maximum forward motion speed to maximize the cutting efficiency and speed of the saw blade without overloading the saw blade or the plant driving the saw blade. The control system  80  reduces the likelihood that operator error will damage the saw blade or the power plant driving the saw blade. The saw monitors whether the saw blade has “climbed out” of the cut (i.e., the cutting depth is less than desired) or whether the load on the saw blade has become too excessive (i.e., the power plant RPM&#39;s fall below a predetermined minimum power band), and makes adjustments to the forward motion speed of the concrete saw to compensate for such changes. The control system  80  thus maximizes the speed at which a slab of concrete or other hard surface can be cut while at the same time protecting the saw blade from excessive wear. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general invention concept as defined by the appended claims and their equivalents.