Abstract:
A method and system for tensioning a belt, the system including a tensioning measuring head, a controller, and an air impact gun. The tension measuring head includes a vibration sensor and a belt striker. The controller activates the belt striker and receives signals from the vibration sensor indicative of the vibrations set up in the belt being tensioned. The measured vibrations are indicative of the tension on the belt, and are used by the controller to deactivate the air impact gun when the belt tension is determined to be at a desired level.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention is directed toward manufacturing and assembly techniques and, more particularly, toward an automated method for tensioning an automobile power steering belt.  
           [0003]    2. Description of Related Art  
           [0004]    During assembly of automobile engines, it is necessary to install various accessory devices on the engine and to connect at least some of these accessory devices to rotary power from the engine. For example, the air conditioning compressor and the power steering pump must be mounted adjacent the engine and connected, via pulleys and belts, to the engine crank shaft pulley.  
           [0005]    Conventionally, an adjustable mount is provided to permit the pump to be moved relative to the crank shaft pulley to vary the tension on the belt. As such, this portion of the manufacturing process is manual, and depends greatly upon the skill of the assembler. If the tension on the belt is not enough (i.e., belt too slack), the belt may slip. If the tension on the belt is too great (i.e., belt too tight), the belt may wear prematurely. Accordingly, setting the belt to the proper tension has largely been based upon the “feel” of the assembler, which is the result of experience and individual perceptions that is difficult, if not impossible, to standardize among different assemblers. Moreover, switching of belt materials, which may require relatively more or less tension, is problematic due to the tendency of assemblers to continue to set the belt tension in the manner in which they are accustomed.  
           [0006]    Therefore, there exists a need in the art for a method and device to automate setting of the belt tension.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed toward a method and apparatus to automate and standardize the setting of tension on a belt.  
           [0008]    In accordance with the invention, a belt tensioning apparatus is provided as a station on the automobile assembly line. Palletized engines are directed to the belt tensioning station and are released from the station after having their belt(s) appropriately tensioned.  
           [0009]    In accordance with a method of the present invention, a vibration sensor is placed adjacent the belt and a tensioning device, which is operable to increase tension on the belt, is activated. The belt is thereafter struck to cause the belt to vibrate. The belt vibrations are measured with the vibration sensor and a frequency of the measured belt vibrations is compared with a predetermined desired vibration frequency. If the measured vibration frequency is below the predetermined desired vibration frequency, the belt tensioning, striking and vibration measuring continues. When the measured vibration frequency is equal to or greater than the predetermined desired vibration frequency, the tensioning device is deactivated. The predetermined desired vibration frequency corresponds to a predetermined belt tension.  
           [0010]    In further accordance with the method of the present invention, following deactivation of the tensioning device, a final belt tension check is performed wherein the belt is struck at least one further time to cause the belt to further vibrate. The further vibrations are measured by the vibration sensor and a frequency of the further belt vibrations are compared to a predetermined range of belt vibration frequencies. If the further belt vibration frequency is within the predetermined range of desired belt vibrations, the belt tension is determined to be acceptable.  
           [0011]    In accordance with a belt tensioning system of the present invention, a belt striker, vibration sensor, tension controller, and tensioning device are provided. The tension controller is operable to activate the belt striker and to receive measured belt vibration signals from the vibration sensor. The tension controller compares a frequency of the measured belt vibrations with a predetermined desired belt vibration frequency. The tension controller is also operable to activate and deactivate the belt tensioning device in response to measured vibration frequency. When the measured vibration frequency is below the predetermined desired belt vibration frequency, the tensioning device is activated to increase tension on the belt and, when the measured vibration frequency is equal to or greater than the predetermined desired vibration frequency, the tensioning device is deactivated by the tension controller.  
           [0012]    In further accordance with the present invention, the belt striker and vibration sensor are carried on a tension measuring head. The tension measuring head also includes a proximity sensor that is in communication with the tension controller and operable to indicate to the tension controller when the tension measuring head is properly positioned relative to the belt to be tensioned.  
           [0013]    In further accordance with the present invention, the tensioning device is an air driven gun, and the system further includes a solenoid air control valve. The tension controller is operable to open the solenoid air control valve to activate the air driven gun and to close the solenoid air control valve to deactivate the air driven gun. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    These and further features of the invention will be apparent with reference to the following description and drawings, wherein:  
         [0015]    [0015]FIG. 1 is a schematic illustration of a belt tensioning station according to the present invention, with the operator tightening the retainer bolts to a predetermined tension immediately prior to placement of a tension measuring head relative to the belt being tensioned;  
         [0016]    [0016]FIG. 2 is a schematic illustration of the belt tensioning station of FIG. 1 with the tension measuring head on the belt and with the operator tightening the tension adjustment bolt;  
         [0017]    [0017]FIG. 3 schematically illustrates the electrical communication between the system components of the present invention; and,  
         [0018]    [0018]FIG. 4 is a flow chart of the operating sequence according to the method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The system is described hereinafter as it relates to properly tensioning a power steering pump belt. Moreover, the preferred and illustrated system is described hereinafter in its intended operating environment as a work station of an automotive assembly line. However, it is considered apparent that the system and method of the present invention could be equally useful in tightening other automotive belts, and could also be useful in non-automotive environments.  
         [0020]    The system is adapted for use in conjunction with an engine  10 , which includes a pulley  12  mounted on the crank shaft. A power steering pump, which includes a pulley  14  and an adjustable mount, is secured to the engine  10 . The adjustable mount is used to tension a power steering pump belt  16 , which is wrapped around the crank shaft pulley  12  and power steering pump pulley  14  and is operable to transfer rotary motion from the crank shaft pulley  12  to the power steering pump pulley  14 .  
         [0021]    Conventionally, the power steering pump adjustable mount includes retainer bolts that may be threadably secured to the engine  10 , and a pulley tensioning bolt that is used to adjust the distance or spacing of the power steering pump pulley from the crank shaft pulley and thereby adjust the tension on the pump belt. It is believed that the structure and method of mounting the power steering pump on the engine  10  is conventional and well known in the art and, therefore, will not be discussed in detail hereinafter. Moreover, insofar as the present invention is not limited to any specific pump and pulley arrangement, the present invention is clearly not limited to the structural features of the engine described and illustrated herein.  
         [0022]    The power steering belt tensioning system includes a tension controller  18 , a solenoid control valve  20 , a first air-driven impact gun  22 , a second air-driven impact gun  24 , and a tension measuring head  26 . The tension controller  18  includes a programable logic controller  28  (hereinafter PLC  28 ) and a tension control unit  30 .  
         [0023]    The first impact gun  22  is used to tighten the pump retainer bolts, and will hereinafter be referred to as the retainer bolt impact gun  22 . The second impact gun  24  is used to tighten the power steering pump belt tensioning bolt, and will hereinafter be referred to as the belt tensioning impact gun  24 . Each of the impact guns is pneumatic or air driven. However, the retainer bolt impact gun  22  is connected to an available shop air line, while the supply of air to the belt tensioning impact gun  24  is controlled by a solenoid control valve  20  which, in turn, is actuated by the tension controller  18 , as will be discussed hereinafter.  
         [0024]    The general operation of the belt tensioning system will be discussed hereinafter primarily with reference to the drawing of FIG. 3 and the flowchart of FIG. 4.  
         [0025]    The tension measuring head  26  includes a proximity switch  32 , a belt striking solenoid  34 , and a vibration sensor  36 . Two-way communication of various electrical signals between the tension control unit  30  and the measuring head  26  is provided via a cable  38 . The PLC  28  directly receives a proximity signal from the measuring head  26 , and also communicates with the tension control unit  30 . The PLC  28  is operable to provide visual and aural indication, via lights and speaker(s) to the operator. These indicators are preferably provided on a conveniently arranged display (FIG. 1). The PLC  28  is further operable to provide tactile feedback, via the belt second tensioning gun  24 , that indicates to the operator that a primary belt tensioning has been completed, as will be clear from the following discussion. The PLC  28  also receives environmental and process information via a series of position switches and operator-actuated switches.  
         [0026]    The pump and engine  10  are prepared for belt tensioning (FIG. 4, Step  100 ) by placing the pump on the engine. The retaining bolts are tightened to a first predetermined torque to hold the pump on the engine, and the belt is placed around the pulleys.  
         [0027]    The tension measuring head is then placed on the belt (FIG. 4, Step  102 ). The proximity sensor  32  detects when the tension measuring head  26  is in place relative to the belt  16  to be tensioned, and sends a start signal to the PLC  28 . The PLC  28  also receives a measuring head set signal from the tension control unit  30 , via line  40 , indicating that the tension measuring head  26  is in place. When the PLC  28  receives the first start signal and the tension measuring head set signal, it initiates the primary belt tensioning by sending two signals to the control unit (via lines  41  and  44 ) to begin continuous detection and measurement of the belt tension.  
         [0028]    During the primary belt tensioning (FIG. 4, Step  104 ), the PLC  28  activates the solenoid control valve  20  to supply air to the belt tensioning impact gun  24 , thereby allowing the operator to turn the belt tensioning bolt to increase the tension on the belt  16 . Simultaneously, the tension control unit  30  sends pulses to the belt striking solenoid  34 , causing the striking solenoid  34  to repeatedly strike the belt  16  which, in turn, causes the belt to vibrate at a frequency that is proportional to the tension on the belt  16 . The vibrations developed in the belt  16  are sensed by the vibration sensor  36 , and signals corresponding to the sensed vibration are sent to the tension control unit  30 . The tension control unit  30  converts the measured vibrations into vibration frequency signals that are compared to a predetermined desired vibration frequency, which is correlated to the desired belt tension. Therefore, as the operator turns the tensioning bolt to increase the tension on the belt  16 , the increasing belt tension is monitored by the tension control unit  30 .  
         [0029]    The tension control unit  30  includes memory that has stored therein a vibration frequency corresponding to a desired predetermined belt tension. The tension control unit  30  continuously compares the measured belt vibration frequency (tension) to the predetermined desired belt vibration frequency (tension; FIG. 4, Step  106 ). When the measured belt vibration frequency is equal to the predetermined desired vibration frequency, the tension control unit  30  sends a signal to the PLC  28  to end the primary belt tensioning. In response to this signal, the PLC  28  turns off or closes the solenoid control valve  20 , shutting off air to the tensioning impact gun  24 , and causing the gun  24  to become inoperable to further tension the belt  16  (FIG. 4, Step  108 ).  
         [0030]    Turning off the air to the impact gun  24  is readily perceived by the operator, even in loud environments, and tells the operator that the desired tension has, at least preliminarily, been achieved. Thereafter, the retainer impact gun  22  is used by the operator to tighten the pump retaining bolts, which are thereafter tightened, preferably using a torque wrench (not shown), to a second or final predetermined desired torque to secure the pump to the engine  10 .  
         [0031]    Once the retainer bolts are at the final desired torque, the operator presses the final check button  42 , which sends signals to the PLC  28  to activate the tension control unit  30  for the final tension check (FIG. 4, Step  110 ). More specifically, the PLC  28  sends a pass tension range signal (via line  45 ) and a single measurement signal (via line  46 ) to the tension control unit  30 . The tension control unit  30  initiates a final belt tension check by activating the belt striking solenoid  34  once. The resulting vibration, which corresponds to the power steering belt tension, is sensed by the vibration sensor  36  and compared to a predetermined and preset range of values stored in the tension control unit memory (FIG. 4, Step  112 ). If the power steering belt vibration frequency is within the predetermined range, the tensioning process is complete (FIG. 4, Step  114 ). Accordingly, the tension control unit  30  returns a signal (via line  48 ) to the PLC  28  which, in turn, illuminates the tension OK indicator  49 . Assuming that the pallet release switch  50  is in the automatic position, the PLC  28  releases the engine  10  so that it can proceed down the assembly line. If the pallet release switch  50  is in the manual position, the pallet will wait until the operator pushes the pallet out button  52 .  
         [0032]    If the measured vibration frequency is below the predetermined range, the belt tension is too low. Accordingly, the tension control unit  30  sends a “slack” signal (via line  56 ) to the PLC  28  which, in turn, illuminates a “slack” indicator  58 . Alternatively, if the measured vibration frequency is above the predetermined range, the belt tension is too great. Accordingly, the tension control unit  30  sends a “tight” signal (via line  60 ) to the PLC  28  which, in turn, illuminates a tight indicator  62 .  
         [0033]    If the final belt tension check results are not OK, i.e., “slack” or “tight”, the operator may retest the belt tension by pressing the retry button  64 , which will re-initiate the final belt tension check (FIG. 4, Step  116 ). Alternatively, or assuming that the belt tension remains “slack” or “tight” after the retry, the operator can repeat the tension testing procedure (i.e., by loosening the retainer bolts to the first predetermined torque, etc.; FIG. 4, Step  118 ). As a further alternative, the operator may send the engine  10  to another station adapted to handle tensioning problems. Since the belt is too slack or too tight, the engine  10  will not be released until the operator presses the pallet out button  52 .  
         [0034]    It is noted that the tension control unit  30  has a data output cable  66 , preferably an RS232 output line. Such data output will help coordinate the tensioning of belts, and may be used to associate or tag the tension data to each engine, as will be helpful in routing the engines having “slack” or “tight” belts for further adjustment.  
         [0035]    The present invention has been described herein with particularity, but it is noted that the scope of the invention is not limited thereto. For example, although the preferred and illustrated device for tightening the bolts is an air driven impact gun, it is contemplated that other devices, such as electric drills, may be used, in which case the control unit/PLC will cut off power to the drills when the desired belt tension has been reached. Also, it is contemplated that the various indicators and operator-actuatable buttons and switches may be conveniently provided on the display screen. Therefore, the present invention is considered to be possible of numerous modifications, alterations, and combinations of parts and, therefore, is only defined by the claims appended hereto.