Patent Publication Number: US-2016243709-A1

Title: Robotic gripper

Description:
The present invention relates to robotic devices and, in particular, grippers for robotic devices. This application is a continuation-in-part of U.S. patent application Ser. No. 13/324,626, filed on Dec. 13, 2011 (soon to issue as U.S. Pat. No. 9,327,411), all of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Robotic grippers are known in the prior art. Prior art robotic grippers use a sensor located at the end of the robotic fingers to determine the presence of an object (such as a microwell plate). However, this method is very un-reliable due to reflections, or different color and shapes and materials of the objects that are being gripped. 
     Servo Motor Failure 
     Prior art grippers also utilize a servo motor to close the gripping fingers and hold the fingers in place. With a servo motor current is a function of torque, and current is used to keep the motor in position as heat continues to build up. With the prior art servo motor control method the motor heats up and failures are commonplace. 
     Worm Gears 
     Worm gears are know in the prior art. Worm gears are typically used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. 
     Worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place. 
     Force Sensors 
     Force sensors are known in the prior art. A load cell is a type of a force sensor that converts the deformation of a material, measured by strain gauges, into an electrical signal. The most common type of load cell uses a bending beam configuration. As force is applied to the beam, it bends slightly and this bending/strain of the beam material changes the electrical output of the strain gauges mounted on the material. As the strain of the material is proportional to the force applied, the load cell can be calibrated to engineering force units by correlating this change in electrical signal to change in force applied. 
     What is needed is a better robotic gripper. 
     SUMMARY OF THE INVENTION 
     The present invention provides a robotic gripper. Each of two gripper fingers is attached to a bearing carriage. Each bearing carriage defines a rack gear and is adapted to ride on a bearing rail. A single pinion gear has two gear elements. Each of the two gear elements are meshed with one of the two rack gears so as to drive the two bearing carriages in opposite direction upon rotation of the pinion gear. A worm gear is fixed to the single pinion gear. A worm screw is meshed to the worm gear and adapted to cause rotation of the worm gear and the single pinion gear and a gripping action or a releasing action of the two gripping fingers, depending on the rotation of the worm screw. A motor is adapted to drive the worm screw in a first rotary direction and a second rotary direction. In a preferred embodiment a load cell force sensor is connected to one of the gripper fingers for detecting and controlling the amount of compressive force being exerted on the object being gripped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-2  show a preferred embodiment of the present invention. 
         FIG. 3  shows a gripper connected to a robot via a top mount bracket. 
         FIG. 4  shows a control screen for controlling a gripper via a computer. 
         FIG. 5  shows a block diagram showing the components of a preferred gripper. 
         FIG. 6  shows a top mount attachment bracket and a gripper finger rotation point for permitting four points of contact. 
         FIG. 7  shows a perspective view of a preferred gripper showing internal components. 
         FIGS. 8 a -8 c    show preferred gearing mechanisms of a preferred gripper. 
         FIG. 9  shows a preferred flow chart for operation and control of a preferred gripper. 
         FIG. 10  shows a gripper connected to a robot via a rear mount bracket. 
         FIG. 11  shows a preferred gripper controlled by a remote robot control computer. 
         FIG. 12  shows the utilization of a translator serial box to translate command signals from a remote robot control computer to a preferred gripper. 
         FIG. 13  shows a load cell force sensor connected to a preferred gripper. 
         FIG. 14  shows another preferred embodiment of the present invention. 
         FIGS. 15 and 16  show preferred serial box PCBs. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the present invention, gripper  1  ( FIG. 1 ) uses force to detect the presence of an object (such as a microwell plate  2 ). This force is created by a small NEMA  11  size stepping motor  22  ( FIGS. 5, 7 ) driving mechanical gears to make this force. A force detection point can be programmed into controller  19  software by the user to the user&#39;s specific requirements. Once the force detection value is met, power is held constant at the point of an object detection from stepper motor  22  and gripper fingers  3  and  4  are no longer driven inward any further by the motor. 
     A preferred range of gripper finger separation is shown in  FIG. 2 . The range of gripper finger is sufficient so that a microwell plate may be gripped either in a portrait position or a landscaped position. 
     No Separate Sensor Required 
     In one preferred embodiment, gripper  1  ( FIG. 1, 3 ) does not utilize a sensor attached to the ends of fingers  3  and  4  to detect microwell plate  2  being gripped. Instead, by utilization of encoder  21  feedback ( FIG. 5 ), an error function that corresponds to a stalled stepper motor  22  condition is transmitted to the controller software of controller  19 . When this event occurs, gripper  1  recognizes that it has grabbed an object. At this point an output signal is sent from gripper  1  to controller  11   b  via communication line  11   c  for robot  11  reporting that gripper  1  has grabbed an object and the robot arm can move. Preferably, this output from encoder  21  also turns on a red indicator light  37  on gripper  1  ( FIG. 1 ) for a visual reference. 
     Control Through Electrical Inputs and Outputs 
     Gripper  1  is preferably controlled via electrical inputs and outputs. For example,  FIG. 9  shows four inputs and two outputs.  FIG. 9  also depicts a preferred operational flowchart for control of gripper  1 . 
     Stepper Motor Utilization 
     In one preferred embodiment, Gripper  1  uses a stepping motor  22 , in contrast to the prior art servo motor. For example, in a preferred embodiment stepper motor  22  is a closed loop stepper motor. The stepper motor uses a rotary encoder, and AllMotion® controller  19 . Hence, the driver only puts as much current into the motor as required to clamp the target microwell plate  2  at which point power to the motor is held constant leaving the plate clamped between fingers  3  and  4 . In contrast with the prior art servo motor utilized for grippers, stepper motor  22  only utilizes a small amount of current and overheating is avoided. Also, as stated above, the utilization of stepper motor  22  means that an additional presence sensor is not required. When fingers  3  and  4  have together gripped the plate causing a stall of motor  22 , a signal is sent to controller  19  automatically via stepper motor  22  as an error function signal which turns off power to the motor. 
     Gear Connections 
       FIGS. 8 a -8 c    show preferred gear connections. Pinion gear  97  is keyed to worm gear  34  as shown in  FIG. 8 c   . Worm gear  34  meshes with worm screw  33  as shown in  FIG. 8 c   . Rack gears  98  and  99  are meshed with pinion gear  97  as shown in  FIG. 8 a   . Top bearing carriage  202  is connected to rack gear  97  and rides on top bearing rail  201  as shown in  FIG. 8 a   . Bottom bearing carriage  302  is connected to rack gear  99  and rides on bottom bearing rail  301  as shown in  FIG. 8 b    bottom view. Gripper finger  3  ( FIG. 1 ) is connected to top bearing carriage  202  and gripper finger  4  is connected to bottom bearing carriage  302 . Worm screw  33  drives worm gear  34  which in turn drives top rack gear  98  and  99  in opposite directions to open or close fingers  3  and  4 . 
     Worm Drive 
     The gripper will not drop a plate if gripper  1  loses power or if controller  19  cuts power to stepper motor  22  after fingers  3  and  4  have gripped a microwell plate. This is due to the worm drive gearing along with the duel rack and pinion mechanical gearing. Worm screw  33  can easily turn worm gear  34 , but when power is lost, worm gear  34  cannot turn worm screw  33  backwards ( FIGS. 8 a -8 c   ). This is because the angle on the worm screw is so shallow that when the worm gear tries to spin it, the friction between the worm gear and the worm screw holds the worm screw in place and the microwell plate is not dropped. 
     Rack and Pinion Gears 
       FIGS. 8 a -8 c    show pinion gear  97  engaged with rack gear  98  and rack gear  99 . Rack gears  98  and  99  are mounted on opposite sides of pinion gear  97  as shown. This configuration allows for the opening and closing of the gripper fingers by the utilization of just one pinion gear. 
     Controlled Utilizing Remote Robot Control Computer and Control Screen 
     In a preferred embodiment of the present invention, gripper  1  is controlled utilizing a remote computer  555  and a control screen  401  ( FIG. 11 ). In a preferred embodiment, control screen  401  is created utilizing Dynamic-link library (DLL).  FIG. 4  shows details of a preferred control screen  401 . Operating parameters for gripper  1  can be customized by an operator using control screen  401 . For example, gripping force can be set as desired utilizing the control screen. A wide range of force can be setup on gripper  1  to pick up objects. The ability to vary the gripping force is utilized depending upon the width of the plate, whether it is lidded or unlidded and whether it is empty, partially full or full. Currently, in a preferred embodiment, the gripping force range is from a few ounces to over 50 lbs of force. As the motor size of stepper motor  22  ( FIGS. 5 and 7 ) is increased, even greater force is achievable. 
     Stand Alone Control 
     Gripper  1  as shown and described above is fully self controlled. The only external inputs needed are DC electrical power from 12 to 24 VDC, less than 3 amps. 
     Manual Override 
     In a preferred embodiment, a manual override switch which runs the worm gear backward is attached to the back of gripper  1  to release the gripping force in the event of a failure. 
     Top Mount and Rear Mount 
       FIG. 3  shows gripper  1  mounted to robotic arm  502  of robot  11  via top mount bracket  501 . Top mount bracket  501  is also shown in  FIG. 6 . It is also possible to mount gripper  1  via a rear mount bracket. For example,  FIG. 10  shows gripper  1  mounted to robotic arm  504  via rear mount bracket  505 . 
     Gripper Compatibility with Various Robots 
     Gripper  1  may be utilized with a variety of robots despite the programming code of the robots. For example, in  FIG. 12  robot control computer  655  for robot  803  has been programmed utilizing a unique language not recognized by gripper  1 . However, it is still possible to use gripper  1  with robot  803 . Translator serial box  565  is inserted between robot  803  and robot control computer  655 . Translator serial box  565  may be connected to robot  803  and robot control computer  655  utilizing a variety of connection protocols. For example, serial box  565  may be connected via a USB communication, Controller Area Network (CAN bus), or Modbus serial communications. 
     Translator serial box  565  includes microcontroller  609 . In one preferred embodiment microcontroller  609  is programming on printed circuit board (PCB)  421 A ( FIG. 15 ). PCB  421 A is configured to receive and transmit inputs and outputs via USB cable  422 . 
     In another preferred embodiment, microcontroller  609  includes programming on PCB  421 B ( FIG. 16 ). PCB  421 B is configured receive and transmit inputs and outputs via serial cable  423 . 
     Microcontroller  609  ( FIG. 12 ) has been programmed to recognize gripper control instructions transmitted from robot control computer  655 . Translator serial box  565  translates the gripper control instructions to instructions recognizable by gripper  1 . Translator serial box  565 , similarly, has been programmed to translate and then transmit data information from gripper  1  back to robot control computer  655 . By utilizing translator serial box  565  in conjunction with gripper  1 , a user can attach gripper  1  to virtually any robot that has the capability to grip objects despite the specific programming of the robot. This is a very valuable feature of the present invention because it means that robots that utilize gripper  1  do not have to be reprogrammed to accept and control gripper  1 . 
     Load Cell 
     In another preferred embodiment of the present invention, a separate force sensor is connected to one of the gripper fingers  3  or  4 .  FIG. 13  shows another preferred embodiment of the present invention in which a force sensor (load cell  373 ) is connected to gripping finger  4 . Load cell  373  is preferably connected directly to serial box  565  via cable  374  (see also  FIG. 14 ). As an object is gripped between gripping fingers  3  and  4  load cell  373  is compressed. The compressive force value is transmitted to serial box  565  which includes programming to recognize if a preset force value has been reached. Once the preset force value has been reached, a signal is sent to motor controller  19  ( FIG. 5 ,  FIG. 7 ) to turn off motor  22 . 
     An advantage of utilization of load cell  373  is that operator can set a predetermined single preset force value that can be utilized for a variety of object weights, sizes and types. This saves time for the operator in that the operator does not have to enter a unique force value for each object type being gripped. 
     Input/Output (I/O) Modules 
       FIG. 14  shows digital I/O module  383  and analog I/O module  384 . Both modules may be utilized for control of gripper  1 , as shown. 
     Barcode Reader 
       FIG. 14  shows barcode reader  393  mounted onto gripper  1 . Barcode reader  393  is mounted and configured to record the identifying barcode of the object being gripped. This information is preferred transmitted via line to serial box  565 , as shown. 
     Collision Sensor 
     In a preferred embodiment of the present invention collision sensor  979  is positioned between gripper  1  and robot arm  981 . Preferably a mechanical switch and air pressure is utilized to set the trip point of sensor  979 . The gripper detects an impact when the trip point of the sensor has been met. After an impact has been detected, serial box  565  is preferably programmed to halt the movement of robot  803  to avoid any damage to gripper  1  or the object being gripped. 
     Although the above-preferred embodiments have been described with specificity, persons skilled in this art will recognize that many changes to the specific embodiments disclosed above could be made without departing from the spirit of the invention. For example, although it was stated that in a preferred embodiment motor  22  is a stepper motor, it is also possible to replace motor  22  with a variety of motor types. For example, in another preferred embodiment motor  22  is a servo motor. Therefore, the attached claims and their legal equivalents should determine the scope of the invention.