13. Safety and Sensing

Let’s start off with some videos.

As is obvious in the videos, safety must always be addressed when dealing with robots.  While there are industry standards regarding how safe is safe around robots, there are a few main concepts that separate the robot and its activity from nearby operators or others.

1.  Fencing – Prevent the entry of anyone into the workcell.  Must be gated and some form of interlock must be integrated into the robot.  Lock-out, Tag-out procedures must be followed so that no one can be in the workcell when the gate is closed and the operation resumes.

2.  Light Curtains – Light curtains are used to form an invisible fence around dangerous equipment.  A light curtain is simply an array of photoelectric sensors which are, as a group, tied into the emergency stop.  Additionally, light curtains must be positioned such than no one can be inside the machine without being detected.  In other words, a light curtain can detect you while you are breaking its beam  Two styles are technically possible to use, but only one should be employed.

a.  A common photoelectric light curtain includes a Infrared light transmitter and an Infrared light receiver.  If all of the receivers see infrared light then there are no obstructions (operators) in the path of the light curtain.  This type of light curtain can also use a mirror at a 45 degree angle to allow the light to bend around corners.  It is feasible to imaging an application using one light curtain to protect four sides of machine using mirrors.

b.  It may seem okay to use a photoelectric sensing light curtain that contains the transmitter and receiver in one housing while using a mirror on the opposite side of the machine.  The light travels from the transmitter, to the mirror, and back to the receiver.  In the same way, if there is an obstruction the light curtain knows.  However, these types of light curtains can be dangerously overridden by placing a mirror in front of the sensor array making the safety feature of the light curtain useless.

3.  Pressure Sensing – A pressure sensing pad is employed by placing it on the floor in front of an opening in the safety fence of a workcell.  This pad can sense the pressure of an operator standing on it and if wired into the emergency stop loop it can prevent the workcell from operating while the operator is standing on it.  These are commonly used along with a light curtain to know if an operator is either entering the workcell (through the light curtain) or still in the workcell (on the pressure pad)

4.  Laser Scanning – A Laser can be used to scan an area and report back the 3D spatial location of everything in an area.  During setup, a Laser Scanner can be regioned into different areas for different levels of safety.  SICK is a popular manufacturer of these devices.  Check out the products that SICK has to offer to understand the capabilities of this type of device as it is becoming very popular in industry.   The devices can be mounted to the side of the workcell under the robot and an area can be defined in the setup of the scanner.  When an unauthorized object (operator) enters the scanned area the system is stopped.

5.  Occupied Hand Sensing – Several different devices are being used to detect the presense of an operator before the beginning of a cycle.  This is the opposite of all other technologies above in that it operates because if the operator is in one position he or she therefore cannot be inside the machine.  This only works and is only safe for the operator.  The operator could still start the machine while someone else was in the way.  Essentially, this is just two buttons that must be held down during operation.  The buttons are far enough apart on a control panel that both hands of the operator must be used to start the machine.  Many times this is only a part of the safety equipment employed in an application and is not normally used by itself.

You should now be prepared to answer the following questions.

  1. True or False?  Lock-out Tag-out procedures are designed to keep unauthorized personnel from entering specific areas of the manufacturing facilities.
  2. True or False?  Fencing located around robots must not contain an entry point to allow maintenance. 
  3. True or False?  Fanuc Dual Check Safety (DCS) technology allows safety fencing to be removed therefore reducing the overall size of the Workcell.
  4. The new generation in safety for ABB robotics allows the robot to continue operating while humans are in the Workcell.  Which of the following causes the robots to stop completely?
  5. A Light curtain is placed at the entry gate to a Workcell and is used to protect humans from an unsafe environment but it cannot detect which of the following unsafe conditions.
  6. A pressure sensing pad ____.
  7. The S3000 Advanced family of products offered by SICK contains how many protective fields?

2 Responses to “13. Safety and Sensing”

  1. The Linguist Says:

    For #3, do you mean completely removed or and part removed, such as reduced?

    • adamwsonu Says:

      By safety fencing I mean fencing which protects the outside of the workcell from robots traveling outside of their normal work area. I can see how this is somewhat confusing, but in the video the “guard” is not there to keep the robots in, it is there to keep the people out. This is different because keeping large robots from crashing through a fence is harder than keeping people from pushing down a guard.

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