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How-to-Guide: Linear Axis Setup

Francois Giguere Head of Automation / Jan 14th, 2019

 

This How-to-Guide covers the setup of motors and sensors on a Vention Linear axis.

Background

Vention linear axes equipped with the MachineMotion controller provide a true motion control platform. This allows precise & accurate motion to be performed.

For motion control to be possible, a position reference must exist. This is what homing refers to, the action of finding the position reference of an axis. This position reference is also called home or zero.

End-stop sensors are used to perform homing operations. In order for the homing to be properly done, end-stop sensors must be placed in the appropriate location and connected to the right port on the MachineMotion controller. Installation of end-stop sensors also depends on how the motor is installed on the linear axis.

Motors

Rotation Direction

By convention, the motors have a positive and a negative rotation direction. This is an important consideration when installing the motor on a linear axis. When sending motion commands to the controller (for example a relative move of +200mm), it is important that the axis moves in the desired direction.

The rotation direction convention is shown in Figure 1 and Figure 2:

Figure 1: Motor Positive Rotation Direction (Front Shaft Perspective)



Figure 2: Motor Negative Rotation Direction (Front Shaft Perspective)



Linear Axis Direction

In order to satisfy the application requirements, positive rotation of the motor shaft should result in linear motion in the desired direction. Figures 3 to 6 show how the linear axis move depending on where the motor is installed.

Figure 3: Motor Placement #1



Figure 4: Motor Placement #2



Figure 5: Motor Placement #3



Figure 6: Motor Placement #4



End-Stop sensors

Linear axes require the use of end-stop sensors, for two main reasons:

  • Perform homing operations (placing the axis in a known position, called home or zero)
  • Disable motion in the event of an over or under travel event.

Inductive sensors are the preffered option for end-stop sensing since they are non-contact and less subject to environmental interference.

Connections

Home Sensor (also called under-travel sensor)

The home sensor should be connected to the SENSORxA on the MachineMotion controller. For axis 1, the home sensor should be connected to SENSOR1A, for axis 2 SENSOR2A and for axis 3 SENSOR3A.

Over-Travel Sensor

The over-travel sensor should be connected to the SENSORxB on the MachineMotion controller. For axis 1, the home sensor should be connected to SENSOR1B, for axis 2 SENSOR2B and for axis 3 SENSOR3B.

Position

Home / Under-Travel Sensor

When moving the axis in the negative direction, the gantry should be moving towards SENSOR1A (home / under-travel sensor).

Over-Travel Sensor

When moving the axis in the positive direction, the gantry should be moving towards SENSOR1B (over-travel sensor).

The image below details how to connect and position the end-stop sensors for a specific motor position. Important points:

  • The home sensor is positioned such that a negative motion moves towards it
  • The home sensor is connected to port SENSOR1A
  • The over-travel sensor is positioned such that a positive motion moves towards it
  • The over-travel sensor is connected to port SENSOR1B



Figure 7: End-stop Connections Example for a Specific Motor Connection


Direction Reversal

It is posible that for design reasons, the motor has to be placed at a specific place on the linear axis (due to space or mechnical constraints). This could result in an undesired positive motion direction of the linear axis. For this reason, there is a also a software command that permits reversing the direction of a given axis. The basic Vention Apps offer this feature:

Figure 8: Basic 1-Axis Linear Motion App showing the location of the reverse axis feature

 

This configuration reverses the motor default rotation direction, but also reverses the position of the home and over-travel sensors.

Going back to the example of Figure 7, reversing the axis results in the following configuration.

  • The home sensor is positioned such that a negative motion moves towards it
  • The home sensor is connected to port SENSOR1B
  • The over-travel sensor is positioned such that a positive motion moves towards it
  • The over-travel sensor is connected to port SENSOR1A



Figure 9: End-stop Connections Example for a Specific Motor Connection using software axis reversal



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