How to create 2D random movement?

So far I have code which translates my game object in random position, but it does not detect when it's collided with box collider 2D. i don't know why? In my scene I have maze with attached box colliders 2d with unchecked isTrigger and use by effector.

 using UnityEngine;
 using System.Collections;
 
 public class randomMovement : MonoBehaviour {
     public int ranNum;
     public GameObject blinky;
     public float speed = 0.3f;
     // Use this for initialization
     void Start () {
         ranNum = 1;
     }
     
     // Update is called once per frame
     void FixedUpdate () {
         ranNum = Random.Range (1, 5);
         switch (ranNum) {
         case 1:
             blinky.transform.Translate(Vector2.up*speed);
             break;
         case 2:
             blinky.transform.Translate(-Vector2.up*speed);
             break;
         case 3:
             blinky.transform.Translate(Vector2.right*speed);
             break;
         case 4:
             blinky.transform.Translate(-Vector2.right*speed);
             break;
 
         }
 
     }
 
     void OnCollisionEnter2D(Collision2D col){
         Debug.Log ("Collided!");
         if (col.gameObject.name == "maze")
             ranNum = Random.Range (1, 5);
     }
     }